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In Reply to: RE: Most manufacturers don't talk about it but voicing is real..... posted by E-Stat on February 13, 2024 at 13:21:28
I know you've tried lots of stuff and found things that work for you. What would be ideal is to know why they work. Now, that is a difficult question to answer and, I suspect, many/most manufacturers don't know - and I don't mean that as a criticism.
Follow Ups:
I've observed a direct correlation to using (and modifying to have) gear with stiff power supplies for greater transparency and dynamics.
Similarly, I've found inherently linear circuits using simple topologies and minimum *correction* render a more realistic presentation of acoustic music.
YMMV.
nt
Zero feedback applied to circuit is a good place to start.
I don't think there really are any audio circuits with zero feedback - those without global feedback probably have local degeneration. The closest I can think of is a single-ended triode, which hardly qualifies for the moniker 'linear'. And is there really anything wrong with global negative feedback? Not AFAIK, providing it is properly designed. We know feedback suppresses errors added in the amplification process yet I am not aware of any well reasoned argument why it is a bad thing. If you haven't read Bruno Putzey's 'F-Word' I have linked it below. He hypothesizes why feedback has such a low approval rating in the audiophile world. If the technical stuff is not of interest I recommend everyone to read the 'Backlash' section commentary.The conundrum, to me, is 'does low/no feedback sound preferable' because of something bad that global feedback does or is it because it does not fully suppress errors that are perceived as 'character' and give the audiophile something to fixate upon? Is a true distortion-less sound just bland?
Another thought, Putzeys is adamant that as much feedback be used as possible. This, IMHO, is not trivial any may be beyond the abilities of many/most audio(phile) designers who add 'just enough' feedback - that may be worse than adding none.
Edits: 02/14/24 02/14/24 02/14/24
Speculate however you please.
The linked article by Jason Stoddard in his series "Schiit Happened: The Story of the World's Most Improbable Start-Up" was an interesting read even for me, someone with limited knowledge of electrical engineering.
Edits: 02/15/24
I speculate whether Jason knowing what he is doing correlates with Schitt gear being affordable :)
I didn't read it completely and I saw no mention of GanFET's like the Peachtree etc. which supposedly use no feedback
The type of amplifying device - BJT, J-FET, MOSFFET or GaNFET - doesn't really make a difference to the discussion. They all thave non-linear Voltage-In to Current-Out characteristics hence they distort and, hence, feedback is needed to correct that.
The GaN advantage is their bandwidth - maybe doesn't bring too much to the linear amplifier table but it is advantageous for switching amplifiers in that they can switch more quickly and push the switching noise further from the audio band. They are the device du jour for switching amplifiers. Going back to Bruno Putzey, when asked about re-designing his Purifi module to use GaN instead of MOSFETs he said that there would only be a marginal improvement because he has applied a lot of feedback so errors are well suppressed. He thinks that maths is more important (i.e. being able to design an architecture with a lot of feedback across the audio band) than sexy FETs. If designers can't do the maths, and have lower feedback designs, then they will see more benefit from GaN.
Yes and triode amps have the best linearity of any amplification device ever made. ARe they completely linear? No, but they are linear enough to get away with any feedback beyond degeneration (sometimes even without that). The only other device that can kind of do this is the FET if run in Class A and without feedback beyond degenration.
The thing not mentioned is what feedback does to the distortion characteristics beyond just the level of THD and IMD. It has a clear impact on the pattern of those harmonics away from a low harmonic order dominant to a high harmonic order dominant pattern.
Triodes are square law devices, like FETS. This is not linear. You could operate them only over a narrow range of their characteristic where they will approximate a linear characteristic but that is the same with any non-linear device - if you operate it only over a tiny portion of its range it will approximate to linear (whether that range is large enough to do anything practical is TBD). Degeneration and global feedback work in the same way, so if you think global feedback is bad you should not look at degeneration as good (a difference is that degeneration applies to one device so stability is not an issue, but then global feedback stability around many stages is not an issue if it is done right).The topic of feedback translating low order harmonics to high order harmonics is an interesting one. It was raised decades ago in Wireless world magazine with an example of a single stage amplifier that had a large amount of purely second harmonic. After applying feedback the second harmonic was reduced considerably but also low levels of higher harmonics appeared. The F-Word article that I linked to in a previous post covers this case in the Section 'Storyline 2: Re-entrant distortion'. At worst, this is a case of going from no high order harmonics to a small amount of high order harmonics but never 'high order dominant'. And, there are no truly square-law devices, they all have some imperfections that make them not pure square law so they create high order harmonics on their own - I have never seen a single-ended triode power amp spectrum that did not already contain a spray of 3rd, 4th, 5th etc harmonics.
Edits: 02/16/24 02/16/24
3/2 law actually...not square law (or quadratic if you prefer)
It is actually pretty simple. A single ended triode will yield all harmonics but with a monotonic decay where each subsequent harmonic is significantly lower than the one before it...with 2nd of course being the most abundant.
Perfect FETs actually behave in some cases better, like a Class A push/pull output stage... the problem is that you will never have perfect FETs and so you will get plenty of distortion in the real world.
A good simulation paper is the following:
http://www.its.caltech.edu/~musiclab/feedback-paper-acrobat.pdf
Thanks. I have a Beethoven recording by James Boyk of which I am fond. I will read through in detail and see whether Boyk is a better EE or pianist :)
Clinging to old audiophile myths from decades past is not uncommon in these parts. Part of the blame go to some manufacturers who perpetuate these myths to promote their stale designs.
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