LDR3x.V2 DIY Passive Preamp Controller Board w/ Remote

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tortugaranger

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Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
« Reply #100 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.

robertopisa

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Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
« Reply #101 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.

tortugaranger

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Multichannel Volume Control
« Reply #102 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

poseidonsvoice

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Re: Multichannel Volume Control
« Reply #103 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.

tortugaranger

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Re: Multichannel Volume Control
« Reply #104 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

tortugaranger

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Change V2 Preamp Impedance via Remote & Auto Calibration
« Reply #105 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

kernelbob

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Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
« Reply #106 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.

JohnR

Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
« Reply #107 on: 15 Jul 2014, 06:41 am »
On the V1 board, is the impedance of the Hi-Z update 10k or 20k?

tortugaranger

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Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
« Reply #108 on: 15 Jul 2014, 11:03 am »
On the V1 board, is the impedance of the Hi-Z update 10k or 20k?

10k

tortugaranger

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Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
« Reply #109 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

tortugaranger

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Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
« Reply #110 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

dantakayama

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Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
« Reply #111 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

robertopisa

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Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
« Reply #112 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

kernelbob

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Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
« Reply #113 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

dantakayama

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Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
« Reply #114 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

dantakayama

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Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
« Reply #115 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

robertopisa

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Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
« Reply #116 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

dantakayama

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Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
« Reply #117 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

tortugaranger

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Re: LDR3x DIY Passive Preamp Controller Board w/ Remote
« Reply #118 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:

tortugaranger

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High Praise from Customer
« Reply #119 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