[tortugaranger]

So, if LDR really is better, than say, Shallco switch stepped attenuators with 0.1% TX2575 resistors, then you have a benefit-but without publishing very precise measurements from an AP sys 2 of a passive with the above two volume controls there is little evidence to prove that the LDR is better.  Let's see a comparison of noise and distortion spectra at: 0 dB, -4 dB, -8 dB, -16 dB, -32 dB, -64 dB.

Thanks for your comments.

If specs and measurements were all it took to line up audio gear on a continuum from worst to best then audioland, as we know it, would be a very different place indeed. No measurement is going to convey the benefits of LDRs over other alternatives. I've not exhaustively measured all aspects of the LDR performance but our LDR manufacturers have done quite a bit of work and it's not all that impressive on paper. Distortion specs are middling. I've had people tell me point blank the LDRs will not, can not, and do not work in audio applications and would sound like crap if you tried to use them. Which of course is totally ridiculous because the proof is in the listening and not in the measurements. I realize and fully accept that there's a segment of potential buyers for whom lack of detailed measured data is a non-starter. I'm an engineer and I love hard data. But at the end of the day all I really care about is what does it sound like.

When I first started working with LDRs back around 2009 I was shocked at their sound quality relative to pots and stepped attenuators. I had a few friends try out early prototypes and got nothing but rave responses. Frankly I was worried I was deluding myself but with rare exception most everyone who gets an earful of LDR attenuation has a similar reaction.

Eventually we will get around to offering a buffer option which will take care of those few cases where additional current drive is needed. The trick will be to do no harm in the process which should be doable. And by harm I mean add noise and/or coloration.

[RDavidson]

R: the above is only true as a thought experiment, or technically.  From the standpoint of audability, it is entirely possible to design and implement a buffer circuit which will be below the threshold of audability, and hence, be transparent.

I understand. I was objecting to your statement about a buffer being "absolutely" transparent. It can't be. No component is 100% transparent. But for the sake of the topic, we can limit the range of the concept of signal transmission transparency to the source output signal and components following the source. In this case, I still say anything in the signal path all the way to the sound produced by the transducers will affect the signal to some degree (including the transducers themselves). The degree of audability that a component in the chain affects transparency, would assume one has heard and possibly measured the source signal directly for comparison.

To keep discussion on track, I like zero gain, buffered, preamps. I think an LDR with a really good class A (maybe JFET) buffer, would be AMAZING. Absolutely transparent? No. Perhaps the least compromized preamp solution? Yes, quite possibly. Would I be very interested in trying such a preamp and possibly purchasing it? Yes. Absolutely.

[barrows]

barrows,

Why don't you participate in the Tortuga LDR tour? Do your tests if you want, listen to how  it sounds compared to your "fully transparent" active pre and come to your conclusions first hand.

My time for testing audio gear is quite limited, I would rather spend my free time for pleasure listening rather than testing.  I help develop products (no preamps) and test those, and do my own DIY stuff as well, so my plate is pretty full.
I do not have a preamp at all, nothing sounds better than no preamp, I make no claim to having a transparent active pre.
I build my own DACs, make sure I am well matched for gain, and use digital volume control, which as long as it is used within reasonable attenuation limits is totally transparent (within the limits of audibility).  I use a single input DAC (USB or Ethernet, I am working with both) to avoid degrading switches in the digital signal path, and have a single balanced interconnect pair going to my amp.  I am big believer in less being more.

I find the thread a little confusing, as on the one hand it appears to be about the benefits of LDRs for volume control, and on the other hand it is also a discussion of passive preamps.

Since I have no need for an additional (signal degrading) component, there would be no point in joining the tour.

I do have experience, in the past, with passive and active preamps of course.  But I have moved beyond their capabilities in my set up.  Next thing to try will be the Ethernet DAC approach, with an I/V consisting of only 4 MOSFETS and 8 resistors for balanced output, further simplifying the signal path.

[Shakeydeal]

I build my own DACs, make sure I am well matched for gain, and use digital volume control, which as long as it is used within reasonable attenuation limits is totally transparent (within the limits of audibility).

Yeah, but how do you spin yer rekkids? There is nothing more important than that......


Shakey

[tortugaranger]

To keep discussion on track, I like zero gain, buffered, preamps. I think an LDR with a really good class A (maybe JFET) buffer, would be AMAZING. Absolutely transparent? No. Perhaps the least compromized preamp solution? Yes, quite possibly. Would I be very interested in trying such a preamp and possibly purchasing it? Yes. Absolutely.

What this tells me is we better finish getting that buffer designed, tested and launched. If having a buffered LDR attenuator is what people want then we should deliver that option. What will be interesting is the little bypass switch in the back that will allow you to hear it with and without the buffer. I'm quite curious myself. 

[barrows]

"What will be interesting is the little bypass switch in the back that will allow you to hear it with and without the buffer. I'm quite curious myself."

Me to!

But I would suggest, that if one hears a degradation in sonics with the buffer switched into the circuit, the correct conclusion to draw will be that the buffer design (including its power supply, in fact the power supply may be more important than the buffer circuit itself) is not good enough.  But, it is a shame to have those switches in the signal path.  I have participated in listening tests (and seen measurements, even measurements show distortion of the best relays vs a straight wire) of switches vs a wire, hence my preference to get as many junctions out of the signal path as possible (including jacks, relays, switches, solder joints, etc)

As to the poster who asked about LP playback in my system: I do not do it.  I prefer a single source for the aforementioned reasons, and my focus for the past 6 years or so has been to get my digital performance as high as possible.  I do appreciate the sound of vinyl, but it is not transparent (this is another discussion, OT, and hence I will not address it here again).  That said, I have been collecting LPs over the last few years, and there will be a time when I have a turntable and phonostage in my system again (I will probably switch interconnects though, rather than add a signal degrading preamp with source switching).

[rajacat]

My time for testing audio gear is quite limited, I would rather spend my free time for pleasure listening rather than testing.  I help develop products (no preamps) and test those, and do my own DIY stuff as well, so my plate is pretty full.
I do not have a preamp at all, nothing sounds better than no preamp, I make no claim to having a transparent active pre.
I build my own DACs, make sure I am well matched for gain, and use digital volume control, which as long as it is used within reasonable attenuation limits is totally transparent (within the limits of audibility).  I use a single input DAC (USB or Ethernet, I am working with both) to avoid degrading switches in the digital signal path, and have a single balanced interconnect pair going to my amp.  I am big believer in less being more.

I find the thread a little confusing, as on the one hand it appears to be about the benefits of LDRs for volume control, and on the other hand it is also a discussion of passive preamps.

Since I have no need for an additional (signal degrading) component, there would be no point in joining the tour.

I do have experience, in the past, with passive and active preamps of course.  But I have moved beyond their capabilities in my set up.  Next thing to try will be the Ethernet DAC approach, with an I/V consisting of only 4 MOSFETS and 8 resistors for balanced output, further simplifying the signal path.

So your schedule is too busy for testing gear. Why don't you sign up for the tour and just listen, don't measure, to the Tortuga in your own highly revealing system? Surely that wouldn't take much time and then you'd be able to comment on the Tortuga with first  hand knowledge and your opinion would have more substance.

[RDavidson]

What will be interesting is the little bypass switch in the back that will allow you to hear it with and without the buffer. I'm quite curious myself. 

Hmmmm......maybe rather than a switch you could have internal jumpers? I know this would take away the convenience factor, but I think performance would be less compromized. Another thought is to use external jumpers, as commonly seen on NAD integrated amps.
OR........and I'm not sure how difficult this would be, but could you have 4 outputs (2 buffered and 2 straight)? What's cool about this is it would have no compromizing switches or jumper connections, AND it'd allow the user to mix and match outputs as needed. Maybe one could use a straight output to their amp, and a buffered output to a sub. That'd be sweet!

[DaveC113]

I think zero gain preamps are a good thing for most systems these days but am also of the opinion a buffer is a good thing, otherwise the output section of your source would have to be a prime consideration. I am also of the opinion, based on my own experience, that gain devices (like a source's output) should not simultaneously have to provide current, so they should be buffered. I do think an LDR volume control paired with a tube based white follower would be close to an ideal preamp while a non-buffered attenuator's performance is going to vary depending on the system it's used in.

I also agree with barrows about leaving out as many parts as possible, good switches are expensive and if you can do without that would be best.

[Early B.]

What this tells me is we better finish getting that buffer designed, tested and launched. If having a buffered LDR attenuator is what people want then we should deliver that option. What will be interesting is the little bypass switch in the back that will allow you to hear it with and without the buffer. I'm quite curious myself. 

I agree, and expect a better sounding preamp once you're done, along with a much higher price tag.  

My experience with three different passives, including an LDR preamp, is the need for power. I don't care what the specs say, I came to the conclusion that a powered preamp simply sounds more, ummm... powerful. The "fewest parts in the signal path" approach has little merit, IMO. I'd suggest adding a buffer to the LDR attenuator that incorporates a well designed, overbuilt power supply.   

[Shakeydeal]

My experience with three different passives, including an LDR preamp, is the need for power. I don't care what the specs say, I came to the conclusion that a powered preamp simply sounds more, ummm... powerful. The "fewest parts in the signal path" approach has little merit, IMO. I'd suggest adding a buffer to the LDR attenuator that incorporates a well designed, overbuilt power supply.

Then I would suggest you evaluate your system. You probably have an amp with low input sensitivity and low input impedance. That situation surely requires more drive than a passive device will offer. I don't want transparency at the expense of body, weight and drive, but I give up none of these with the LDR. Then again, my system is more suited to this situation.

Shakey

[Early B.]

I also agree with barrows about leaving out as many parts as possible, good switches are expensive and if you can do without that would be best.

Perhaps add a switch to the prototype so you, as the designer, can know exactly what the buffer is doing. I don't see much benefit for customers to be able to switch back & forth between active and passive.

[Shakeydeal]

I just looked at the specs on your amp and it's not surprising that you need an active preamp.

Input sens 1.5v

Gain 26db

Input Z 47K

Shakey

[Early B.]

Then I would suggest you evaluate your system. You probably have an amp with low input sensitivity and low input impedance. That situation surely requires more drive than a passive device will offer.

When I said, "I don't care what the specs say...", I meant that my amps and sources at the time all conformed to the input sensitivity and impedance specs for all of the passive preamps I've tried, but specs alone are insufficient in determining the resulting sound.

[Shakeydeal]

Understood.

But if you were using the amp listed in your system while trying any of these passive devices, you weren't doing them any justice. Now if you had a different amp, well, that's different isn't it?

[Early B.]

I just looked at the specs on your amp and it's not surprising that you need an active preamp.

Input sens 1.5v

Gain 26db

Input Z 47K

Shakey

Those are specs from the MK3 model. I have the MKI. The input sensitivity on my amp is 1.1v. Besides, I didn't own this amp when I used the other passive preamps I've owned. 

[Shakeydeal]

Ok. But just remember that even though listening is the final arbiter of good sound, in this instance the specs do mean something. I am not a specs/graph whore by any means. But when mating amps to preamps, they tell quite a story.

Just sayin......

Shakey

[barrows]

I am a little confused:

"Input sens 1.5v

Gain 26db

Input Z 47K"

The above specs do not describe an amplifier which would be challenging to drive.  There are many amplifiers with much lower input Z than this.

[tortugaranger]

Perhaps add a switch to the prototype so you, as the designer, can know exactly what the buffer is doing. I don't see much benefit for customers to be able to switch back & forth between active and passive.

There will be a buffer bypass switch in the prototype and maybe even in a tour unit but not in a final commercial unit. And I will definitely convey my impressions of performance with and without the buffer in the circuit path.

However, I confess there's a part of me that would love to ship a tour unit around with a big fat red bypass switch on the front panel with a sign under it that reads: "Caution: Bypassing the buffer may disrupt you're preconceptions regarding the necessity of a buffer in an LDR preamp."

[Shakeydeal]

I can tell you from experience that amplifiers with sens. of <1v and input impedance of 100K are FAR easier for a passive linestage to drive. You start straying too far away from these specs and it's a crap shoot.

What I am saying is that if you don't need additional gain, the additional gain itself won't make a preamp sound "more powerful". Ultimately, when you are using 1/4 of the volume control, you are throwing away unnecessary gain. You add it, only to attenuate it. How does that make sense?

Shakey