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You said,"PP and/or balanced circuitry is commonly used to PARTIALLY SHORT OUT
A.C. interference that is Common to both sides of a signal--
hence, the "Common Mode" moniker. ***Of course, some artifacts
of music are also found in the Common Mode***, so they also get reduced/processed by a PP and/or balanced circuit."With regard to the portion between the ***, would you please give a technical explanation of how this comes to be?
Just for clarity I will paraphrase what I think you said,
[Some parts of the music signal are Common Mode (found on each of the two wires, equal in amplitude and out of phase with regard to each other) and in the case of a unbalanced single ended circuit or connection, those two wires would be.....the one signal wire and the one ground wire).
So when that unbalanced signal is subjected to a balanced circuit or a balanced connection the portion of the music that was Common Mode gets PARTIALLY SHORTED OUT.]
Please explain.
Thank you.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 07/01/17Follow Ups:
I know many of you like your SE amps and with the right speakers they can be very good. I'm not knocking SE here.But let's face it. 99.99999% of the worlds power amplifiers are PP and have been since the later 1940s.
Not to mention many amplifiers in non audio applications, RF, scientific, are also PP topologies when higher power is required.
If they are as bad as Dennis claims, how could that be?
Edits: 07/05/17
It looks like his advertising is directed to an audience that is getting stroked to care *NOTHING* about that 99.99999%. It studiously impugns anything but his stuff, using words that indeed have no real meaning, though they are designed to sound alarming. You're missing something! is a fine way to get a non-technical audiophile's attention it seems. His terminology panders to that non-technical back ground. They'll not have the means to understand it is a steaming pile of Marketing.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
"It looks like his advertising is directed to an audience that is getting stroked to care *NOTHING* about that 99.99999%. It studiously impugns anything but his stuff, using words that indeed have no real meaning, though they are designed to sound alarming. You're missing something! is a fine way to get a non-technical audiophile's attention it seems. His terminology panders to that non-technical back ground. They'll not have the means to understand it is a steaming pile of Marketing."
Coming at this as someone whose career has been in science, I have always been, and I remain, puzzled by the standpoint of the "extreme" audiophile community who seemingly believe that an SET amplifier is endowed with qualities beyond the understanding of science.
Looked at dispassionately, a typical SET amplifier has, as I understand it, some very obvious and almost unique characteristics, which are easily measurable by the humblest of modern equipment, which would lead one to expect that it would have some quite pronounced acoustic qualities (related to the high distortion, especially second harmonic, and perhaps a non-flat frequency response). Most people who listen to SETs seem to report that indeed they endow the music with certain very distinctive qualities.
What I have never understood is: Where is the surprise in all this? Isn't the SET amplifier giving rise to exactly the kind of qualities that one might expect, given the nature of the distortions that it displays when measured?
It is certainly interesting that the human ear and mind finds these particular kinds of distortion euphonious and pleasing. But once this experimentally-discoverable psycho-acoustic phenomenon has been understood, there is nothing remotely surprising about the fact that people can find that SETs sound nice.
What is perhaps more surprising, or more difficult to understand, is the psycho-social phenomenon of why some people will pay vast amounts of money to buy a piece of over-priced equipment that produces these particular acoustic effects, when the same thing could be achieved for far less money. The peddlers of these overpriced amplifiers seem to thrive by by presenting an assortment of pseudo-scientific "explanations" which, like the one that prompted this thread, are completely lacking in any real scientific basis. And, at the same time, a disdain for real science and an appeal to almost supernatural qualities of their products.
Your post reads like it should be over in Propellerhead Plaza...
I heard my first SET amplifier (an Audio Note UK system) back in 1994 when I was 21. It had more instrument texture, nuance, natural clarity and presence than anything I heard heard to date, and while an undergrad at Caltech I spent all of my free time visiting every stereo store I could in LA to hear what was available. Young and healthy human ears and brains are more sophisticated than an Audio Precision analyzer.
"I heard my first SET amplifier (an Audio Note UK system) back in 1994 when I was 21. It had more instrument texture, nuance, natural clarity and presence than anything I heard heard to date, and while an undergrad at Caltech I spent all of my free time visiting every stereo store I could in LA to hear what was available."
I don't think anything I said would be in contradiction with what you are saying. I am merely saying that I think there are rational scientific explanations for why this would be the case.
Chris
The most common "explanation" for the SET sound is gentle clipping and 2nd harmonic distortion. I have made SET phono stages and headphone amplifiers, both of which are operated no where near clipping and have easy loads to drive, which have very low measured distortion yet sound noticeably different from other devices, be they solid state or tube. I believe there is more to the picture, yet to be discovered and understood, than standard bench tests.
Perhaps I should expand upon my previous response to your posting.I apologise if I picked the wrong word by describing the sound from an SET amplifier as "pleasing," since it might perhaps have carried a connotation of condescension that was not intended. I was just looking for a word that conveyed the idea that the sound gave a more satisfying all-round experience for the listener. And in that sense, I would describe a system that "had more instrument texture, nuance, natural clarity and presence than anything I heard heard to date" as a system that had a more "pleasing" sound. Perhaps there is a better word I could have used.
Now, as regards my statement that I suspect that these phenomena can be accounted for in terms of rationally understandable scientific principles, let me expand a little on this. Of course, ultimately, one (or at least a scientist such as myself) would wish to be able to explain everything we observe in terms of the most fundamental concepts and building blocks (quarks, leptons, strings,...????), but obviously at present that is not feasible. But explanations of phenomena in terms of more general observed phenomena can also be perfectly "scientific," even if they do not go all the way back to the level of the fundamental building blocks.
In the present context, I would take the observed psycho-acoustical characteristics of the human mind and ear as scientific phenomenological observations. A couple of examples are:
1) Humans find mixtures of frequencies that are related by simple rational ratios to be pleasing to the ear, and on the other hand irrationally-related mixed frequencies tend to sound unpleasant. Based on this observation, one can predict that if one made a sound-producing system in which all frequencies were shifted upwards or downwards by a constant additive amount, then music played through this system would sound absolutely dreadful. And this is, I believe, borne out by experimental observations. (A simple way to test this is if one has a shortwave receiver with narrow-band filtering that can block the central carrier frequency, and one then replaces this with a local BFO operating at a slightly different frequency.)
2) Humans find that the addition of the second harmonic to a tone or set of tones can provide a pleasing (in my generic sense) alteration to the overall effect. In particular, in a piece of music it can lead to an augmentation of the feeling of "liveliness," and maybe it can allow the brain to interpolate or extrapolate and give more of a lifelike overall experience. (Research in psycho-acoustical phenomena, as with many other aspects of the interaction of the brain with our exterior senses, seems to indicate that the brain does an amazing job of "filling in" the things that are inadequately conveyed to it by our sense organs.)
As a rather trivial hypothetical example, if it were the case that broadcast music stations used single or double-sideband AM transmissions where the carrier was removed and needed to be restored in the end-user's receiver, then one could easily make a general "scientific" observation that the best-sounding receivers would be those that restored the correct suppressed carrier frequency, rather than one that was displaced up or down by some amount. This would not be in the least bit controversial.
In a similar vein, it is a perfectly legitimate scientific endeavour to look for what characteristics of an SET amplifier might be responsible for giving humans the feeling that the performance is more "alive," or have more instrument texture, nuance and clarity. It seems reasonable to suspect that the phenomenological observations noted in point (2) above could be playing an important role, especially when one notes that one of the most striking distinguishing features of an SET amplifier is the relatively large percentage of second-order harmonic distortion.
Thus, I don't see why there should be anything controversial about the suggestion that if one can identify certain generic and measurable characteristics of SET amplifiers that distinguish them from most other amplifiers, then it is quite likely that it is these characteristics that are playing an important role in accounting for why they produce the audible sensations ("presence," "nuance," "instrument texture," or whatever) that they do. Thus, technical measurements of an amplifier's distortion and other characteristics (such as frequency response) might very well allow one to predict what kinds of overall impression it could give to the listener. You may be right that there are further characteristics of an SET amplifier that have yet to be identified and measured, but I wonder if there is really solid evidence for this?
Chris
Edits: 07/07/17
You say again "one of the most striking distinguishing features of an SET amplifier is the relatively large percentage of second-order harmonic distortion." As I previously said, I have made SET phono stages and headphone amplifiers which have very low measured distortion in their normal operating range yet they still sound different and I believe superior. I don't believe this is attributable to 2nd harmonic distortion when the THD is less than 0.1%. Another differentiating factor which you have not mentioned is the fact that they do not split or mirror the phase as do differential and push-pull amplifiers do. I believe this is a contributing factor to the SET sound.
An example: Back in the 90s Audio Note UK made two tube amplifiers that were as identical as possible, one a parallel single ended, the other a push-pull. The reviews all said the single ended version sounded better.
"I have made SET phono stages and headphone amplifiers which have very low measured distortion in their normal operating range yet they still sound different and I believe superior. I don't believe this is attributable to 2nd harmonic distortion when the THD is less than 0.1%"
I think simple SE amplifiers made with direct heated triode output tubes that do not use feedback are notable by what is lacking in the HD. Namely, upper order HD.
I believe it's not the (relatively) high amounts of 2nd HD that make them "sound so good", it's the lack of 5th, 7th and 9th.
I believe (but can not prove) that the smallest amount (maybe even an amount that can't be measured) of 7th and it's game over. The electronics sound like electronics instead of music.
I could be proven wrong on all counts but this is what I believe and it is what guides me when designing circuits and picking operating points.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
and Crowhurst even fought for a weighting system which would have assigned higher penalties for 5,7, and 9. There is text somewhere on the net about him and some BBC guys advocating for this but were shouted down by manufacturers. and they specifically mentioned upper odd harmonics at some crazy low levels being very annoying.
Yes and these were serious proposals.One would be multiplying the percentage measured by the order. 5th would be the measured % times 5. 7th would be the measured % times 7.
The other proposed method would have been the % measured times the square of the order. 5th would be the measured % times 25 and 7th would be the measured % times 49.
These proposals were intended to better reflect the annoyance factor.
THD doesn't tell us much in terms of the annoyance factor. We need to now the orders of the HD.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 07/07/17
"and Crowhurst even fought for a weighting system which would have assigned higher penalties for 5,7, and 9. There is text somewhere on the net about him and some BBC guys advocating for this but were shouted down by manufacturers. and they specifically mentioned upper odd harmonics at some crazy low levels being very annoying."I agree that that is a very interesting point, and maybe is highly relevant. Do you, as a matter of interest, know if SET amplifiers tend to have lower odd-harmonic distortions than PP amplifiers? I just don't know one way or the other; I don't recall ever having seen studies of this question.
In any case, such things should lie within the threshold of measurability, presumably, and so they would be part of the whole package of "measurements that can be correlated with observation" in the spirit of the scientific method.
Chris
Edits: 07/07/17
"I believe it's not the (relatively) high amounts of 2nd HD that make them "sound so good", it's the lack of 5th, 7th and 9th.I believe (but can not prove) that the smallest amount (maybe even an amount that can't be measured) of 7th and it's game over. The electronics sound like electronics instead of music."
You may be right that it is a lack of higher odd-harmonic distortions that is responsible. (Is this actually a property of an SET, by the way? I can see why it would tend to have more even-harmonic distortion than a PP amplifier, but is there a reason why it would have less higher odd-harmonic distortion? I'm not doubting, just asking.)
However, what about the suggestion that the higher odd-harmonics below the threshold of measurability, could be responsible? A modern state-of-the-art spectrum analyser is amazingly sensitive. Is there really any reason to suspect that amounts below the threshold could have audible effects? Or is this an example of the very human desire (in some humans at least) to believe that there are things that lie beyond our understanding? If it could be demonstrated in convincing experiments that such effects were occurring, I would be only too happy to accept them. But I wonder what evidence there might be?
As a matter of practicality, I would have thought that any real-world amplifier in existence today would have 5, 7 and 9th order distortions that are actually within the range of measurability by present-day spectrum analysers, and so speculation about the possibility of such distortions below the measurable threshold would be, at this stage at least, academic. (Again, if I am wrong about this, I would be happy to be corrected.)
Chris
Edits: 07/07/17
Chris
It has been noted that the use of negative feedback can reduce second harmonic distortion, however Dr. Earl Geddes (among others) has noted that added second harmonic distortion is relatively difficult to hear compared to other types of distortion. The second harmonic is an octave above the fundamental and harmonizes with the fundamental which makes it difficult to separate in our perception from the fundamental. While negative feedback reduces the second harmonic, it can actually increase higher odd order harmonic distortion. As the second harmonic is the biggest number, reducing it makes the total harmonic distortion number look better at the expense of increasing higher order odd harmonic content which has been shown to be perceived as unmusical. But you don't have to believe me on this, Jean Hiraga wrote several articles examining this subject going back into the late 70's and 80's which we didn't get here in the US unfortunately until the oughties when they were reprinted in AudioXpress. See the link here for the Amplifier Musicality article which was followed by rebuttals from two experts, and which was followed by a rebuttal by Hiraga with no rebuttal to Hiraga's rebuttal.
Paul
I'm pressed for time right now but a DHT is very linear. If loaded and driven correctly, and without NFB, there is not much of a mechanism for producing upper ordered HD."Norman Crowhurst wrote a fascinating analysis of feedback multiplying the order of harmonics, which has been reprinted in Glass Audio, Vol 7-6, pp. 20 through 30. Mr. Crowhurst starts with one tube generating only 2nd harmonic, adds a second tube in series (resulting in 2nd, 3rd, and 4th), and then makes the whole thing push-pull (resulting in 3rd, 5th, 7th, and 9th), and last but not least, adds feedback to the circuit, which creates a series of harmonics out to the 81st. All of this complexity arises from theoretically-perfect tubes that only create pure 2nd harmonics!"
__
I believe there are studies showing that humans can hear well down into the noise floor.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 07/07/17 07/08/17
I think you may have to look closely at the word rational. Let's say we know 100 things about audio we can test. Could there be 100 more we do not know yet. Infinity is a pretty big place. To go from I know a few things about the human body and energy to I know everything is hardly what I would
call rational.
So the real question is who is drinking the koolaide???
Enjoy the ride
Tom
" Let's say we know 100 things about audio we can test. Could there be 100 more we do not know yet. Infinity is a pretty big place. To go from I know a few things about the human body and energy to I know everything is hardly what I would call rational."
Well a question one has to ask is, is there any compelling evidence that the 100 things we already know are insufficient to account for the observed phenomena? I get the impression sometimes that some people just don't want the things we already understand to be able to explain the things we observe.
As I have said before, I am not for one moment disputing that SET amplifiers may sound different, and indeed better, than other amplifiers. There are some "obvious" reasons why this might be the case. Is there compelling evidence that the obvious and already understood reasons are insufficient to explain the observed phenomenon?
Chris
Why are there no commercial applications for SET amps? What amps were used when the recording mixer did his work?
Wait a minute: The analog record circuitry in the classic Ampex 351 tube tape recorder was all single ended. Its internal playback electronics were push-pull.
Edits: 07/07/17
Of course lots of 1950/60s studio and broadcast line level gear was single ended and it worked just fine.
Gusser, I'm curious to know, though, what kind of amplification and processing stages a typical audio signal will have gone through, in a modern recording studio and CD production plant, on its way from the studio microphones to the output of the home-user's CD player.
Would the amplification stages typically be op-amps, with lots of feedback? Could you walk us through the steps the signal might typically follow, between the microphones and the CD player's output? That would be really interesting.
Chris
Today most work is done on digital workstations. The large mixing consoles with multiple flat screens are just control surfaces talking to a bunch of commodity PC's over Ethernet. The audio processing is all via AES in and out - so much for all the SPDIF jiter scares! AES and SPDIF are virtually identical - especially in terms of jitter performance.Now the microphone preamp before the ADC is analog of course and mostly an OPAMP design. There are some studios that use discrete transistor mic preamps and some even tube preamps. But beyond the ADC, the audio remain digital, in fact a computer file. Tape is long gone except again for tiny esoteric operations. All storage is via hard disk and that data is shipped and modified around a lot including between facilities over the public internet - encrypted of course.
In the 1980s, large mixing consoles were all OPAMP. Hundreds of them in a 128 input board. Anywhere from two to ten stages per module. I once cared for a Neeve console that had 128 inputs and the internal bussing was wide standard ribbon cable. They ran balanced +/-/G across a 50 wire cable with no twists either. No crosstalk and no noise. It just shows what is possible with god engineering as Neeve is well known for. So much for esoteric audiophile cables! If any of that hype was true, Neeve would have used them. Cost was no object on his products.
The 1970 was the rein of discrete transistor OPAMPS. And they were not as good to spite what some audio magazines want you to believe.
Edits: 07/10/17 07/10/17
Thanks for the summary of the path from the microphone; very informative.
Presumably there is quite a bit of analogue processing after the DAC in the home CD player? Low-pass filtering to block the digitisation artifacts, and so on? Op-amps, typically?
What I'm thinking, then, is that probably at the two ends of the chain (microphone amplifier, and output stages of the CD player) the typical setup will involve op-amps, with the usual very large negative feedback applied. I'm just wondering where that leaves the people who argue that negative feedback is a bad thing.
Chris
After listening to a fair group of SE amps, I have yet to hear one I wanted to build, except for geetar amps.
For stuff SE needs, like gapped OPT's there is some benefit to the linearizing effect this has on the sonics delivery. I may try gapped PP at some point if I can live with the reduction in LF performance the drop in overall primary L gives. Since I run electronic cross overs, this could be sooner than later...
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Bi-amping is your friend: I run parallel single ended 2A3s above 160Hz and McIntosh push-pull tubes in the bass.
"Bi-amping is your friend"
I totally agree.
Gapped transformers and good bass performance are, IMO, mutually exclusive.
The gap reduces the inductance, the reduced inductance causes the loadline to become elliptical (in the presents of low bass) and all the frequencies follow that elliptical loadline increasing the HD.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Yah, it is a fight...for the bass amps, I think I want as much as I can get. Anything else above that, the gapped core sonics are not to be despised.
It does not take anything like a SE, full Class A idle current worth of a gap to be of use. Just enough gap to knock 10% off is quite worthwhile. it is likely one of the reasons I like cut C-cores; their effective gap is much larger than an interleaved stack of E's and I's.
I think I need some 49% Ni cut C's...
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
"Why are there no commercial applications for SET amps? What amps were used when the recording mixer did his work?"
Indeed, this gets to the nub of the question. When someone chooses to use either a tube SET or PP amplifier, or an SS amplifier, in their home stereo system, they are just making a selection that sits at the end of a long chain of totally "conventional" SS amplification and processing stages. If this last step of the chain makes a big difference, it seems likely that it is because of what it is adding, rather than what it is not adding, to the signal that has been fed into it.
I have never understood why this is a controversial point, but somehow the suggestion that the SET amplifier is adding colourations that are "pleasing," "nuanced," or whatever, seems not to go down too well sometimes!
Chris
cpoyl
The SET craze arrived here in the US in the 90's by way of Sound Practices magazine, and this was over a decade later than it arrived in Japan. The reception then by the audio mainstream here was interesting to say the least. John Atkinson declared the first SET tested in Stereophile a "...tone control". By far the best article from that time was a test of a 300B SET in Audio magazine*. The author was quite surprised at the slew rate performance of this 8 Watt amp. With a sine wave as a test signal we are frequently focused on the top and bottom of the wave and where and how drastic clipping occurs. However the greatest rates of change are in the middle sections of the wave. The results that the author got from his tests revealed that the slew rate (in volts per micro-second) of this 8 Watt amp could only be equaled by 90 Watt class A transistor amp! Now this begs the question of course as to how much slewing induced distortion is audible in an amps performance, or at what point does it become an issue. There seems to be a lack of interest in the mainstream audio magazines to look into this dark room, as there is a similar lack of interest to look into frequency modulation distortion and amplitude modulation distortion in speakers, but this is not surprising in that J.Gordon Holt didn't like horns, and John Atkinson has stated that he is "...suspicious of horn loaded designs." Along with the interest in SET's came a renewed interest in horns which are at a distinct advantage over direct radiator speakers in regards of FM and AM distortion performance.
Paul
*It would be nice if someone less lazy than me would dig up the mid 90's Audio article, or find a link to it online.
Both very fast slew rate and TIM are easily simulated and measurable in any audio amplifier. Just send it fast rise time square waves and thee issues will quickly arise. In the late 1970s TIM was all the rage but few audiophiles understood the engineering behind it and thus the flaw in this measurement.Nothing in nature can produce an acoustic wave with rise times that fast. Our 15psi atmosphere simply won't allow it. Not to mention there is no microphone or speaker that can move or react that fast. So unless artificially electronically generated, no sound can have a rise time that fast.
Which translates to amplifiers with fast rise times and low TIM are indeed very good engineering designs. But the truth is, it's a useless attribute because no audio amplifier will ever be called upon to reproduce rise times that fast.
Now that's not to say square wave testing is useless. It is very useful and important to test the amplifiers stability. But the ability for an audio amplifier to have rise times in the video range is of no use in reproducing sounds on Earth.
Edits: 07/06/17
Gusser
Transient intermodulation distortion was discovered by M. Otala (when he accidentally miswired a SS amp). He wrote a number of papers about it and he concluded that "...the ear seems to be very sensitive to it". A web search turned up a number of references to TIM but none stating that a TIM spec is a "useless attribute". If there is a threshold in volts per microsecond where improvements in slew rate and TIM become inaudible in an amp, then that would be good to know. Perhaps you can supply references to support this.
I agree that square wave testing is useful as a diagnostic tool, but that the square wave does not exist in the sound domain in nature. The Audio article (which I can't find) referenced slew rate and sine waves as I recall.
Paul
Yes I know all about M. Otala and his papers. He had an agenda obviously to promote his name. His technical findings are true and accurate. But that doesn't mean they show a PRACTICAL problem. TIM is a classic text book exercise when it comes to audio amplifiers.Now when Elon Musk populates Mars and in a few ten thousands years when our bodies adjust to the thinner atmosphere, Perhaps TIM will be a legitimate factor for audio amplifiers on Mars where sound can travel faster!
TIM is not necessarily about slew rate. It was promoted as an attack against feedback. The old Einstein time paradox where you can't experience something before it happens. And it's and a serious problem in some areas of electronics design. But not for audio. The path delay of a typical audio amplifier is too short to have any detrimental effect on an audio signal coming from a natural source.
I have no doubt there are a plethora of papers online about the horrors of TIM. But do these papers have traceable credibility? Hint, Stereophile is not an accredited reference!
As for MEANINGFUL measurements, don't use a square wave generator like Mr. Otala did. Take a modern digital waveform snap shot of a musical session. Measure the fastest rise time. Multiply by 5 using the classic engineering 5x bandwidth rule. Then see what the required rise time of the total amplifier circuit is. Now in fairness perhaps some early solid state gear with slow power transistors did fall short, But no amplifier designed past 1980 transistor technology should have a TIM problem.
Edits: 07/07/17
So apparently Otala's work ushered in a golden age in transistor amp design, until Joe Roberts showed up with Sound Practices in the 90's and ruined everything.
Paul
Otala's work ushered in nothing. He documented a phenomena that while technically accurate and easily demonstrable with simple test equipment, it has no practical influence in natural music and sound reproduction.
Now I did say that early 1960s slow power transistors may have caused this effect to be audible, but that was fixed by the progression of transistor technology in the 1970s onward.
As for Joe Roberts, he is the national sales rep for Silbatone as well as an accredited Anthropologist. What does that have to do with this discussion?
Gusser
The original post here by Tre' was a request for an explanation from Dennis Fraker concerning a statement Dennis made about common mode effects in amps. The subsequent post by Cris I responded to addressed the request by Chris for information explaining the SET phenomena, and I made a reference to frequency modulation distortion in speakers among other things in my post. As you have stated your comments in the present discussion were in reference to FM distortion in amps. The two things are related but they are not the same thing of course. Otala claimed that FM distortion was audible in transistor amps and he provided data to support this. You seem to be claiming that FMD in modern transistor amps is not audible and you have not supplied any supporting evidence or links for this. When I did a web search to respond to your first "hogwash" post I found some controversy concerning Otala's procedure for minimizing FMD by limiting negative feedback to a certain level in amp stages Otala specified, but I didn't find anything agreeing with your position that FMD has become inaudible in transistor amps. BTW with the post above here you seem to have moved the goal post from the 80's into the 70's, and Otala's first manuscript was submitted in 1976.
Denis is a manufacturer of SET amps and has promoted their use over other amp types. Once again the SET amp craze was introduced to the US through Sound Practices magazine by editor Joe Roberts who was a self confessed solid state Krell high end salesman who was listening to Western Electric speakers (sourced from the ceiling of a shoe store) and powered by a Western Electric 300B tube amp, and he thought this sounded better than what he listened to at work.
I would be interested to read any references you provide concerning the non audibility of FMD in transistor amps with a beginning reference point some time in the 70's as of now. My comments in the present discussion were in regards to Modulation Distortion In Loudspeakers which was the title of a JAES paper by P.W. Klipsch from 1968.
Paul
I never spoke of "FM distortion" It is called TIM or Transient Inter-modulation Distortion" And you have provided no evidence TIM is audible. Just because you can simulate the problem with test equipment doesn't mean you can hear it with normal program materiel. The subjective camp is always saying how they can hear things no test equipment can measure. But here's the truth with TIM, even legacy test equipment can measure distortions that cannot be normally heard.How about my test example. Let me refine it further:
Capture a 15khz square wave from a hobbyist quality signal generator on an audio workstation. Then record any random sampling of music or acoustically generated sound effects, gunshots etc, and compare the rise-times. Now tell me if any of those natural rise-times are a steep as the 15khz square wave? Further analyze and measure the rise-times. Then tell me if the path delay through a typical DC coupled amplifier is anywhere near the rise time of the test material? One popular claim is that dues to the path delay of the amplifier, the feedback fails to "catch the leading edge" and that is TIM. That sounds quite plausible to a non-engineer. But enter mathematics and we see how minuscule the problem is. The leading edge is so slow in relation to the amplifiers path delay that all that is missed is a minuscule fraction of the leading waveform edge. Now in light of all the other larger distortions, mainly from the speaker system, that tiny fraction of a waveform edge distortion is audible?
This proves TIM is a theory exercise. It can easily be simulated with even cheap test gear. But it never happens in the real world of audio reproduction. Also note by specifying hobbyist grade test gear, I am putting the test in the TIM camp's favor. A pro signal generator would have much steeper rise times.
My professional background is the design of broadcast television equipment. Today it's mostly digital but in the late 1970s when I started it was mostly analog. I have designed many analog video amplifiers during that era and we used negative feedback extensively. We never worried about TIM and note that TIM should be a much larger problem with video frequencies, eg 6mhz. So if a video amplifier circuit which is very similar to an audio version is fast enough for TIM to be irrelevant, how can it possibly be a problem with audio amplifiers?
I am not interested in articles or AES paper paraphrases from Strereophile, Absolute Sound, or similar consumer product sales magazines. Lets look at this from a solid engineering perspective and analyze the problem. When you do it becomes very clear.
Again I'm not saying Mr. Otala's results are wrong. They are quite correct from a pure technical perspective. But what is wrong is the conclusion that this phenomena is detrimental in modern DC coupled amplifiers.
Edits: 07/10/17 07/10/17
Gusser
Thank you for a plausible explanation of your theory that TIM is a non issue in modern (post some time in the 70's) transistor amp design. As to evidence contra to this, Otala (and others) published two JAES papers addressing this: 1. Threshold of Audibility of Transient Intermodulation Distortion (in 1978); and 2. Psychoacoustic Detection Threshold of Transient Intermodulation Distortion (in 1980). In the first paper a group of six of the most sensitive subjects (from a previous test of 68 listeners) were tested and it was found that "The results show that in certain passages of music, 0.003% of distortion is clearly audible". This was followed by ""Low distortion values were perceived only as changes in the sound character, and not as distortion" which could possibly provide somewhat of an opening for your position. The second paper described further testing with improved test equipment and conditions. Otala has provided test results and data to support his assertion that TIM is audible. Another google search by me with the subject "transient intermodulation distortion+audibility" didn't turn up anything saying that TIM is not audible in modern transistor amps, but to be honest I stopped reading after 30 references. There is ample evidence that TIM is audible, but anyone is welcome to make a case for whether or not it's it's an important a concern in modern solid state amp design.
Paul
But rather than scrape references to papers online, why don't you address my theory as to why TIM is not a factor on real audio signals?Those papers you recently referenced are for IEEE and AES members. Otherwise you have to pay for them. So again did you read them or just cite the synopsis. Because buried within them may be the answer I am providing.
P.S. I hold membership in IEEE, SMPTE. SBE
Edits: 07/11/17 07/11/17 07/11/17
Gusser
As Otala has performed tests demonstrating that TIM in transistor amps is audible and that it can be detected down to a level of 0.003% by 6 out of the 68 listeners in his test group, then it would seem that there would need to be tests with a group of at least that size to seriously contradict Otala's findings. Neither you or I have been able to find any references to tests like this. Let's try it another way, can you supply the name of a transistor amp from the 80's with TIM specs lower than the 0.003% which was clearly audible to the 6 golden ears? Just what number would you buy as being below the level of audibility, and what amps have specs matching this? Feel free to add in any TIM specs for SET's too as we are on the Tube DIY Asylum
I quoted directly from sentences in both of the abstracts of the JAES papers I referenced, and I assumed that this would be obvious to anyone who has read the papers as you claim to have As to digging occult information out of these papers, well I would have to go down to the library, I would need help with the microfiche machine, and my knee is acting up causing me to drag my foot at times. Well you get the idea. If you were to write a rebuttal to the Otala papers to the JAES, then I would drop the Hogwash stuff, and you'll have to use your real name as you'll be subject to peer review. I've been to a number of JAES meetings and nobody wore a mask or used a pseudonym.
Paul
> As to evidence contra to this, Otala (and others) published two JAES
> papers ... In the first paper a group of six of the most sensitive
> subjects (from a previous test of 68 listeners) were tested and it
> was found that "The results show that in certain passages of music,
> 0.003% of distortion is clearly audible".> As Otala has performed tests demonstrating that TIM in transistor amps
> is audible and that it can be detected down to a level of 0.003% by 6
> out of the 68 listeners in his test group ...6 out of 68 is a really poor sampling, on the level of a statistical error. While TIM theory looks profound, real audibility is an open question. Its a common behavior in human society to raise a problem (often miniscule or even non-existent), in order to develop and sell "unique solution". BTW, TIM issue was widely used in advertising material back in 198x.
I own two amps engineered to minimize TIM (Sansui G Pure DC series). They sound great. I heard, had (and built myself) others, solid state and vacuum tube, which design don't take into account TIM at all. They also work great.
Thus, I assume, TIM made more noise by itself rather to contribute anything useful.
Edits: 07/12/17
LGIt would be nice if there was an easily accessible example of TIM distortion on the web or disc, demonstrated with a short musical performance repeated with more and more levels of TIMD until the effect became obvious. Unfortunately none of the Stereophile Test Discs have this, or anything else I have. To be honest I'm not really sure what it would sound like. The 6 golden ears of the 68 testees really couldn't detect it as distortion at 0.003% in Otalas test, they could only tell there was a difference. It would certainly be nice to have another test following Otala's with a larger group which would provide a better base rate, but how likely this is to happen I can't say. My original comments in the present discussion were directed at intermodulation distortion in loudspeakers, which is related to FIM in amps but really quite a bit off topic from the original post by Tre' up page.
As to how important FIM distortion in amps in the entire audio scheme of things is I really can't say. The subject is somewhat interesting to me but it's largely overshadowed by issues in speakers. I built a Hafler DH200 in the 80's but the specs show only IM distortion @ 0.005% and TIM is not mentioned. I though it sounded great when I built it, but it got replaced by what became a highly modified Dyna ST70 in my horn rig, and after that it served in our HT until a Yamaha 5.1 amp bumped it out several years ago. The Hafler sounded good in the HT with Pioneer CS80's until one time the Dyna was awaiting parts and I brought the Hafler back down into the horn rig in the basement and it sounded terrible! Very dull and slow, typical of what has been described as the "mosfet haze". Turning the volume up changed things, but you don't really want to listen to a string quartet for instance at heavy metal levels. This is likely due to the capacitance at the gate of the mosfets changing with the drive level as per the late Alan Wright's observations. So I really don't know what to make of the TIM thing and how it fits into the audio hierarchy, but until we get something better I'm going with Otala's test results. BTW my ST70 is currently triode wired with the ultra-linear tap disconnected, and I wouldn't expect it to do well in THD tests, but it's going to stay this way until I get something better.
Paul
Edits: 07/13/17
> It would be nice if there was an easily accessible example of TIM
> distortion on the web or disc, demonstrated with a short musical
> performance repeated with more and more levels of TIMD until the
> effect became obvious. ...
> To be honest I'm not really sure what it would sound like.
> The 6 golden ears of the 68 testees really couldn't detect
> it as distortion at 0.003% in Otalas test, they could only
> tell there was a difference.
It would require recording from test amplifier dummy load, and playing recorded data again on benchmark unit, thus, subjecting test data again to distortions of benchmark amp (no matter how miniscule they are), speakers, and room acoustics.
As Gusser stated before, TIM issue doesn't make practical sense, and IMHO, it is entirely correct. Someone wanted to make a party, they had a drink and show, now its over.
High stability of the amplifier is much more important factor, and it something that is time to time neglected with aftermath from HF spurious oscillation and loss of clarity to burned components and speaker coils.
LG
It's always nice to have a civil discussion here about audio concepts which don't get get looked at very often.
Paul
But you still don't acknowledge the engineering problems I raised that clearly contradict Otala's claim that this is audible with program material. Ahh, but did he even say that? I do agree it might be audible with test signals but then that's not real program material we listen to.
Just more "appeal to authority". Typical audiophile response when presented with real engineering problems that dispel their beliefs..
I think I see where you're going with this, you are intending to write a JAES paper and you are testing some of the ideas out here. Here's some suggestions to clean up the argument:
To say something is hogwash is to say it's useless and should be thrown away, so drop the hogwash and just say that. You would be expected to provide at least some rudimentary test results, so just have some buddies over for beers and test them. If you add some TIM to a musical selection you are adding energy to the signal and thus effectively raising gain, and that's an old Hi fi salesman trick to turn the volume up a bit to make the thing you are trying to sell sound better. With this you can probably get some people to actually prefer the TIM'd examples, and Otala did note that some of the test subjects did. It's also fairly easy to prove that people are guessing during audio tests if you make them guess, so do rapid switching among orchestral recordings with both loud and quiet passages. After awhile they won't even know what ocean they're in.
You have criticized Dennis and Jeff for promoting speculative and unsubstantiated theories, and you also leave yourself open for criticism in this regard if you don't provide something a bit more concrete. Lisa Randall once said to me when I asked her a question about Loop Quantum Gravity that "It's just a theory", though she did admit she respected the author of LQG. So far you just have an interesting theory, but the ear is the final arbiter in all things audio to paraphrase Olson. And it wouldn't hurt for you to make some appeals to authority too.
BTW Otals did say that the 0.003% TIM was clearly audible to the six golden ears on musical selections, but he noted that they could only hear a difference, but not identify which version had the TIM added. That alone would seem to open an area to study. Also Otala did use square waves as you stated, but he also used triangle waves in some of the tests too.
We're pull'n for ya!
Paul
"You have criticized Dennis and Jeff for promoting speculative and unsubstantiated theories, and you also leave yourself open for criticism in this regard if you don't provide something a bit more concrete. Lisa Randall once said to me when I asked her a question about Loop Quantum Gravity that "It's just a theory", though she did admit she respected the author of LQG. So far you just have an interesting theory, but the ear is the final arbiter in all things audio to paraphrase Olson. And it wouldn't hurt for you to make some appeals to authority too."Stupid analogy! I have provided evidence based on simple physics why TIM is not an issue with acoustically produced sound. You have yet to comment on the theory I have presented. All we hear is "Otala says, Otala says".
As for listening tests, first of all 6 out of 83 is hardly a convincing sampling. We also don't know the controls present or how these tests were conducted. ABT, DBT? "I'm going to play some TIM for you, tell me if you hear it?" Yes some classic audiophile tests were that unprofessional.
You also fail to separate the technical facts of TIM versus the final effects on the systems as a whole. Sure it can be simulated, but does it present an issue in real world audio reproduction? Basic atmospheric and mechanical physics says it can't.
Ok so you don't like TIM being called hogwash. Perhaps you are right in that TIM is real and can be demonstrated - with test equipment. But what is hogwash is that we can hear TIM with modern audio amplifiers designed with late 70s / early 80s technologies.
I'm tired of hearing your monotonous references to 40 year old research papers - OK, 39 years old in fact. Show me how an acoustically produced square wave rise time within the human hearing range can exceed the path delay of a typical DC coupled audio amplifier. Show me a microphone that can capture such an event even if out atmosphere would allow such a pressure wave to propagate in the fist place?
Again show me the math that supports TIM audibility! I know a test generator can do it. But what about real music, sound effects, and speech?
P.S. "If you add some TIM to a musical selection you are adding energy to the signal and thus effectively raising gain"
This is not totally correct either. You are thinking solely of harmonic distortion. IM distortion does not follow the same rules. Look up Bessel functions.
Edits: 07/12/17
nt
a
do please explain how slew rate does not translate into bandwidth.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
There is of course an argument used by the amp sales folk that goes something like this: it has to be able to do what you can't hear in order to sound good.
In dealing with an amp that can only do what you can hear, the reasons for its BW limits are liable to be contributing their effects where we can hear them.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Do please explain how high slew rate fails to translate into high-frequency bandwidth if you'd be so kind...:)
Cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Douglas
I made no intentional reference to high frequency bandwidth (though this does come within the TIM territory), but perhaps your question is rhetorical and it looks like you have begun to answer it in your "hogwash" reply up page here.
PAUL
I think you all are a bit harsh on Dennis. I think he gets a lot shit because of Jeff.
I know the non technical marketing statements makes some peoples blood boil but everyone can do better in being respectful...
"I think you all are a bit harsh on Dennis. I think he gets a lot shit because of Jeff.I know the non technical marketing statements makes some peoples blood boil but everyone can do better in being respectful... "
Personally, I have no problem at all with his, or anyone's, claims about the musicality, or what have you, of their amplifiers. I do not doubt that they can sound very good. My own suspicion is that the reasons why they may sound distinctive and satisfying are rather straightforwardly correlated with easily measurable colourations (or, one may say, distortions) that they introduce. But that in no way detracts from their being very satisfactory for the purpose of providing a pleasing musical reproduction.
I do take issue, though, when someone makes a claim of an explicitly technical nature, if that claim is in fact false. One example that falls into this category is the recent assertion that in a standard unbalanced output ("live" plus ground) signal, part of the music is in common mode. Another is the example Tre mentioned, of the claim that the output tube in an SET was passing "hundreds of amps." These assertions are simply wrong, and as such, I think if anyone makes such statements and asserts that they are true then it is legitimate for others to jump in and point out the error.
Chris
Edits: 07/07/17 07/07/17
DF is an icon to some people on the Tube DIY forum, it is kind of neat to read his "Frakerisms" and rants about the status quo of conventional mainstream thinking.
I don't think I would have gotten as heavily into SE tube amps or Altec speakers without the influence of either DF or JM.
It's all good to me, take what is useful and ignore the static.
In a thread where Dennis and I were talking about a theoretical SE output stage where the output tube was biased at 60ma of idle current and the input signal was limited to only drive the output tube's current to 120ma. max, Dennis stated that within that 120ma. "envelop" there are "Hundreds of amps of current". ???!!!???
This is only one example of Dennis saying crazy things that lead me to believe that he is not a BS artist per se but is ignorant WRT electronics and may indeed believe all the crazy things he types.
But if Dennis is going to present himself as an expert (and I believe he does) and then say crazy, unsubstantiated things (like the one at hand "some artifacts of music are also found in the Common Mode") he needs to expect to be called on it.
If that is disrespectful on my part then so be it.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Hey Tre you know Dennis talks in his own language which is foreign to most of us but he has been doing this for decades. You are much more informed than most of the number guys that are on the forum these days. That being said you might have to defend the SET crowd. If I remember correctly you run set with transistor sub.
All the guys that built cool stuff are not around anymore. Hell even the late grizmo would listen question listen again and scream tone is every thing. Now we have people who want to debate the same tired nonsense. At least Henry (when he was around) was good debater.
The one thing I find interesting is the numbers guys come on a DIY TUBE forum and want to tell me my musical background and abilities are all in my head and really I am tone deaf. I should just go to best buy and spend 600.00. Is there koolaide any better than Dennis's???
For the record 6sl7 belong in a phono stage and I do not even use them there. Well your thread turned into a SET is cult that PT Barnum would love to sell to. Well guess I will fire up my limited bandwidth amps with the crap distortion vinyl front end and pretend it sounds better than the state of the art 599.99 best buy wonder.
Enjoy the ride
Tom
"Well guess I will fire up my limited bandwidth amps with the crap distortion vinyl front end and pretend it sounds better than the state of the art 599.99 best buy wonder."
That's a good idea. I think I'll do the same.
Listening to a clean Mo-Fi copy of Little Feet "Waiting for Columbus" I picked up today at the thrift for $2
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Actually Tre' you've always provided a good technical explanation and I've not seen a lot of bashing from you.
I think the way you handle it typically is a good example. I don't have a problem with you calling Dennis out on his poor choice of wording.
The problem is the "pile on" and then it turns into how is amp is a poorly designed piece of shit. :)
Well in all fairness, Dennis is hardly alone in that game! Plenty of $40,000 plus amplifiers that measure and sound worse than a $499 Best Buy AV receiver.
I wonder if he's referring to cancellation of the second harmonic generated in the stage?
It appears he was referring to the cancellation of the signal , not the distortion
George
no matter, turned into a good thread anyhow!
Yes he is.
He is also thinking of balanced connections where all things in the common mode are rejected.
He is also thinking of unbalanced signal where nothing can be in the common mode.
The problem is, he doesn't understand any of them and is thinking of all three of them in a very wrong way.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
I would love to see the explanation he'd give should he have decided that PP amps sound better to him...LOL
I'm also curious as to how far from the usual Horsepower Race, gNFB designs he would have deviated; his SE stuff is RotM.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
I think if he was PP guy he would a uneducated/ignorant PP guy, in much same way as he is a SE guy.
RoTM = run of the mill?
If so then I strongly disagree.
He's SE amp is poorly designed from the power supply to the driver stage to the operating point and load impedance of the output stage.
"Run of the mill" stuff is better than that!
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Hey Tre, wondering if you happen to have a schematic of one of dennis amps?
is this why you said they are poorly designed because you seen his schematic?
Thanks
Lawrence
I have, more or less, seen a schematic.
When I talked to Dennis he indicated that there were a few things that were very close but not spot on.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
I think you may at some point be able to draw reasonable conclusions from a description. High-mu triode, direct coupled to a 2A3 grid paints a fairly solid pic. The admitted frequency response matches this practice.
The description of the PS allows other conclusions to be drawn, and operating responses modeled...:)
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Yes, Run of the Mill...:)
It has B+, it has a low mu triode final, and a high mu triode voltage amplifier.
As to implementation, it is set up as a signal processor...again, nothing surprising there, save perhaps the magnitude of the processing.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
With similar success you can get same kind of meaningful information from countless BS artists in audio cable industry.
Turning abracadabra into attractive and lucrative marketing slogans is something your technical mind is not capable about.
"Of course, some artifacts
of music are also found in the Common Mode"
Everything in the "music signal" is applied differentially across the balanced input and will be amplified. Above statement shows a basic misunderstanding of how balanced circuits operate.
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
"Above statement shows a basic misunderstanding of how balanced circuits operate."
I would say it shows a basic misunderstanding of electricity. :)
--------------------------
Buy Chinese. Bury freedom.
"Above statement shows a basic misunderstanding of how balanced circuits operate."You are, of course, correct but I was hoping Dennis would let us know what he was thinking when he wrote that.
Down below he was asked, by another inmate, to please explain but Dennis hasn't yet.
Maybe Dennis has decided to heed Mr. Lincoln's advice, albeit a little too late.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 07/01/17
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