How close to the real thing?

Timlub, It looks to me like Fas42 places a lot of importance on soundstage and imaging. There are different types of 'distortion' that affect that- primarily of bandwidth. The better it is the more intact the phase relationships, which are what defines image location.

The ability of the speakers to 'disappear' is equally important to a system's ability to convince as is detail and tonality.

When feedback is applied to an amplifier, low level harmonic noise is injected into the output of the amplifier. This is nearly all high-frequency information. Now it happens that room ambiance in recordings is often also high frequency and is also low level. The result is that by adding feedback, the low level detail associated with room size can be masked by the harmonic noise floor that is present in the amplifier. In fact *all* detail below this level will be masked. That is why amplifiers that run little or no feedback often seem to have bigger, wider and deeper soundstages.

Hi Atmasphere,
Ok, no disagreements...Feedback reduces distortion and have seen changing feedback levels change the effects, no arguments....
I guess, what I am questioning is... Labeling Distortion as a catch all phrase. It doesn't work.

Hello Atmasphere,

Wouldn't such be dependent on the topology being used, Tubes react differently vs SS with regards to negative feedback
(local or global).

Class-D amps run a lot of feedback, "alot" and they don't have issues with sound staging and details, actually they are quite possibly kings of it, but do exhibit a grainy artificial sound IMO vs conventional amplifiers (class-a, a/ab)

Mapman, -- "not all distortion is necessarily unpleasant" , I agree with your comments 100%. And, there is definitely "nice" distortion, which is quite easy to do, and is a perfectly valid way of obtaining listening pleasure. One of my earliest high end experiences was listening to a dealer's highly tweaked in home setup, we are talking here of Goldmund Reference TT, Audio Research D250, Infinity columns: of course the playback on a selected LP was absolutely stunning. He didn't like CD, of course, but had a CAL, so I tried one of my "test" CD's. The experience was bizarre, sounded smooth and pleasant enough, but half the sound content had disappeared! My half reasonable setup of the time at home absolutely walloped his in terms of conveying the musical message on that particular CD.

So "nice" distortion works, but it is "horses for courses" ...

Frank

Tubes and transistors seem to act very similar to feedback. I've less experience with class D, but from what I am seeing there are several techniques of using feedback and some work better than others, so it would be unsafe to generalize that feedback works in all class D amps without increasing odd ordered harmonics. In some it seems to work well though.

Not heard one yet that images as well as I am used to but I've not heard them all either.

Weseixas, Timlub, thanks for your reaction and comments to Atmasphere and Mapman, they are coming from very close to what my take on the situation is.

What I hope to inject into this conversation is something that for me has been very intriguing and frustrating over many years. That, which all hard core tweakers know, is that fiddling with any and everything makes a difference, and my reaction has been, what the hell is going on ?? Agreed, the topology, or circuit type of the amplifier can make a big difference, but once you improve your amp, then you more clearly hear the effects of making changes to other components, and the impact of everything else becomes more significant. Hmmm... not sounding too good at the moment ... gee, I wonder if that fluorescent light outside in the garage is on or off?

The trouble is, that last sentence is NOT funny, because it's true! Again, everything matters, and why does it matter? Because all the little, little things alter the makeup of my "micro" distortion, and the ear/brain has no trouble, no trouble at all picking up the change. It may sound better or worse, but it will definitely sound different!

Distortion can be linear, that is, altering the frequency response and phase angles, or nonlinear, which is everything else. The latter is the "baddy", big time: my experience is that if you minimise nonlinear distortion then linear distortion becomes totally benign, and the ear/brain can dismiss it as irrelevant. I've had a very ordinary amplifier (Sony) with classic tone controls, and managed to get the overall system working extremely well; then wound the bass and treble fully up and down, and I couldn't hear anything happening to the sound! Why, because the ear/brain could reject those changes as being unimportant to the musical message, enough "good" information was coming out of the speakers to compensate for a change that would normally be very obvious.

Yes, feedback is somewhere in there. But there is correct feedback, and "bad" feedback! If feedback was inherently not good then no piece of recorded music could ever be made to sound good, since every recording device and studio is riddled with feedback design techniques and circuitry, going back to almost the very start of electronic recording.

The quip earlier about the light points to a key factor that people play around with: power supply quality, or maybe, maybe it's RFI!? The trouble is, it's all very messy, but it ALL has to be taken care of!

Why should one? Because, if you do, then the level of "nasty", NOT "nice", micro distortion is reduced to the level that the ear/brain says "Yes! I can now accept this as being a thrilling experience, I won't be fatigued no matter how long I listen, it's magic, it's real!". And the convincing soundstaging, etc, automatically follows ...

Frank

Atmasphere, there is no way that well-designed solid state amplifiers "tend to have these higher odd orders all the time. This is one of the reasons they tend to sound hard or bright. Now its important to note that these harmonics do not have to be very distorted, usually 100th of a percent are audible, simply because these harmonics are so important to the human ear." Total harmonic distortion, meaning any and all spurious frequencies away from the fundamental, is normally at about -70db or better, usually better, and there's no way that such low-level distortions could possibly cause amps to sound hard and bright.

The most likely cause of hard and bright sound are no-so-good speakers, that have too much upper midrange energy when driven by an amp with a low output impedance and flat frequency response. Connect a tube amp with a rising output impedance in the same frequency range, which will cause a roll-off in the overall response, and voila, hardness suddenly gone.

Irvrobinson, I would agree with you about those distortion levels, but certainly would not blame the speakers directly. I would suggest rather that the combination of equipment and setup is allowing other distortion mechanisms to intrude, into the electronics of amp and CD player, say. Typically the power supplies of much equipment are pretty hopeless in suppressing interference into sensitive areas, and this is the sort of thing that normal THD measuring never captures.

So, either you boost the quality of the power supply, as, say Naim does, or you cotton wool the power being fed to the gear with filters, special power cords, etc, etc.

Frank

I'm in agreement with Irv, there are a lot of speakers with unbalanced frequency bandwidth. SS amps IMO tend to be more accurate in their reproduction of the original signal, have better bandwidth, dynamics, rhythm and pace.

That aside i have heard great sound from both SS and Tubes, so go figure.

How close are we to the real thing ?

Fas42, assuming the goal for all equipment is as much accuracy as possible, I do lay the entire blame on speakers. Solid state electronics can be designed to be, for home audio purposes, perfectly neutral, in that their noise and distortions are inaudible, and their frequency responses are flat regardless of load.

Speakers, on the other hand, are usually "voiced" Sometimes this is because the designer wants to achieve a certain "sound", but they are also voiced to apply judgment of how much high frequency roll-off the designer wants to apply to make the speaker sound natural in a room with certain absorption assumptions. I suppose you could argue voicing in the bass might also be necessary, because of room variations.

The latest speakers, designed with the latest driver technology and sophisticated crossovers designed with the latest software, can produce awesomely flat frequency responses these days. The latest speaker designs seem to have frequency responses that remind me of curves we used to see for amps in the 1960's. (Distortion levels too.) But lots of speakers are still "voiced" to sound a certain way according to a designer's biases, and the best drivers and crossovers (and cabinets too) are actually very expensive, so a lot of high end speakers still have response curves that look like saddles (too much bass and too much treble), and compromised crossovers that produce anomalies at the crossover points.

The differences in solid state electronics are far smaller. With tube electronics, one can design them to be as neutral as SS types (VTL comes to mind), but things like SET amps will have nearly unpredictable interactions with a particular speaker.

I also tend to believe that practically, in most well thought out real world setups, that a higher % of those using SS amps will sound closer to the real thing to me.

I say this based on the fact that I hear more variations from what sounds rel to me more with tube gear I hear and use than with (good) SS rigs.

I suspect that Mapman is correct for reasons coming from the other side. I have been surprised how my new Tube guitar amp changes character depending on how long it has been on and such. If I can change the source based on tube temp? than it makes sense that a tube output system may display this as well?

Paulsax, if I don't leave my ss gear on 24/7 it takes at least an hour to sound its best. With the high cost of tubes and electricity, few leave their tube gear on.

Yes, feedback is somewhere in there. But there is correct feedback, and "bad" feedback! If feedback was inherently not good then no piece of recorded music could ever be made to sound good, since every recording device and studio is riddled with feedback design techniques and circuitry, going back to almost the very start of electronic recording.

This is incorrect. The Ampex 351 tape machine, used by both RCA and Mercury (and a host of others) has a zero-feedback recording circuit. Neumann microphones use small tube preamps which are zero feedback. I can go on but you get the point.

there is no way that well-designed solid state amplifiers "tend to have these higher odd orders all the time. This is one of the reasons they tend to sound hard or bright. Now its important to note that these harmonics do not have to be very distorted, usually 100th of a percent are audible, simply because these harmonics are so important to the human ear." Total harmonic distortion, meaning any and all spurious frequencies away from the fundamental, is normally at about -70db or better, usually better, and there's no way that such low-level distortions could possibly cause amps to sound hard and bright.

OK- you obviously understand how low the distortion levels are we are talking about. I think I did express that 100th of a percent is audible- seems like that needs more emphasis. Since we humans use the odd orders (5th, 7th and 9th) in order to determine how loud a sound is, obviously while the ear is not sensitive to *some* things, this is one thing that the ear is *very* sensitive to. BTW all of this has been known since the 60s and Norman Crowhurst was writing about this subject in the 1950s.

So this is indeed a way that explains why transistor amps can sound harsh while having otherwise flat frequency response. Note also that with many transistor amplifiers, as power output decreases there is a dip in distortion and then it rises again as power output continues to decrease. This is one of the reasons that low level detail is challenging for transistor designs.

It also points to the way to make transistors work as well as tubes, FWIW. I can point to several SS amp manufacturers that have been exploring zero feedback designs and some of them are as good as some of the best tube amps I have heard. Mind you this coming from a tube amplifier manufacturer...

This is incorrect. The Ampex 351 tape machine, used by both RCA and Mercury (and a host of others) has a zero-feedback recording circuit. Neumann microphones use small tube preamps which are zero feedback. I can go on but you get the point.

Sorry Atmasphere, but you're mistaken - recording, mastering, and broadcast equipment all does indeed use a variety of "feedback design techniques and circuitry, going back to almost the very start of electronic recording," as Fas42 states. Specifically, the Ampex 350 and 351 used frequency-dependent negative feedback in the cathode circuit of the record output tube, and negative feedback around the playback head amplifier for playback EQ. Additionally, the 351 had a push-pull (12AU7?) transformer-coupled line-output amp with a separate feedback winding for global NFB, very similar to a little transformer-coupled power amp.

And then there's the record cutting lathe - virtually all high-fidelity cutting heads use negative feedback from a separate winding to provide global negative feedback from the motion of the cutterhead back to the cutting amplifier.

Do Ayre and Pass use zero feedback desings in their amps? I only know they sound really good.

Hi Kirkus, I just pressed on your system and I'm so happy I did. How very cool! To saner times...

Wow, that JBL Marantz Mac setup is something else!

Hi Kirkus, that was not what I recalled so I looked up the Ampex schematic... Its not the record head that has feedback- prior to that the record calibration circuit does use a feedback mechanism. The rest of the circuit has none.

I did think about the playback after posting :/

Of course LP lathes do use feedback, primarily used to control resonance. You can't get channel separation in a Westerex 3D, for example, if you don't use feedback. However there is work being done to this day to try and find a way around that. Apparently feedback is not popular with mastering engineers and for good reason: if the electronics even turn on in the wrong order at power-up, the cutting head can be destroyed.

I have a set of Western Electric mic preamps that are zero feedback. I pulled them out of a dumpster about 30 years ago and boy am I glad I did. They are really transparent, after being updated with Jensen transformers and otherwise rebuilt.

Hello Atmasphere,

Are you involved in making your own recordings.....

Atmasphere says:

"OK- you obviously understand how low the distortion levels are we are talking about. I think I did express that 100th of a percent is audible- seems like that needs more emphasis. Since we humans use the odd orders (5th, 7th and 9th) in order to determine how loud a sound is, obviously while the ear is not sensitive to *some* things, this is one thing that the ear is *very* sensitive to. BTW all of this has been known since the 60s and Norman Crowhurst was writing about this subject in the 1950s.

So this is indeed a way that explains why transistor amps can sound harsh while having otherwise flat frequency response. Note also that with many transistor amplifiers, as power output decreases there is a dip in distortion and then it rises again as power output continues to decrease. This is one of the reasons that low level detail is challenging for transistor designs."

First of all, pardon my ignorance for not knowing that you are a producer of tube amplifiers. That just occurred to me last night while reading some of your responses, and I do realize that arguing tube versus solid-state with you is probably not productive.

But your explanation above is such nonsense that I can't help but reply. I'll buy that humans are very sensitive to certain kinds of harmonic distortion, but I'll reiterate that the distortions you are discussing in high-quality solid-state amps are very likely well under -70db, probably more like -80db, and that's below the noise level of the large majority of recordings. Certainly that is under anything reproducible from vinyl.

Furthermore, the 9th harmonic of frequencies above 2KHz is above audibility for most people, especially accounting the -70db level of the tones we're discussing.

So I think quoting research references just clouds your argument. And then concluding that all of this mumbo-jumbo you're discussing indeed describes why solid-state amps sound harsh and lack low-level detail is just so much malarkey. Solid-state amps have neither of these characteristics you claim they do just for promoting your tube products.

Tube amps can demonstrate interactions with loudspeakers this can result in an altered system frequency response, and those alterations can highlight (or hide) details in recordings. But this isn't because of some imagined limitations of solid-state amps, or even negative feedback. I could more easily argue the differences are due to the inferior performance of some tube amps. While everything in audio can be reduced to personal preference, my preference is to try and make as many factors in the reproduction chain as neutral as possible.

Irvrobinson, in a nutshell, frequency response variation is not why tubes sound different! I've heard that idea expressed before, but its hard to find real world examples so I have to chalk it up to mythology. This is easily proven by using a speaker with a flat impedance curve.

The fact of the matter is that the ear interprets non-clipping harmonic distortion as tonality. With tubes, quite often we see a great deal of lower ordered harmonics, which the ear hears as warmth or 'bloom', IOW because the lower orders are seen by the ear as musical, humans are more tolerant of their presence although such will mask detail.

In the case of transistor amplifier audible distortions we are indeed talking about -70, -80 db phenomena. General Electric proved how sensitive humans are to odd orders back in the mid 60s- its not like this is rocket science, but OTOH if you don't know about this quality of human hearing there may be nothing I can say.

So I think quoting research references just clouds your argument.

So when making a point of fact, one should never point to basic long-standing research?? Don't confuse the situation with facts??

However, it is readily proven, and here is how it is done. Take any amplifier and speaker, you will also need a VU meter and a sine/square wave generator. This is very simple test equipment. Set the sine wave to 1KHz 0VU into the speaker.

Now cover the meter and turn the signal all the way down. Set to square wave (odd ordered harmonics). Turn up the volume until you perceive the same sound pressure. Uncover the meter. You will find that it is reading between 20 and 30 db less.

The human ear is very sensitive to odd orders because it uses them to tell how loud sounds are. To claim that we cannot hear something that is 70 db down is beside the point- we are not talking about something that is being masked. I think you must be thinking that these harmonic distortions are somehow going to always be buried and they are not. This is one of the most basic rules of human hearing.

Now negative feedback is well-known to inject odd ordered harmonics into the output of the amplifier although at low level. Its easy to hear too- but best done on an amplifier that is functional operating open-loop (transistor amplifiers that meet that requirement are rare but they do exist). Norman Crowhurst pointed out in the mid-50s that the addition of negative feedback injects harmonics up to the 81st into the output of the amplifier- this stuff is not imagined by any stretch. Take a look at Nelson Pass' article on distortion:

Audio, Distortion and Feedback at
http://www.passdiy.com/projects.htm

if you have trouble believing that I do my homework. Nelson Pass is one of the leading designers alive today.

Chaos Theory says that an amplifier that has loop feedback is an example of a chaotic system that exhibits several stable states. Interestingly and not by coincidence, the formulae you see to express feedback in an amplifier are *identical* to the classic formulae for basic chaotic systems.

Now Chaos uses the term 'bifurcation' to refer to distortion and what it says confirms what Norman Crowhurst pointed out decades earlier, that the addition of feedback will destabilize the amplifier and inject low level harmonic and inharmonic noise (the inharmonic noise is the result of intermodulations at the feedback node).

The way this happens is that the amplifier has a time period, called propagation delay, which is a finite time in which it takes the input signal to propagate to the output. It is nowhere near the speed of light! In fact it is so slow that at high frequencies by the time the feedback gets back to the input of the amp to do its work, the input signal will be seen to have changed. For this reason the negative feedback is always lagging behind and so is unable to correct the signal it was supposed to. As frequency goes up, the phenomena becomes more pronounced.

With steady-state signals the damage is not too severe, but with a constantly-changing waveform (music) the resulting distortion is much higher than -70 db.

Now most transistor amplifiers are push-pull and so they have even-ordered harmonic cancellation at the output. If the amplifier is balanced throughout (and many of them are) then this even ordered cancellation will occur throughout the amplifier (we do this in our amplifiers for the same reason). So really, the main distortion components of a transistor amplifier are going to be almost entirely odd orders!

Now you may think I am a big tube proponent, but if that is the case you may not have read some of my earlier comments. It is *easier* to make tubes sound more like music because it is easier to build tube amps that work without feedback. But go back and look at what I said about transistor amps without feedback.

12-17-10, Irvrobinson: Your explanation above is such nonsense that I can't help but reply.... And then concluding that all of this mumbo-jumbo you're discussing indeed describes why solid-state amps sound harsh and lack low-level detail is just so much malarkey. Solid-state amps have neither of these characteristics you claim they do just for promoting your tube products.

Irv, I would suggest that it would not be too difficult to find more appropriate targets for this kind of insulting language than someone who has devoted a career to studying these matters, and who for many years has designed and manufactured some of the world's finest and most respected amplifiers.

Disclaimer: I have no affiliation with Atmasphere or his products, not even as a user.

Regards,
-- Al

Agree and not just about Irv's response to Atmasphere , but for everyone in general no need to make it personal when in disagreement.

That aside It must be said Ralph did peg SS a bit in his response before pulling out the encyclopedia and totally forgot to mention Tube fog and distortion ..... :) :) :)

I think the most interesting aspect to the original poster's question is the fact that it forms the logical basis to objectively improve our art - that is, "Does it sound real?" is actually a falsifiable question. The answer is definitely highly dependent on an unfathomably large number of personal differences in perceptional acuity . . . but one can always ask oneself this question and come up with a relevant answer. So the main thing we *should* be striving for in the technical studies of audio (i.e. measurement and controlled listening tests) is repeatability.

For reading on some of the logical basis of falsifiability, I'd recommend starting with the work of Karl Popper, or at least his Wikipedia page:
http://en.wikipedia.org/wiki/Karl_Popper
http://en.wikipedia.org/wiki/Falsifiability

Under the logic of falsifiability, it takes just ONE instance of having experienced reproduced sound as being real . . . to validate the conditional plausibility of all the technical and methodological basis for its reproduction. Not that the reverse isn't true as well, but if "reproduction" as an abstract is the goal, then at least for me its occurrences are much more noteworthy than its absences.

Here's the problem I have with setting up camp in any of audio's little belief-systems (i.e. tubes/transistors, cones/panels, feedback/no-feedback, analog/digital, etc.). If I'm truly honest with myself, I have at times been dumbfounded by amazing experiences from really crappy stuff, and also underwhelmed by my experiences with some really beautiful machinery.

And since audio is really a trivial pursuit (no lives at stake, no big "origins of the universe" questions), I view the the craft of audio thusly (my quote):

To examine a wide variety of data from both measurement equipment and listening experiences, and establish correlations that logically fit as much of the data as possible . . . then assume causality based on well-established principles of physical science.

This is why I think audio is so interesting in general -- we get to explore a truly genuine frontier, consisting of abstract and profound questions of the limits of human perception in sound and music. We also get to explore many aspects of human psychology in the listening process, and sociology in the marketplace and hobbyist communities. And really, the assemblages metal, wood, plastic, paper, and whatnot that we fashion to this pursuit are not really so profound . . . after all, it's all going to be in a landfill in a couple hundered years at the very most.

Atmasphere, here's the main reason why I'm so routinely perplexed by your dogged determination to proselytize the whole anti-feedback thing . . . What do you do when you have an amazing experience listening to music through a system, and THEN learn that it's a solid-state amplifier using a pile of global NFB? Because it's happened for me often enough that I can't imagine it hasn't happened at least a few times to anybody that's made a career in audio.

Well, the whole negative feedback issue has been beaten to death pretty thoroughly already in other threads.

My conclusion is that it is just one of many design and execution factors that affect results depending on how well it is executed.

Having heard a lot of gear over the years, my ears tell me that good engineers working for companies making good products have a much better handle on all such things that matter these days than they did 30 years ago.

Hi Mapman,
I was speaking to an old friend of mine who built equipment 35 years to 25 years ago and hasn't built since. He was just telling me that he just might start building again considering the improvements in parts ie, speed, linearity, etc. I'm sure that you have heard some terrific old amps. After talking with him, I believe that even the old engineers could come up with some terrific products today. I believe a good engineer is a good engineer, we just must wade through so much mediocrity to find them. Good Listening, Tim

"My conclusion is that it is just one of many design and execution factors that affect results depending on how well it is executed."

That seems sensible to me. It's hard to believe that anyone would employ negative feedback in their design if there wasn't, at least in the designer's mind, some net benefit to doing so. Maybe not directly, but perhaps because it allows the employment of something else in the design that more than compensates.

Better yet , how many KT88's would one need for 500 watts necessary for the real thing ?

.......

How close are we to the real thing?

Since I listen exclusively to classical, I find this subject fascinating.

The truth is: we are very far. Why? - Because audio and acoustics are still treated as an art, not a science. I think that audio is now in the same stages as medicine was in the Middle Ages: we know the basics (anatomy), but the remedies are still experimental. A trepanation is made to extract madness; blood letting is supposed to be the cure for many illnesses. Our amps, cables or speakers are tweaked in the same empirical way.

Sound engineers and other people along the music production line DO NOT scientifically aim at achieving an exact reproduction of the acoustic sound; instead, they mainly make sure that the recording sounds nice, and they all use different microphones, monitors, consoles, room sizes, etc.

On the listener's end, we all use different amps, speakers, and our rooms all have different acoustics.

If there was a real willingness to achieve the sound of the real thing, the whole process would have strict standards: microphones, amplifiers, consoles, cables, loudspeakers, rooms, etc. would have ideal specifications. Listeners who can afford would be able to reproduce these specifications at home - if necessary going as far as building a room to the exact specifications.

The Middle Ages ended 600 years ago. Let's hope we won't have to wait that long for audio to be close to the real thing. All what it takes, is one producer setting up a recording standard that can be replicated at home.

Weseixas...
KT88's? UT or Triode?

Hi Kirkus, that one is easy! Its the same issue of when you hear a really good digital recording, one that is really convincing. What would it sound like it had been done analog?

The whole experience here comes down to one of expectation and intent. If you *know* that the system is underpar (maybe its only a table radio) *then* you don't have much expectation of it. But if its a real high end system- it had better bring home the bacon, because it has some high expectation attached.

I heard a system across the hall from me at THE Show about 10 years ago, maybe a little more. It was Joni Mitchell, singing with a full orchestra. It had been recorded by Sony, digitally, in 6 channels. The system was entirely solid state. The format was a digital reel to reel, 1/2" wide. I really did not hear the system, it was only the experience of the music.

So what would it have been like if it was 2" analog with my amps on each speaker? Hey, maybe it would have been better. We'll never know. I can say this though- if that system/recording does the job for you, if somehow it manages to sound *real* than that is worth paying attention to.

I have never said that feedback should be eschewed- all I have done is point out what it does. Now if you are reading between the lines, you will also see that I have also been pointing to how things can be dealt with. I'll give you a couple of examples. FWIW, these are all on the cutting edge of the art.

1) since feedback is bad, build tube or transistor amps without,
2) since the evil of feedback has a particular cause (propagation delay), build circuits that gets around this problem. Then you can have all the feedback you want.

There are people who are doing both, or at least are approaching both. Nelson Pass is one, Spectron is another. I think there are some class D amps out there that do some timing things to get around this issue too. And of course there are all the zero feedback tube amps out there...

Kirkus, thank you: your statements, "it takes just ONE instance of having experienced reproduced sound as being real" and "been dumbfounded by amazing experiences from really crappy stuff, and also underwhelmed by my experiences with some really beautiful machinery", is precisely where I'm coming from. My particular angle, "obsession", etc, for many years has been to work out, and am now repeating myself, what the HELL IS going on!! I have been attempting this essentially by the process of elimination, and for me the answer is (drum roll ...) the glib statement, Everything Matters! I've found unless one becomes totally anal (sorry!) about the whole kit and kaboodle, or you fluke it to some degree, then it won't happen, it won't be "real"!

To whip out yet another analogy -- love those things :-) -- take a typical commercial passenger aircraft. To me, the audio industry is full of people who say, for example, it's all about the engines, you've gotta have turbines using this very special metal, and the fuel lines going to them have to be made out a really esoteric plastic, don't worry about the wings or landing gear, any old stuff will do. Another says, no, no, no, it's all about the cockpit, unless you get this set up perfectly it's hopeless, what's used in the rest of the airframe is pretty irrelevant ...

Would you fly in a plane designed or maintained by these people? No, I don't think so ... and for me that's what it's all about in hifi too, to get the experience of a system sounding "real" each and every time you listen to it, you have to fussy about EVERYTHING ...

Frank

Waryn,

Ever Heard of the practice of medicine .. yes they are still in the dark there 2 my friend...

Regards,

Frank ,

I hope Kirkus have you figured out, this way at least one of us can follow along ... :) :)

Tim,

Triode.......

Atmasphere, I noticed that the output impedance of one of your amps is about 4 ohms, and I assume that impedance is not perfectly linear across all ten octaves. So, isn't that high output impedance going to affect the audible frequency response of the amp-speaker combination, and in ways that vary with every different loudspeaker's impedance curve?

Mapman says:

"Well, the whole negative feedback issue has been beaten to death pretty thoroughly already in other threads.

My conclusion is that it is just one of many design and execution factors that affect results depending on how well it is executed."

I couldn't agree more.

Atmasphere, unfortunately the way you present the concept of feedback with the term "propagation delay" helps to 'propagate' (sorry, couldn't help it ... :-) ) a misconception about negative feedback. Yes, "negative feedback is always lagging behind" but it is still able to "correct the signal it was supposed to". If it ends up lagging by 180 degrees, half a wavelength, with gain still happening, then you have positive feedback, and an oscillator, and fried tweeters!

So, the feedback ALWAYS lags, even by some tiny amount, but that is just part of the understood design of any working circuit. You can easily buy one of those "terrible" opamps with much more global feedback then a typical audio power amp, that is working comfortably at microwave frequencies, that is, beyond 1,000,000 kHz -- not bad for such a "mediocre" part!

Global feedback in an audio device, on the other hand, with discrete components is typically rolled off (because it has to be for stability, remember the oscillator!) to become non-existent at the higher frequencies, where it is most necessary, and where the ear is most sensitive to distortion -- that is part of the real problem. Also, that is why nearly all gear has rising distortion at higher power, and higher frequencies; in other words, it is not the presence of feedback that's the problem but that at the very time it is most needed, it's done a bunk ... :-) !!

Frank

Frank ,

The time smearing can be significant, this is what Atmasphere was alluding to, I do believe this is so if one get's carried away with NFB. Most SS designers today understand such and dont drink from the NFB pond in excess. The only way to eliminate it's usage is to design amplifiers which are very stable( matching transistors goes along way here) I do Believe Nelson Pass has made an even bigger step and acquired some pretty interesting devices, so we will see.

Tube amplifiers also use less NFB than there SS counterparts, so if NFB is really,really, bad then.....:):)

IMO output stage Bias is also very important in creating "that sound" associated with SS amps, how you balance the 2 ( Bias amt/NFB) when attempting to reduce distortion gives the amp that certain SS "character".

Regards,

Sorry Weseixas, re ".. can follow along ...". My earlier comment was just firstly agreeing with Kirkus that a lot of people have had special listening moments without it quite making sense why, and secondly, that my answer is to be fussy, fussy, fussy, just like people who make and look after aircraft are, which is why flying is so relatively safe, ie. equivalent to audio sounding "real".

Frank

Hi Frank, opamps usually have much lower propagation delays than power amps do! So feedback is more effective with them.

To improve the effect of feedback and decrease the resulting odd ordered harmonic generation, decrease the propagation delay of the circuit.

Irvrobinson, while our amplifiers tend to have higher output impedances, that impedance curve is nearly identical to the frequency response curve of the amplifier, IOW linear from 2Hz-100KHz.

The system was entirely solid state. The format was a digital reel to reel, 1/2" wide. I really did not hear the system, it was only the experience of the music. So what would it have been like if it was 2" analog with my amps on each speaker? Hey, maybe it would have been better.

Atmasphere, I'll admit I don't quite know what to make of this. Although I respect that you have sufficient confidence in your design approach that you feel your products could ALWAYS make a subjective improvement over anything else, it seems that your judgement (or at least your recollection) of this particular experience is totally dependent on your knowledge of the technical matters of its presentation.

This is what I would call a "Maggie Blackamoor" conclusion, after the character on Little Britain: http://www.youtube.com/watch?v=hUpHDtpoY9w

But since I brought up the subject of scientific philisophy (and also to avoid at least a bit of the well-trampled "NFB argument" road). . . to be a bit more precise this would thought of as a plainly "coherentist" argument. That is, the truth or validity of a given conclusion is based upon how coherent it is with an existing perspective or set of beliefs. For the coherentist, the method by which a theory is refined (made more precise) is when data is presented that incoherent with the current belief system, the belief system is revised to restore coherence with new data.

But the logical problem is obvious, it's the same with all theories of justification: it fundamentally relies on one's intellectual "concience" to formulate ideas that evolve beyond one's own belief system. In the field of audio this is particularly problematic, becuause our understanding of many of the perceptual and psychological mechanisms lags far beyond our practical understanding of the physical science on which our technology is based . . . technology that we so routinely use to (attempt to) fool these perceptual and psychological mechanisms.

But we can also see from this line of reasoning that the traditional audio "objectivist" arguments have NO better grounds in modern scientific practice than the "subjectivist" . . . they are both in actuality simply "justificationist". It's simply that "objectivist's" belief system usually can't include a reality outside simple regurgations of common-practice electrical analysis found in an average undergraduate EE textbook, and the "subjectivist's" belief system is so fundamentally undisciplined as to be able to include some really silly, wacky sh*t.

"Irvrobinson, while our amplifiers tend to have higher output impedances, that impedance curve is nearly identical to the frequency response curve of the amplifier, IOW linear from 2Hz-100KHz."

And how does that 4ohm+ output impedance affect interaction with the loudspeakers, since loudspeakers do not usually have anything like linear impedance curves? Won't this effect the system frequency repsonse? Or are you assuming very high impedance speakers with very smooth impedance curves, like Soundlabs?

Human ears (and brains)are complex sensors and information processors of an order far exceeding science or technologies ability to model exactly.

Given this truth, any hypothesis regarding being able to accurately predict the outcome of an individual's listening experience based on science alone, even in a properly executed scientific experiment or series or experiments, has to come into question.

Irvrobinson,

how does that 4ohm+ output impedance affect interaction with the loudspeakers

As Atmasphere states, provided that the output impedance is purely resistive in nature, that is, it does not behave like a capacitor or coil to any degree over the frequency range mentioned, then its effect will be totally benign. Even if it were ridiculously high, say 100ohms, same applies. All the latter would mean is that the speaker would never get very loud!

I also agree with Atmasphere regarding "decrease the propagation delay of the circuit", this is exactly what needs to be done to allow any feedback to do its job. Some people may not be aware that several highly regarded SS amps consisted of nothing more than an output stage driven by a high quality opamp, with, by normal standards, extremely high levels of GFB.

"objectivist's" belief system usually can't include a reality outside simple regurgations of common-practice electrical analysis found in an average undergraduate EE textbook, and the "subjectivist's" belief system is so fundamentally undisciplined as to be able to include some really silly, wacky sh*t.

Human ears (and brains)are complex sensors and information processors of an order far exceeding science or technologies ability to model exactly.

Agree 100% with both of the above

Frank

Irv raises a good point about the interaction of high amplifier output impedance with speaker impedance vs. frequency variation. An OTL amp having a 4 ohm or other comparably high output impedance will not be a suitable match for some speakers. See Ralph's Competing Paradigms paper for additional discussion of this subject.

Regards,
-- Al

Kirkus, I think you missed my point! The quote you put up is edited and not what I said. Try re-reading my post, without the idea that I am trying to make you wrong- that was not my intent at all.

Irv, maybe you were joking but Sound Labs have anything but a flat impedance curve. Just because a speaker has a variable impedance curve does not mean that an amplifier with a high output impedance cannot drive it well, without tonal anomalies. It is all in the intention of the designer, as the article that Al linked points out.

A vital point here is that distortion in amplifiers and speakers is perceived by the ear as a tonality, and without this understanding that tonality won't get measured. This is close to the heart of the subjectivist/objectivist debate. Once you understand how the ear/brain perceives things, a lot of this debate goes away.

Atmasphere, maybe I did miss your point, but I did re-read your post . . . and I think my quote was verbatim. But the logical problem remains -- I'll see if I can't address it first via Mapman's quote:

Human ears (and brains)are complex sensors and information processors of an order far exceeding science or technologies ability to model exactly.

Given this truth, any hypothesis regarding being able to accurately predict the outcome of an individual's listening experience based on science alone, even in a properly executed scientific experiment or series or experiments, has to come into question.

This argument is closely akin to Progress ad Infinitum, one of the tropes of skepticism as outlined by Roman philosophers (Sextus Empericus?) in the first century A.D. . . . that is, anything that can be regarded as proof must in and of itself be proved, on and on to infinity. So under this line of thinking, knowledge in and of itself cannot advance or become closer to the truth . . . leading to the trope of Assumption, that all scientific knowledge is merely theory and not truth.

But our entire craft of audio is among countless obvious artifacts that indicate that our knowledge of the physical world is indeed expanding and becoming more precise, thus closer to the truth. Karl Popper dealt extensively with the logical basis for this through his concept of "verisimilitude", or the extent to which a scientific theory resembules the truth.

It is through this concept that we can look at the evolution of ideas from Copernicus, to Galileo, and to Newton . . . with today's knowledge that all their views of the physical world were false. But each of them was able to formulate ideas with greater verisimilitude, building on the work of those that preceeded them. And for the original topic of this thread, I think it's indeed undeniable that our ideas about the understanding of sound perception and reproduction have greatly increased in verisimilitude, and gotten us closer to the truth . . . especially when viewed over the span of the last 150 years or so.

It is on this basis that I fundamentally disagree with the popular audiophiles' notion that Mapman articulated. We can indeed use science to predict the outcome of an individual's listening experience, even though the extent to which we can is still significantly inconsistent and variable. But we are continuously improving our ability to do so, as the logical result of our scientific theories ever evolving toward increasing verisimilitude.

My point to Atmasphere is this: as people involved in the design and manufacture of artisan audio equipment, we are of course required to evaluate the "truthiness" (Stephen Colbert's word) of the performance of our own, and others', equipment. And we then use such an asessment to determine the verisimilitude of our theoretical ideas.

It's my impression from many of your past postings that there are a handful of conceptual errors in your understanding of the traditional application of negative feedback and its Nyquist stability criteria . . . to the point that a discussion of the associated theory and measurement performance is moot.

But I (very respectfully) remain curious as to whether or not you've ever had an auditory experience that pegs the needle on your own personal, internal "sonic truthiness" scale? And has it ever been delivered by equipment that has a design approach that's incongruous with your own? (Please note that the phrase "pegs the needle" is an important one, meaning that at the time of the experience, an experience closer to the truth cannot be imagined and/or is simply irrelevant).