[tortugaranger]

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/

[poseidonsvoice]

Suhweeeet!

Best,
Anand.

[uraqt]

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

[tortugaranger]

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. 

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! 

[TrungT]

"cool bean" indeed. 
Sign me up! 

[glynnw]

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..

[TrungT]

Phone camera:

[tortugaranger]

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. 

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. 

Cheers,
Morten

[tortugaranger]

Hi Trung,
How did you attach the Display Module to the acrylic  front panel?
Regards,
Morten

[TrungT]

Hi Morten
The display is mounted on the "L" bracket.
 

[Vlad]

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

[tortugaranger]

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. 

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

[Vlad]

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

[jtsnead]

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?

[tortugaranger]

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

[tortugaranger]

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

[glynnw]

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?

[tortugaranger]

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

[glynnw]

Couldn't ask for more.  Thanks.

[tortugaranger]

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