Why Tube Amps Sound Different (and better) Than SS Amps

[Atmasphere]

And exactly how do you know what feedback sounds like other than its bad it must be feedback? The Spectral with its wide bandwidth is using plenty of feedback. Perhaps it is good because of it.

You can try reading Bruno Putzey's paper where he takes the position there is no such thing as too much feedback as long as it is a stable system. The more the better.

http://www.linearaudio.nl/linearaudio.nl/images/pdf/Volume_1_BP.pdf

Nelson Pass disagrees. IMO he makes some of the best solid state around, proof is in the pudding, as they say.

A little 'FWIW': if you apply Chaos Theory to amplifiers, the ones with negative feedback are the Chaotic systems. Norman Crowhurst charted their Strange Attractors about 55 years ago.

 

[Phelonious Ponk]

I thought we learned those lessons a long time ago and no one wants to brag about how much negative feedback they use now days.

I thought the operating principle around here was we don't know everything (anything?), all is yet to be fully understood, what we think we know could be swept away at any time by discovery...maybe Putzey has discovered something that overrides what we thought we learned long ago. Or maybe he just figured out how to use negative feedback better than they knew how to use it in the 70s...or maybe this WBF principle of the preeminence of the undiscovered only applies when it allows us to believe what is contradicted by the available evidence?

Tim

 

[MylesBAstor]

 

[esldude]

I thought the operating principle around here was we don't know everything (anything?), all is yet to be fully understood, what we think we know could be swept away at any time by discovery...maybe Putzey has discovered something that overrides what we thought we learned long ago. Or maybe he just figured out how to use negative feedback better than they knew how to use it in the 70s...or maybe this WBF principle of the preeminence of the undiscovered only applies when it allows us to believe what is contradicted by the available evidence?

Tim

I believe you've got it Tim. Lets see some people think moderate feedback SS is better than lots. Less is even better. They obtain a wide bandwidth SS amp that uses lots of feedback and sounds maybe the best they have heard. Why would they not conclude maybe more feedback is good? Further, no one answered my question about what too much feedback sounds like. And I guess discussing class D is definitely a no-no with this crowd.

Anything that contradicts what I think is meaningless because we don't know everything (and therefore nothing). Anything that supports what I think is good and solid knowledge that 'everyone' must know by now. You and I might get there yet Tim.

Oh, and I forgot, the most important thing is who said it, not what they said.

 

[esldude]

Or is the trick designing the best circuit possible and using as little feedback as possible? Because again, what other distortions does the high use of feedback create? Also is Bruno talking about Class D amplifiers?

Listen there were several tube amps over the years where one could adjust feedback (think played with a VAC and Audio Note years ago that featured adjustable feedback; IIRC, some amp still do). All amps sounded much better with a little feedback (particularly in the low end) but of course this result is also going to depend upon the speaker used in combination.

Why don't you read the paper. I provided the link. Do I have to read and digest it for you too?

Curious idea for someone who is involved with positive feedback.

Guess I am surprised there aren't more tube based switching amps out there. Some nice transmitter tubes and the proper design could be pretty neat.

 

[KeithR]

And exactly how do you know what feedback sounds like other than its bad it must be feedback? The Spectral with its wide bandwidth is using plenty of feedback. Perhaps it is good because of it.

You can try reading Bruno Putzey's paper where he takes the position there is no such thing as too much feedback as long as it is a stable system. The more the better.

http://www.linearaudio.nl/linearaudio.nl/images/pdf/Volume_1_BP.pdf

Of course its not all dependent just on one thing such as feedback. I don't think anyone is stating that. There are no feedback amps that don't sound good either

Soulution also believes in Putzey's thesis (extremely high levels of feedback reduce all the harmonic distortions). I find both Soulution and Mola Mola amps to be not terribly good sounding (although at shows on speakers I know well, not my own home). YMMV. I can't remember if Halcro did as well.

Ralph will probably have a better technical answer for why I hear them that way.

 

[microstrip]

We should remember that Bruno Putzey is an audio expert, and owns a position of merit between the best audio engineers and designers, but not specially on feedback in linear power amplifiers for audiophile purposes. He is the man behind the famous Hypex class D designs and Grimm ADCs/DACs. He has solid roots in audio :

Then, when Bruno was 16, a friend of his father’s visited the Putzeys home in Herent, Belgium, with an amplifier built around two pairs of EL84 vacuum tubes in push-pull configuration. The young Putzeys was bowled over. ”I thought, this thing can give me a sense of the music that the other amps can’t.” He taught himself how to design electronic circuits with tubes, a really odd activity for a teenager in the late 1980s, when personal computers were ascendant.

This small IEEE Spectrum article is mandatory for those wanting to know more about his career: http://spectrum.ieee.org/computing/hardware/bruno-putzeys-the-sound-of-music-extended-play

 

[Al M.]

And exactly how do you know what feedback sounds like other than its bad it must be feedback? The Spectral with its wide bandwidth is using plenty of feedback. Perhaps it is good because of it.

There is a general difference between tube and SS designs with regard to level of feedback. What I hear in most SS amps is a lack of micro-dynamics. A certain flatness of sound, a lack of (timing) speed, that suppresses some of the life and natural flow of the music -- regardless if macro-dynamics are good or not (they mostly are in SS amps). And yes, I know that the Spectral uses lots of negative feedback -- that is why I mentioned the DMA-260 amp as an example where it works -- but Spectral has always been about speed as well. Apparently they have found a way to get around the liveliness problem that negative feedback seems to introduce.

From the Atma-Sphere paper:

As alluded earlier, negative feedback has been found to be an inexact solution to amplifier distortion. This is due to propagation delays (the very small but measureable amount of time it takes for a signal to move from the input of an amplifier to the output) which are a normal phenomenon of amplifiers. In order for negative feedback to work according to the math, it must be applied to counter the input signal in real time. Propagation delay in the amplifier circuit prevents this; the negative feedback will always be lagging the original input signal. This lag results in ringing effects and enhancement of the odd-ordered harmonics that the human ear/brain system uses to measure the loudness of a sound (specifically the 5th, 7th and 9th harmonics).

 

[microstrip]

There is a general difference between tube and SS designs with regard to level of feedback. What I hear in most SS amps is a lack of micro-dynamics. A certain flatness of sound, a lack of (timing) speed, that suppresses some of the life and natural flow of the music -- regardless if macro-dynamics are good or not (they mostly are in SS amps). And yes, I know that the Spectral uses lots of negative feedback -- that is why I mentioned the DMA-260 amp as an example where it works -- but Spectral has always been about speed as well. Apparently they have found a way to get around the liveliness problem that negative feedback seems to introduce.

From the Atma-Sphere paper:

As alluded earlier, negative feedback has been found to be an inexact solution to amplifier distortion. This is due to propagation delays (the very small but measureable amount of time it takes for a signal to move from the input of an amplifier to the output) which are a normal phenomenon of amplifiers. In order for negative feedback to work according to the math, it must be applied to counter the input signal in real time. Propagation delay in the amplifier circuit prevents this; the negative feedback will always be lagging the original input signal. This lag results in ringing effects and enhancement of the odd-ordered harmonics that the human ear/brain system uses to measure the loudness of a sound (specifically the 5th, 7th and 9th harmonics).

Al M.,

Generalizations about the sound properties of negative feedback are a dangerous field - the effect of feedback will depend on the topology and implementation details of the circuit. The good designers know about the difference between the theoretical model and the real implementations and have specific ways of circumventing some of the problems, but any solution is always a compromise and, as the magic, comes at a price.

Ralph prefers to avoid feedback, some other people, as Spectral or Soulution, just to name two brands referred in this thread have specific and expensive ways of dealing with it. As Jeff Rowland wisely said " I believe there is a trend toward the creation of a more natural representation of the original performance. This seems to represent the overarching aim of all audio designers, whether working with tubes or solid-state. We are all trying to climb the same mountain. Our paths may be different, but I believe we certainly respect one another’s efforts."

 

[Al M.]

Al M.,

Generalizations about the sound properties of negative feedback are a dangerous field - the effect of feedback will depend on the topology and implementation details of the circuit. The good designers know about the difference between the theoretical model and the real implementations and have specific ways of circumventing some of the problems, but any solution is always a compromise and, as the magic, comes at a price.

Ralph prefers to avoid feedback, some other people, as Spectral or Soulution, just to name two brands referred in this thread have specific and expensive ways of dealing with it. As Jeff Rowland wisely said " I believe there is a trend toward the creation of a more natural representation of the original performance. This seems to represent the overarching aim of all audio designers, whether working with tubes or solid-state. We are all trying to climb the same mountain. Our paths may be different, but I believe we certainly respect one another’s efforts."

Quite little to disagree here, Microstrip. As you and I both affirm, there apparently are ways to get around the problem of the effects of feedback. But I do think negative feedback tends to have a sound signature -- at least, I find there tends to be a general difference between tube and SS amps in liveliness as outlined above, and this probably has to do with topology (I would find the notion that tubes themselves are inherently somehow more lively than transistors magic ). But some manufacturers obviously do find convincing solutions, Spectral being one of them.

 

[Orb]

ABX is a great way to tell if you can hear [whatever] at all. But a blind test isn't needed for this! Either you can hear the added harmonics pulse on and off or you can't. Myles, you're in NYC, less than two hours from me. I'll be glad to drive in to visit you to test this stuff in person if you're willing.

--Ethan

Ethan,
then why do you and some other objectivist insist on dbt ABX for digital/amps/etc for it to be a valid statement regarding being audible/differences?
Sorry but the reason is applicable to both that and also discussing hearing differences regarding thd or anything else IF one insists on statistical significance for it be perceived audibly.
Might as well say no need to blind test comparisons if they are level matched; which comes back to how sighted is not equal to blind abx (such as JA and JGH with the tube Carver amp).

Cheers
Orb

 

[microstrip]

Micro, why do many of us prefer a purposely distorted stereo signal? Why do we have to distort stereo to make it sound good?

First, it is not not a purposely distorted signal - it is more a signal having a different distortion from others, and probably not suffering from the problems of others.

Second, you can not separate the performance of the amplifier of the whole system.

Third, as an well known author has written and I have often repeated "Stereo, therefore, is not really a system at all but, rather, a basis for individual experimentation."

Forth, as the potential of 2-channel playback is very often misrepresented and purposely diminished, people do not understand that some manipulation of the signal besides that carried by speakers and the room can enhance the stereo system capabilities.

Fifth, because the objectives of sound reproduction achievement are measured using human ears, not oscilloscopes.

 

[Ethan Winer]

then why do you and some other objectivist insist on dbt ABX for digital/amps/etc for it to be a valid statement regarding being audible/differences?

Tom gave you one good answer. To me, a blind test is needed to let someone prove they really can hear what they claim, especially when their claim defies 100 years of audio science. One guy here says he can hear 0.001 percent distortion if it's odd-order, and another guy says even 0.00001 percent is audible. Oh, really? Prove it! But they never EVER allow themselves to be tested. As we just saw above. I can't for the life of me imagine why some people prefer to believe in unicorns and fairy dust against all logic and evidence. But clearly they do.

Another advantage of ABX, versus other blind test methods, is people can test themselves on their own system, over long periods of time if they'd like, while avoiding the feeling they must "perform" in front of someone else. They can be as honest or not with themselves, and learn or not learn about their own hearing acuity as they choose.

I don't think blind testing is needed when differences are obvious, such as a sharp roll-off above 8 KHz or 10 percent distortion etc.

--Ethan

 

[microstrip]

(...) I can't for the life of me imagine why some people prefer to believe in unicorns and fairy dust against all logic and evidence. (...)

Although I have no scientific evidence of it, I firmly believe that people believing in unicorns do not believe in fairy dust and those believing in fairy dust do not believe in unicorns. According to logic and evidence those who believe in unicorns should believe in Pegasus and those believing in fairy dust believe in Neverland. BTW, all audiophiles, believers or not, dream about carrying blind tests (ABX or similar) comparing the real Tinker Bell bell tingles with the recorded version of it using their preferred media. It is the ultimate test of audiophile perfection ...

 

[Atmasphere]

To me, a blind test is needed to let someone prove they really can hear what they claim, especially when their claim defies 100 years of audio science. One guy here says he can hear 0.001 percent distortion if it's odd-order, and another guy says even 0.00001 percent is audible. Oh, really? Prove it! But they never EVER allow themselves to be tested. As we just saw above. I can't for the life of me imagine why some people prefer to believe in unicorns and fairy dust against all logic and evidence. But clearly they do.

--Ethan

Ethan, you seem to be trolling. Is there really 100 years of audio science? Do you know someone that believes in unicorns? How do *you* know that someone else whom you've never met has not allowed themselves to be tested? If this site had a Report function I would report this post for active trolling (I'm a moderator on a site unrelated to audio, I know what trolling looks like); seems to me you don't like it if anything is suggested that is different from your world view.

Some people like to think everything about audio is known and measurable and that its been that way for some time. The problem is that how we percieve sound is not really understood. Of course I have explained that before; pardon the expression but that seems to have fallen on deaf ears.

I've already pointed out that objective numbers exist on the subjectivist experience- and that this research is on-going. Audio is not at a dead-end. There are a lot of clues offered in this thread about what might happen next. Those that keep a finger on the pulse of on-going physiological research are going to be in a lot better position to do something about improving audio than those that don't.

 

[MylesBAstor]

Although I have no scientific evidence of it, I firmly believe that people believing in unicorns do not believe in fairy dust and those believing in fairy dust do not believe in unicorns. According to logic and evidence those who believe in unicorns should believe in Pegasus and those believing in fairy dust believe in Neverland. BTW, all audiophiles, believers or not, dream about carrying blind tests (ABX or similar) comparing the real Tinker Bell bell tingles with recorded the version of it using their preferred media. It is the ultimate test of audiophile perfection ...

Uh huh It's ok for Ethan to use the strawman argument but no one else. BTW Ethan where was it you told JA you got your engineering, science or math degree from?

 

[thedudeabides]

Why bother gentlemen?

Really.

By the way Mr. Winer, I believe in the audio equivalent of unicorns and fairy dust AKA my ears.

GG

 

[Al M.]

Some people like to think everything about audio is known and measurable and that its been that way for some time. The problem is that how we percieve sound is not really understood.

Precisely. As a scientist who is well aware of the fact that, the more we know the more we know what we don't know, I find the naive and exuberant confidence of some engineers that we already know all that is to be known and to be measured in audio quite touching.

Remember the early days of digital when all "measured so perfect" but it was still irritating as hell? Now of course we know that jitter is digital's worst enemy and the human ear is extraordinarily sensitive to jitter (certainly vastly more sensitive than to harmonic distortion). But jitter was a phenomenon that had hardly even risen to the surface of awareness of the 'all-knowing engineers' in the olden days of "perfect sound forever".

(And as people here know, I am a fan of digital and not willing to go back to analog, so I have no axe to grind with the digital medium itself with my above observations. Jitter is now also much better taken care of than in the olden days, and it brilliantly shows in the audible results.)

 

[MylesBAstor]

Precisely. As a scientist who is well aware of the fact that, the more we know the more we know what we don't know, I find the naive and exuberant confidence of some engineers that we already know all that is to be known and to be measured in audio quite touching.

Remember the early days of digital when all "measured so perfect" but it was still irritating as hell? Now of course we know that jitter is digital's worst enemy and the human ear is extraordinarily sensitive to jitter (certainly vastly more sensitive than to harmonic distortion). But jitter was a phenomenon that had hardly even risen to the surface of awareness of the 'all-knowing engineers' in the olden days of "perfect sound forever".

(And as people here know, I am a fan of digital and not willing to go back to analog, so I have no axe to grind with the digital medium itself with my above observations. Jitter is now also much better taken care of than in the olden days, and it brilliantly shows in the audible results.)

Yeah but Ethan claims all the improvements in digital since 1980 are fairy dust too. Ethan has stated that 1980s digital is as good as it gets.

 

[Al M.]

Yeah but Ethan claims all the improvements in digital since 1980 are fairy dust too. Ethan has stated that 1980s digital is as good as it gets.

You can't be serious.