[ThuanDB]

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.

+1.

I used to prefer minimalist approach, abandoned an Adcom active preamp to go with CD direct variable gain, then EVS attenuators, then a TVC (transformed volume control).  My honeymoons with those passive devices were not very long, due to lifeless, weak bass presentation in trade of lower noise floor and a perceived transparency.

For the last few years I've been fairly happy with a Dodd Audio variable gain tube preamp.  It seems responsive well to the changes in the setup.  But perhaps like many audiophiles here, I keep my ears and eyes open.  I've found this forum discussing the LDR preamp and ordered one unheard based on positive reviews and what it promises to offer.  I hope it will beat or at least equal my current active preamp.

[tortugaranger]

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.

I agree and would like to steer us around this topic detour.

Amp sensitivity per se has very little to do with compatibility with a Tortuga LDR passive or passives generally. Input sensitivity is the input voltage level (from the source/preamp) which drives any given amp to its full output. Typically these range from 0.7 to 2.0 with most somewhere in the middle. Reason being that most source components have a nominal line stage output voltage within this same range.

What is far more relevant is the combination of amp power output (at full voltage input) together with the sensitivity of the speaker. A very low wattage SET tube amp with highly sensitive speakers works great with our LDR passive - plenty of volume available at mid range attenuation levels. But hook up a low sensitivity speaker to that same low wattage tube amp and you will likely discover you need some premap gain (more voltage) in which can no passive will suffice.

What is most relevant is the bridging impedance ratio between the amp's input impedance and the output impedance of the source. If this ratio is big enough, the source doesn't have to work very hard to deliver its audio energy (minimal current demand).

What we've found in practice based on customer experience is most combinations of sources and amps are well suited for LDR passives and very few are not.

[33na3rd]

Just for giggles, I hooked my LDR3.V2 to a Dynaco ST-150.

Zin = 35K, Input sensitivity = 1 volt.

I was surprised how good the combination sounded.

[DaveC113]

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."

IME if you build a good tube buffer it will sound better in a large majority of circumstances, and not just because of pleasant coloration.

[tortugaranger]

IME if you build a good tube buffer it will sound better in a large majority of circumstances, and not just because of pleasant coloration.

And there you have the crux of the LDR passive challenge boiled down into one sentence or even part of a sentence. The perception that with a "buffer it will sound better". In the end it may simply be easier and more productive to add a buffer than to try to convince an informed skeptic that it's not necessary.

The irony here (and it is truly ironic) is that we arrived where we are (passive LDR with no buffer) by working backwards from a tube preamp with pot, to a tube preamp with an LDR attenuator, to no tube/buffer and only a passive LDR attenuator and at each step the sound quality improved. Whereas many here are saying, no, go back, put the tube buffer back in because it will sound better.   

[Shakeydeal]

Morten,

As much as you try, you can't convince everyone. As the saying goes, "save the saveable".

Some don't qualify......

Shakey

[ThuanDB]

I'd say, whatever well executed will sound good.  And "Less is More" is not always true.  Recently I added a Cisco switch in between audio PC and control PC, and the set up sounds better, more to my liking.  Back to this thread discussion, a very good active pre is not likely going to beat a very good passive pre (such ad the LDR).  Here I think "Less is More" does work although there are additional ingredients (LDR, design, execution).  In a nutshell, I think Tortuga LDR is a breakthrough with superb sound quality, remote control, upgradability, and passionate service.  When mine arrives in a few days, will find out if I'm wrong.

Congratulations Morten.  I think you're onto something special.

[rajacat]

I just don't understand why the skeptics don't sign up for the tour? It's free except for postage.

[tortugaranger]

I just don't understand why the skeptics don't sign up for the tour? It's free except for postage.

RJ perhaps the smartest thing to do is to have multiple tours running in parallel.

[ThuanDB]

There are always skeptics, and there are always ones who leap on faith.  I'd let the time and the words of mouth do the work.

[DaveC113]

And there you have the crux of the LDR passive challenge boiled down into one sentence or even part of a sentence. The perception that with a "buffer it will sound better". In the end it may simply be easier and more productive to add a buffer than to try to convince an informed skeptic that it's not necessary.

The irony here (and it is truly ironic) is that we arrived where we are (passive LDR with no buffer) by working backwards from a tube preamp with pot, to a tube preamp with an LDR attenuator, to no tube/buffer and only a passive LDR attenuator and at each step the sound quality improved. Whereas many here are saying, no, go back, put the tube buffer back in because it will sound better.   

The operative word here is a GOOD tube buffer. Many preamps do not have good driver sections and many simple buffers are compromised in their design and implementation. Indeed, if you put in a crappy buffer it will sound crappy. I think you have not experienced or built a decent buffer yet, and you do not seem open to the idea this is possible. Your anecdotal experience with one tube preamp means very little to nothing. Anyway, you seem pretty set on your ideas... and belittling of mine, so I am out.

[Shakeydeal]

"The operative word here is a GOOD tube buffer. Many preamps do not have good driver sections and many simple buffers are compromised in their design and implementation. Indeed, if you put in a crappy buffer it will sound crappy. I think you have not experienced or built a decent buffer yet, and you do not seem open to the idea this is possible. Your anecdotal experience with one tube preamp means very little to nothing. Anyway, you seem pretty set on your ideas... and belittling of mine, so I am out. "

Please see my post earlier in this thread regarding the tube preamps I have owned. I'm sure at least some of these qualify as "good".

Shakey

[glynnw]

You might consider having a few basic units available to potential customers, not just those on the tour.  Then if they like it, they buy it or return it for a model with more features.  Several companies are doing variations of that, though most want payment first and then refund all or part of it.  This should bring in customers faster than waiting to hear it on a tour.

For myself, as I have said here before, a few seconds of hearing this product in my system was all it took.  Later I became tempted by the active passive argument again, so I had Roger Modjeski build me a small preamp with just a switch for no gain/ +6 dB gain and no other controls.  I placed it in my system between the Tortuga and my amps and heard no change, other than the gain when I flipped the switch.  So for me pure passive remains the way although it's nice to know I can add some gain if needed.  I think this also paints of good picture of Roger's abilities to design good gear.

In short, try it and you will probably prefer it to whatever you have now.  And the prices are great.  And no, Morten doesn't pay me to say this stuff.

[tortugaranger]

The operative word here is a GOOD tube buffer. Many preamps do not have good driver sections and many simple buffers are compromised in their design and implementation. Indeed, if you put in a crappy buffer it will sound crappy. I think you have not experienced or built a decent buffer yet, and you do not seem open to the idea this is possible. Your anecdotal experience with one tube preamp means very little to nothing. Anyway, you seem pretty set on your ideas... and belittling of mine, so I am out.

Dave, No belittling intended certainly. That's not my style. Sorry if I offended. The premise of this thread is that LDR Passive Preamps sound better than they have a right to according to conventional preamp design. That has been demonstrated over and over. Not to you, but to enough other folk that my personal anecdote isn't relevant. The conundrum here is I'd like to convince a broader audience of the merits of our LDR preamps but am confronted with the presumption that because the design doesn't conform to conventional preamp design (buffer - and maybe gain too) that it can't possibly be as good as we say and so that segment of potential buyers are closed off to trying it...unless or until I but a buffer back in...yes, a good one, but it's GOT to have one! A maddening bit of go around and around you have to admit. 

[sfox7076]

I own a Tortuga LDR and I own a Concert Fidelity LSX.  Which do I like more?  The Concert Fidelity.  However, the retail price is 10x the Tortuga on a good day.  LDR's are great, but they do have some quirks in implementation and, because it is DIY, design choices.  That said, it is hard not to like them if built right.  OK, but I have to say that I hate the encoder dial with a passion.  It eventually drives me nuts every time I try to change a setting for one reason or another.  Regardless, the sound is stellar.  It will never replace the Concert Fidelity.  And maybe that is because I love the tube sound/distortion it provides (and I used the d word), but that is just my opinion.  I don't feel I miss any details in the music in either case, just find the CF to be more engaging to my ears.

Shawn

[tortugaranger]

I own a Tortuga LDR and I own a Concert Fidelity LSX.  Which do I like more?  The Concert Fidelity. 

At $24,000 list I would hope you like it better! 

[steve f]

At the risk of complicating the issue, why does anyone here want a tube buffer? Solid state please.

[tortugaranger]

At the risk of complicating the issue, why does anyone here want a tube buffer? Solid state please.

I've had a few interesting discussions with some audio friends who feel quite strongly that the place to put tubes is in the preamp - for that tubey goodness - and keep the amps SS for all the reasons SS is good. I'm currently using a slightly modified Music Hall 25.2 DAC with a tube output stage, a Tortuga passive pre, and SS amps. The presence of that tube does add a nice quality to the sound. Just my 2 cents.

[tortugaranger]

A couple of thoughts since this thread has been quite active. There's a lot we could be doing in terms of product development but there's only so many hours in the day. So this type of feedback and discussion is very useful.

We've been working on two separate approaches to a buffer design/option for some time now. Frankly it's been an on again off again process because I've been waffling on whether it makes sense to ultimately pursue a buffer given how well the LDR Passives perform without one. At present I remain agnostic as to whether a really well designed buffer will improve performance - I just don't know. Early results with prototypes have been inconclusive. Feedback such as Glynn's experience with Modjeski's build only adds to that uncertainly.

In parallel we've also been using variations of our buffer design work towards developing an LDR headphone amplifier. An LDR headphone pre/amp simply must have a gain/buffer stage so one way or another we are going to end up with a buffer design - perhaps both a SS and a tube version.

As some point I suspect we'll make the decision to add a buffer option to our existing LDR design or launch a separate parallel LDR active preamp product....with the only caveat being .... do no harm. Maybe, just maybe, it will even be a bit better. We shall see.

[DaveC113]

Dave, No belittling intended certainly. That's not my style. Sorry if I offended. The premise of this thread is that LDR Passive Preamps sound better than they have a right to according to conventional preamp design. That has been demonstrated over and over. Not to you, but to enough other folk that my personal anecdote isn't relevant. The conundrum here is I'd like to convince a broader audience of the merits of our LDR preamps but am confronted with the presumption that because the design doesn't conform to conventional preamp design (buffer - and maybe gain too) that it can't possibly be as good as we say and so that segment of potential buyers are closed off to trying it...unless or until I but a buffer back in...yes, a good one, but it's GOT to have one! A maddening bit of go around and around you have to admit. 

Ok, thanks. The issue for me is a passive pre's performance without a buffer is going to depend on the source and amp, a buffer removes that dependency. The lack of standards wrt audio components means every system is different. I do maintain that a good buffer will be better in most cases, my view on the subject is mostly learned from John Broski, who is one of the most talented electronics designers around imo. His theory that a gain stage should be followed by a buffer with extremely high impedance is absolutely correct IME, which means the performance of a passive pre is largely dependent on the design of the source's output stage, and can be made even worse by an amp with low input impedance.

For example, if your DAC's tube output stage is a single triode without being follower by a buffer, it's performance driving an amp is going to suffer. In this case a buffer will make a huge improvement. Don't believe me, try it with a tube based white follower and see what happens.