I do consider comparisons between tube amps and ss ones bogus if they're based on a THD measure alone.
I concur - I recall many years ago reading an article in 'Electronics & Wireless World' which explained how electronics distortions and speaker distortions are orthogonal, as you mention. I can't recall who the author was. But in my view the problems with ss amps are in the areas of intermodulation, not THD. I'm not of the view that 0.1% THD is audible if its low-order harmonics. If its pure crossover distortion then probably it is audible - I recall being able to hear crossover distortion on a subwoofer amp sample which I think measured in the region of 0.03%.
THD is a static measurement but please don't confuse 'dynamic distortion' and 'static distortion' with this usage of the word 'static'. THD measurements do not discriminate between the ways distortion occurs. Dr. Geddes papers do, and consign dynamic distortion to 'future work'. I agree its an attempt to provide a more useful alternative to the single THD figure, I don't see it succeeding owing to the limitations previously mentioned.
'Dynamic distortion' is just a way of talking about (what I see as the most common) forms of distortion - ones that cannot be modelled by simply a static transfer function. Take crossover distortion - I think Mr. Self initially modelled this statically, he showed SPICE plots of transconductance of output devices. However, as Bob Cordell points out, there are dynamic contributions to crossover distortion (quite apart from thermal variations of bias) which are germane. These dynamic (increasing with increasing frequency) distortions are one of the reasons Bob continues to recommend MOSFETs as output devices whereas Doug Self generally dismisses them as an expensive and non-linear fad.
I think your reading of my criticisms is a tad too generous to Dr. Geddes work. I consider it largely irrelevant for the reasons I have already given. His two AES conference papers are also self-contradictory if you take a close reading, this does not lend credibility to his arguments. If and when he undertakes the 'future work' he alludes to in his paper, my view may well change substantially.
Bruno Putzeys in my estimation is a very smart cookie and most generous in sharing his considerable insights into audio (particularly digital and switching audio) on various forums. I think I may have mis-quoted him earlier though - I think rather than saying 'if you use feedback...' he's more likely to say 'use feedback, lots of feedback'.
I agree. But I was talking about Cdom.
If the open loop bandwidth is, say, 100 Hz; a 2000 Hz signal get 6 dB lower feedback than an 1000 Hz signal. An instrument (string, flute ...) having a fundamental of 1000 Hz, produce overtones (here harmonics) at 2000 Hz, 3000 Hz etc at certain levels, definining the sound of that instrument. But your amplifier is adding increasing distortion the higher the frequency, thus altering the sound of the instrument. The phase of the overtones are changed as well. This is the background of my claim for 6-10 kHz open loop bandwidth.
Input stage distortion and TIM is another matter. I am aware of certain OPAMP's good reputation as audio amplifiers. It is telling me that I may be too much focused on open loop linearity, but it also tell me that these OPAMP's in other aspects maybe are designed quite well.
And I agree that THD is not a proper tool in revealing amplifier weakness, as all know the higher the harmonic content of that distortion, the worse. This is true for both amplitude and phase. And dynamic distortion (like crossover distortion) is masked when doing THD measurements.
Yes it is e.g. about -110dB in second harmonics and 0,01degree in phase shift at 2kHz. You believe, we can hear it? You can load VAS and get flat OLG to e.g, 30kHz. Result? Big increasing in overall THD and IMD, too..
Try well known Baxandall diferential test with music to hear (and measure) resulting artefacts to realize what we are able to hear and what not
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I wonder though how much people really like "Good" opamps.
The LM4562 get mentioned a lot as one of the best available today, but I remember when the thing got out, nobody really liked it. I heard complaints like "it sound dull" or "it sound lifeless" or "it sounds 2D"
The same with the NE5534. Basically on paper and in measurements a very good opamp, but most people seem to dislike it.
BurrBrown is very beloved but seems to add "something" in the harmonic structure that is very much loved. Apogee D/A converters earned their name with as (FAT, warm and deep sounding) merely by the use of Burr Brown opamps.
So what is it what we really want?
With kind regards,
Bas
The LM4562 get mentioned a lot as one of the best available today, but I remember when the thing got out, nobody really liked it. I heard complaints like "it sound dull" or "it sound lifeless" or "it sounds 2D"
The same with the NE5534. Basically on paper and in measurements a very good opamp, but most people seem to dislike it.
BurrBrown is very beloved but seems to add "something" in the harmonic structure that is very much loved. Apogee D/A converters earned their name with as (FAT, warm and deep sounding) merely by the use of Burr Brown opamps.
So what is it what we really want?
With kind regards,
Bas
But if your wide bw opamp has more distortion at higher freqs, it alters the sound MORE than the low bw opamp. Following your reasoning, the important point is the actual THD percentage at a specific freq, not the BW as such.
jd
science vs perception
to quote wakibaki "Until science reclaims audio engineering we're all trying to operate in a fog."
I believe my band director's perception in 1965 that Altec-Lansing Voice Of the Theater speakers on a theater tube amp were worth the price of admission to hear, has been proved valid versus the other technologies available at the time. He didn't use an instrument, he used ears trained by ten years of musical education.
Science is interesting but expensive.
Musical education is expensive but a lot of fun.
There is plenty of snake oil being sold in the high end audio field, but unless it pleases the musicians among us it is not worth producing.
to quote wakibaki "Until science reclaims audio engineering we're all trying to operate in a fog."
I believe my band director's perception in 1965 that Altec-Lansing Voice Of the Theater speakers on a theater tube amp were worth the price of admission to hear, has been proved valid versus the other technologies available at the time. He didn't use an instrument, he used ears trained by ten years of musical education.
Science is interesting but expensive.
Musical education is expensive but a lot of fun.
There is plenty of snake oil being sold in the high end audio field, but unless it pleases the musicians among us it is not worth producing.
Here I disagree. If my amp has 0.1 % THD in the audio band, and your amp has 0.001 % THD at 100 Hz and 0.1 % at 10 kHz, I would like to think that an instrument with a fundamental at 5kHz, would sound more natural with my amp. And it is not difficult to make a class A amp with 0.01 % distortion in the audio band.
It is very difficult to find an objective way to verify my claims, as it is impossible to separate one design criterion from another. And if you claim that the distortion level is of a magnitude that is inaudible, I can give you right. But my point is the relative change in THD with frequency.
Yes.
I have no references to prove the point, however I believe that it is important. (That is why I asked how to achieve constant distortion with frequency, earlier in this thread). I do not know if a general difference between 0.1 and 0.001 can be perceived, but I think that a dynamic change from 0.1 to 0.001 may be perceived, and not in a good way. According to the datasheets this rise often starts quite low, sometimes from 1000 Hz.
An externally hosted image should be here but it was not working when we last tested it.
I thought you might like to see my 'studio'. Left to right, books, some amplifiers & effects, guitars, oscilloscope, LH stereo speaker,lab PSU, condenser mic, earphones, joystick, DI box, computer with mixing desk, keyboards (alphanumeric and velocity sensitive midi, synth), below these:- some laptops, DVD player, stereo amp, above:- printer, monitor, HD projector screen, USB condenser mic, on floor:- satellite receiver, bluray, soldering iron, some high power torches, HDMI switch, RH stereo speaker,battery charger, DMM, some more books and the 2 command chairs with world map above.
In the back half of the room are at least 200 reference books on subjects from nuclear physics, through metallurgy, ballistics, software design, mechanical engineering, RF design (lots of those), mathematics, aviation, history of science, music - and then there's all the fiction.
I've been playing the guitar for ~44 years now. I have a lot of respect for ears, but in the end they're easy to deceive. Being a musician, I get a bit impatient with people who get obsessive about the quality of reproduced music. As it happens I've also got a broad experience of general electronics, and ALL of IT is science based. Everywhere except HOME audio.
When you look at information on the internet you have to make a judgement about it's value. You have to evaluate its provenance. I don't expect Douglas Self to have performed blind tests or subtraction/comparison tests on every circuit he recommends, but I do expect him to have performed extensive instrumented testing at the very least. I'm happy to take the recommendations in his book or on his site.
I wish I could say the same of some of the conclusions that people rush to publish here. In so many instances they're representative of the 'subjective' rubbish unleashed on us all by Stereophile and its ilk.
They're obviously NOT universally valueless, and I think the standard has improved considerably since my last contribution, although I am a little disappointed that opamps 'reputations' have been introduced into the discussions, because in this world of chinese whispers there are few things quicker acquired than a reputation.
w
My own observations suggest that while there are differences between systems, these are largely due to differences in speakers and the power available to drive them, once an amplifier is reasonably competently designed. That such increasingly rare amplifier generated differences as there are, should properly be ignored, given the uncertain path that signals have traversed in the recording process. The whole point is to DIY some electrronics, hopefully not at exorbitant cost, enjoy the music, and not to indulge in endless nit-picking and one-upmanship. Pick a low-noise opamp recommended for audio at a price to suit your pocket that you can source preferably from more than one supplier locally and go with that. Just like a professional designer with a budget to meet would if designing a mixing desk.
Great pic - did you use a fish-eye lens for that or stitch together shots?
I notice your reading material is a bit unbalanced. Where are the psychology and management, communications skills and business books?
Yep but you've omitted to say that minds are even easier to deceive than ears. Perhaps you're unaware of this because of the lack of psychology books on your shelves?
Why would other people's obsessions bother you? Live and let live, we all have our obsessions, they're just a part of life. It doesn't follow that being a musician guarantees you impatience towards other people's obsessions.
Observations waki, observations. Show us the 'rubbish' and explain why its rubbish so we can learn from you. Or alternatively, you can learn that your characterisation is misguided. That's why observation is so important. Anyone can claim something, but science doesn't progress through claiming, rather by showing.
So far you've fessed up to impatience and now disappointment. How are these emotions relevant to being a scientist? Is not science about being objective?
OK so give us examples of your observations. Which postings on this forum show this?
If there are perceived sonic diffedrences between say an NE5534 and an LM4562, I seriously doubt its because you can hear the difference in the distortion components, or the fact that one has a few more dB of feedback at frequency x than the other one.
Bottom line is these op-amps are damn good for the money you pay (and especially the 5534).
Talking about feedback, there has been a lot written about wide open loop bandwidth amplifiers ('WOLBA') and it actually has nothing to do with TIM. You do not need a WOLBA to create a zero TIM amplifier or to create an ultrafast amplifier. The reason some people want WOLBA's is because it is supposed to reduce PIM. However, if you read Robert Cordell's article on the subject, the theory shows that if you have sufficient feedback, the PIM problem is fully resolved. Ditto for the other argument which goes along the lines that reducing loop gain in the audio band also changes the distortion's harmonic structure . . . but in an NE5532 or an LM4562 its so low you will not hear it anyway.
Bottom line is these op-amps are damn good for the money you pay (and especially the 5534).
Talking about feedback, there has been a lot written about wide open loop bandwidth amplifiers ('WOLBA') and it actually has nothing to do with TIM. You do not need a WOLBA to create a zero TIM amplifier or to create an ultrafast amplifier. The reason some people want WOLBA's is because it is supposed to reduce PIM. However, if you read Robert Cordell's article on the subject, the theory shows that if you have sufficient feedback, the PIM problem is fully resolved. Ditto for the other argument which goes along the lines that reducing loop gain in the audio band also changes the distortion's harmonic structure . . . but in an NE5532 or an LM4562 its so low you will not hear it anyway.
Why does anyone give an opinion about IC op amps without being able to hear a sonic difference between them? I find it still possible to hear differences in IC op amps. Each IC op amp that I am testing already meets TIM, harmonic distortion minimums, as defined by research done over the decades. Still, I hear differences in my own designs, even though I have no favorite manufacturer of them I don't CARE if the IC's are National, Analog Devices, or Burr-Brown. I chose what works best in the circuit that I have designed for an IC op amp. Of course, it is MY business to make a good decision as to which op amp to use. That is what counts, nothing else. IF they all sounded essentially the same, I would not bother to audition them.
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Many people are even able to appreciate the SQ improvement of the metal can LM4562HA/LME49720HA over the plastic versions. That includes members of the team that designed them ! The LM4562 series are very demanding of their power supplies for best results though.
SandyK
I did not say they do not sound different John - just that I doubt its because of the distortion or harmonic structure of the distortion because it is so low on those two devices.
Amplifiers do sound different (I have 2 in my house right now and I can hear it). But, we need very carefully controlled experiments to be able to definitively be able to say 'its feedback' or its x or y because the other variables in the signal chain exert so much influence (speakers, speaker/room interface, signal source, amp/cable system).
Have you taken a look at the PSRR on these devices? I would have thought this was one of their strong points. Having said that, its pretty easy to engineer a decent power supply for op-amps, so just do it is my motto.
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