'Transparency', to me, is hearing through to the essence of the sound. Added low level distortion may not be that important, but high feedback seems to reduce the actual information in the sound, or else to add an unnatural edge.
I remember being in Dr. Dorf's 'Control Theory' class (very high feedback theory) nearly 40 years ago, mentioning to a classmate that I had achieved .005% IM distortion at 1W and a good deal better, below 1W level. This was 104dB! So when listening to my amplifier, I listened to IM distortion BELOW -94dB, up to 104SPL! Who can hear that? I did, over time, and direct comparison to a triode amp, which surprisingly measured just as good as my amp in IM, damping factor (40), and bandwidth of 100KHz. Why?
TIM, IIM PIM, or something else?
I remember being in Dr. Dorf's 'Control Theory' class (very high feedback theory) nearly 40 years ago, mentioning to a classmate that I had achieved .005% IM distortion at 1W and a good deal better, below 1W level. This was 104dB! So when listening to my amplifier, I listened to IM distortion BELOW -94dB, up to 104SPL! Who can hear that? I did, over time, and direct comparison to a triode amp, which surprisingly measured just as good as my amp in IM, damping factor (40), and bandwidth of 100KHz. Why?
TIM, IIM PIM, or something else?
I feel the need to support the legitimacy of the listener experiences of John and Grey.
To do otherwise is rather presumptious, isn't it? It presumes that the relationship between ones theory and reality is reliable, more reliable than the real observations.
When it comes to the combination of the extremely complex subjects of feedback and non-linear systems, I would be very, very careful not to judge the efficacy of human observers against simplistic theories. After all, the evidential correlation between numerical measures and human observations is somewhat loose.
Surely more wise and fruitful to seek to improve the theory than to discredit the observer?
To do otherwise is rather presumptious, isn't it? It presumes that the relationship between ones theory and reality is reliable, more reliable than the real observations.
When it comes to the combination of the extremely complex subjects of feedback and non-linear systems, I would be very, very careful not to judge the efficacy of human observers against simplistic theories. After all, the evidential correlation between numerical measures and human observations is somewhat loose.
Surely more wise and fruitful to seek to improve the theory than to discredit the observer?
Improve the theory, that is also what I am trying to promote. IF I had not had the negative experiences that I had, almost 40 years ago, I would be pretty confident that nothing new in audio had to be learned about amp design. It just isn't how it turned out, and that forced me to look beyond the textbooks of the time (and even today), in order to make the best possible audio designs.
You know what I mean. I'm assuming the objective is to make something that pleases a human rather than an oscilloscope.
Mmm, this is still caught in here. Maybe a glass of water... 😀
My objections are not directed toward subjective impressions- quite the opposite, they're the most important ones, we have no disagreement there. I do, however, have a little problem with calling anything other than controlled subjective evaluation "real" observations. Do a double-blind level-matched comparison and then we can call an observation "real." Other than that, it's all story-telling, including (especially) my own subjective impressions, when I give them.
OK, maybe I'm being a touch pedantic.
My objections are not directed toward subjective impressions- quite the opposite, they're the most important ones, we have no disagreement there. I do, however, have a little problem with calling anything other than controlled subjective evaluation "real" observations. Do a double-blind level-matched comparison and then we can call an observation "real." Other than that, it's all story-telling, including (especially) my own subjective impressions, when I give them.
OK, maybe I'm being a touch pedantic.
The Heimlich Maneuver might be a little bit of a challenge over the internet (even if I knew how to perform it). So may I instead withdraw the world "real", which wasn't right, and agree with your sentiment?
Brian
Brian
janneman,
A post proving feedback works...?
Fascinating.
So you're saying that the mere fact that you can hear a difference according to the level of feedback means that it's a positive difference?
Au contraire!
No one here has claimed that feedback doesn't change the sound, and most certainly not me. If it didn't change the sound then it would be a mere laboratory curiosity. The question is whether the changes are positive or not. People who use oscilloscopes and distortion meters rather than ears think it's a gift from the gods. People who use their ears in addition to test instruments know better.
You really need to think a little longer before posting.
Grey
P.S.: I always love it when feedback proponents throw in the word "transparency." It's like the neo-conservatives here in the US appropriating "patriotism." No one else is allowed to use the word. It's supposed to be a show-stopper. Once someone lays claim to the concept, they attempt to take a moral high ground that isn't theirs to own.
Interestingly, what passes for transparency shares some characteristics with Redbook CD circa, say, 1990, in that there's a deep velvety background that shouldn't be there. In CD, the ambience was lost due low level information being ignored once it fell below the LSB. Dither helped with that problem, but no one has advanced a mechanism (that I know of) as to why high levels of feedback do pretty much the same thing.
But, as with CD, there are always those who defend the sound as being more "accurate," more "detailed," more..."transparent." As with CD, the sound is touted as pure, perfect sound forever. Sadly, as with CD, they claim that the defects they hear are from elsewhere, not their 'perfect' component.
Ain't so.
A post proving feedback works...?
Fascinating.
So you're saying that the mere fact that you can hear a difference according to the level of feedback means that it's a positive difference?
Au contraire!
No one here has claimed that feedback doesn't change the sound, and most certainly not me. If it didn't change the sound then it would be a mere laboratory curiosity. The question is whether the changes are positive or not. People who use oscilloscopes and distortion meters rather than ears think it's a gift from the gods. People who use their ears in addition to test instruments know better.
You really need to think a little longer before posting.
Grey
P.S.: I always love it when feedback proponents throw in the word "transparency." It's like the neo-conservatives here in the US appropriating "patriotism." No one else is allowed to use the word. It's supposed to be a show-stopper. Once someone lays claim to the concept, they attempt to take a moral high ground that isn't theirs to own.
Interestingly, what passes for transparency shares some characteristics with Redbook CD circa, say, 1990, in that there's a deep velvety background that shouldn't be there. In CD, the ambience was lost due low level information being ignored once it fell below the LSB. Dither helped with that problem, but no one has advanced a mechanism (that I know of) as to why high levels of feedback do pretty much the same thing.
But, as with CD, there are always those who defend the sound as being more "accurate," more "detailed," more..."transparent." As with CD, the sound is touted as pure, perfect sound forever. Sadly, as with CD, they claim that the defects they hear are from elsewhere, not their 'perfect' component.
Ain't so.
G.Kleinschmidt said:
I agree, Glen.
I think it is pretty presumtuous for those that don't like (or understand) negative feedback to think that they have a corner on the subjective listening market, or on experience for that matter.
A lot of pretty terrible amplifiers have been made both with and without negative feedback. A lot of extraordinarily good amplifiers have also been made with and without negative feedback.
Cheers,
Bob
G.Kleinschmidt said:
That's the advantage of having such a detailed understanding of the theory of how things work. There is never a loss for words or references to backup what you know.
On the other hand, observations of reality really stink. No credible references availible for things that don't fit the well documented world view and only one's experience, insight and gut instincts to help piece them together into any usable form.
Even then, the conclusions drawn are subjective,
Hardly enough to sustain anyone in any serious technical discussion!
Sometimes I don't understand why some people (myself included) can't accept what has already been figured out by the smart people in the world. It would save so much time and energy that is now being wasted by trying to educate the the less fortunate.
Oh well. History repeats itself, again.
I do have to apolgize for my bad attitude. I was out Christmas shopping and got a bit of a headache trying to pick out an surround sound system for my son in law and daughter. I'll be better after a bit... .
Mike
traderbam said:
Brian,
I shall not claim to fully understand this very sophisticated prose.
However, I don't think anybody (not me anyway) wants to 'discredit the observer'. But 'improving the theory' must necessarily also include the theory of perception, of how we perceive the world around us, how we come to a concious judgement after processing (mostly unconciously) those myriad sensory inputs, and integrate them with past (crippled) memories, and expectations. That doesn't discredit the observer, it emancipates the observer.
Jan Didden
GRollins said:
Thank you.
GRollins said:
Is that a rethorical question? I'm not aware I did say that. I also don't think it is true.
Grey, you are intelligent enough not to need putting words in peoples mouth they didn't say. It detracts from you.
GRollins said:
I have no idea what you're talking about. Do you mean I am not allowed to use the word 'transparent' because I believe feedback is a very worthwhile tool or what? Do you mean it was unclear what I meant when I used the word? If I am saying that an amlifier works transparently when it amplifies a signal, is that less clear than saying, for instance, 'the speakers really sing', or, 'that cable really brought out the emotions' etc? Would you prefer we would use those terms, so we can all spend the next few centuries discussing semantics?
Jan Didden
The precision of language
How about an analogy? The shops are full of flat screen TVs this season and there seem to be two main technologies, LCD and plasma.
Suppose you observed two screens on a wall of equal size showing the same movie and the brightness of both were adjusted to be the same. One is plasma and one is LCD.
The sales assistant asks you to choose which one is the most realistic. You watch them carefully. Neither is perfect...that is, neither would fool you into thinking you are seeing a live event through a glass window - not even close. You notice that the LCD looks a little sharper but is a little smudgy on movements, but the plasma has better contrast but the colours are a little washed out by comparison and somehow more artificial but then again the LCD doesn't seem to do textures as clearly somehow...the patina on that table just doesn't look right. You tell the assistant that it is a tough choice but, perhaps the LCD is more realistic.
The assistant has been recording your comments. She then asks you which you would choose to buy. "Oh, I think I'd buy the Plasma because, although it is slightly less realistic, the blurring of the LCD really bugs me more than patina."
With your permission the assistant sends the recording of your comments to the engineering lab of the LCD mfr. The engineers know how to measure picture sharpness. Except they don't call it sharpness. Indeed, they have several terms that all contribute to sharpness like silicon junction edge profile and edge leakage and photonic dispersion error (I'm making these terms up - Ed.).
When the LCD engineers hear your comments about sharpness being better than plasma they pat each other on the back and cheer. The customer recognizes the fruits of our achievements and confirms our superior measurement process. But when they hear your comments about smearing, they look puzzled. "Smearing" what does that mean? "That sounds very subjective and is not in a language we recognize, and we are experts. Our measurements don't show anything that we could guess would lead to this smearing comment". "The trouble with customers is that they are not objective. You simply cannot rely on them like you can on objective measurements. People aren't reliable, some see the same thing in one way and some in others. The last time we got feedback the customer said something about not being able to feel the textures clearly - what the heck does that mean? But they didn't mention smearing. We simply cannot rely on these people. Let's get back to work and improve the junction edge profile even more on our screens - that'll show the plasma people."
How about an analogy? The shops are full of flat screen TVs this season and there seem to be two main technologies, LCD and plasma.
Suppose you observed two screens on a wall of equal size showing the same movie and the brightness of both were adjusted to be the same. One is plasma and one is LCD.
The sales assistant asks you to choose which one is the most realistic. You watch them carefully. Neither is perfect...that is, neither would fool you into thinking you are seeing a live event through a glass window - not even close. You notice that the LCD looks a little sharper but is a little smudgy on movements, but the plasma has better contrast but the colours are a little washed out by comparison and somehow more artificial but then again the LCD doesn't seem to do textures as clearly somehow...the patina on that table just doesn't look right. You tell the assistant that it is a tough choice but, perhaps the LCD is more realistic.
The assistant has been recording your comments. She then asks you which you would choose to buy. "Oh, I think I'd buy the Plasma because, although it is slightly less realistic, the blurring of the LCD really bugs me more than patina."
With your permission the assistant sends the recording of your comments to the engineering lab of the LCD mfr. The engineers know how to measure picture sharpness. Except they don't call it sharpness. Indeed, they have several terms that all contribute to sharpness like silicon junction edge profile and edge leakage and photonic dispersion error (I'm making these terms up - Ed.).
When the LCD engineers hear your comments about sharpness being better than plasma they pat each other on the back and cheer. The customer recognizes the fruits of our achievements and confirms our superior measurement process. But when they hear your comments about smearing, they look puzzled. "Smearing" what does that mean? "That sounds very subjective and is not in a language we recognize, and we are experts. Our measurements don't show anything that we could guess would lead to this smearing comment". "The trouble with customers is that they are not objective. You simply cannot rely on them like you can on objective measurements. People aren't reliable, some see the same thing in one way and some in others. The last time we got feedback the customer said something about not being able to feel the textures clearly - what the heck does that mean? But they didn't mention smearing. We simply cannot rely on these people. Let's get back to work and improve the junction edge profile even more on our screens - that'll show the plasma people."
Re: The precision of language
Yes, all good points. I was using the word 'transparent' assuming the reader would understand from the context that I meant: 'letting it (the signal) through without any change'. I was immediately corrected when John Curl said: 'transparent' to me is being able to listen through to the essence of the music' or words to that effect. No wonder some of these posts get longer and longer; we need more and more qualifiers to specify what we mean by the words we use.
I wonder how we got into this mess. I still can't help to think that if we were just a bit more open to and interested in what the poster is trying to say instead of trying to find points to criticize, it would all be a lot easier. But I'm probably as guilty as the next guy anyway. 🙁
Jan Didden
traderbam said:How about an analogy? The shops are full of flat screen TVs this season and there seem to be two main technologies, LCD and plasma.
Suppose you observed two screens on a wall of equal size showing the same movie and the brightness of both were adjusted to be the same. One is plasma and one is LCD.
The sales assistant asks you to choose which one is the most realistic. You watch them carefully. Neither is perfect...that is, neither would fool you into thinking you are seeing a live event through a glass window - not even close. You notice that the LCD looks a little sharper but is a little smudgy on movements, but the plasma has better contrast but the colours are a little washed out by comparison and somehow more artificial but then again the LCD doesn't seem to do textures as clearly somehow...the patina on that table just doesn't look right. You tell the assistant that it is a tough choice but, perhaps the LCD is more realistic.
The assistant has been recording your comments. She then asks you which you would choose to buy. "Oh, I think I'd buy the Plasma because, although it is slightly less realistic, the blurring of the LCD really bugs me more than patina."
With your permission the assistant sends the recording of your comments to the engineering lab of the LCD mfr. The engineers know how to measure picture sharpness. Except they don't call it sharpness. Indeed, they have several terms that all contribute to sharpness like silicon junction edge profile and edge leakage and photonic dispersion error (I'm making these terms up - Ed.).
When the LCD engineers hear your comments about sharpness being better than plasma they pat each other on the back and cheer. The customer recognizes the fruits of our achievements and confirms our superior measurement process. But when they hear your comments about smearing, they look puzzled. "Smearing" what does that mean? "That sounds very subjective and is not in a language we recognize, and we are experts. Our measurements don't show anything that we could guess would lead to this smearing comment". "The trouble with customers is that they are not objective. You simply cannot rely on them like you can on objective measurements. People aren't reliable, some see the same thing in one way and some in others. The last time we got feedback the customer said something about not being able to feel the textures clearly - what the heck does that mean? But they didn't mention smearing. We simply cannot rely on these people. Let's get back to work and improve the junction edge profile even more on our screens - that'll show the plasma people."
Yes, all good points. I was using the word 'transparent' assuming the reader would understand from the context that I meant: 'letting it (the signal) through without any change'. I was immediately corrected when John Curl said: 'transparent' to me is being able to listen through to the essence of the music' or words to that effect. No wonder some of these posts get longer and longer; we need more and more qualifiers to specify what we mean by the words we use.
I wonder how we got into this mess. I still can't help to think that if we were just a bit more open to and interested in what the poster is trying to say instead of trying to find points to criticize, it would all be a lot easier. But I'm probably as guilty as the next guy anyway. 🙁
Jan Didden
The Absolute Sound has attempted to create--and define rigorously--listening terms so as to provide a common ground for discussion. For this, they are ridiculed in much the same way that I am in discussions like this, but at least they are trying to provide a common terminology that everyone can agree on.
Once attention has been drawn to some audible effect, then perhaps those who get their jollies by arguing theory can set about trying to box it in and define it rigorously in the mathematical sense. Unfortunately, it's less common that the math leads people to discover things--it's usually the other way around, with things being noticed, then explained in the theoretical sense.
The problem is that we can't allow others to see through our eyes or hear through our ears. We can be exposed to the same sensory input but aren't necessarily paying attention to the same cues. Case in point: I, my ex-wife, my uncle, and my aunt were on our land up in the mountains. I looked up and said, "Someone's coming." They couldn't hear anything even once I had drawn their attention to it. Shortly thereafter a man (trespassing) puttered by on one of those little four-wheeled off-road dinguses. The four of us were presented with the same sounds, but even telling them what to listen for was fruitless. They simply weren't able to hear the motor of the off-road vehicle. Yes, the argument could be made that my aunt and uncle were older and had less acute hearing, but my ex-wife's hearing was excellent. Arguably better than mine, in fact.
There's no pointer--in the sense of a stick that a teacher uses to point at things on a blackboard--that you can use to indicate what subset of sounds are of interest at the moment. Most people listen to the totality of the sound and are unable to focus on any one portion of it even when asked to do so.
Others have the ability to focus, but zero in on the wrong target. At least in this case, you begin to have a basis for discussion. If they have the knack of restricting themselves for a moment to one portion of the sound, and if you can direct their attention to the same things you're noticing, then you can have a meaningful discussion as to whether one parameter is better or worse than it was before.
The word transparency has become a loaded word, unfortunately. It is a good, intuitively obvious word to use in listening, because it has the connotations of being able to listen through a window to the original sound as it was heard when it was being played. The sad thing is that it's been used so often by people who advocate high levels of feedback that it has by degrees been slanted to mean that particular sound--the sound of large amounts of feedback. This creates the inherent mindset that if some of that sort of sound is good (And who would be so brazen as to vote against "transparency?" Why the word is almost as wholesome as Mom and apple pie!) then more must be better, and so people seek ever more transparency. The word itself has become its own advertisement; a sound bite that sounds so wonderfully concise that you're made to feel almost unpatriotic if you argue against it.
Look up the word meme. If you're in a hurry, the Wikipedia has a good entry.
I try to avoid the use of the word transparency. Likewise accurate. I use the word detail only with misgivings. Why? Because all three of these otherwise wonderful descriptive words have been corrupted.
My mother used to resent the co-opting of the word "gay" to mean homosexual. She did not have a single prejudiced bone in her body; indeed, she had several gay friends. The problem, at least here in the US, is that you can no longer use the word gay to mean happy or cheerful or carefree, even though those definitions still exist in the dictionary, because it has become synonymous with homosexual. That is the only use for the word gay at this point in time.
And so it is with transparency, accurate, and detail. They no longer mean what the dictionary says they mean. In the vernacular, they mean the sound achieved by the use of lots of feedback.
I, for one, rue their loss.
Grey
Once attention has been drawn to some audible effect, then perhaps those who get their jollies by arguing theory can set about trying to box it in and define it rigorously in the mathematical sense. Unfortunately, it's less common that the math leads people to discover things--it's usually the other way around, with things being noticed, then explained in the theoretical sense.
The problem is that we can't allow others to see through our eyes or hear through our ears. We can be exposed to the same sensory input but aren't necessarily paying attention to the same cues. Case in point: I, my ex-wife, my uncle, and my aunt were on our land up in the mountains. I looked up and said, "Someone's coming." They couldn't hear anything even once I had drawn their attention to it. Shortly thereafter a man (trespassing) puttered by on one of those little four-wheeled off-road dinguses. The four of us were presented with the same sounds, but even telling them what to listen for was fruitless. They simply weren't able to hear the motor of the off-road vehicle. Yes, the argument could be made that my aunt and uncle were older and had less acute hearing, but my ex-wife's hearing was excellent. Arguably better than mine, in fact.
There's no pointer--in the sense of a stick that a teacher uses to point at things on a blackboard--that you can use to indicate what subset of sounds are of interest at the moment. Most people listen to the totality of the sound and are unable to focus on any one portion of it even when asked to do so.
Others have the ability to focus, but zero in on the wrong target. At least in this case, you begin to have a basis for discussion. If they have the knack of restricting themselves for a moment to one portion of the sound, and if you can direct their attention to the same things you're noticing, then you can have a meaningful discussion as to whether one parameter is better or worse than it was before.
The word transparency has become a loaded word, unfortunately. It is a good, intuitively obvious word to use in listening, because it has the connotations of being able to listen through a window to the original sound as it was heard when it was being played. The sad thing is that it's been used so often by people who advocate high levels of feedback that it has by degrees been slanted to mean that particular sound--the sound of large amounts of feedback. This creates the inherent mindset that if some of that sort of sound is good (And who would be so brazen as to vote against "transparency?" Why the word is almost as wholesome as Mom and apple pie!) then more must be better, and so people seek ever more transparency. The word itself has become its own advertisement; a sound bite that sounds so wonderfully concise that you're made to feel almost unpatriotic if you argue against it.
Look up the word meme. If you're in a hurry, the Wikipedia has a good entry.
I try to avoid the use of the word transparency. Likewise accurate. I use the word detail only with misgivings. Why? Because all three of these otherwise wonderful descriptive words have been corrupted.
My mother used to resent the co-opting of the word "gay" to mean homosexual. She did not have a single prejudiced bone in her body; indeed, she had several gay friends. The problem, at least here in the US, is that you can no longer use the word gay to mean happy or cheerful or carefree, even though those definitions still exist in the dictionary, because it has become synonymous with homosexual. That is the only use for the word gay at this point in time.
And so it is with transparency, accurate, and detail. They no longer mean what the dictionary says they mean. In the vernacular, they mean the sound achieved by the use of lots of feedback.
I, for one, rue their loss.
Grey
Grey,
I have never associated the word 'transparent' with feedback at whatever levels. I always thought that transparent means that what goes in comes out. I really don't care how that is achieved; it just that I think, with what I currently know, the best chances for such 'transparency' is a well designed feedback amplifier. I'm willing to argue that case, but of course the problem is always that different people call different things 'transparent'.
I can easily enjoy the warm sound of a simple SE amp with lots of harmonics, playing a good full-range speaker, but I cannot call that 'transparent'. What comes out is too different from what goes in.
Jan Didden
I have never associated the word 'transparent' with feedback at whatever levels. I always thought that transparent means that what goes in comes out. I really don't care how that is achieved; it just that I think, with what I currently know, the best chances for such 'transparency' is a well designed feedback amplifier. I'm willing to argue that case, but of course the problem is always that different people call different things 'transparent'.
I can easily enjoy the warm sound of a simple SE amp with lots of harmonics, playing a good full-range speaker, but I cannot call that 'transparent'. What comes out is too different from what goes in.
Jan Didden
we do have engineering definitions of "accuracy", "resolution", "information"
whatever processing goes on in our head the issue of amplifier performance is defined by its performance as a information "channel" - in the Shannon-Hartley sense
hi rez digital mastering/distribution (24/96 or 192, or even DSD)makes it glaringly obvious that we're dealing in information channels with specified bandwidth, noise, bit rate
our amplifier measurements are possible at pro level mastering resolution - where is the "room" for arguing high feedback amplifiers are less accurate than worse measuring low/non feedback amps?
whatever processing goes on in our head the issue of amplifier performance is defined by its performance as a information "channel" - in the Shannon-Hartley sense
hi rez digital mastering/distribution (24/96 or 192, or even DSD)makes it glaringly obvious that we're dealing in information channels with specified bandwidth, noise, bit rate
our amplifier measurements are possible at pro level mastering resolution - where is the "room" for arguing high feedback amplifiers are less accurate than worse measuring low/non feedback amps?
janneman said:
That's exactly my point. It has become a self-fulfilling prophecy. People assume blindly that negative feedback must be better simply because it reduces the accepted distortions. I am not advocating TIM, SIM, or whatever, I'll leave that to John, but there's something wrong with the sound of high feedback circuits. They don't reproduce images as well as lower feedback circuits.
Claiming that "obviously":
1) The image information is an illusion created by distortion products,
2) The higher feedback circuit's reproduction of image "must" be correct because it has lower THD or IMD,
3) The lower feedback circuit (assuming solid state) is somehow generating tube-like distortions that enhance or otherwise create out of whole cloth an image where none was before,
is nonsense.
I find it curious that NFB proponents are able to convince themselves that the image created by lower feedback circuits is somehow false. Out of all the possible ways for distortion to behave, it strains credulity to believe that it just so happens that these particular distortions purely accidentally, against all odds, happen to produce an image more like what you hear in a concert hall. Is is mathematically impossible? No. But it's really, really hard to believe.
All you have to do is listen. It's that simple. Facts first, then you can theorize all you want. The image is better on low feedback circuits. Why? All I can suggest is the same thing I have said in the past: That it's a phase problem. It's not so hard to see that imaging information is likely contained in the relative phases of the various frequencies. It's a known fact that feedback has phase-related problems; taken to extremes, it becomes positive feedback. The work-around there is to limit bandwidth, obviously, but the question remains: Are there phase problems before that? My working hypothesis is yes and it's producing results. As a fringe benefit it fixes other things, like that obnoxious upper midrange emphasis, although that wasn't my initial goal.
I have no problem with the idea that a voltage amplifier should have a high input impedance and a low output impedance. I'm running my current circuit at 100k per input leg (balanced inputs) with no deterioration of bench performance and it's on my list of things to do to see what happens if I go to 1M. For a stereo amplifier, I think most solid state people would agree that 100k (single-ended) is pretty decent in the Zin sweepstakes (although it's pretty ordinary in tube circuits). The output impedance is pretty much just the MOSFETs and Source resistors. It's arguably higher than it should be, but my experience with tube circuits (e.g. conrad johnson Premier One) has been that amps with low damping factors can have stunning bass. I think that is in large part due to power supply design--making sure that current is available on demand...as in right now rather than having to wait. I'm still working on the art for the next front end PCB, but the last front end gave me something on the order of .08% THD. Bandwidth was around .5Mhz. Once I get the next front end in place I'll see where things lie, but those numbers aren't too shabby. I can live with them.
And all that with no feedback.
Grey
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