This is the best Volume Control for DIY I know of.

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glynnw

This is the best Volume Control for DIY I know of.
« on: 29 Aug 2013, 07:19 pm »
I have absolutely no monetary interest in Tortuga Audio - this is simply written as a fanboy.  I received one of these LDR boards and remote a week ago and it is absolutely the clearest volume control I have ever heard - by a mile.  Add rca inputs and outputs, almost any 12V wall wart, solder the three legs of the Infrared Receiver to the board (This all takes less than an hour easily) and you have what in my opinion is the best passive volume control available. I have been using a TVC for a couple of years and I like this better. 2 days ago I put my TVC back in and took it back out of the system after 15 minutes.

Specific examples - On David Gray's album White Ladders, on the title cut, I now hear so much background noise the cut is almost no longer enjoyable.  I never noticed this until I got the LDR.

On The Mamas and the Papas Greatest Hits (I am an old man) on Dream a Little Dream With Me, at the start Mama Cass is saying something in a low voice that I have never full understood.  Now I know exactly what she said.

I am a loyal Bottlehead follower and have built several preamps with non-supplied volume controls, since I insist on always having remote balance.  This is ideal for any DIY builder.

The negatives:

This does not have the extra few dB of gain a TVC can supply.  I can live with that.

A few recordings now sound harsh.  Since recordings I know were done well still sound great, I can only surmise that I am hearing harshness in the recording I never noticed before.  I am using JRiver and can use it's DSP to compensate on the few recordings where it's needed.

This also has a 12V trigger which I now use to turn on the system through my PS Audio Power Plant.  This makes for 1 less remote controller to have lying around.
 
I guess that wraps it up.  I have been listening to this for a week and am still in awe.  Usually that wears off after a couple of days. 

poseidonsvoice

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Re: This is the best Volume Control for DIY I know of.
« Reply #1 on: 29 Aug 2013, 11:13 pm »
Great review :thumb:

Mind sharing which TVC you had?

Thanks,
Anand.

James Romeyn

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Re: This is the best Volume Control for DIY I know of.
« Reply #2 on: 30 Aug 2013, 01:13 am »
That gear indeed seems unbeatable as long as you don't need extra gain.  That's quite a testimony based on your prior attenuator. 

A friend of mine was looking at light resistor attenuators a year or more ago.  IIRC there were significant performance negatives with the earlier light resistors.  If I'm wrong I apologize.  But if that's correct, what was the downside and what was the remedy?

Nothing in the world can make up for the audio sins of a bad preamp, that's for sure. 

Get a can of Caig DeOxit Gold and clean every contact in sight.  If you've not used it, you should hear improvements similar to your new attenuator, really!  Especially that harshness you mentioned that seems software dependent. 


glynnw

Re: This is the best Volume Control for DIY I know of.
« Reply #3 on: 30 Aug 2013, 03:52 am »
I prefer not to say which TVC, but it is extremely well regarded. The company did me a big favor at one time and I will never denigrate one of their products.   I have also had a Placette, Welborne Labs with nude Vishay, a handmade shunt, still have a set of Ultimate Attenuators in the closet.  Sorry, but no cleaning of contacts is going to be comparable.  I really want to hear what someone else thinks of this Tortuga LDR.  After over a week of playing with it, this afternoon I still got completely involved in listening to how it makes things I know well sound so much better. I remain stoked!

WireNut

Re: This is the best Volume Control for DIY I know of.
« Reply #4 on: 30 Aug 2013, 07:09 am »
From a photo I've seen of the Tortuga passive unit it appears to use IC's which would cause me to look at something else. What is LDR technology and how could it better an autoformer volume control ?


 

poseidonsvoice

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Re: This is the best Volume Control for DIY I know of.
« Reply #5 on: 30 Aug 2013, 11:55 am »
From a photo I've seen of the Tortuga passive unit it appears to use IC's which would cause me to look at something else. What is LDR technology and how could it better an autoformer volume control ?

Wirenut,

I see the IC's only with supportive circuitry, so honestly no worries.

Not all TVC's are created equally however, and there are few AVC based units for comparison out there. I think if Morten goes for a 'tour' he may increase sales so people can compare in their own systems. Definitely a cool product...

Best,
Anand.

*Scotty*

Re: This is the best Volume Control for DIY I know of.
« Reply #6 on: 30 Aug 2013, 12:34 pm »
The LDR is not exactly passive. While the device has no gain, it does have a transfer function and a certain amount of measureable IM and THD.
 I wouldn't loose any sleep over the prescence of ICs in the circuit, they have to be there.
Scotty

James Romeyn

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Re: This is the best Volume Control for DIY I know of.
« Reply #7 on: 30 Aug 2013, 02:33 pm »
...Sorry, but no cleaning of contacts is going to be comparable....

Premature till you try it.  Performance wise it's plain wrong to lump Caig DeOxit Gold with any other contact cleaner/treatment.  Since sampling its predecessor products (two generations prior) I've never gone a day without a can in my possession.  The better the system the bigger is the improvement.

tortugaranger

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Re: This is the best Volume Control for DIY I know of.
« Reply #8 on: 30 Aug 2013, 03:07 pm »
From a photo I've seen of the Tortuga passive unit it appears to use IC's which would cause me to look at something else. What is LDR technology and how could it better an autoformer volume control ?

The digital/IC parts of our LDRx passives are there solely to facilitate precise regulation of the LDR current (brightness) on the LED side of the LDR cans. And of course the current/brightness of the LED side is proportional (although non-linearly) to the resistance on the audio signal side of the LDR. Whatever evils one may assign ICs in an analog device, with LDR's there's optical isolation between the control side and the audio signal of LDRs. Still, we do apply filtering to mitigate any impact the IC side may have on the audio side via the optical connection.

I don't have any personal experience with transformer based volume control so I don't have a direct informed view. What I can say is that several of our customers have owned and extensively used TVCs and have told us that our LDRx passives beat their TVCs without ambiguity. I don't have a technical explanation for this but who am I to argue?  :green:

Cheers,
Morten

« Last Edit: 31 Aug 2013, 11:09 am by tortugaranger »

tortugaranger

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Re: This is the best Volume Control for DIY I know of.
« Reply #9 on: 30 Aug 2013, 03:25 pm »
A friend of mine was looking at light resistor attenuators a year or more ago.  IIRC there were significant performance negatives with the earlier light resistors.  If I'm wrong I apologize.  But if that's correct, what was the downside and what was the remedy?

While I don't purport to be the oracle of all things LDR, the historical challenge, and to a lesser degree the challenge today, is that LDRs can exhibit highly variable performance characteristics from one to the next even from the same batch from the same manufacturer. Add to that the fact that their current vs. resistance relationship is nonlinear. Plus up to a few years ago most LDRs didn't have the resistance range to pull off a decent audio attenuator design. Today you get LDRs that can be controlled from +100k down to ~50R. In our designs we don't run them much below ~100-150R mostly to ensure longevity. @ 50R you're running close to their recommended current limit which will age them as with any LED based device. We overcome the variability and nonlinearity through testing and software based correction curves that results in precise attenuation control. To execute that approach, each LDRx preamp product has its own custom correction curves embedded in its software. It's a PITA but the results speak for themselves.

Cheers,
Morten

Atlplasma

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Re: This is the best Volume Control for DIY I know of.
« Reply #10 on: 3 Sep 2013, 11:00 pm »
My curiosity got the best of me. I have a balanced master and slave board on order and will post comments as soon as they arrive and are operational.

tortugaranger

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Re: This is the best Volume Control for DIY I know of.
« Reply #11 on: 4 Sep 2013, 12:21 pm »
Received our first customer feedback on the LDR3x being used in a balanced (master/slave board) configuration. It was posted on DIYAudio so I'm quoting it here with a link to the post. This is yet another instance of our LDRx preamps being compared to a TVC by a user/owner of both. 

9.5.13 Correction:  Turns out he only implemented a single ended setup with the master board due to lack of a balanced source.

Quote
I received the kit, thanks. I have temporarily housed it in a plastic project box with very cheap and nasty phono sockets. I am delighted to report that it is clearly and unexpectedly better than my amorphous core TVC with its WBT "Next Gen" silver phono sockets. Thanks for the outstanding product!

Link to post on DIYAudio: http://www.diyaudio.com/forums/vendors-bazaar/230114-tortuga-audio-ldr3x-diy-preamp-controller-w-remote.html#post3619276
« Last Edit: 5 Sep 2013, 12:03 pm by tortugaranger »

WireNut

Re: This is the best Volume Control for DIY I know of.
« Reply #12 on: 19 Sep 2013, 12:32 am »

I think if Morten goes for a 'tour' he may increase sales so people can compare in their own systems. Definitely a cool product...


I second that motion. Morten, you should do a tour. Just one input/one output in a plastic box is all we need. I'm itching to try a passive in my bi-amp system. The thought of getting rid of my 2 box preamp with boo-coo caps, noisy tubes, ext, is very intriguing.







 

jtwrace

Re: This is the best Volume Control for DIY I know of.
« Reply #13 on: 19 Sep 2013, 12:47 am »
The thought of getting rid of my 2 box preamp with boo-coo caps, noisy tubes, ext, is very intriguing.
That's a no brainer IMO. 

JeffB

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Re: This is the best Volume Control for DIY I know of.
« Reply #14 on: 19 Sep 2013, 01:25 am »
I am curious.  One of the purported problems with passive pre-amps is impedance mismatch between source and amplifier.  There are those who say that as long as the source output impedance is low enough and the amplifier impedance is high enough that all is good.  And then others will say that even with this condition satisfied that there is still a loss of "drive".  The big selling point of TVCs is that they better manage the impedance mismatch.
I don't know how an LDR relates to this impedance mismatch issue.  Is it simply a means of creating resistance(much like a resistor) but which more evenly passes all frequencies.  Or does it somehow also improve the "drive" like a TVC is purported to do.  I guess I am really wondering if this notion of lack of "drive" due to impedance is a misplaced notion of why passives may be inferior to actives.  It would also imply that actives are on the wrong path to optimal sound also as they seemed to be focused on improving this "drive" issue.  Could it be that the real issue is simply one of the linearity of the resistance?

WireNut

Re: This is the best Volume Control for DIY I know of.
« Reply #15 on: 19 Sep 2013, 01:56 am »

One of the purported problems with passive pre-amps is impedance mismatch between source and amplifier. 


Right. Impedance and gain questions for my bi-amp system have put me off purchasing passive units. Hence the need for a tour.











 




 

     

tortugaranger

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Re: This is the best Volume Control for DIY I know of.
« Reply #16 on: 19 Sep 2013, 02:20 pm »
I am curious.  One of the purported problems with passive pre-amps is impedance mismatch between source and amplifier.  There are those who say that as long as the source output impedance is low enough and the amplifier impedance is high enough that all is good.  And then others will say that even with this condition satisfied that there is still a loss of "drive".  The big selling point of TVCs is that they better manage the impedance mismatch.
I don't know how an LDR relates to this impedance mismatch issue.  Is it simply a means of creating resistance(much like a resistor) but which more evenly passes all frequencies.  Or does it somehow also improve the "drive" like a TVC is purported to do.  I guess I am really wondering if this notion of lack of "drive" due to impedance is a misplaced notion of why passives may be inferior to actives.  It would also imply that actives are on the wrong path to optimal sound also as they seemed to be focused on improving this "drive" issue.  Could it be that the real issue is simply one of the linearity of the resistance?

I very much appreciate this comment because it highlights the central issue surrounding passives generally.

Anecdotally, you can find published user accounts on various forums etc. which excoriate passive (resistive) preamps as lacking drive and dynamics, having flabby sound, the list goes on....or to sum it up...they suck! I strongly suspect that the root of these disappointments with passives generally is the impedance mismatch issue possibly compounded by sources with low line stage voltage and/or very limited current "drive" capacity. So if you couple a source with a weak line stage and high'ish output impedance (say 1k)  with an amp with a low input impedance (say 15k) and then place a passive resistive attenuator between these 2 components where the attenuator's impedance varies from 50k+ to 1k- to 50k+ over the 0-max  volume range, chances are you might not like the results. These components probably need a buffer between them, i.e. an active preamp.

What I've experience subjectively (as have practically all of our customers so far) is using our LDR passive between a contemporary source (decent line stage voltage/current plus reasonably low output impedance - say 500-800R) and an amp having an input impedance of say 40-50k or higher, the impedance mismatch issue is effectively made moot. A handy reference number is if you have amp:source impedance ratio of ~50:1 or higher, you're highly likely to have a very satisfying listening experience. No lack of drive or dynamics.

Now lets take a look at the DC (0 HZ) impedance curve that is typical of our LDRx attenuators. The first pic below shows the raw test data from a build of our LDR3x. It plots the series and shunt resistances for both the left and right side LDRs. Resistance is plotted logarithmically. Now check out the 2nd pic showing this same data but with resistance plotted linearly. Notice the distinct bathtub shape of the resistance curves that are more clearly evident in the linear plot. As it turns out we only need the very high series resistance on the left side and the very high shunt resistance on the right to achieve the last few dB of attenuation on either end of the attenuation curve. Normal listening is done mostly in the middle range where the impedance is relatively low - say a few K - and relatively flat.  Another view of this same data is shown in the 3rd pic which shows the series/shunt resistances as dB of attenuation.

Please note that this dB vs. step curve is NOT the dB vs. step curve of the LDRx. We pick points along this curve to build the 70 step audio taper curve that gets programmed into each LDRx with each step being close to ~1 dB. See the last pic for our typical audio taper curve.













tortugaranger

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Re: This is the best Volume Control for DIY I know of.
« Reply #17 on: 19 Sep 2013, 02:39 pm »
I second that motion. Morten, you should do a tour. Just one input/one output in a plastic box is all we need. I'm itching to try a passive in my bi-amp system. The thought of getting rid of my 2 box preamp with boo-coo caps, noisy tubes, ext, is very intriguing.

Ok. I'll go ahead and set this up. No need for plastic box. We already produce/sell the LDR1 which is a finished unit with 1 input and 2 parallel outputs. It uses a different board than the LDR3x but in every way that matters it's identical to the LDR3x in technology/design/software. How does that sound as an approach?

WireNut

Re: This is the best Volume Control for DIY I know of.
« Reply #18 on: 19 Sep 2013, 03:18 pm »
Ok. I'll go ahead and set this up. No need for plastic box. We already produce/sell the LDR1 which is a finished unit with 1 input and 2 parallel outputs. It uses a different board than the LDR3x but in every way that matters it's identical to the LDR3x in technology/design/software. How does that sound as an approach?

That would be fantastic :thumb:


briang

Re: This is the best Volume Control for DIY I know of.
« Reply #19 on: 19 Sep 2013, 05:10 pm »
I would be more than happy to contribute a few $s for this.  I would be looking to replace an axiom audio passive.

Thanks,

Briang