AudioCircle

Industry Circles => Tortuga Audio => Topic started by: tortugaranger on 18 Feb 2013, 11:37 am

Title: LDR3x.V2 DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 18 Feb 2013, 11:37 am
We are coming out with an LDR based passive/active preamp controller board (the LDR3x) for the DIY community hopefully before the end of April. This is a result of development work we're doing on our line of LDR based passive preamps including the development of a balanced LDR passive pre.

With the LDR3X board you'll be able to build either a passive or active preamp that provides exceptional LDR attenuation, remote selection from 3 input signals, and be controllable via IR remote as well as manually via a pot, encoder, buttons etc.

Also, by using a pair of these in a master/slave configuration, you'll also be able to configure a balanced LDR based preamp.

More info can be found in a recent post on our website: Tortuga Audio Plans LDR3X Preamplifier Controller for DIY Community | Tortuga Audio

The LDR3X preamp controller board will likely be viewed as pricey when compared to typical dirt cheap Chinese made audio boards. This board will be made in relative small quantities here in the US. Also, quite a bit of testing and custom tuning goes into each board given the unique characteristics and variability of LDRs. By its nature, this doesn't lend itself to mass production and low cost. As least not yet. I'm trying to keep it under $300.

I value your inputs and suggestions. In fact, every member on AudioCircle who provides constructive input, comments, suggestions or questions via this thread will be entered into a drawing from which I'll randomly choose 1 winner to receive a free board (including shipping) once they become available. So have at it and thanks.

Cheers,
Morten


(http://www.audiocircle.com/image.php?id=75504)
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 13 Jun 2013, 01:39 pm
Good news! Orders were placed earlier this week for production boards and parts for the LDR3x Preamp Controller Board. http://www.tortugaaudio.com/product/ldr3x-diy-preamp-controller-board/ (http://www.tortugaaudio.com/product/ldr3x-diy-preamp-controller-board/)

Barring any last minute glitches we expect to have finished boards ready to ship starting June 24th if not sooner!

If you're interested in the LDR3x Preamp Controller Board, you can still pre-order one at a 20% discount off the regular price via the following link. http://www.tortugaaudio.com/product/ldr3x-diy-preamp-controller-board/ (http://www.tortugaaudio.com/product/ldr3x-diy-preamp-controller-board/)

The pre-release discount ends once we have finished boards ready to ship.

Cheers!
Morten
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 30 Jun 2013, 12:04 pm
It's taken a bit longer than planned but we're pleased to announce that the LDR3x DIY Preamp Controller Board has been released and pre-release orders are shipping!

(http://www.tortugaaudio.com/images/ldr3x_1.jpg)

The LDR3x allows you to build your own high performance LDR based passive (or active if you include a buffer) preamp that can be controlled remotely and also locally via rotary encoder/switch or discrete pushbutton inputs and a simple potentiometer.

Built around precisely matched digitally controlled LDRs, the LDR3x offers the DIY'er the ability to build preamp that will rival the audio performance of even the best high end preamps.

We'll be posting more pics next week and tweaking the technical manual which has been updated as of today (6.29.13) to reflect the final design/build. We still need to include more detailed artwork describing the board and the interfaces.

You'll notice from the pic that the board isn't fully populated. The board has certain functionality that isn't available to the DIY'er and thus those relavant parts are not included. We also plan on using these boards in  future iterations of our own preamp products.

You can find more information and purchase the LDR3x via the website/store at: LDR3x DIY Preamp Controller Board | Tortuga Audio

You can also find a recent review of our LDR6 Passive Preamp at 6moons.com via this link http://www.6moons.com/audioreviews/tortuga/1.html  (http://www.6moons.com/audioreviews/tortuga/1.html) to get a feel of what to expect by way of sound quality with the LDR3x. Expect quite a lot actually.

Final pricing is:
Master Board for unbalanced inputs - $295
Matched Master & Slave Boards for balanced inputs - $495
Tortuga Audio IR Remote - $49

All questions, comments and inquiries welcome.

Cheers,
Morten
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: jtwrace on 30 Jun 2013, 12:23 pm
The board has certain functionality that isn't available to the DIY'er
Such as?
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 30 Jun 2013, 12:45 pm
The board has certain functionality that isn't available to the DIY'er.

Such as?

Such as the J4 header which allows the LDR3x to interface with a particular NewHaven graphical display module. This is still in development and may one day become available to the DIY'er but would require a software upgrade via a replacement CPU if/when that day arrives. No specific plans on that at this time. We plan on including a graphical display in our next iteration of our LDR passive preamp products which will supercede our current LDR1/LDR6 line.

Such as the J7 header and the 3 rows of diode/resistors which will allow the LDR3x to interface with a future 3 input switch board wherein LDR's are used in lieu of electro-mechanical relays. This is the same design approach we use in our LDR1/LDR6 passive preamp products. We are planning to eventually release a 3 input switch board for the LDR3x. It would include an upgrade kit to populate these components and would interface via a 2-5 IDC cable to header J7. We don't have any timing on this yet.

That's all of the "such as's" I can think of.

Best!
Morten
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 25 Jul 2013, 01:24 pm
We've made some changes!

1) Our LDR DIY Preamp Controller Master Board now also includes our custom IR remote. All you need to supply is your own 12 VDC power supply and you'll have a fully functional state-of-the-art LDR attenuator/preamp controller

2) If you're looking to build a balanced preamp, we've reduced the price of our optional Master Board by $50

(http://www.tortugaaudio.com/images/Remote.png)(http://www.tortugaaudio.com/images/ldr3x_1.png)

The LDR3x - What Is It?
What's Included?
Functionality
How Much Does One Cost?
How Do I Buy One?
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 5 Aug 2013, 01:07 pm
We're running a whopping 33% off summer sale on our DIY LDR preamp controller board. :D
We accept all major credit cards plus PayPal.

PM me or email me at morten@tortugaaudio.com with any questions. Or just post you questions and comments here.

Here's the link to our website/store for more info: LDR3x DIY Preamp Controller Board | Tortuga Audio (http://www.tortugaaudio.com/product/ldr3x-diy-preamp-controller-board/)

Enjoy!
Morten  :thumb:
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 13 Aug 2013, 11:50 am
A quick shout out to our new friends in Singapore, Portugal and New Zealand!

(http://www.tortugaaudio.com/images/singapore_portugal_newzealand.jpg)
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 18 Aug 2013, 12:34 pm
Received the following unsolicited feedback in an email from a recent LDR3x customer. Had to share. :D
Quote
"Today I received the LDR3 board and I am FLOORED by the sound quality.  I've been using a TVC [transformer volume control] for several years and was very happy, but the LDR simply blows it away.  I am hearing detail I never knew existed in recordings I have listened to hundreds of time before. Bass is better, treble is clearer, etc....the sound is killer.  I am retired and have been pursuing this hobby seriously for 40 years.  The last 20 years of my career was as a music wholesale salesperson - I worked for Telarc for 7 years and then for an indie distributor where I sold several audiophile labels, so I have some serious experience listening.  This volume control is fabulous." - Glynn Wilson
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: J Payton on 18 Aug 2013, 06:14 pm
I may be interested in a balanced version of your DIY kits.

Do you supply literature on how to wire and hook the unit up.

Specifically I like to see how to wire for manual volume control as this would be used at my desk system so remote control isn't really necessary. Also what is needed (a potentiometer, momentary push buttons, etc).

I've made quite a few projects (Dac, Ncore Amps, Misc Class D amps) but typically need some good instructions or schematics to put a together.

JP
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 18 Aug 2013, 07:44 pm
I may be interested in a balanced version of your DIY kits.

Do you supply literature on how to wire and hook the unit up.

Specifically I like to see how to wire for manual volume control as this would be used at my desk system so remote control isn't really necessary. Also what is needed (a potentiometer, momentary push buttons, etc).

I've made quite a few projects (Dac, Ncore Amps, Misc Class D amps) but typically need some good instructions or schematics to put a together.

JP

Good point and I'm working on that. Expect to have something available in another day or so.

Cheers,
Morten
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 20 Aug 2013, 06:56 pm
I may be interested in a balanced version of your DIY kits.

Do you supply literature on how to wire and hook the unit up.

Specifically I like to see how to wire for manual volume control as this would be used at my desk system so remote control isn't really necessary. Also what is needed (a potentiometer, momentary push buttons, etc).

I've made quite a few projects (Dac, Ncore Amps, Misc Class D amps) but typically need some good instructions or schematics to put a together.

JP

We just uploaded the latest LDR3x Technical Manual which should now provide what you're looking for.

This latest revision is a big improvement in that it provides much more detailed info on how to wire up the LDR3x to unbalanced and balanced audio signals and also how to connect the optional manual control inputs and outputs.  :thumb:

You can view/download the latest manual by going to the following link and scrolling down to the bottom the page. LDR3x DIY Preamp Controller Board | Tortuga Audio (http://www.tortugaaudio.com/product/ldr3x-diy-preamp-controller-board/)

For those who have already purchased an LDR3x you'll be getting an email with this updated manual attached.

As always, if you see something that's just plain wrong, doesn't make sense or needs additional clarification, give me a shout here, via PM or via morten@tortugaaudio.com

Enjoy! :D
Morten
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 29 Aug 2013, 07:52 pm
Just a quick reminder that if you've been hesitating about ordering a LDR3x Passive Preamp Controller Board w/ Remote, the current sale on the LDR3x ends at midnight next Sunday (9.1.13).

Right now the LDR3x goes for $195 including remote ($295 for the balanced Master/Slave board combo).

Visit our website/store to find out more: http://www.tortugaaudio.com/product/ldr3x-diy-preamp-controller-board/ (http://www.tortugaaudio.com/product/ldr3x-diy-preamp-controller-board/)
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: JohnR on 30 Aug 2013, 01:22 pm
Hi Morten, I'm wondering if it's possible to separate the analog grounds for the two channels (by cutting a track on the board if necessary)?
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 30 Aug 2013, 02:46 pm
Hi Morten, I'm wondering if it's possible to separate the analog grounds for the two channels (by cutting a track on the board if necessary)?

As currently designed, separating the left/right channel grounds would require cutting the ground trace and somehow effecting a new connection to the now dangling ground trace. Doable but ugly and all to easy to bugger the board in the process.

I realize there's a school of though that takes a dim view of a common audio ground as implemented here.  :o   In the end, we took the common ground approach because we felt it was more important to achieve the best possible left/right channel attenuation balance with reference to the same ground. At least with single ended systems. As a practical matter, we've not found this to be a problem with our passive preamps and so far the proof is in the listening.  :D

(http://www.audiocircle.com/image.php?id=86099)
 
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: JohnR on 30 Aug 2013, 03:17 pm
Hi Morten, thanks for the info, actually the reason I asked was because I'm trying to figure out if the LDR can go between a balanced output DAC and a Broskie cathode follower:

http://www.tubecad.com/2006/08/blog0075.htm

(http://www.tubecad.com/2006/08/12/balanced_dac_and_broskie_cathode_follower.png)

The thought was that if the grounds were not common then an extra pair of coupling caps would not be needed. However, I've realized since then that if using the boards in balanced mode/one per channel, then it should work if the ground were simply not connected. I'm assuming the analog ground is not connected anywhere else?

It also occurs to me as I write this that I'm making it too complicated...! It would be simpler and easier to put the LDR after the CF output and use it "passive",  built into its own box it can be used with any other equipment as well.
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 30 Aug 2013, 03:39 pm
The thought was that if the grounds were not common then an extra pair of coupling caps would not be needed. However, I've realized since then that if using the boards in balanced mode/one per channel, then it should work if the ground were simply not connected. I'm assuming the analog ground is not connected anywhere else?

It also occurs to me as I write this that I'm making it too complicated...! It would be simpler and easier to put the LDR after the CF output and use it "passive",  built into its own box it can be used with any other equipment as well.

While you could go with a Master/Slave dual board balanced approach on the input to the follower, I agree that putting a single passive on the downstream end is both simpler and cleaner all around.

Yes, with balanced you could leave out the ground connection.  And yes, the analog ground on the LDR3x is isolated from the power ground.
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: rklein on 30 Aug 2013, 06:21 pm
I just spent some time talking with Morten on the phone about various possibilities regarding his product line.  He was certainly very open to some of the ideas that I posed to him concerning both his DIY products and finished retail product line.  :thumb:  I respectfully, will defer that conversation and let him post on what ideas he would like to implement here on AC. 

I plan on ordering the LDR3x Master & Slave Boards w/ remote (for balanced signals).  For me and my system and for the price of admission (current promotion), I have to see for myself and listen with my own ears, how the LDR based passive preamp differs from the passive pre I am currently using.

Regards,

Randy
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: C17FXR on 31 Aug 2013, 05:33 pm
Morten
I like what you've done with your LDR volume control. It fits right into the requirements I have for a remote control.
I'm looking to implement this into my buffered preamp that consists of a stepped attenuator built around a Shallco with Audio Note resistors.
Quite pricey I must say but very transparent, my only complain being the lack of remote control.
I have been looking into possibly implementing a LDR control into the mix but just haven't found one the suits my needs until I seen your offerings.

But I have a question concerning the LDR3x DIY. Is the circuit board made with the same material as the LDR1 and LDR6?
"Cool blue nickel immersion gold printed circuit boards. Premium materials. Lead-free board & solder. No corrosion."

 
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 31 Aug 2013, 05:45 pm
But I have a question concerning the LDR3x DIY. Is the circuit board made with the same material as the LDR1 and LDR6?
"Cool blue nickel immersion gold printed circuit boards. Premium materials. Lead-free board & solder. No corrosion."

In a word....yup! Same style/specs and same US fabricator. Been very pleased with the quality.

And I would think that with proper planning and attention to detail that the LDR3x would make for a very nice retrofit attenuator/controller for any existing active preamp - especially if you're looking to add remote control capability.

Retrofitting into an active preamp is something several people have mentioned they're thinking about or going ahead with. Based on my own experience with conventional resistive attenuator vs. LDR, I'd would expect a noticeable improvement in sound quality.

If you do this, please let us know what you think of the results.

Best,
Morten
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 31 Aug 2013, 05:48 pm
Just a quick reminder that if you've been hesitating about ordering a LDR3x Passive Preamp Controller Board w/ Remote, the current sale on the LDR3x ends at midnight next Sunday (9.1.13).
Right now the LDR3x goes for $195 including remote ($295 for the balanced Master/Slave board combo).
Visit our website/store to find out more: http://www.tortugaaudio.com/product/ldr3x-diy-preamp-controller-board/ (http://www.tortugaaudio.com/product/ldr3x-diy-preamp-controller-board/)

In light of the extended Labor Day weekend here in the US, we're extending the sale price for the LDR3x up until midnight this Monday, Sept 2nd.

Enjoy the weekend!
Morten
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 31 Aug 2013, 06:50 pm
I was asked recently about running dual outputs from the LDR3x since we do provide dual outputs with out LDR1. I thought I'd also post my response here since it may be of broader interest.

____________________________
The dual outputs on the LDR1 are simply 2 outputs in parallel. They're not isolated from each other. I have several customers running their second output into subs. No problems reported.

For quite some time I ran an early prototype of the LDR1/6 into an active stereo crossover that fed into twin 3-channel LM4780 chip-amps configured in parallel (so 6 ~100 watt chip-amps). These tri-amps drove each of the 3 way GR OB7's that I built from scratch from the basic OB7 plans. I bought the drivers and sound proofing from GR but didn't use/build a passive crossover. In addition to feeding the chip-amps, I also split off left/right signals that went to a pair of Rythmik Servo Sub Amps/Drivers. As far as I could tell, the OB7s were not impacted by the signals going to the Rythmiks. I ran this setup both with and without the subs - no problem.

Just FYI, I've since moved on in the total opposite direction of DAC into LDR6 into monoblock LM4780 amps into 8.5 inch Audio Nirvana full range drivers in a plain vanilla vented box. Stopped using the subs and will probably put the OB7's and Rythmiks up for sale one day. I'm totally in the tank with the Audio Nirvana full range drivers. Love em.

I have other customers who are starting to play with 12V batteries and/or cleaner linear supplies. My working theory is it won't provide discernable improvements but that's just a theory. Very interested in getting feedback on the results.

Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: JohnR on 2 Sep 2013, 12:39 am
While you could go with a Master/Slave dual board balanced approach on the input to the follower, I agree that putting a single passive on the downstream end is both simpler and cleaner all around.

Thanks Morten. Sweet and simple it is then!  :thumb:
Title: Getting an unbalanced out for a subwoofer from a balanced LDR3x
Post by: tortugaranger on 10 Sep 2013, 03:30 pm
An LDR3x customer asked about getting an unbalanced out for a subwoofer from a balanced LDR3x setup.

It may help to first get a basic picture of what's going on with balanced audio. Below is a succinct overview taken from: http://www.ians-net.co.uk/articles/balanced_lines.php (http://www.ians-net.co.uk/articles/balanced_lines.php)  I also recommend anyone working with balanced audio to consult with this excellent article by Rane: http://www.rane.com/note110.html (http://www.rane.com/note110.html)
Quote
To remove noise from a signal we need some way of working out what is our wanted signal and what can be thrown away. Balanced lines achieve this by transmitting two versions of the signal down their length. The source equipment sends the normal signal down one conductor and a polarity-inverted signal down the other. This is usually done using either transformer-based or electronic output stages.

The cable itself is designed with the conductors having very similar impedances and twisted along their length so that any noise is picked up equally by both conductors, no matter where in the cable it occurs.

The receiving equipment has a transformer or electronic differential amplifier, and takes the inverted signal and returns it to it's correct polarity. At this point, the wanted signals on each conductor are both the same polarity, whereas any noise is of opposite polarity. Summing the signals from the two conductors together reinforces the wanted signal and cancels anything unwanted, leaving a recovered signal which is very close to the original. (this is known as Common Mode Rejection - i.e. any signal which is the same on both conductors is removed.)

Even balanced lines aren't perfect, though - slight differences in impedance, twisting or input gain will allow some noise to slip through. This isn't generally a problem unless you're using very long runs or working in areas of high interference.

(http://www.audiocircle.com/image.php?id=86755)

There are 3 basic options for getting an unbalanced signal from an balanced output to feed a subwoofer.

1) Quick and dirty - Just take the + (non-inverted) signal together with the signal ground and send it to the subwoofer. The downside is you lose half the original signal amplitude but that may not matter with a sub. The other downside is you've defeated the noise rejection capability of using balanced signals so any noise picked up along the way will still be there.

2) Transformer - This is the BEST way to convert a balanced signal to an unbalanced signal. The downside is it's probably the most expensive. Jensen makes top notch transformers for this that run somewhere around $75-100 each. Figure 2 of these for stereo unbalanced outs - $$$.  EdCor makes far less costly transformers for this ($~25 for a stereo pair) but some would argue at a loss of performance relative to Jensens; maybe...maybe not.

Info on Jensen: http://www.jensen-transformers.com/datashts/11bmcf.pdf (http://www.jensen-transformers.com/datashts/11bmcf.pdf)
Inf on EdCor: http://www.edcorusa.com/c/47/ttpcseriesmatchers (http://www.edcorusa.com/c/47/ttpcseriesmatchers)

2) Differential Opamps - This is the second best way. Cheaper than Jensens but then again you'll need a split power supply for the opamps. A company called ThatCorp (love that name!) specializes in differential opamps for audio signal line drivers and receivers.

Info on ThatCorp: http://www.thatcorp.com/Balanced_Line_Receivers.shtml (http://www.thatcorp.com/Balanced_Line_Receivers.shtml)
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: thingfish on 13 Sep 2013, 11:34 pm
Hi Morten
I would expect for a 3 input design that there be 6 series LDR's and 2 shunts, otherwise we are back to compromises with switches, electronic or relays, which correct me if I am wrong why LDR's are used in the first place, ideally wired directly to the RCA socket.

It appears impossible to have anything less than 8 LDR devices if you want purity of signal path with 3 inputs 

Perhaps some discussion or answer on this could be enlightening.

Cheers thingfish


Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 14 Sep 2013, 01:24 pm
Hi Morten
I would expect for a 3 input design that there be 6 series LDR's and 2 shunts, otherwise we are back to compromises with switches, electronic or relays, which correct me if I am wrong why LDR's are used in the first place, ideally wired directly to the RCA socket.

It appears impossible to have anything less than 8 LDR devices if you want purity of signal path with 3 inputs 

Perhaps some discussion or answer on this could be enlightening.

Cheers thingfish

I will sidestep the topic of "purity" since wading into that territory all too often becomes indistinguishable from a discussion about religion or politics.

As to using LDRs as analog switches in lieu of mechanical switches, I'm a big fan!  :thumb: When LDRs are "off" they are well north of 1M of resistance - off enough! When they are full "on" they can be in the range of 40-60R which is de minimis relative to the downstream attenuator impedance. Again, on enough!

Thus, LDRs can indeed be used for selecting from multiple audio inputs. The argument for doing so is the avoidance of yet another mechanical interface point (the relay) in the signal path, gold plated contacts etc. notwithstanding. In fact, we use LDRs precisely for this purpose in our 6-input LDR6 Passive Preamp component. Including the LDR input "switch", we end up with 2 LDRs in series (1 fixed, 1 variable) and 1 in shunt (variable) per channel - or 6 total per stereo input.

Customers building their own preamps using our LDR3x DIY Passive Preamp Controller Board are left to their own devices as to how to implement input device selection. The LDR3x provides current sink switching  to ground for up to 3 relays.....or LDR circuits. While we don't currently offer an input switching board, we are considering offering one in the future and it would indeed use LDRs in lieu of mechanical relays.

I would offer one caution in using LDRs as signal switches. For purposes of longevity, I don't recommend running them hard up against their LED current limit (20-25 ma in the case of the Advanced Photonix units we use) even though this yields the lowest "on" resistance. Better to back them off somewhat despite the slight rise in resistance. Still, commercial LEDs have a nominal lifetime expectancy of 50,000 hours. If you listened to music 5 hours a day, that's 10,000 days or 27 years....long enough I'd say!

As to why LDRs are used at all, my emphatic answer is because they are sonically superior in the signal path, i.e. they sound better! Better than pots, better than resistors, and by accounts from a growing number of our customers - better than transformer based volume controls.  :o

Cheers!
Morten

Title: Mounting the IR Receiver to a front panel
Post by: tortugaranger on 18 Sep 2013, 12:51 pm
Perhaps one of the bigger challenges to implementing your own passive preamp with the LDR3x is how to mount the IR receiver (assuming you don't mount it directly in the board but choose to mount it behind the front panel of your enclosure).

Mounting the IR receiver is inherently awkward. The good news is this Vishay receiver is very robust and doesn't need a perfect line of sight to the remote to work reasonably well. If you are able to cut a slot in your front panel roughly the width and height of the curved front of the receiver then you could simply glue it on to the back of the front panel. But cutting slots cleanly in metal isn't that that easy (doing a hack job of it is quite easy however!! ). The second approach is to drill out a round hole in your front panel -  try 50% the width of the receiver but no more than 100% the width. Then you'll need to glue a pair of standoffs (can be made from wood) on either side of the hole on the back side of the front panel. The depth of the standoffs need to be just a bit deeper than the depth of the receiver. Then, using either a pair of toothpicks or a piece of wood similar to the wooden stick/handle found in an ice cream bar, glue that on to the back of the receiver such that it overhangs enough to reach the standoffs. Then glue that assembly on to the standoffs.

The simple diagram below might help. It's a top view looking down on the edge of the front panel with the receiver mounted behind the drilled hole.


(http://www.audiocircle.com/image.php?id=87093)

Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: rklein on 18 Sep 2013, 02:14 pm
I have read that the wooden stick from a Dove Ice Cream Bar has best damping qualities followed by Haagen-Dazs.  If you want Cheap & Cheerful I would recommend Good Humor or Popsicle Brands.  :wink:

Morten:

Thanks for posting this idea.  :thumb:

Regards,

Randy
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 18 Sep 2013, 02:29 pm
I have read that the wooden stick from a Dove Ice Cream Bar has best damping qualities followed by Haagen-Dazs.  If you want Cheap & Cheerful I would recommend Good Humor or Popsicle Brands.  :wink:

I have it good authority that Dead Heads prefer Ben & Jerry's Peace Pop sticks for their IR Receiver backing plates. But personally, I go with the warmer smoother sound you get with Magnum's.  :icon_lol:
(http://www.audiocircle.com/image.php?id=87095)
(http://www.audiocircle.com/image.php?id=87096)

Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: glynnw on 18 Sep 2013, 04:24 pm
I mounted my board in a small metal case and drilled a hole in the face, gluing a red transparent piece of plastic behind the hole for cosmetic effect.  Using single strand stiff wire from the board to the leads of the infrared receiver, I am able to position the receiver wherever I wish and it stays there with no additional support, simply held in place by the stiff wire.  I'm not smart enough to have planned this, but I'll take lucky any day.

And I continue to be blown away by the sound quality.
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: WireNut on 18 Sep 2013, 05:22 pm
I mounted my board in a small metal case and drilled a hole in the face, gluing a red transparent piece of plastic behind the hole for cosmetic effect.  Using single strand stiff wire from the board to the leads of the infrared receiver, I am able to position the receiver wherever I wish and it stays there with no additional support, simply held in place by the stiff wire.  I'm not smart enough to have planned this, but I'll take lucky any day.

And I continue to be blown away by the sound quality.

glynnw,

Send up some pics if you can.

 
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: glynnw on 18 Sep 2013, 07:20 pm
I just posted some pictures under the Tortuga customer pictures thread.
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: gregfisk on 2 Oct 2013, 10:24 pm
Morten, or anyone else that would like to chime in.

I purchased a kit and would like my preamp to have 3 inputs which I understand I need relays for. Could someone recommend a relay for this project? I'm in the alarm business and can get relays no problem, but not sure if they would be as good as something spec'd for audio.

Also, could someone recommend wire that I should use in building my passive pre?

Thanks,

Greg
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 5 Oct 2013, 01:23 pm
Morten, or anyone else that would like to chime in.

I purchased a kit and would like my preamp to have 3 inputs which I understand I need relays for. Could someone recommend a relay for this project? I'm in the alarm business and can get relays no problem, but not sure if they would be as good as something spec'd for audio.

Also, could someone recommend wire that I should use in building my passive pre?

Thanks,

Greg

There's a huge number of excellent electromechanical relays to choose from. I would focus on quality small signal DPDT relays that are sealed with gold clad contacts. One example would be: http://www.mouser.com/ds/2/316/ds-catalog-27518.pdf (http://www.mouser.com/ds/2/316/ds-catalog-27518.pdf) but the choices are mind boggling:  http://www.mouser.com/Electromechanical/Relays/Low-Signal-Relays-PCB/_/N-5g38?P=1z0x3ypZ1z0x3tdZ1z0x3ysZ1z0x3ubZ1z0x3yuZ1yzrzc0Z1yzsm3fZ1yzrygbZ1z0z2xk (http://www.mouser.com/Electromechanical/Relays/Low-Signal-Relays-PCB/_/N-5g38?P=1z0x3ypZ1z0x3tdZ1z0x3ysZ1z0x3ubZ1z0x3yuZ1yzrzc0Z1yzsm3fZ1yzrygbZ1z0z2xk)  I know this doesn't help narrow things down.
Title: Revised LDR3x Pricing
Post by: tortugaranger on 6 Oct 2013, 07:08 pm
Just a heads up note that we revised the pricing/structure on our LDR3x. We decided to pull at pricing info in one location which is why the details aren't located here.

You can find the details in our Product Pricing & Specials topic which can be found here: http://www.audiocircle.com/index.php?topic=119842.msg1265348#msg1265348 (http://www.audiocircle.com/index.php?topic=119842.msg1265348#msg1265348)
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: gregfisk on 7 Oct 2013, 05:48 pm
Morten, thanks for all the good info. regarding relays.

What do people use for wire inside amps and preamps when building them.

Can someone point me to some info. or a source for what gauge or type of wire is typical?

Thanks,

Greg
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 7 Oct 2013, 06:02 pm
Morten, thanks for all the good info. regarding relays.

What do people use for wire inside amps and preamps when building them.

Can someone point me to some info. or a source for what gauge or type of wire is typical?

Thanks,

Greg

Wire is one of those topics that some people follow into strange places that I prefer not to go.  :roll:
That said, I've had excellent results using MilSpec Teflon coated silvered wire from www.wesbellwireandcable.com up in New Hampshire.  :thumb:
Title: New LDR3x Review on DIYAudio
Post by: tortugaranger on 8 Oct 2013, 12:09 pm
Check out this latest review that was posted on DIYAudio. The reviewer manages a French/Canadian DIY forum called QuebecDIY (all in French) but also posted his impressions on DIYAudio.

http://www.diyaudio.com/forums/vendors-bazaar/230114-tortuga-audio-ldr3x-diy-preamp-controller-w-remote.html#post3658377
Title: Encoder board/assembly
Post by: tortugaranger on 2 Dec 2013, 02:11 pm
We are now offering an encoder board/assembly for those DIY'ers who want to control their LDR3x preamp controller manually. Our encoder provides effectively all the same functionality as the remote.

Using the encoder board avoids the awkward soldering of multiple wires to the 5 tiny encoder pins.   :thumb:

It's priced at $23 which includes shipping via USPS Priority in the US. There's an additional shipping charge for international orders (best to order at the same time as the LDR3x board to avoid add'l shipping costs).

Over the next 30 days or so we'll also be introducing a 2 digit (8 segment) display module and a 3 input switching board.

Here's a link to the encoder page at the webstore: http://www.tortugaaudio.com/product/encoder-board/ (http://www.tortugaaudio.com/product/encoder-board/)

(http://www.tortugaaudio.com/images/Encoder_1.jpg)
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: rklein on 2 Dec 2013, 02:34 pm
Quote
Wire is one of those topics that some people follow into strange places that I prefer not to go.  :roll:
That said, I've had excellent results using MilSpec Teflon coated silvered wire from www.wesbellwireandcable.com up in New Hampshire.  :thumb:

Hi Morten:

Which part number for the above mentioned Milspec wire...   M22759, M16878 or M27500 ?

Thanks,

Randy
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 2 Dec 2013, 02:45 pm
Hi Morten:

Which part number for the above mentioned Milspec wire...   M22759, M16878 or M27500 ?

Thanks,

Randy

M16878  :D     http://www.wesbellwireandcable.com/PTFE/high-temperature-wire-ptfe-type-e.html (http://www.wesbellwireandcable.com/PTFE/high-temperature-wire-ptfe-type-e.html)
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: juanitox on 8 Dec 2013, 10:32 am
 :( hi ,  mine is not working ,  i have passed all week to try to make it work but i failed.     i have tried 12V and 5V power supply , an apple remote than a 10K volume pot and i have no sounds coming out  :duh:

please tell me if you have an idea ?   or i will send you back for repair?

best regards

rohan
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 8 Dec 2013, 12:04 pm
:( hi ,  mine is not working ,  i have passed all week to try to make it work but i failed.     i have tried 12V and 5V power supply , an apple remote than a 10K volume pot and i have no sounds coming out  :duh:

please tell me if you have an idea ?   or i will send you back for repair?

best regards

rohan
Hi Rohan,

We test each board with actual music before we ship them out and to date we've had 100% success with the boards working. While that is no guarantee per se, it's more likely that some little detail has been overlooked in setting up your board.

Based on customer experiences to date, the two mostly likely explanations are either: a) somehow the board isn't getting turned on; or, b) incorrect wiring of the audio signal wiring to/from the board

I've found photos of customers' setup to be very useful in sorting out issues like this. I suggest you email me a few pics of your setup that includes all wiring etc. to morten@tortugaaudio.com

I'm reasonably confident we can resolve this once I'm looking at what you're looking at. Of course in the unlikely case that it turns out the board is indeed bad, I'll ship out a replacement. No worries.

Cheers,
Morten
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 8 Dec 2013, 06:21 pm
Hi Rohan,
We test each board with actual music before we ship them out and to date we've had 100% success with the boards working. While that is no guarantee per se, it's more likely that some little detail has been overlooked in setting up your board.
Based on customer experiences to date, the two mostly likely explanations are either: a) somehow the board isn't getting turned on; or, b) incorrect wiring of the audio signal wiring to/from the board
I've found photos of customers' setup to be very useful in sorting out issues like this. I suggest you email me a few pics of your setup that includes all wiring etc. to morten@tortugaaudio.com
I'm reasonably confident we can resolve this once I'm looking at what you're looking at. Of course in the unlikely case that it turns out the board is indeed bad, I'll ship out a replacement. No worries.
Cheers,
Morten

Based on additional info provided by Rohan so far, the root of the problem appears to be related to using a conventional manual pot to control volume. This is a feature of the LDR3x and is provided for those who prefer control via conventional front panel controls like pots, push buttons and switches. Unfortunately, the pot control mode is incompatible with controlling volume via remote/encoder. The compromise solution is to utilize an encoder instead of a pot. Manual control via an encoder is fully compatible with control via remote and can be used to control the LDR3x interchangeably.
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: juanitox on 9 Dec 2013, 07:39 am
unfortunatly , after few try it seems more compacted that this.  the board goes into auto-mute with the remote..   :duh:
but make no mistake it's just a fonction problem  when i have sounds out the Ldr3x is far better than my khosmo vishay attenuator  :thumb:

thanks  to morten for his great support and fantastic service , very rare those days  :thumb:
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 10 Dec 2013, 01:48 am
thanks  to morten for his great support and fantastic service , very rare those days  :thumb:

Thanks Rohan.

Replacement board is on its way along with a few extra goodies. One way or another, we'll get you up and running with a passive preamp!

Cheers!,
Morten
Title: Lock-up at Zero Volume - Just UnMute The Unit
Post by: tortugaranger on 14 Dec 2013, 04:00 pm
Hi All,

Recent owners of the LDR3x including recipients of the HiZ upgrade have noticed that when they reduce volume to zero they then find they can't raise volume back up again (and the status light blinks indicating the unit is muted). Kind of like a mute lock-up. Not to worry.  Read on.

If this happens, just press the Mute/UnMute button. Once the unit is un-muted you can again raise the volume. This is happening due to a changes in the software related to a future product offering.

Here's what's going on. We're about to come out with an optional display module that will display volume level and status information. The user will be able to increase and decrease the brightness of the display module using the remote. In order to add this functionality, we had to add a new operating mode - the Brightness Adjust Mode. The Brightness Adjust Mode is turned on whenever the volume hits zero. At that point the raise/lower  keys become increase/decrease brightness keys. To exit this mode, just press the Mute button and the unit returns to normal volume control again.

More on this once the Display Module is released.

Cheers,
Morten




Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: glynnw on 14 Dec 2013, 04:45 pm
I am ready to buy the display ASAP.  Hooray.
Title: DM1 Display Module
Post by: tortugaranger on 21 Dec 2013, 03:55 pm
We are pleased to announce the pre-release of our DM1 Display Module which we anticipate will be ready to ship by Januaray 6, 2013 (just waiting on the boards to be fabricated).

The Display Module ("DM1") is 2 digit (0.56 inch tall), 7-segment numerical LED display board (1.8 x 1.8 inches) that can be interfaced with the LDR3x Preamp Controller Board to provide numerical/visual feedback of volume level and status of the LDR3x.

You can use just a single module (master) or dual modules (master/slave) for left/right channel display. And they come in blue, green, yellow and red.

Pricing is as follows:
Single Display (right channel/master only) - $59
Add 2nd Display Later (left channel/slave) - $39
Dual Displays Purchased Together (left/right - master/slave) - $89 ($10 discount)
LDR3x Firmware Upgrade - $20 (required for all LDR3x units purchased prior to 12.18.13;  included with all new LDR3x)

You can now pre-order the DM1 and/or find a lot more info on the DM1 on our website/store: http://www.tortugaaudio.com/product/display-module/ (http://www.tortugaaudio.com/product/display-module/)
Pre-order means you can order one now but won't have to pay until the DM1 is released and ready to ship.

Happy Holidays!  :thumb:

(http://www.audiocircle.com/image.php?id=91746)
Title: Re: Lock-up at Zero Volume - Just UnMute The Unit
Post by: Atlplasma on 6 Jan 2014, 07:52 pm
Hi All,

Recent owners of the LDR3x including recipients of the HiZ upgrade have noticed that when they reduce volume to zero they then find they can't raise volume back up again (and the status light blinks indicating the unit is muted). Kind of like a mute lock-up. Not to worry.  Read on.

If this happens, just press the Mute/UnMute button. Once the unit is un-muted you can again raise the volume. This is happening due to a changes in the software related to a future product offering.

Here's what's going on. We're about to come out with an optional display module that will display volume level and status information. The user will be able to increase and decrease the brightness of the display module using the remote. In order to add this functionality, we had to add a new operating mode - the Brightness Adjust Mode. The Brightness Adjust Mode is turned on whenever the volume hits zero. At that point the raise/lower  keys become increase/decrease brightness keys. To exit this mode, just press the Mute button and the unit returns to normal volume control again.

More on this once the Display Module is released.

Cheers,
Morten

Has anyone had a problem with the volume playing very loud at turn on and then not responding to the remote or manually turning the pot?
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: rajacat on 6 Jan 2014, 08:00 pm
I didn't have that problem with the tour LD1 unit.
Title: Re: Lock-up at Zero Volume - Just UnMute The Unit
Post by: tortugaranger on 6 Jan 2014, 08:21 pm
Has anyone had a problem with the volume playing very loud at turn on and then not responding to the remote or manually turning the pot?

That behavior will occur if the audio signal ground is not properly connected (grounded!)  to the J1-AG terminal. I've had this happen during unit build/checkout and chased this ghost all over the place only to fix it by tightening the screw on the audio ground connection.

What's happening is there's no reference ground to attenuate against. It would be like connecting a potentiometer to only one leg and the wiper (called a rheostat). You get series resistance but no shunt (to ground) resistance.
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: Atlplasma on 6 Jan 2014, 08:47 pm
I have to run an errand but will look at the J1 terminal when I return.
Title: Re: Lock-up at Zero Volume - Just UnMute The Unit
Post by: Atlplasma on 7 Jan 2014, 11:11 pm
Has anyone had a problem with the volume playing very loud at turn on and then not responding to the remote or manually turning the pot?

Okay. The problem apparently was due to me mixing up the left and right XLR inputs. If you do that in a balanced configuration, volume control goes out the window with the LDR.
Title: Re: LDR3x balance control issues
Post by: ClefChef on 8 Jan 2014, 04:18 am
Morten - I have two boards #2967 and #2969 with latest software I presume.

Are they compatible with Apple remote? Their remote controllers seem to control my Squeezebox Touch, so I think Apple may not work with them. Previously I received a board with controller that did not interfere with Logitech products - has the situation changed?

Both boards appear to have problems with balance control - instead of balancing right/left I get volume decrease when balancing Left and volume return when balancing Right from left position, nothing happens when trying to balance Right from center position.

I measured shunt and series LDR's on both boards and they track simultaneously on both channels when trying to adjust the balance, both shunts increase or decrease, both series increase or decrease together, not apart as they are supposed to.

Checking the resistances I noticed that the differences in resistance values between channels vary significantly (up to 1k) on both shunt and series on center balance on different volume positions within 10k (most critical) range.

I checked and re-checked both boards, making sure I did not confuse inputs and outputs. Having successfully built several LDR3x I am scratching my head.

I wonder if all these issues could be related to some new software problems, or could it be a defect?
Title: Re: LDR3x balance control issues
Post by: tortugaranger on 8 Jan 2014, 12:18 pm
Morten - I have two boards #2967 and #2969 with latest software I presume.

Are they compatible with Apple remote? Their remote controllers seem to control my Squeezebox Touch, so I think Apple may not work with them. Previously I received a board with controller that did not interfere with Logitech products - has the situation changed?

Both boards appear to have problems with balance control - instead of balancing right/left I get volume decrease when balancing Left and volume return when balancing Right from left position, nothing happens when trying to balance Right from center position.

I measured shunt and series LDR's on both boards and they track simultaneously on both channels when trying to adjust the balance, both shunts increase or decrease, both series increase or decrease together, not apart as they are supposed to.

Checking the resistances I noticed that the differences in resistance values between channels vary significantly (up to 1k) on both shunt and series on center balance on different volume positions within 10k (most critical) range.

I checked and re-checked both boards, making sure I did not confuse inputs and outputs. Having successfully built several LDR3x I am scratching my head.

I wonder if all these issues could be related to some new software problems, or could it be a defect?

All LDRx units shipped after 10.1.13  work with both the Tortuga remote and the Apple remote. It's automatic and doesn't require any special steps to enable or switch.

The balance adjust confusion you described is due to an incorrect compiler setting when your chips were programmed. The compiler thought it was programming a balanced audio build whereas your boards are single ended. This is a harmless error until you try to use the balance adjust feature.

With balanced audio boards channel balance adjustments is done by adjusting the master (right) and slave board (left) whereas with unbalanced boards it's done with the left/right channel within a single board. If the programming gets switched, trying to chase this down with  with resistance readings will make no sense because.....well...it makes no sense.

The  fix to is to burn a new pair of chips (correctly!) and ship them to you. No worries.

Cheers,
Morten


Title: Re: Lock-up at Zero Volume - Just UnMute The Unit
Post by: tortugaranger on 8 Jan 2014, 12:25 pm
Okay. The problem apparently was due to me mixing up the left and right XLR inputs. If you do that in a balanced configuration, volume control goes out the window with the LDR.

Glad you got it worked out. Working with balanced audio is inherently more complex than single ended and with complexity comes more opportunities to find new ways that don't work. I've discovered quite a few myself :wink:

Cheers,
Morten
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: Atlplasma on 9 Jan 2014, 12:32 am
I'm really liking the LDR in my set up but would like to integrate a sub for more base. Has anyone tried doing that with an Art Cleanbox or another type of low pass filter?
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 9 Jan 2014, 08:40 pm
I'm really liking the LDR in my set up but would like to integrate a sub for more base. Has anyone tried doing that with an Art Cleanbox or another type of low pass filter?

Just an FYI, when I was running a sub off my LDRx preamp I simply used an external output splitter and ran parallel ICs to the sub (which had an integral adjustable filter). I wasn't able to discern any negative impacts on the audio quality coming through my main amps/speakers. Then again everything was RCA so no need to convert from RCA to XLR or visa versa.
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: Atlplasma on 9 Jan 2014, 10:31 pm
Just an FYI, when I was running a sub off my LDRx preamp I simply used an external output splitter and ran parallel ICs to the sub (which had an integral adjustable filter). I wasn't able to discern any negative impacts on the audio quality coming through my main amps/speakers. Then again everything was RCA so no need to convert from RCA to XLR or visa versa.

My M&K sub lets you adjust the cross over as well, but it is supposed works better with a separate low-pass filter that keeps the highs out of the signal. I bought one a year ago to go between my Dodd buffer and the Ncore amps, and it integrated the sub without any problems. I'm assuming I can do something similar with the LDR3x. The Cleanbox is affordable, so maybe I'll just experiment.

Or I guess I could use RCA to XLR cable to plug into my existing low-pass filter box. Decisions. Decisions.
Title: DM1 Display Module Released 1.13.14
Post by: tortugaranger on 12 Jan 2014, 05:16 pm
We are pleased to announce that our DM1 Display Module companion product to our LDR3x Preamp Controller Board is being released tomorrow (Monday 1.13.14).  It can be used as a single or dual display.

The first pic shows the front (left) and rear (right) view of the DM1. Roughly 1.8 inch square. Control interface is via the rear.

The second pic shows a "live" shot of dual modules. The master (right) module connects to the LDR3x. The slave (left) module connects to the master via a ribbon cable. The reason the left shows 44 and the right shows 42 indicates there's a 2 step bias favoring the left channel (channel balance adjustment is a feature of the LDR3x).

The last pic below shows dual modules (blue) behind a dark gray acrylic front panel. The blue ghosting around the numbers is a photographic artifact and isn't visible when you look at the real thing. When the DM1 is turned off, you can't see them behind the acrylic (assuming of course that it's dark behind the acrylic panel).

More info on the DM1 can be found here: http://www.tortugaaudio.com/product/display-module/ (http://More info on the DM1 can be found here: http://www.tortugaaudio.com/product/display-module/)

(http://www.tortugaaudio.com/images/DM1_FrontandRear_Clear.png)
(http://www.tortugaaudio.com/images/DM1_Dual_Live_1.jpg)
(http://www.tortugaaudio.com/images/DM1_Dual_Live_2.jpg)
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: poseidonsvoice on 12 Jan 2014, 06:07 pm
Suhweeeet!

Best,
Anand.
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: uraqt on 18 Jan 2014, 11:29 pm
HiZ Upgrade installed, both display boards "attached and working " but not in case!! Sounds and looks great !!! so easy not sure that's it's DIY!!!

Thank you very much Morten!!!

C
Title: Auto Calibrating LDRx
Post by: tortugaranger on 25 Jan 2014, 05:25 pm
I've been working on the design for the next version of the the LDRx controller board and believe I've come up with a viable approach to auto calibration.  :o

With auto calibration, the command table for each LDR is automatically adjusted to keep each LDR as close as practicable to its ideal resistance level for each step of the attenuation schedule. With 70 steps and 4 LDRs (8 for balanced units), that's 280 individual calibrations (560 for balanced units) for each full calibration cycle. We currently do the equivalent of this every time we build an LDRx preamp but it's done with external test gear and the results are then burned into the software. Auto calibration would be totally self-contained and would be repeated indefinitely.

While there are many details yet to be worked out, auto calibration would only take place while the LDRx is turned off. For this to work the inputs/outputs to the preamp would have to be disconnected or at the very least temporarily isolated. I'm working through the best way to handle this with isolation so users don't have to disconnect their ICs.

Along with our HiZ (high impedance) feature, perfecting auto-calibration would arguably be the definitive development in LDR volume control technology. Cool beans!  :thumb:
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: TrungT on 25 Jan 2014, 06:40 pm
"cool bean" indeed.  :thumb:
Sign me up!  ;)
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: glynnw on 27 Jan 2014, 06:23 am
Just finished my 2nd Tortuga build, this time with the display.  It is much easier to assemble with the the display than without - the wiring is simple and straight forward.  Comparing the looks of the interior of the first one with no display with the second brings to mind the word elegant.  The wiring as provided is much easier to use and deal with than making all my own wiring and the finished product is much neater .  I have one question.  I see where the display will show brighness levels, but cannot find where I am shown how to actually adjust the brighness.  As delivered, behind gray plastic, I can barely see the numbers.  But it is up and playing beautiful music as I write this and all functions working..
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: TrungT on 27 Jan 2014, 06:38 am
Phone camera:
(http://www.audiocircle.com/image.php?id=93708)
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 27 Jan 2014, 02:22 pm
I have one question.  I see where the display will show brighness levels, but cannot find where I am shown how to actually adjust the brighness.  As delivered, behind gray plastic, I can barely see the numbers.  But it is up and playing beautiful music as I write this and all functions working..

Hi Glynn,

Glad to hear your DIY preamp project came together.  :D

To adjust display brightness, first mute the unit. Once the volume hits zero while muted, it enters Brightness Adjust Mode. Just use the Raise/Lower buttons to increase/decrease the brightness. When satisfied, press the Mute button again unmute and exit the Brightness Adjust Mode.

In summary, when the LDR3x is muted, use the volume raise/lower buttons to adjust brightness.  :thumb:

Cheers,
Morten
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 27 Jan 2014, 02:24 pm
Hi Trung,
How did you attach the Display Module to the acrylic  front panel?
Regards,
Morten
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: TrungT on 27 Jan 2014, 03:37 pm
Hi Morten
The display is mounted on the "L" bracket.
 :thumb:
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: Vlad on 5 Feb 2014, 01:02 am
Hi,
I am considering this board for my diy preamp, but I would need an active buffer stage with some gain (e.g. 6dB, 10dB, etc, programmable would be best).
As I understand such buffer is not part of the LDR3x board and must be connected externally, right? What kind of buffer would you recommend?

Thanks,
Vladimir
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 5 Feb 2014, 01:32 pm
Hi,
I am considering this board for my diy preamp, but I would need an active buffer stage with some gain (e.g. 6dB, 10dB, etc, programmable would be best).
As I understand such buffer is not part of the LDR3x board and must be connected externally, right? What kind of buffer would you recommend?

Thanks,
Vladimir

Hi Vladimir,

What you're describing is essentially an active preamp with an LDRx volume control in lieu of a conventional pot.  A true buffer typically has unity gain. A buffer with gain is....well....an active preamp. And around we go.

Since you're prepared to tackle a DIY preamp project and are looking for some preamp gain, you might consider starting with a used active preamp and retrofitting that preamp with a LDR3x. All things being equal, this an LDR3x will be a definite improvement over the baseline design. Once you begin considering this option you have your choice of practically any conventional preamp as a starting point for your project. That's a lot of choices.  :D

As soon as you introduce active gain you begin to degrade the essential benefit of the LDRx passive preamp which is the uncolored and unvarnished clarity that is rarely matched with an active preamp. I recognize that passionate audiophiles will argue the benefits of active vs. passive preamps but in the end it comes down to whether you want to get out of the way of the music (passive) or add your preferred coloring to the signal (active).

Most source-amp-speaker combinations really don't need the additional gain of an active preamp. A notable exception would be a relative low powered amp together with inefficient speakers. I'd be interested to hear if this is why you're looking for gain or if there's some other reason.

To answer you specific question about buffers, I personally don't have first hand experience with buffers other than prototypes that we have in development here at Tortuga Audio. The challenge with buffers  for passives is making them totally transparent. In general, this is more readily achieved with solid state designs.

Others who visit this forum may well have other views and I encourage their commentary.

Good luck with your project.

Cheers,
Morten
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: Vlad on 5 Feb 2014, 06:59 pm
Thanks Morten,

I don't have any specific plans at the moment - I was thinking about building a universal preamp that could be used with different kinds of amps - either normal sensitivity (1-2V) or power buffers (e.g. Firstwatt F4, etc.), so speaker efficiency doesn't really matter in this case. I agree that volume control feeding directly into power amp and avoiding any active gain stages is the best solution, but it is limited to a specific source-amp combination.

Vladimir
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: jtsnead on 5 Feb 2014, 07:19 pm
As a follow up to above, I am currently comparing a Wyred 4 Sound STPSE passive/active if you will, to a Dodd Audio buffer with volume control.

I was leaning towards a Tortuga already built but I wanted to try balance connections

I mainly got the Wyred because my new phono stage offers balanced ins/outs, also my Oppo 105 and Class D amp offers balanced ins/outs so I was going to change my cables to balanced but only after I decide if I like the Wyred better than the Dodd.

Upon initial listening it deffinetly has better bass, resolution and layering

I wonder how a Wyred STPSE with a LDR as a volume control would work or would it even be any better?
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 6 Feb 2014, 06:34 pm
As a follow up to above, I am currently comparing a Wyred 4 Sound STPSE passive/active if you will, to a Dodd Audio buffer with volume control.
I was leaning towards a Tortuga already built but I wanted to try balance connections
I mainly got the Wyred because my new phono stage offers balanced ins/outs, also my Oppo 105 and Class D amp offers balanced ins/outs so I was going to change my cables to balanced but only after I decide if I like the Wyred better than the Dodd.
Upon initial listening it deffinetly has better bass, resolution and layering
I wonder how a Wyred STPSE with a LDR as a volume control would work or would it even be any better?

We're still several weeks from releasing our finished balanced passive (LDR3B) although we do currently offer a preamp controller board (LDR3x) to the DIY community that can be configured for balanced signals. Using an LDR3B as a balanced volume control downstream of the Wyred would work but in my view would be overkill since both units have multiple switchable inputs. Although the Wyred does have tons more input/output options and looks like an excellent overall design. 

I believe the Wyred uses discrete pairs of high quality switched resistors for attenuation.  Based on feedback from our customers I'm reasonably confident in saying that our LDRx based volume control will most likely sound better than any conventional stepped attenuator. We've received numerous similar feedback regarding transformer based volume controls costing way more than our current products.

We have done some special projects for customers where we've taken our current LDR1 or LDR6 Passive Preamps and customized them with unique input/output configurations. If you're interested we could customize an LDR1 to be a single input/output balanced attenuator that you could put downstream of the Wyred. Then just run your Wyred at wide open throttle effectively bypassing its volume control and use the LDR1 for attenuation and to switch everything on/off with its 12 volt trigger out.

And if you're willing to wait another 2-3 months or so we could similarly offer an equivalent single input/output version of our LDR3B even though we're not likely to offer a single input/output version as a standard product.

Cheers,
Morten
Title: Introducing the LDR3x IOBoard
Post by: tortugaranger on 8 Feb 2014, 08:06 pm
After going through several design iterations, we're close to finalizing a simple 3 input (2 output) companion switching board for the LDR3x preamp controller board.

Below is a summary. If you have any thoughts, wish lists, must haves, can't stand, can't live withouts etc, now is the time to pipe up with your input.

1) Switches between 3 stereo inputs  using control signals from the LDR3x
2) Provides for connecting 2 outputs in parallel
3) Left/right channel grounds are kept separated (should each be tied to power/chassis star ground)
4) 0.1 inch pitch screw terminals for landing inputs/outputs/grounds
5) as alternative to 4), also has solder holes for terminating I/O plus ground
6) 0.1 inch pitch screw terminal for interfacing with the LDR3x board
7) Uses LDRs as signal switches in lieu of electromechanical relays. Roughly 40-60 ohm resistance when on, several megaohms when off.
8] Control/power interface with pin/jumpers to the LDR3x. Note that the LDRs have to be current limited when switched on. This is handled by 6 diode/resistor pairs that need to be installed on the LDR3x board and will be provided with the IOBoard.
9) 1.6 by 2.5 inch board size

(http://www.audiocircle.com/image.php?id=94460)
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: glynnw on 10 Feb 2014, 08:05 pm
Except for final cosmetics I have finished mt 2nd Tortuga project, this time with the digital readouts..  I am a balance nut - I adjust it constantly.  The digital readout makes it much easier to get consistent settings for certain recordings.  But I now have a problem with the new board.  It worked fine for a couple of days, but then Friday the balance suddenly shifted to the right.  Shortly after turn-on the sound is almost all coming from the right speaker, although there is still some sound from the left.  It's as if it gets worse as it warms up.  The controls still work - volume, balance, etc, but the image is so far to the right it cannot be corrected with controls.  I tested my other gear - all OK - and when I replace it with my orginal Tortuga volume control, the problem is gone.  Is there a reset sequence I can operate to return it to "stock" setting or what?
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 10 Feb 2014, 08:24 pm
Except for final cosmetics I have finished mt 2nd Tortuga project, this time with the digital readouts..  I am a balance nut - I adjust it constantly.  The digital readout makes it much easier to get consistent settings for certain recordings.  But I now have a problem with the new board.  It worked fine for a couple of days, but then Friday the balance suddenly shifted to the right.  Shortly after turn-on the sound is almost all coming from the right speaker, although there is still some sound from the left.  It's as if it gets worse as it warms up.  The controls still work - volume, balance, etc, but the image is so far to the right it cannot be corrected with controls.  I tested my other gear - all OK - and when I replace it with my orginal Tortuga volume control, the problem is gone.  Is there a reset sequence I can operate to return it to "stock" setting or what?

Hi Glynn,

I've seen this happen before and while it's quite rare what's happened is one of the LDRs has gone bad. As we've sold more and more of the LDR3x units we've noticed that maybe 1% or so of the LDRs (out of hundreds!) go bad very early on. On the other hand I've had a unit running nonstop for almost 5 years and it's rock solid.

Very recently we introduced a new quality control process where we now burn-in each LDR for at least 24 hours at full current before testing them and including them in builds. I'm confident this will help us cull out the odd weak LDR so this doesn't happen. The LDRs in our design operate with a huge safety margin relative to their max ratings so we're definitely not stressing them out during normal operation.

I will ship you out a replacement board which you should have later this week. Just send the old one back at your convenience.

Cheers,
Morten

Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: glynnw on 10 Feb 2014, 09:15 pm
Couldn't ask for more.  Thanks.
Title: LDR3x Dimensions
Post by: tortugaranger on 18 Feb 2014, 03:52 pm
I've received several requests for dimensional data so here goes.

The LDR3x board is 2.5 x 4.73 inches. The 4 corner mounting holes are 2.21 x 4.43 inches. The mounting holes are 0.15 inch in diameter.

I suggest a minimum additional 0.5 inch all around to allow for connections etc. so plan for an area of 3.5 x 6.0 inches for a single board and 6.5 x 6.0 inch for 2 boards side by side. You could also stack them vertically in which case you'd need at least 1 inch between boards.

Cheers,
Morten
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: glynnw on 1 Mar 2014, 02:01 am
Will the upcoming 3-input board accomodate unbalanced RCA connectors at all positions or are some of them required to be balanced?  I use all unbalanced RCAs.
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 1 Mar 2014, 12:23 pm
Will the upcoming 3-input board accommodate unbalanced RCA connectors at all positions or are some of them required to be balanced?  I use all unbalanced RCAs.

If you're asking about the version 2 LDR3x Preamp Controller Board, it will be similar to the version 1 board (actually version 0 but lets call it 1) in that it will interface with a 3 input relay switch board (as a current sink).

If you're asking about our upcoming input relay board, each board handles 3 singled ended (unbalanced) stereo inputs. To implement balanced inputs you will need a pair of LDR3x boards and a pair of input relay boards.

Unlike with the version 1 design where you had a normal master board and a dumb (no processor) slave board, with the V2 LDR3x the master/slave boards are identical smart boards except that the slave takes direction from the master which it knows to do by setting a couple of jumpers. Both boards will handle their own auto-calibration.
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: glynnw on 1 Mar 2014, 08:37 pm
I have 2 LDR3X boards, both of which I believe are version 1.  Since version 2 will auto-calibrate, will the original boards eventually be out of calibration?
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 2 Mar 2014, 01:03 pm
I have 2 LDR3X boards, both of which I believe are version 1.  Since version 2 will auto-calibrate, will the original boards eventually be out of calibration?

There's no simple yes or no answer here. LDRs are made with an LED and a photoresistor and all LEDs slowly change their luminosity vs. current behavior over their nominal 50,000 hour life. Thus it is practically a given that any LDR based volume control will see the specific behavior of it's LDRs change over time. The key question is does it matter?

We go to great pains to use a matching set of 4 LDRs for each build. We then test each board with its specific LDRs and use that test data to derive a specific set of attenuation tables that are unique to that board and its LDR set. That all gets burned into the final software build for that board. The whole process is a time consuming PITA and involves quite a bit of custom programming and data processing. That's version 1 calibration.

As long as the calibrated matched set of LDRs continue to behave and age in a similar manner over time it won't matter. I've had a unit running more or less full time for almost 5 years and it works perfectly.

It's really not much different than a matched set of tubes aging over time. Who cares if they change (and they do) as long as they change together.

What version 2 auto calibration will do is move the initial calibration process from an external process to a repeatable internal one with improved precision. It will mitigate the degree of necessity for highly matched LDRs. And to some extent it will mitigate the effects of aging. It will also relieve us of maintaining a calibration database of every board we build.

And in the event a version 1 board was to drift out of calibration to the extent it became a problem, they can also be sent in for recalibration or swapped out for a version 2 board.
Title: Version 2 of the LDR3x Preamp Controller Board Coming Soon - the LDR3x.V2
Post by: tortugaranger on 3 Mar 2014, 03:36 pm
We are sold out of the original LDR3x and since release of the Version 2 board is in sight, we are no longer offering the Version 1 board. We will of course continue to support the version 1 board.

We are really pumped about the LDR3x.V2 board  :D  Here's the announcement and some more info on the LDR3x.V2:   http://www.tortugaaudio.com/ldr3x-v2-preamp-controller-board-coming-soon/ (http://www.tortugaaudio.com/ldr3x-v2-preamp-controller-board-coming-soon/)

We are taking pre-orders for the LDR3x.V2. You can pre-order the LDR3x.V2 here: http://www.tortugaaudio.com/product/ldr3x-passive-preamp-controller-version-2/ (http://www.tortugaaudio.com/product/ldr3x-passive-preamp-controller-version-2/)

Cheers,
Morten  :thumb:

(http://www.tortugaaudio.com/images/LDR3x_Rev2_withTortuga_300x.jpg)
Title: Cardas RCA Jacks
Post by: tortugaranger on 13 Mar 2014, 08:15 pm
We are pleased to announce that we are now using Cardas RCA jacks in builds of our LDR3 Passive Preamp.  :thumb:

These are gorgeous beefy brass jacks with rhodium over silver plate. These are their "long" jacks suitable for both thin and thicker rear panels. We plan on using Cardas jacks going forward in all our new product designs. Unfortunately, we can't use these with our LDR6 Passive Preamp due to space constraints.

We are also selling these to the DIY community but only in pairs. Pricing is per Cardas guidelines. Here's the link to our website:  http://www.tortugaaudio.com/product/cardas-rca-jacks-pair/ (http://www.tortugaaudio.com/product/cardas-rca-jacks-pair/)

(http://www.tortugaaudio.com/images/RCA_GRFA_L.jpg)
Title: Re: Cardas RCA Jacks
Post by: tortugaranger on 14 Mar 2014, 05:08 pm
We are pleased to announce that we are now using Cardas RCA jacks in builds of our LDR3 Passive Preamp.  :thumb:

These are gorgeous beefy brass jacks with rhodium over silver plate. These are their "long" jacks suitable for both thin and thicker rear panels. We plan on using Cardas jacks going forward in all our new product designs. Unfortunately, we can't use these with our LDR6 Passive Preamp due to space constraints.

We are also selling these to the DIY community but only in pairs. Pricing is per Cardas guidelines. Here's the link to our website:  http://www.tortugaaudio.com/product/cardas-rca-jacks-pair/ (http://www.tortugaaudio.com/product/cardas-rca-jacks-pair/)

(http://www.tortugaaudio.com/images/RCA_GRFA_L.jpg)

Just to clarify. These beautiful RCA jacks retail for $31.04 a pair and are semi-permanently on sale for only $24.83 - that's for 2 jacks.  :thumb:
http://www.tortugaaudio.com/product/cardas-rca-jacks-pair/ (http://www.tortugaaudio.com/product/cardas-rca-jacks-pair/)
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 19 Mar 2014, 09:48 pm
We are pleased to announce that we are now taking pre-orders for  the new IO Relay Board.  :D
We expect to be shipping the IO Board on or before April 7th barring any glitches with  our suppliers.
The IO Board price is $59 which includes  the power/control connectors between the board and the LDR3x Preamp Controller Board.
It will work with both versions 1 & 2 of the LDR3x Preamp Controller Board or any other preamp control device that provides +5V and switching to ground.

You can find more info and pre-order the board here: http://www.tortugaaudio.com/product/io-relay-board/ (http://www.tortugaaudio.com/product/io-relay-board/)

(http://www.tortugaaudio.com/images/IOBoardPreSale300x206.jpg)
Title: IO Board & Power Supply Board/Transformer
Post by: tortugaranger on 5 Apr 2014, 12:56 am
We are pleased to announce that we are now taking pre-orders for  the new IO Relay Board.  :D
We expect to be shipping the IO Board on or before April 7th barring any glitches with  our suppliers.
The IO Board price is $59 which includes  the power/control connectors between the board and the LDR3x Preamp Controller Board.
It will work with both versions 1 & 2 of the LDR3x Preamp Controller Board or any other preamp control device that provides +5V and switching to ground.

You can find more info and pre-order the board here: http://www.tortugaaudio.com/product/io-relay-board/ (http://www.tortugaaudio.com/product/io-relay-board/)

(http://www.tortugaaudio.com/images/IOBoardPreSale300x206.jpg)

The IO Boards are in. Still waiting on one back ordered component which was shipped but hasn't arrived yet. Should have them by Sat or Mon at the latest. The planned release date is this Monday, April 7th so it looks like we're going to hit the target on that one.

We also just received our Power Supply Boards. Haven't said anything about the PS Board yet so this will come as a surprise. It will include a small board together with a separate 10VA toroidal transformer that will be sold as a set. The board and the transformer each have to be mounted separately (they aren't packaged together).  The PS takes 115 or 230 VAC and produces 12 VDC. It uses full bridge rectification followed by an arguably overlarge 4700 uF filter capacitor followed by regulators. While is was designed to accommodate a conventional 7812 voltage regulator, we'll be using a 12 VDC version of our new SMPS dc-dc regulator instead. It accommodates 2 regulators in parallel so it can handle either a single ~400 ma output (more than plenty for the LDR3x), dual ~400 ma outputs,  or up to a single ~800 ma output with the dual outputs in parallel. The board is designed to land the transformer primary and secondary windings at clearly marked termination points on opposite ends of the board. There's also a provision for interfacing a 115/230 AC supply voltage select switch (or just using local jumper wires). Once the transformer is connected to the board all that's left is to connect is the main hot/neutral/ground. While all input/output connections will have screw terminals, everything can also be alternatively connected via solder pads. Lastly, there are ample solder pad connections to land multiple grounds to the board with the intent of using the board as a central star grounding point. More info on the Power Supply will be provided next week once we have all the components in, gets some photos taken and get it loaded up on our website. Pricing will be announced next week as well.
Title: IO3 Board
Post by: tortugaranger on 5 Apr 2014, 08:33 pm
Here's build #1 of the new IO3 Relay Board.
Officially released as of 4.5.14 (2 days early! )  :thumb:
Everything including grounds can be connected either via screw terminal blocks or solder pads.
Interfaces with the LDR3x as shown in our updated documentation here: http://www.tortugaaudio.com/documentation/#document-18 (http://www.tortugaaudio.com/documentation/#document-18)
$59 - includes interface cabling etc. to the LDR3x

More info here: http://www.tortugaaudio.com/product/io-relay-board/ (http://www.tortugaaudio.com/product/io-relay-board/)

(http://www.audiocircle.com/image.php?id=97349)
Title: PS12 Power Supply for the LDR3x
Post by: tortugaranger on 9 Apr 2014, 08:41 pm
Fresh pics of the new PS12 Power Supply that uses switch mode dc power regulators and a 10VA toroidal transformer.

Comes in a few variations including:
1) 12 V - 400ma - single regulator
2) 12 V - 800ma (or 2 x 400ma) - dual regulators
3) 12 V - 400ma & 5 V - 400ma - dual regulators

More info can be found here: http://www.tortugaaudio.com/product/ps12-power-supply/ (http://www.tortugaaudio.com/product/ps12-power-supply/)

(http://www.tortugaaudio.com/images/PSPic2.jpg)
(http://www.tortugaaudio.com/images/PSPic1.jpg)
(http://www.tortugaaudio.com/images/PSPic3.jpg)
(http://www.tortugaaudio.com/images/PSPic4.jpg)
Title: PS12.5 Power Supply for the LDR3x
Post by: tortugaranger on 12 Apr 2014, 03:11 pm
Fresh pics of the new PS12 Power Supply that uses switch mode dc power regulators and a 10VA toroidal transformer.

Comes in a few variations including:
1) 12 V - 400ma - single regulator
2) 12 V - 800ma (or 2 x 400ma) - dual regulators
3) 12 V - 400ma & 5 V - 400ma - dual regulators


Based on feedback we've tweaked the power supply offering and as a result are now calling it the "PS12.5" in recognition of the mix of 5 different 12V and 5V variations it comes in which are:

1) 5V-400ma - single regulator
2) 12V-400ma - single regulator
3) 2 x 5V-400ma (800 ma total) - dual regulator
4) 2 x 12V-400ma (800 ma total) - dual regulator
5) 5v-400ma & 12v-400ma - dual regulator

Also, note that we've added a pair of 47 uF caps to the ouput (positions C5 & C6) which further helps stabilize the supply and improve transient performance. These were intended all along but are missing in the build we used for the pics.

More info can be found here: http://www.tortugaaudio.com/product/ps12-power-supply/ (http://www.tortugaaudio.com/product/ps12-power-supply/)

(http://www.tortugaaudio.com/images/PSPic1.jpg)
Title: Some Pics of the new LDR3x.V2 Preamp Controller Board
Post by: tortugaranger on 8 May 2014, 05:37 pm
A few pics of the new LDR3x.V2 board.  :thumb:

* $259 - http://www.tortugaaudio.com/product/ldr3x-passive-preamp-controller-version-2/ (http://www.tortugaaudio.com/product/ldr3x-passive-preamp-controller-version-2/)
* Handles up to 3 inputs via optional input relay board
* Controlled via Apple Remote and/or rotary encoder (not included)
* Auto-calibration of LDRs via 12 bit DAC/ADCs - always optimized - drift/aging a non-issue
* Replaceable LDR modules - like tubes, LDRs can go bad - just replace with a $20 module
* Attenuation between -60 and 0 dB via 70 attenuation steps
* Smooth ramp down/up muting
* Minimum 10k input impedance. See graph below and find our more about attenuation/impedance here: http://www.tortugaaudio.com/documentation/#document-18

(http://www.tortugaaudio.com/images/ldr3x.v2.topview2.jpg)
(http://www.tortugaaudio.com/images/ldr3x.v2.bottomview1.jpg)
(http://www.tortugaaudio.com/images/ldr3x.v2.ldrs_.jpg)
(http://www.tortugaaudio.com/images/LDRMod_Dime.png)
(http://www.tortugaaudio.com/images/impedance_atten_curves_log.jpg)
Title: LDR3x.V2 input impedance spec changed from 10k to 20k
Post by: tortugaranger on 18 May 2014, 05:15 pm
After some critical listening to the new ldr3x.V2 board, we've bumped the input impedance spec from 10k to 20k. At least on our test rig (SS amp with 20k input impedance), it resulted in noticeably improved sound. The sound stage got wider and more 3 dimensional and the stereo center moved further back and not as out in front as before. And the dynamics improved as well. I knew it was better because I blew through 3 hours of listening to one tune after another because it sounded so damn good.  :green:

This is very reminiscent of the improvements noted back when we introduced the HiZ upgrade last year. We really aren't doing anything different in that respect with the V2 but the Auto Calibration feature makes it much much easier to change the impedance and note the difference. It took about 10 minutes to run through the full calibration cycle for the 4 LDRs and after firing it back up again the benefits of 20k were quite obvious.

So, the ldr3x.V2 is now officially a 20k input impedance preamp controller board. The updated attenuation and impedance curves are shown below. A detailed explanation of these curves can be found in our online documentation here:  http://www.tortugaaudio.com/documentation/#document-19 (http://www.tortugaaudio.com/documentation/#document-19)

The really cool thing (at least from a developer's perspective) is this change required editing one line of software code and changing the number 10000 to 20000. Cool beans.  :thumb:

Now, back to digging out from under our backlog of orders.

Cheers,
Morten


(http://www.tortugaaudio.com/images/impedance_atten_curves_log1.jpg)
Title: Re: LDR3x.V2 input impedance spec changed from 10k to 20k
Post by: tortugaranger on 20 May 2014, 12:11 pm
Regarding the impedance change to the V2, I received the following question on another site so I thought I'd post it and my response here.

Quote
Do you think the same benefit would be had by upping the input impedance in v1 boards? If so, is it possible?

I'm going to wait for feedback and consensus from V2 owners before deciding anything about further upgrades to the V1. When it comes to overall quality of sound it may prove to be a case of differences without distinction. Or not.

We went around the track a few times with the V1 last year trying 10k, 20k and even 50k impedance settings before settling on 10k. Even then, there were some who reported that 50k was superior.

Changing the impedance of the V1 is a PITA. We have to dig out their original test data for each individual unit, rerun the data through our modified program, burn a new chip, ship the chip, swap out the old with the new etc. If we added up all of our time and materials for all that, I doubt many would be happy with the price tag. I'd want to be very sure it was worth it before offering that up.

At least with the V2 design, we can email out software revisions or just post them on our website for owners to download and upload into their V2 boards.

We may end up posting 10k, 20k and 50k versions of the V2 software and let owners try all or none and decide what sounds best. I suspect the answer will be more system dependent than not. It would definitely be interesting.

Cheers,
Morten
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: glynnw on 20 May 2014, 04:15 pm
Can you test an amp and determine what impedence in the LDR3X will work best with it?
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 28 May 2014, 01:25 pm
Can you test an amp and determine what impedence in the LDR3X will work best with it?

Sorry for the slow response but was offline for a week of vacation.

The established guidance when connecting audio devices is to either match impedance (output impedance of source = input impedance of amp) or to have sufficiently high bridging impedance ratio (10:1 where amp input  impedance at least 10x greater than source output impedance). Matching impedance may be ideal but it's impractical so most sources have less than 1k output impedance and most amps have input impedances of 10k or greater.

When you place a preamp between a source and amp you now have 2 instances of impedance bridging: between the source (DAC, phono stage, CD etc. ) and preamp, and between the preamp and amp.

When we were able to raise the input impedance of our LDRx preamps to 10k last year (the HiZ upgrade), this improved matters between the source and preamp.

However, as the graph below shows, any passive attenuator employing voltage division (like pots or LDRs) has a varying output impedance that reaches a max of 25% of the input impedance at -6dB (loud!!!). In the case of a 10k unit, that's a max output impedance of 2.5k. For a 20k unit, it's 5k. This would then argue for amps having at least 25k input impedance for a 10k passive attenuator or 50k for a 20k passive attenuator.

Then again, as a practical matter few of us listen to music at -6dB attenuation. In the more likely range of -40 to -20 dB attenuation, the passive preamps output impedance is more likely to be in the 1-2k range which means that an amp with 20k input impedance of greater should suffice but arguably 40-50k or higher may be better (that's "may", not "will").

Beyond this level of general guidance you get into more subtle and equipment specific issues.
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: robertopisa on 28 May 2014, 08:32 pm
So Morten, to make an example with my situation: I have a source DAC with balanced output impedance of 5 ohm, and my amp has >10kOhm of input impedance.

Using your 25% rule at -6dB, it seems that the optimal impedance for the above situation is 4kOhm, as 25% of it is 1kOhm and then 10 times is thus 10kOhm.

Is it so? In that case, it would be better to program your firmware with 4kOhm (great and flexible idea to have this V2 feature!)

Thanks
Roberto


Sorry for the slow response but was offline for a week of vacation.

The established guidance when connecting audio devices is to either match impedance (output impedance of source = input impedance of amp) or to have sufficiently high bridging impedance ratio (10:1 where amp input  impedance at least 10x greater than source output impedance). Matching impedance may be ideal but it's impractical so most sources have less than 1k output impedance and most amps have input impedances of 10k or greater.

When you place a preamp between a source and amp you now have 2 instances of impedance bridging: between the source (DAC, phono stage, CD etc. ) and preamp, and between the preamp and amp.

When we were able to raise the input impedance of our LDRx preamps to 10k last year (the HiZ upgrade), this improved matters between the source and preamp.

However, as the graph below shows, any passive attenuator employing voltage division (like pots or LDRs) has a varying output impedance that reaches a max of 25% of the input impedance at -6dB (loud!!!). In the case of a 10k unit, that's a max output impedance of 2.5k. For a 20k unit, it's 5k. This would then argue for amps having at least 25k input impedance for a 10k passive attenuator or 50k for a 20k passive attenuator.

Then again, as a practical matter few of us listen to music at -6dB attenuation. In the more likely range of -40 to -20 dB attenuation, the passive preamps output impedance is more likely to be in the 1-2k range which means that an amp with 20k input impedance of greater should suffice but arguably 40-50k or higher may be better (that's "may", not "will").

Beyond this level of general guidance you get into more subtle and equipment specific issues.
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: wilsynet on 29 May 2014, 04:29 am
So in summary, the rough guidance is less than 1K output Z for sources and greater than 20K input Z for amplifiers.  Is that right?
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 29 May 2014, 12:04 pm
So in summary, the rough guidance is less than 1K output Z for sources and greater than 20K input Z for amplifiers.  Is that right?

The operative phrase being "rough guidance" but yes.
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 29 May 2014, 12:33 pm
So Morten, to make an example with my situation: I have a source DAC with balanced output impedance of 5 ohm, and my amp has >10kOhm of input impedance.
Using your 25% rule at -6dB, it seems that the optimal impedance for the above situation is 4kOhm, as 25% of it is 1kOhm and then 10 times is thus 10kOhm.
Is it so? In that case, it would be better to program your firmware with 4kOhm (great and flexible idea to have this V2 feature!)
Thanks
Roberto

Your example is consistent with the guidance but as with most things in audio there's more going on than just impedance matching/bridging.

A preamp with only 4k of input impedance in front of a source (DAC in your instance) having a 5 ohm output impedance would have an impedance bridging ratio of 4000/5 = 800:1  (plenty big) which implies that the preamp will present very little load on the DAC. This may work out great but it also depends on the voltage level and current capacity of your DAC's line stage output. Impedances notwithstanding your DAC may be happier (perform better) driving into a higher absolute impedance than just 4k.

In the case of the DAC (~500R) and amp (~20k) I use for development/testing, guidance would suggest that increasing the preamp's impedance from 10k to 20k shouldn't have been necessary purely in terms of impedance yet doing so improved the sound nevertheless. My rather simplistic working theory is it reduced the load on the DAC resulting on more of the audio signal's energy/dynamics getting through the preamp to the amp rather than draining to ground. Said differently, it cut the current load on the DAC by 50% in going from 10k to 20k.

The challenge with impedance guidance and passive preamps is that each combination of source-preamp-amp has its own unique issues. Most of the time the guidance gets you in the zone but to find the optimal settings requires some trial and error.

As we gain some more experience with the V2 design and performance, I plan on posting versions of the firmware with various impedance settings of say 5k, 10k, 20k and 50k. It will be interesting to get feedback on the relative merits.
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: robertopisa on 29 May 2014, 02:14 pm
Thanks Morten, it is a great idea. This is a selling point wrt classical passive volume control as one should stick to one impedance. Instead, here, it suffices to load a firmware, this is very interesting.
-R


As we gain some more experience with the V2 design and performance, I plan on posting versions of the firmware with various impedance settings of say 5k, 10k, 20k and 50k. It will be interesting to get feedback on the relative merits.
Title: Multichannel Volume Control
Post by: tortugaranger on 4 Jun 2014, 12:34 pm
It took a bit longer but we've worked out the kinks in the balanced audio master/slave software and are shipping balanced versions of our LDR3x.V2 units (2 boards required for balanced audio). Since the communication between the master and slave boards is done via a simple UART serial protocol together with a slave select signal, there really isn't any reason we couldn't daisy-chain numerous slaves together.

This would allow for multi-channel volume control where a single master could control numerous slave boards. For example, if you had tri-amped speakers (3 amps - 3 drivers) with an external crossover and wanted to implement a 2x3 channel DIY passive preamp, you would need 3 LDR3.V2 boards for a total of 6 channels. One would be designated the master and the other 2 would be slaves.

If this was a fully balanced system, you'd need 6 LDR3.V2 boards - 1 master and 5 slaves.

We may soon get a chance to try this out on an even more extreme scenario. We're working with an outside project/developer that needs 6 channels of balanced audio volume control feeding into both the left and right speakers - for a total of 12 V2 boards;  1 master and 11 slaves!!  :o
Title: Re: Multichannel Volume Control
Post by: poseidonsvoice on 4 Jun 2014, 02:51 pm
It took a bit longer but we've worked out the kinks in the balanced audio master/slave software and are shipping balanced versions of our LDR3x.V2 units (2 boards required for balanced audio). Since the communication between the master and slave boards is done via a simple UART serial protocol together with a slave select signal, there really isn't any reason we couldn't daisy-chain numerous slaves together.

This would allow for multi-channel volume control where a single master could control numerous slave boards. For example, if you had tri-amped speakers (3 amps - 3 drivers) with an external crossover and wanted to implement a 2x3 channel DIY passive preamp, you would need 3 LDR3.V2 boards for a total of 6 channels. One would be designated the master and the other 2 would be slaves.

If this was a fully balanced system, you'd need 6 LDR3.V2 boards - 1 master and 5 slaves.

We may soon get a chance to try this out on an even more extreme scenario. We're working with an outside project/developer that needs 6 channels of balanced audio volume control feeding into both the left and right speakers - for a total of 12 V2 boards;  1 master and 11 slaves!!  :o

How about multichannel single ended setup for home theater? 1 master and 7 slaves. Are individual trimmers possible? Ballpark cost for the basic kit?

Best,
Anand.
Title: Re: Multichannel Volume Control
Post by: tortugaranger on 4 Jun 2014, 03:21 pm
How about multichannel single ended setup for home theater? 1 master and 7 slaves. Are individual trimmers possible? Ballpark cost for the basic kit?
Best,
Anand.

I interpret that as needing 2x8 channels (8 stereo channels), hence 8 V2's. Individual trimmers are possible with some fairly straightforward software changes. The challenge with trimmers is the present man-machine interface which is the Apple Remote plus display modules. Sufficient display info but not enough buttons.

Would need to put the Master into "Trim Mode", then be able to select 1 of N channels (excluding the Master channel 1 which is the reference), raise/lower the trim offset for currently selected channel, and then save the results. Master would then convey the trim settings to each Slave. These additional control inputs  could be readily done via an iPhone or Android smartphone remote app. A smartphone remote app is on our to-do list but timing of this is currently vague as in "sometime later this summer maybe".  Would also need some custom pin-connector drops/wiring to run serial data to multi-slaves since we didn't provide for daisy-chaining connections in the V2 design but that's not big deal.

For a multi-unit order we could offer a 20% discount which would put this somewhere in the $16-1700 range for 8.

Cheers,
Morten
Title: Change V2 Preamp Impedance via Remote & Auto Calibration
Post by: tortugaranger on 15 Jul 2014, 12:11 am
Several customers have asked to try different impedance levels to optimize performance so I've been thinking of ways to accommodate this feature and it's quite doable.

So we will be coming out soon with another software update for the V2 that will allow V2 owners to adjust the V2's input impedance (and thus indirectly the output impedance). The default is currently 20k. Will probably be able to select from 5k, 10, 15, 20, 30, 40 or 50k via the Apple Remote. After selecting and saving the new impedance setting you'll have to run AutoCal for the setting to become effective. Having done this manually back and forth between 1k and 50k and settings in between I've not encountered any problems.

Don't know yet if it will be possible to switch impedance settings "on the fly" while playing music. That would require running AutoCal at various impedance levels and saving the results from each run. Would be cool to try though. Great way to optimize impedance.

Cheers,  :thumb:
Morten
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: kernelbob on 15 Jul 2014, 12:58 am
Morten, what a great idea!  I'm very interested in how the variable impedance settings would affect the unit's output impedance.  As you know from our exchanges, I'd like to maximize the ratio of a power amp's input impedance to the Tortuga's output impedance.  I know that a ratio of 10:1 is sometimes quoted as a minimum, but I'd like to achieve higher ratios.  In shopping for a new poweramp, I've found input impedances ranging from 200 kohms down to 15 kohms, so the preamp's output impedance is a factor for a good match.  Thanks (again) for your continued work pushing the envelope on the Tortuga designs.
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: JohnR on 15 Jul 2014, 06:41 am
On the V1 board, is the impedance of the Hi-Z update 10k or 20k?
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 15 Jul 2014, 11:03 am
On the V1 board, is the impedance of the Hi-Z update 10k or 20k?

10k
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 20 Sep 2014, 04:31 pm
This is a heads up to all V2 board owners that based feedback and our ongoing development/testing of the V2 we have changed our guidance regarding how audio, power and ground should be wired on the V2s. Even if you already have a functioning V2, I recommend you read this revised documentation. By following these new guidelines you'll ensure optimal audio performance, ensure that AutoCalibration works properly, and generally be a happier camper.  :thumb: 

http://www.tortugaaudio.com/documentation/#document-19 (http://www.tortugaaudio.com/documentation/#document-19)
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 30 Sep 2014, 12:50 pm
Here's a reference to another thread where the subject of impedance bridging and suitability of using passive preamps with amps having lower impedances (10k) is discussed.
http://www.audiocircle.com/index.php?topic=129078.msg1363872#msg1363872 (http://www.audiocircle.com/index.php?topic=129078.msg1363872#msg1363872)
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: dantakayama on 11 Oct 2014, 07:26 pm
Hi,
I have been searching a pre-amp to replace my 25 + years old PS Audio 4.6. Lately i have been reading all kinds of passive preamps, including Pacette RVC & LDR based ones. Since my speakers are QUAD ESL-63 and amp is QUAD 909, I almost bought a used QUAD 99 pre. After much reading I just ordered one Lightspeed Attenuator. But I kept thinking I still want the remote volume control. So I'm thinking of building one with Tortuga LDR board and compare the sound with Lightspeed. The man behind Lightspeed does not believe in the remote for degrading sound. I'm curious if i could hear the difference... Anyway, I'm also up to the idea if someone already built one and wants to sell...
I need one stereo RCA input & 1 (2 would be better) output with a remote. All my sources go through a DAC (3 digital sources).

I appreciate any thoughts and inputs.

Thanks,
Dantakayama
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: robertopisa on 13 Oct 2014, 10:28 pm
I owned both the 99pre and the 909amp, the latter is good. What about the 99pre? Well, it was good that you did not buy it :)

Please consider that the Quadlink for the 909amp is actually a balanced connection. So, in line of principle, you can use the balanced version of Tortuga.

As the input impedance of the 909 is 20kohm, how much is the output impedance of your source?

-R
Hi,
I have been searching a pre-amp to replace my 25 + years old PS Audio 4.6. Lately i have been reading all kinds of passive preamps, including Pacette RVC & LDR based ones. Since my speakers are QUAD ESL-63 and amp is QUAD 909, I almost bought a used QUAD 99 pre. After much reading I just ordered one Lightspeed Attenuator. But I kept thinking I still want the remote volume control. So I'm thinking of building one with Tortuga LDR board and compare the sound with Lightspeed. The man behind Lightspeed does not believe in the remote for degrading sound. I'm curious if i could hear the difference... Anyway, I'm also up to the idea if someone already built one and wants to sell...
I need one stereo RCA input & 1 (2 would be better) output with a remote. All my sources go through a DAC (3 digital sources).

I appreciate any thoughts and inputs.

Thanks,
Dantakayama
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: kernelbob on 14 Oct 2014, 12:38 am
Hello Dantakayama,

I'm auditioning the LDRxB.  This passive controller retains the punch and power in the bass while providing transparency, air, and superb high frequency extension.  As with all passives, attention to impedance and how the source and amps mate with the LDRxB matter.  If your source DAC has sufficient drive and if your amps present a half decent impedance, the Tortuga is mighty impressive.  It has no problem driving my Spectron monoblocks which each present 25 kohms.  I don't know yet if it can handle my bi-amped system, since the net impedance of both amps drops even further.  Anyone out there have experience with active buffers (tube or solid state) to ameliorate very low amp impedance?

I haven't tried other LDR passives, but given that LDRs resistance curves drift with age, the self calibration capability of the Tortuga offers several advantages.  First, this means the individual LDRs will remain matched over the years with an occasional calibration.  In the event you want/need to replace an LDR or if a new improved version is available in the future, the LDRs can be replaced in the field much as a tube can be pulled and replaced.

As for the remote option, I wouldn't want a controller that didn't have remote volume control.  My understanding is that the hand held remote controls the volume exactly as the front knob on the preamp.  With the Tortuga, you're actually sending a control signal to a microprocessor which essentially sets the LDR brightness level based on the current lookup table generated from the last self calibration.  Since I use a balanced system, including the preamp, this ensures that the + and - phases of each channel remain matched for the life of the unit,

As I said, I haven't tried other LDR-based preamps.  If you have a chance to compare multiple vendors' LDR passive preamps, please post your listening impressions.

Best,
Robert
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: dantakayama on 14 Oct 2014, 02:19 am
I owned both the 99pre and the 909amp, the latter is good. What about the 99pre? Well, it was good that you did not buy it :)

Please consider that the Quadlink for the 909amp is actually a balanced connection. So, in line of principle, you can use the balanced version of Tortuga.

As the input impedance of the 909 is 20kohm, how much is the output impedance of your source?

-R

Thanks for your info on 99 pre.
My DAC puts out 99 Ohm according to one review (Audio Xpress) & I'm connecting to 909 with unbalanced RCA.
As for the balanced version, what am I really getting?
Thanks
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: dantakayama on 14 Oct 2014, 02:31 am
Hello Dantakayama,

I'm auditioning the LDRxB.  This passive controller retains the punch and power in the bass while providing transparency, air, and superb high frequency extension.  As with all passives, attention to impedance and how the source and amps mate with the LDRxB matter.  If your source DAC has sufficient drive and if your amps present a half decent impedance, the Tortuga is mighty impressive.  It has no problem driving my Spectron monoblocks which each present 25 kohms.  I don't know yet if it can handle my bi-amped system, since the net impedance of both amps drops even further.  Anyone out there have experience with active buffers (tube or solid state) to ameliorate very low amp impedance?

I haven't tried other LDR passives, but given that LDRs resistance curves drift with age, the self calibration capability of the Tortuga offers several advantages.  First, this means the individual LDRs will remain matched over the years with an occasional calibration.  In the event you want/need to replace an LDR or if a new improved version is available in the future, the LDRs can be replaced in the field much as a tube can be pulled and replaced.

As for the remote option, I wouldn't want a controller that didn't have remote volume control.  My understanding is that the hand held remote controls the volume exactly as the front knob on the preamp.  With the Tortuga, you're actually sending a control signal to a microprocessor which essentially sets the LDR brightness level based on the current lookup table generated from the last self calibration.  Since I use a balanced system, including the preamp, this ensures that the + and - phases of each channel remain matched for the life of the unit,

As I said, I haven't tried other LDR-based preamps.  If you have a chance to compare multiple vendors' LDR passive preamps, please post your listening impressions.

Best,
Robert

Thanks Robert,

According to Morten from Tortuga & George from Lightspeed think I shouldn't have problems with my setup: DAC's output @ 99 Ohm & Quad & 20K Ohm.
Ideally, I like to compare Lightspeed Attenuator & Tortuga, if I can afford both at the same time. I am in search of used Lightspeed, since I'm waiting to build a Tortuga soon.
So far all I've read are very positive. Only the personal listening will tell which one I like. If they are close, then I would go with the remote capable one...
Daniel
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: robertopisa on 15 Oct 2014, 11:03 am
So it seems ok according to the guidelines that Morten posted here.
As for the balanced version, the 909 is not internally balanced but if you have a balanced DAC, you can keep the signal balanced till the 909.
It is worth doing that? It is up to you as it depends on how much you appreciate a balanced connection over an unbalanced one :)
-R

Thanks for your info on 99 pre.
My DAC puts out 99 Ohm according to one review (Audio Xpress) & I'm connecting to 909 with unbalanced RCA.
As for the balanced version, what am I really getting?
Thanks
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: dantakayama on 21 Oct 2014, 02:51 am
So it seems ok according to the guidelines that Morten posted here.
As for the balanced version, the 909 is not internally balanced but if you have a balanced DAC, you can keep the signal balanced till the 909.
It is worth doing that? It is up to you as it depends on how much you appreciate a balanced connection over an unbalanced one :)
-R

I finally got the Tortuga LDR3x.V2 board & remote a few days ago and have been listening as I write this.
So far the sound is definitely better than before. More detail, more pin-point focus of individual instruments and voices have more nuance than before. I can find any negatives here. Plus the remote to change volume &.... I'm also getting plenty of volume, even with 2 amps hooked up (20K & 25K Ohms input)

Definitely not as "Wow!" as when I went from 25+years old B&W Matrix 2 to Quad ESL-63 speakers (also from late 1980s, but re-panelled by QS&D), but wonderful enough not to go back to what I had. I would say the improvement is about the same or a little more than when I finally added DAC (a few years old PS Audio DL-III) to my system recently.

However, the addition of Tortuga had a small but troubling time. Yesterday, the unit did not respond to volume control at all. Then it all together stopped. So I disconnected the LDR & went back to my old set-up & listened some more. That was when I really missed the improved sound of Tortuga. Anyway, I wrote to the company last night (Sunday), and I was surprised to find the response from Morten in my mail-box this morning. Morten offered some possible explanations after I wrote back to him. he then asked me to phone him to resolve the issue. I phoned him this afternoon and he walked me through & at 1st try, the thing worked!!!. Maybe it was because I am only doing a dry run (no soldering done yet). Anyway, I'm a happy camper. I really appreciate the way Morten handled the situation.  I recommend anybody out there looking to get one of these passive-pre. I know I can't afford the new finished units that they offer, but the DIY is fine with me. Heck, I've been buying mostly used stuff till now...

As for the balanced vs. unbalanced: I've been reading the differences & benefits that the balanced setup offers over the unbalanced. Yes, my DAC has both balanced & unbalanced connections. Maybe in the future...get into the balanced connections....But as I said I'm enjoying this now.

Daniel takayama
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 21 Oct 2014, 12:55 pm
However, the addition of Tortuga had a small but troubling time. Yesterday, the unit did not respond to volume control at all. Then it all together stopped.

Thanks for the report Daniel. Glad everything is working now.

The key revelation that came out of our phone chat yesterday is Daniel had everything connected up temporarily to test the V2 out before putting it all permanently into an enclosure. As part of the temporary setup he had the IR Receiver Module sitting loose in the socket on the V2 board but not soldered in place. Thus he was counting on the 3 pins making contact by virtue of slightly bending pins to ensure they connected with the pads in the socket. I do this all the time when checking out boards. It works most of the time........except when it doesn't.

Thus the V2 was responsive to the remote some times and other times it was not. This was because the IR Receiver Module was making intermittent contact. The slightest disturbance of the board can make/break the 3 pin connection when they're not soldered in place or otherwise firmly connected via screw terminal etc.

Best,
Morten :thumb:
Title: High Praise from Customer
Post by: tortugaranger on 26 Oct 2014, 02:58 pm
Received the following note from a customer the other day. Had to share.  :D

"Your newsletter prompted me to say a big belated “thank you” for making the very best preamp I have ever used. From tube to solid state, vintage Western Electric and Marantz to modern Cello and Krell, nothing comes close. My downsized system is unbelievably dynamic yet completely natural and without any hint of strain, harmonically accurate and rich especially with “challenging” brass and woodwind instruments, always happy to play back what it receives. My system has NEVER felt (and sounded) this good." - Steven K Lee
Title: We Are Now Taking Pre-Orders for the LDR3x V2.1 Board
Post by: tortugaranger on 16 Nov 2014, 11:40 pm
The V2.1, our latest version of the LDR3x board is now available for pre-order purchase @ $199.
Expect to release and start shipping the V2.1 by January 5th.
You can find out more about the V2.1 and also pre-order it here: http://www.tortugaaudio.com/product/ldr3x-v2-1/

(http://www.tortugaaudio.com/images/V2.1PCB3D1.jpg)
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: point5028 on 17 Nov 2014, 11:08 pm
Hi

I would like to buy the new one for upgrade. But there is different PCB size between V2.1 and before V2.0 .
V2.0 Board:  2.5 by 4.7 inch
V2.1 Board: 2.5 by 5.0 inch
Dose the 4 corner screw location will be the same or different?
Could you check the distances of screw hole for me.

dave
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 17 Nov 2014, 11:21 pm
Hi

I would like to buy the new one for upgrade. But there is different PCB size between V2.1 and before V2.0 .
V2.0 Board:  2.5 by 4.7 inch
V2.1 Board: 2.5 by 5.0 inch
Dose the 4 corner screw location will be the same or different?
Could you check the distances of screw hole for me.

dave

Even though the V2.1 board is longer by 0.3 inches than the V2 board, the 4 corner screw hole dimensions are exactly the same.
It has something to do with relativity and black holes.  :o
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 22 Nov 2014, 06:58 pm
Along with the updated LDR3x.V2 board (the V2.1), we are also updating our IO3 Input Relay Board - the IO3.2  The updated IO3.2 adds output isolation relays in addition to the 3 input relays. When mated with the new V2.1 board, this allows complete input/output isolation during Auto-Calibration of the LDR3x Passive Preamp Controller Board. Without this isolation the user would have to disconnect their inputs & outputs.

The new IO3.2 board also includes a copper ground plane that can serve as the star grounding point. It includes 6 additional solder pads in the star ground plane for landing various grounds like audio as well as power/earth to a single ground point. Those 6 solder pads don't show up properly in these 3D cad pics.

We have a somewhat similar IO board that we use with out LDRx/LDRxB Passive Preamps but that version uses LDRs as audio switches rather than relays. At present we have no plans to market the LDR based IO board as that is unique to our finished preamp products.

Here are a few 3D cad renderings of both these new boards. The V2.1 is a 6 layer board, hence the exploded view.

(http://www.tortugaaudio.com/images/V2.1_3dcad_4.jpg)
(http://www.tortugaaudio.com/images/V2.1_3dcad_3.jpg)
(http://www.tortugaaudio.com/images/V2.1_3dcad_1.jpg)

(http://www.tortugaaudio.com/images/io3.2_3dcad_2.jpg)
(http://www.tortugaaudio.com/images/io3.2_3dcad.jpg)
(http://www.tortugaaudio.com/images/io3.2_3dcad_3.jpg)



Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: point5028 on 2 Dec 2014, 04:04 pm
I want to buy  LDR Module.  Can you add it to the store?  Thanks!!
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 2 Dec 2014, 04:34 pm
I want to buy  LDR Module.  Can you add it to the store?  Thanks!!

Sure. Will have that up and available within 24 hours or less. Will post an update here when it's live.  :thumb:

Ok, it's live:  http://www.tortugaaudio.com/product/ldr-module/ (http://www.tortugaaudio.com/product/ldr-module/)
Title: Changes to the new LDR3x V2.1
Post by: tortugaranger on 15 Jan 2015, 06:26 pm
By now those of you who already ordered the V2.1 will have received an email update on where we came out on the V2.1 design as we begin building/shipping units.

We ran into a surprising finding with our original concept of a 6 layered board for the V2.1. Unfortunately we did not fully discover this until we'd gone through not only 1 but 2 iterations of production boards (ouch!). Simply put, the 6 layer board didn't sound good enough. In fact it was a step backwards. So after puzzling over that with extensive testing and listening I finally concluded there's no way we're going to proceed with an inferior board. 

The good news is as a result of all the development work over the past 3 months we discovered numerous ways of improving on the existing V2 platform through a combination changes in certain hardware components together with substantial changes in the software. Thus the final V2.1 has achieved our ultimate goal of an improved LDR3x, just not the way we had originally anticipated.

Changes introduced with the V2.1 include:

Improved auto-calibration accuracy:  Auto-calibration accuracy has been substantially improved approaching 0.1% matching between target and actual resistance level at each step of the attenuation range. This was largely accomplished through enhancements in the auto-cal software algorithm. Increased accuracy translates directly into improved stereo imaging and sound stage. Please note that this is also applicable to existing V2 boards via free software updates which can be download from our website.

Precision pre-calibration process: Using precision temporary plug-in 0.1% Vishay Dale resistor modules it’s now possible to pre-calibrate the auto-cal circuit thus substantially improving the overall accuracy of auto-calibration. This further improves channel balance with commensurate improved stereo imaging and sound stage. We now do this as part of commissioning each V2.1 board prior to running auto-cal. This process is only warranted with new boards or after making hardware changes such as changing opamps. This process is also applicable to existing V2 boards but will require updated software (free download) plus the resistor modules. Tortuga Audio will soon be offering a relatively inexpensive 4-pack of pre-calibration modules as an option when purchase the V2.1 or as a separate purchase (the DIY’er can also build these themselves).

Modified LDR Control Circuit:  Component changes were made to improve the accuracy, stability of LDR control while accommodating a wider range of LDR performance specs.

Modified Auto-Calibration Circuit:  Component changes were made to improve the accuracy and stability of auto-calibration.

Socketed Op Amps: Sockets were added rather than permanently hard-soldering of op amps into the board. This make it possible to try alternative compatible single-voltage quad op amps to optimize performance while also allowing for powering the board with higher voltage levels. Sockets allow the DIY user to experiment. Quad op amps are used in both the left/right channel LDR control circuits and also as a buffer in the auto-cal feedback circuit. To be clear, the LDR3x does not have op amps in the audio signal pathway, never has and never will. Op amps are used solely in the LDR control circuit and the auto-cal circuit.

Potential Higher Power Supply Voltage: Although the stock op-amps currently used limit the supply voltage to a maximum of 15 VDC (12 VDC regulated recommended), there is potential to user alternative op-amps that can handle upwards of 36 VDC. While this will not change the performance of the LDR3x it will provide additional flexibility in the designing your DIY preamp or retrofitting the LDR3x into an existing preamp.

Introduction of User Adjustable Input Impedance: User will be able to select up to 5 different input impedance settings between 5k and 50k and test the efficacy of each. Actual settings are user adjustable. Once selected, the LDR3x will have to be run through auto-cal at the new setting before it will be available. This has been discussed previously with respect to the V2 and indeed will be available to existing V2's via software updates. More on this will be posted here and in our documentation as soon as we can.

We are currently busier than one-armed paper hangers! :thumb:

Cheers,
Morten
Title: Higher Voltage Supply for V2.1
Post by: tortugaranger on 16 Jan 2015, 08:38 pm
Several people have asked if they can power the LDR3x.V2.1 board with higher voltage power supplies. As in higher than 12 VDC. The stock buffer op-amp we've been using is limited to 16 VDC. This is a key op amp in the auto-calibration circuit. During normal operation it's not involved in control.

We just finished testing 2 alternative op amps that are capable of operating safely up to 30 VDC - the LT1014 and the OPA4251. The OPA4251 in particular seemed to really speed up the auto-calibration which speaks to its precision and low noise (124 dB common mode rejection). At over $12 a pop wholesale it sure better do something better!

I haven't tested either in the main LDR control circuit but I've found that so called "better" opamps don't behave as well compared to the lowly LM324 we are currently using. Conversely, the LM324 is a total disaster when used in the auto-cal circuit.

So if running your V2.1 board at a higher voltage of up to say 30 VDC is a requirement for your project, I'll be adding the OPA4251 as a high-voltage-supply/auto-cal  upgrade option for around $20. You can always opt for this later since the V2.1 op amps are socketed.

If you have an outstanding order for a V2.1 and want one of these, please contact me via PM or email to morten@tortugaaudio.com

(http://www.ti.com/graphics/folders/partimages/OPA4251.jpg)

Cheers,
Morten
Title: Adjustable Input Impedance
Post by: tortugaranger on 16 Jan 2015, 10:11 pm
The V2.1 version of the LDR3x Preamp Controller Board is now shipping with extensively updated firmware (Rev 2.1.0) that includes the ability to configure up to 5 different input impedance settings each with its own impedance level. Once you define the impedance level for a given level (from 1k to 99k) you then have to run auto-cal one time for that new setting to create an attenuation table for that setting. Once this is set up you can actually switch between impedance settings "on the fly" while listening to music. My own experience with this suggested that 99k was marginally better than the default 20k at least for my test rig. What surprised me though is I ran a 1k as well and while it was a tad less good than the 20k it wasn't at all that bad either.

When the dust settles a bit I'll post the new 2.1.0 firmware for download on the website. This firmware is fully compatible with the original V2 board. A fair bit of documentation also needs to be updated to explain how to do all this - all with that simple Apple Remote no less.

Cheers,  :thumb:
Morten
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: robertopisa on 1 Feb 2015, 07:50 pm
Edit: OT moved elsewhere
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 4 Feb 2016, 02:24 pm
First  prototype of the V3 preamp slave board is finally in house. Much work left to be done before this successor to our V2.1 gets released later this year.

Key changes in the V3 vs. V2.1 include:
Aside from these specific differences, a key objective with V3 is sonic improvements through even tighter channel balance specs and a shorter/simplified audio signal path.

The next step is to begin debugging and testing the board to find out what works and what doesn't. We'll inevitably go through a few prototype versions before the design is finalized. More on the V3 as it evolves.

(http://www.tortugaaudio.com/images/ldr.v3_slaveboard_rev0A.jpg)
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 8 Mar 2016, 03:08 am
Over the past month we've been evaluating the first prototype of the V3 version of our LDR preamp controller design. As a result, we've made some significant changes as outlined and shown below.

The biggest change is the integration of input switching into a now headless (no microcontroller) LDR board (formerly called a slave board). We are convinced that integrating the input switching and thus minimizing the input/output wiring and connection points can only help to improve sound quality.

As with our V2.1 boards, the V3 will have fully integrated autocalibration of the LDRs.

All control has been moved to a single controller board (not shown, formerly called the master board) which mates up directly (or via ribbon cable) to a single graphical OLED (LCD) display module.

One very interesting option that we are continuing to explore is to adopt the Raspberry Pi computer (https://www.raspberrypi.org/help/faqs/Pi (https://www.raspberrypi.org/help/faqs/Pi)) as our core controller in lieu of a microcontroller. For those who've never heard of it, the Raspberry Pi ("RPi") is a $35 Linux computer on a single board the size of a deck of cards. Although it has far more processing power than needed to run our LDR preamps, the RPi is quickly evolving into a feature rich embedded processing device that can make the "internet of things" ("IoT") a reality far sooner than anyone expected. Initially released in 2012, the current version of the RPi has it all - USB, Bluetooth, WiFi, HDMI, video, audio, and significant memory/storage capacity - plus tons of development tools, video display drivers etc, much of which is open source. To be clear, we are NOT proposing to use any aspect of the RPi's audio features, simple it's processing, control and communications abilities.

Even if we don't use the Raspberry Pi for the V3 version of our preamp controller, we might do so later on. Equipped with a proper adapter board, the RPi would be fully compatible with the LDR Board shown board.

Last but not least, the release of the V3 remains at least 6-9 months away and that's probably optimistic.

* The controller board (now shown here):
   * Handles all control processing of the LDR board(s)
   * Connects via ribbon cables to up to 6 stereo LDR boards (12 total channels)
   * Interfaces directly with an OLED display panel to which it can mount to directly
   * Handles encoder input
   * Handles firmware updating via USB connection
   * Handles IR remote input
   * Handles Bluetooth remote input
   * Uses a single 80 pin 8 bit surface mount microcontroller
   * All electronic components are surface mount

* Each LDR board (shown below):
   * Handles a single stereo single ended input (2 channels)
   * Connects to the controller board via 10 pin ribbon cable
   * Is powered by the controller board but has its own voltage regulators separate from the controller
   * Has no digital microcontroller of its own
   * Can accommodate from 1 up to 6 inputs without an external input relay board
      * Input expansion is handled by plugging in additional LDR modules
   * All input switching done via plug in LDR modules (no relays)
   * Utilizes 5 12-bit DACs, 2 12-bit ADCs, and 3 op amps for far more precise and flexible control of the LDRs compared to the V2 board
   * All communications between the controller board and LDR board is handled via a 4 wire SPI serial data link.
   * All electronic components except for LDRs are surface mount
   * Measures 2.8 x 4.5 inch

(http://www.tortugaaudio.com/images/ldr.v3_ldr_board_rev0.jpg)
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: robertopisa on 8 Mar 2016, 06:04 am
Hello Morten,

it is good to hear that you are exploiting your knowledge and experience on LDRs to further refine your nice project! Please move my comments below where appropriate.  I am not an engineer, so take them with a grain of salt (I am a computer scientist).

Cheers
-Roberto

- I think it is good idea to consider the Raspberry or Arduino, but it could introduce a potential source of pollution in the audio path, so it would be better to shield it and galvanically isolate it.

- I like your LDR boards as they have the shortest path from in/out pins to LDRs. In the scheme below, IMHO, they are longer than necessary. Do we really need 6 inputs? Using 3 inputs, you could dispose the overall 8 LDRs very close to the JL1 and JR1 pins on the shorter side of the board. Actually, I personally like the shortest possible path, avoiding multiple inputs and selectors.

- Crazy idea: could shielding the analog paths of LDRs help to lower even more the noise? I mean, having completely shielded in a (sonically dumped?) box the analog path entering the pins JL1 and JR1, going through the LDRs (possibly closer as said in the previous point), and exiting to the out pints. This would further isolate it from the rest of the board below. In the rare case that one LDR should be replaced, this requires to change the entire box of LDRs, but it is not probably that large cost compared to the rest.

To elaborate the last point: currently the LDRs are detachable along the audio signal path. Instead, in the shielded box the LDRs would be soldered along the audio signal path, and the box would be the one detachable, now along the control path. This is meant to keep pristine and short as much as possible the audio path. So the in/out audio pins to solder would be directly on the box, which will communicate with the rest of the board below using the detachable module on the control path. In this way, one could also solder pin 1 of the XLR connection directly on the box, and thus use shielded balanced cable also till this box. Hope I succeeded to describe what I mean.

(http://www.tortugaaudio.com/images/ldr.v3_ldr_board_rev0.jpg)
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: craig sawyers on 8 Mar 2016, 09:24 am
Personally more than 3 inputs would be a benefit.  I have four sources, so six would be just fine for me.

Another question Morten - how does the new architecture handle balanced?
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 8 Mar 2016, 03:32 pm

Hi Roberto. Good to hear from you and thank you for your thoughtful input.

- I think it is good idea to consider the Raspberry or Arduino, but it could introduce a potential source of pollution in the audio path, so it would be better to shield it and galvanically isolate it.

There's little to distinguish an Arduino from our controller board aside from the fact that the Arduino's are mass produced. Both use standard available microcontrollers and are programmed at the basic hardware level. We would have to mate any Arduino with our own custom interface board same as we would for the Raspberry. I prefer the Microchip family of microcontrollers whereas the Arduino uses Atmel although I've worked with both. Our earliest prototype LDR board used an Arduino. Personally, I'm not very keen on the Arduino programming language and prefer working in either C or Pascal. I currently use MirkroElectronika's development hardware and compilers.


The Raspberry Pi is totally different animal wherein we'd be programming on top of a full Linux operating system. A lot more complexity under the hood and we'd be insulated from the microprocessor at the hardware level. Fortunately there are sufficient drivers available for everything we need - and then some - to handle IR receiver and SPI communications, USB, wireless etc. not to mention high level display functionality. Concerns over noise and shielding may be valid but then again our current boards are already running 16 MHZ microcontrollers with shared power supply driving the LDRs and no shielding all without discernible downside.

Quote
- I like your LDR boards as they have the shortest path from in/out pins to LDRs. In the scheme below, IMHO, they are longer than necessary. Do we really need 6 inputs? Using 3 inputs, you could dispose the overall 8 LDRs very close to the JL1 and JR1 pins on the shorter side of the board. Actually, I personally like the shortest possible path, avoiding multiple inputs and selectors.

I'd say it's around 50/50 in terms of comments I receive on the topic of number of inputs. Half are asking for more than 3 and the other half can't fathom why more than 2, perhaps 3 at the most...and some say why not just 1. There's no perfect one size fits all solution here. The current prototype board design comes close  insofar as it has the flexibility to only have 1 input or have up to 6. It's only a matter of adding the LDR modules which are plug in.

It would be a simple matter to minimize trace lengths by eliminating J1L and J1R as such and simply having individual solder pads as close as possible to each input LDR switch. This would have the added benefit of shortening the board up by perhaps another 0.5 inch. However, as a practical matter this doesn't really shorten the signal path. You still have to run wires from each input RCA/XLR jack to the board. The traces may be shorter but the wires to each trace/pad would have to be longer. Pick your poison.

Quote
- Crazy idea: could shielding the analog paths of LDRs help to lower even more the noise? I mean, having completely shielded in a (sonically dumped?) box the analog path entering the pins JL1 and JR1, going through the LDRs (possibly closer as said in the previous point), and exiting to the out pints. This would further isolate it from the rest of the board below. In the rare case that one LDR should be replaced, this requires to change the entire box of LDRs, but it is not probably that large cost compared to the rest.

To elaborate the last point: currently the LDRs are detachable along the audio signal path. Instead, in the shielded box the LDRs would be soldered along the audio signal path, and the box would be the one detachable, now along the control path. This is meant to keep pristine and short as much as possible the audio path. So the in/out audio pins to solder would be directly on the box, which will communicate with the rest of the board below using the detachable module on the control path. In this way, one could also solder pin 1 of the XLR connection directly on the box, and thus use shielded balanced cable also till this box. Hope I succeeded to describe what I mean.

One of the more interesting philosophical issues around design is whether one is designing around a real or imaginary problem. Is noise really a dominant problem here that needs a solution? In my view that remains an interesting question as it relates to the bigger topic of perceived benefit of balanced audio within short run stereo audio...to which I say... I don't know. I can say that with some conviction that noise has not been an issue with any of our LDR preamps aside from the your run-of-the-mill ground loop hum issues which are really a separate noise category best solved through good grounding practices. RF/EM noise has not been a problem as far as I'm aware. Therefore taking special precautions such as shielded boxes and/or cables internally within the preamp do not seem warranted.

Also I doubt anything is gained by having to replace a whole set of LDRs within a removeable shielded box vs. individual LDRs modules. If it's removeable it's still plugged in and not soldered in. Tubes live quite effectively within a plugged in reality, so my thought is LDRs should be able to as well. We use gold plated pins and sockets so corrosion shouldn't be an issue.

One design architecture that we've explored quite a lot is to move the input switching out to the individual RCA/XLR input jack. While this would indeed minimize the signal path of each individual input, you still end up with common signal(s) that have to run back to the LDR board. Plus you'd end up with numerous switching control signal cables running from the LDR board to each input jack which frankly would end up looking really awful.

After going around the track numerous times with various alternatives we arrived at the design you see below in the recent post. By locating the LDR board as close to the rear panel as practical you minimize the signal wire runs to/from the LDR board and ultimately the total signal run distance between the rear panel inputs/outputs and the LDRs. At least that's the thought behind it.   :thumb:

There's one additional step we could take but have resisted. The LDR board could be custom designed to mate up directly with the RCA or XLR jacks. This eliminates any additional wiring between the jacks and the board. The issue  with that is you end up with a different custom board for each and every model of preamp. Many designs use this approach since it has the added benefit of reducing the manhours needed to build a preamp.
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 8 Mar 2016, 04:05 pm
Personally more than 3 inputs would be a benefit.  I have four sources, so six would be just fine for me.

Another question Morten - how does the new architecture handle balanced?

I get a LOT of inquiries asking for more than 3 inputs.

Balanced audio is done by using 2 LDR boards and designating one as the right board and the other as the left board. Within each board, the + and - balanced audio signals are terminated to the right/left channel respectively.
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: DaveC113 on 8 Mar 2016, 04:27 pm


There's one additional step we could take but have resisted. The LDR board could be custom designed to mate up directly with the RCA or XLR jacks. This eliminates any additional wiring between the jacks and the board. The issue  with that is you end up with a different custom board for each and every model of preamp. Many designs use this approach since it has the added benefit of reducing the manhours needed to build a preamp.


PCB mounted jacks often don't have pin1 / ground going to chassis right next to the jack, which can cause the "pin 1 problem".

Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: craig sawyers on 8 Mar 2016, 06:48 pm
Will the OLED module allow the naming of inputs (CD, Deck, Streamer etc)?  Numbered inputs are fine, provided you can remember what you have connected to each number.
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 8 Mar 2016, 06:50 pm
Will the OLED module allow the naming of inputs (CD, Deck, Streamer etc)?  Numbered inputs are fine, provided you can remember what you have connected to each number.


Yes.
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: 33na3rd on 9 Mar 2016, 04:21 pm
Perhaps there could be an optional external OLED housing for folks installing a LDR board into an existing preamp?
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: robertopisa on 10 Mar 2016, 05:54 am
Thanks Morten for letting us discuss your design, I think this should be listed as one the features of your preamps :)

Arduino was an example, I think once you put a more powerful system this is good as long as it is Linux. But it has drawbacks, as you say, it adds complexity. Our preamp should boot and periodically be updated when a new version of the OS or when a new driver is available, as it happens for our NAS. Turning off becomes a shutdown, which takes some time. At the end, the LDR preamp is going to become a sophisticated machine on the SW side, which is good but I am afraid of the complexity. I prefer Occam's razor principle, and go for the simplest way to get the job done (and I have to manage a lot of complexity in my daily work). Everyone has experienced the computer getting stuck with a blue screen, very often because of drivers: what if the preamp got stuck with a blue screen and the volume jumps to maximum? With a micro controller, things are more under control, I would use it in an elevator, not a Raspberry. So it seems to me an overkill to use a Linux system to control the preamp, unless we want Spotify directly on your preamp, so it becomes a network player, another beast :)

As for the noise, I would not underestimate its impact as people spend good money on isolating that noise in computer-based high-end audio. Sonically speaking, it is not a hum but its effect is that it flattens soundstage and makes mid-range dull.

I see that there many requests for many inputs, it makes sense. I prefer the shortest path, and maybe it suffices having extra solder pads close to the LDRs.

With the removable box, one could have connectors already soldered on it, so the signal path would be all isolated from the rest, I like this idea of yours :) Note that the box is still plugged in as you say, but in the control signal path, not in the analog audio signal path, which is different to my eyes:

- current analog audio signal path (my guess, assuming no input switch): connector (XLR/RCA) -> soldering -> wire -> soldering -> trace on the board -> soldering -> socket -> plug -> soldering -> LDR -> soldering -> plug -> socket -> soldering -> trace on board -> soldering -> wire -> soldering -> connector (XLR/RCA)

- analog audio signal path in the box with connectors: connector (XLR/RCA) -> soldering ->  trace on the board -> soldering -> LDR -> soldering -> trace on board -> soldering -> connector (XLR/RCA)

As you can see, the number of steps is half in the signal path. Increasing the steps in the control path is less detrimental to my eyes.

Maybe I am too extreme, but you know, this is our hobby: a preamp is a preamp, a computer is a computer :)

Cheers
-Roberto

Hi Roberto. Good to hear from you and thank you for your thoughtful input.

There's little to distinguish an Arduino from our controller board aside from the fact that the Arduino's are mass produced. Both use standard available microcontrollers and are programmed at the basic hardware level. We would have to mate any Arduino with our own custom interface board same as we would for the Raspberry. I prefer the Microchip family of microcontrollers whereas the Arduino uses Atmel although I've worked with both. Our earliest prototype LDR board used an Arduino. Personally, I'm not very keen on the Arduino programming language and prefer working in either C or Pascal. I currently use MirkroElectronika's development hardware and compilers.


The Raspberry Pi is totally different animal wherein we'd be programming on top of a full Linux operating system. A lot more complexity under the hood and we'd be insulated from the microprocessor at the hardware level. Fortunately there are sufficient drivers available for everything we need - and then some - to handle IR receiver and SPI communications, USB, wireless etc. not to mention high level display functionality. Concerns over noise and shielding may be valid but then again our current boards are already running 16 MHZ microcontrollers with shared power supply driving the LDRs and no shielding all without discernible downside.

I'd say it's around 50/50 in terms of comments I receive on the topic of number of inputs. Half are asking for more than 3 and the other half can't fathom why more than 2, perhaps 3 at the most...and some say why not just 1. There's no perfect one size fits all solution here. The current prototype board design comes close  insofar as it has the flexibility to only have 1 input or have up to 6. It's only a matter of adding the LDR modules which are plug in.

It would be a simple matter to minimize trace lengths by eliminating J1L and J1R as such and simply having individual solder pads as close as possible to each input LDR switch. This would have the added benefit of shortening the board up by perhaps another 0.5 inch. However, as a practical matter this doesn't really shorten the signal path. You still have to run wires from each input RCA/XLR jack to the board. The traces may be shorter but the wires to each trace/pad would have to be longer. Pick your poison.

One of the more interesting philosophical issues around design is whether one is designing around a real or imaginary problem. Is noise really a dominant problem here that needs a solution? In my view that remains an interesting question as it relates to the bigger topic of perceived benefit of balanced audio within short run stereo audio...to which I say... I don't know. I can say that with some conviction that noise has not been an issue with any of our LDR preamps aside from the your run-of-the-mill ground loop hum issues which are really a separate noise category best solved through good grounding practices. RF/EM noise has not been a problem as far as I'm aware. Therefore taking special precautions such as shielded boxes and/or cables internally within the preamp do not seem warranted.

Also I doubt anything is gained by having to replace a whole set of LDRs within a removeable shielded box vs. individual LDRs modules. If it's removeable it's still plugged in and not soldered in. Tubes live quite effectively within a plugged in reality, so my thought is LDRs should be able to as well. We use gold plated pins and sockets so corrosion shouldn't be an issue.

One design architecture that we've explored quite a lot is to move the input switching out to the individual RCA/XLR input jack. While this would indeed minimize the signal path of each individual input, you still end up with common signal(s) that have to run back to the LDR board. Plus you'd end up with numerous switching control signal cables running from the LDR board to each input jack which frankly would end up looking really awful.

After going around the track numerous times with various alternatives we arrived at the design you see below in the recent post. By locating the LDR board as close to the rear panel as practical you minimize the signal wire runs to/from the LDR board and ultimately the total signal run distance between the rear panel inputs/outputs and the LDRs. At least that's the thought behind it.   :thumb:

There's one additional step we could take but have resisted. The LDR board could be custom designed to mate up directly with the RCA or XLR jacks. This eliminates any additional wiring between the jacks and the board. The issue  with that is you end up with a different custom board for each and every model of preamp. Many designs use this approach since it has the added benefit of reducing the manhours needed to build a preamp.
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 10 Mar 2016, 03:18 pm
Thanks Morten for letting us discuss your design, I think this should be listed as one the features of your preamps :)

Arduino was an example, I think once you put a more powerful system this is good as long as it is Linux. But it has drawbacks, as you say, it adds complexity. Our preamp should boot and periodically be updated when a new version of the OS or when a new driver is available, as it happens for our NAS. Turning off becomes a shutdown, which takes some time. At the end, the LDR preamp is going to become a sophisticated machine on the SW side, which is good but I am afraid of the complexity. I prefer Occam's razor principle, and go for the simplest way to get the job done (and I have to manage a lot of complexity in my daily work). Everyone has experienced the computer getting stuck with a blue screen, very often because of drivers: what if the preamp got stuck with a blue screen and the volume jumps to maximum? With a micro controller, things are more under control, I would use it in an elevator, not a Raspberry. So it seems to me an overkill to use a Linux system to control the preamp, unless we want Spotify directly on your preamp, so it becomes a network player, another beast :)

After further research into the Raspberry Pi we've decided to stay with a microcontroller. There's just too much operating system overhead to deal with. Just turning it on and waiting for it to boot each time would be too much. It was tempting but just saying no at this time. Will continue to keep an eye on the RPi as it evolves because I see it eventually becoming a widely used embedded controller for Internet of Things applications.

Quote
As for the noise, I would not underestimate its impact as people spend good money on isolating that noise in computer-based high-end audio. Sonically speaking, it is not a hum but its effect is that it flattens soundstage and makes mid-range dull.

One thing that will be different with V3 is physically/electronically separating the microcontroller and it's power regulator from the power regulator feeding the LDR board. And being that it's still a resistive/passive attenuator, there is still no active contact between the audio signal and the power unless you count the transmission of light as active contact.

Quote
- analog audio signal path in the box with connectors: connector (XLR/RCA) -> soldering ->  trace on the board -> soldering -> LDR -> soldering -> trace on board -> soldering -> connector (XLR/RCA)
As you can see, the number of steps is half in the signal path. Increasing the steps in the control path is less detrimental to my eyes.

This would require each input to have its own series/shunt LDR attenuator circuit plus input/output shut off/isolation LDRs. The complexity and cost would increase drastically. I don't see it as a practical solution but I agree that the cleanest, shortest signal path is the best.

Meanwhile, we are continuing to tweak the design. The latest version is shown below. Here we've minimized the audio signal PCB trace lengths with the resulting trade-off being somewhat longer hookup wires from the jacks to the board. We've also added a "Mono" switch feature. There are other minor changes to the LDR control circuit including a more robust low-pass filter in the LDR control signal to suppress noise. We are also going to add another voltage regulator to this board such that the controller board only provides nominal 5V DC to the LDR board and the LDR board has its own regulators for the DACs, ADCs, and op amps. All communications back to the controller board microcontroller is via 4 wire SPI serial data. We'll soon have prototype boards built so we can continue development work and further shake down the design.

(http://www.tortugaaudio.com/images/ldrx.v3_ldr_board_revA.jpg)
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: craig sawyers on 10 Mar 2016, 07:28 pm
Although the SPI links are likely to be short if the controller is in the same case as the analog stuff, might it be an idea to put the controller in a separate enclosure and galvanically isolate the SPI?  That could be arranged to put the kibosh on any potential for digital breakthrough onto the audio, particularly common mode or coupled ground based.

This sort of thing http://www.linear.com/product/LTM2892 and its ilk.
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: robertopisa on 11 Mar 2016, 03:05 pm
I like the new layout.

I agree that there is no perfect solution for everybody :) I am a bit extreme: the ideal for me is without input selector, a box (containing just the XLR connectors and the soldered LDRs) that is directly fastened on the enclosure and connected with a ribbon cable (for the control path and grounding) to the rest of the board.

-R
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 11 Mar 2016, 03:59 pm
Although the SPI links are likely to be short if the controller is in the same case as the analog stuff, might it be an idea to put the controller in a separate enclosure and galvanically isolate the SPI?  That could be arranged to put the kibosh on any potential for digital breakthrough onto the audio, particularly common mode or coupled ground based.

This sort of thing http://www.linear.com/product/LTM2892 (http://www.linear.com/product/LTM2892) and its ilk.


That's a possibility I hadn't considered. The argument for it not being necessary or advantageous is the fact that serial data is only active (clock and data pulses) when volume is being changed and not during normal listening. The argument for using this is to eliminate any microcontroller MHz clock bleed through from the controller board to the LDR board along the 4 SPI lines.

Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: DaveC113 on 11 Mar 2016, 04:56 pm

That's a possibility I hadn't considered. The argument for it not being necessary or advantageous is the fact that serial data is only active (clock and data pulses) when volume is being changed and not during normal listening. The argument for using this is to eliminate any microcontroller MHz clock bleed through from the controller board to the LDR board along the 4 SPI lines.

I think it would be a good idea.... When I was building the preamp there was a bit of noise evident on the signal when touching the encoder before the display panel/encoder assembly was grounded to the chassis. I don't understand how this is possible but it was on the scope... The noise did not show up when touching a grounded conductor at the same time, and grounding the display/encoder assembly eliminated it.
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 13 Mar 2016, 06:07 pm
I think it would be a good idea.... When I was building the preamp there was a bit of noise evident on the signal when touching the encoder before the display panel/encoder assembly was grounded to the chassis. I don't understand how this is possible but it was on the scope... The noise did not show up when touching a grounded conductor at the same time, and grounding the display/encoder assembly eliminated it.


The way the ALPS encoder is designed, the control shaft (and metal knob) is connected to the common leg (ground) of the encoder. Unless you have everything else properly grounded, touching the encoder may show up as noise. Really no different than touching the metal chassis of most any audio device where the chassis is tied to earth/ground.
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: craig sawyers on 14 Mar 2016, 11:02 am
I get a LOT of inquiries asking for more than 3 inputs.

Hi Morten

The LDRx has the option of 3, 4 or 5 inputs.  I guess a fifth input on the LDRxB is not possible because of rear panel real estate.

But on the LDRx, what is the take up of the 4 and 5 input options?
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 15 Mar 2016, 01:36 am
But on the LDRx, what is the take up of the 4 and 5 input options?

Not exactly sure what you mean by "take up" but if you're asking how we handle the additional inputs our current LDR input switching board design handles 3 inputs. To accommodate additional inputs we have to add a second input switching board which piggy backs on the first one.
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: craig sawyers on 15 Mar 2016, 07:22 am
Not exactly sure what you mean by "take up" but if you're asking how we handle the additional inputs our current LDR input switching board design handles 3 inputs. To accommodate additional inputs we have to add a second input switching board which piggy backs on the first one.

I was just curious, in the context of the recent discussion in which some are completely happy with one single fixed input, some with three, and others who would like six - how much demand there was for the five input version of the LRDx.  I totally understand that this might be commercially sensitive and you'd prefer not to say, but the demand statistics could inform the details of the new design.
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 15 Mar 2016, 04:58 pm
I was just curious, in the context of the recent discussion in which some are completely happy with one single fixed input, some with three, and others who would like six - how much demand there was for the five input version of the LRDx.  I totally understand that this might be commercially sensitive and you'd prefer not to say, but the demand statistics could inform the details of the new design.

In reality the majority LDRx units sold have the default 3 inputs yet there are still requests for 4-6 inputs often enough that we continue to try to find the most flexible approach. The LDR3.V2 has 3 inputs & 2 outputs and I'd say that is the sweet spot for most.

Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: jquark on 26 Jul 2016, 07:03 am
Hello Morten,

Currently auditioning a v1 board and am VERY impressed. Any updates on the v3 board? Will it be released in 2016? 

Thank you for being so interactive with customers and for continuing to improve your already wonderful product.
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 26 Jul 2016, 12:31 pm
Hello Morten,

Currently auditioning a v1 board and am VERY impressed. Any updates on the v3 board? Will it be released in 2016? 

Thank you for being so interactive with customers and for continuing to improve your already wonderful product.

Thanks and glad you like what you're hearing. Yours is a familiar reaction of folks who give our preamp/attenuator a real world test drive with their ears.

The V3 is under active development and our goal is to release it in 2016. At this point that remains a goal only. Still too early to project release dates. The V3 is our most ambitious project to date and we are very excited about its potential.

Cheers,  :thumb:
Morten
Title: Update on the V3 Preamp Controller Board in Development
Post by: tortugaranger on 4 Sep 2016, 07:48 pm
We just published some descriptive info on the LDR.V3 (the "V3") board which continues to be under active development.
It is still WAY too early to suggest a release date. While the hardware design is settling down there's still a ton of software development work to be done.

Here's a link to the V3 article:  http://www.tortugaaudio.com/ldr-v3-preamp-controller-system/ (http://www.tortugaaudio.com/ldr-v3-preamp-controller-system/)

(http://www.tortugaaudio.com/images/LDR.V3_graphic.jpg)
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: glynnw on 5 Sep 2016, 01:21 am
You have been a busy boy.  Not sure if I read the new info right, but please make the display available in red.  I recently built (with your help) a new preamp because I could no longer read the blue from about 10 feet.  According to the all wise internet, this is a common condition.
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 5 Sep 2016, 02:07 pm
You have been a busy boy.  Not sure if I read the new info right, but please make the display available in red.  I recently built (with your help) a new preamp because I could no longer read the blue from about 10 feet.  According to the all wise internet, this is a common condition.

As much as I like the cool blue of our current display modules I'm aware that there's something about human vision that can cause blue to be blurry and hard to focus on. The blue of our V3 OLED display has a different appearance compared to the 7 segment display modules which I think make the OLED much easier to look at. Probably something to do with a different wavelength of blue and the fact that the light comes from an organic LED source.  That said, the OLED display model we chose also comes in yellow but not red. I will definitely make sure we try both blue and yellow and keep this issue in mind.
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: kernelbob on 5 Sep 2016, 03:32 pm
I'm glad to hear that I'm not the only person that finds blue displays to be more difficult to read, particularly at a distance.  Morten was able to use orange (yellowish orange?) displays in my Tortugas.  The only downside is that these displays, even at their maximum level, are not as bright as the blue ones.

Best,
Robert
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: tortugaranger on 5 Sep 2016, 04:47 pm

I found the following explanation about difficulty focusing on blue light which seems to cover it quite well.  Included the link & text.

http://www.candlepowerforums.com/vb/showthread.php?343259-Why-is-it-so-difficult-to-focus-on-blue-LED-lights&s=ca83c861ab440bc750f26569681e7cb4&p=4016046&viewfull=1#post4016046 (http://www.candlepowerforums.com/vb/showthread.php?343259-Why-is-it-so-difficult-to-focus-on-blue-LED-lights&s=ca83c861ab440bc750f26569681e7cb4&p=4016046&viewfull=1#post4016046)
Quote
Red and green (which are, from the evolutionary standpoint, the same frequency, as the red and green cones are recent variants of one another while the blue cones are distinct, they use a different photoreactive enzyme) are the dominant *resolution source* for human vision, while blue cones are much more important for expanding our ability to detect color (chrominance). It's why we have more red and green cones than blue ones (IIRC the ration is 10:1, though that may be way off).Since focus is much more important to spatial resolution (details) rather than color resolution, the human "autofocus" is biased to favor the red-green band. Blue gets short shrift because of its relatively minimal importance to resolution. An experiment: if you mess around with the three color channels of an image in a photo program like Photoshop, messing up the blue channel affects the final color image the least, given the same amount of "messing" (like noise or deresolution).Last but not least: as noted, chromatic aberration means that the different colors won't quite match up. It's not normally visible, likely because our brains auto-compensate when combining the different cone inputs into the final image (Canon digital cameras recently acquired a similar ability.) Not everyone is going to notice the effect: this is probably because blue focusses "shorter" in terms of lens focal length than red. So, you are much more likely to notice "blue fringing" if your unaided vision tends towards the nearsighted side (like mine does), given the focus center on red/green -- and you'll see it worst with distant blue sources than near ones. If you know someone who has worse nearsighted vision than yours and wears glasses (and neither of you have astigmatism) try using their glasses and see what happens.
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: craig sawyers on 7 Sep 2016, 08:25 am
Colour vision is a strange and wonderful thing.  Basically even with significantly skewed lighting, they eye/brain decodes the true colours of objects. Edwin Land, the founder of Polaroid, introduces the Retinex theory of colour vision to explain this, and set up carefully designed experiments to demonstrate colour constancy.

In fact the initial films that Kodak introduced did not include blue at all (eg http://zauberklang.ch/filmcolors/timeline-entry/1230/ ), because of chemical problems with fixable blue.  But although these early films were only two-colour red/green, the images look perfectly acceptable. I used this effect in the early-ish 1980's to demonstrate the feasibility of a video endoscope. Because this was the very early days of full colour CCD's, I used blooming-free Charge Injection Devices (CID) from GE, and a two colour LCD stack, so the instrument did frame sequential green/red switching.

In fact in early experiments using different colour highlighting pens, illuminated with two slightly different red filters, viewers could identify most of the pen colours.

Worked a treat.
Title: Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
Post by: konut on 7 Sep 2016, 03:39 pm
Appropriate to nothing, it appears that humans perception of blue is a, relatively, recent adaptation.

http://www.radiolab.org/story/211213-sky-isnt-blue/