An amplifier is generally minimum phase, so if it has a flat frequency response (and a demon hasn't stuck an all-pass filter somewhere in there), that part is trivial.
Hi ontoaba,
I have a whole section (24.3) on the Baxandall findings in my book. I refer to the topic as "spectral growth" or "re-entrant" distortion. Baxandall showed with a JFET that a device with a square-law characteristic will have its THD increased for higher harmonics, up to a point, as increased amounts of negative feedback are applied. His findings were correct, as far as they went, and can be replicated in simulation.
The first big gotcha in the real world are that beyond about 15 dB of NFB, the distortions of all of the harmonics decrease, and that 15 dB counts ALL feedback applied to the device, both local and global, including degeneration.
Another gotcha is that most circuits are not square-law (e.g., BJT exponential) and thus start out with substantial amounts of the higher order distortions in the first place without negative feedback. Crossover distortion in the output stage, one of the most insidious amplifier distortions, is quite complex and shows none of the behavior of increased higher order harmonics with increased NFB. I have several graphs in Chapter 24 in my book illustrating these effects.
Cheers,
Bob
and a 100W into 8ohm amplifier can output a 20kHz full power transient only if it can accurately achieve 5V/us. There are designers who state that to achieve accurate 5V/us capability the amp needs to be able to achieve anywhere from two times to ten times the theoretical slew rate for that maximum speed signal.
Expect 10V/uS to 50V/us slew rate for a decently reproducing 100W amp.
I suspect that taking the same power amp and adjusting the slew rate between these two limits might make the SQ appear different at different settings.
I am quite sure that if one compared 5V/us to 50V/us slew rate settings that the same 100W into 8ohm amplifier would sound different.
Bob...I believe that a true benefit could be found in making the output-stage non switching..and always conducting even when that amp is pushed hard...Ken-peter is advocating this, and I see the point...could be done with diode controlling or some feedforward.
SY
A funny thing about these minimum phase network..I believe it's mathematical assumption that it is phase linear...what about a 2. way speaker designed around a typical 2.order filter....I can make that linear give or take a 1 dB or two...but the phase is twisting 180 degrees over the frequency range...
SY
A funny thing about these minimum phase network..I believe it's mathematical assumption that it is phase linear...what about a 2. way speaker designed around a typical 2.order filter....I can make that linear give or take a 1 dB or two...but the phase is twisting 180 degrees over the frequency range...
It is a common misconception that something built out of minimum phase building blocks must always be minimum phase as well.
The mentioned speaker is simply an allpass, which is never minimum phase.
A simple - and most of the time accurate rule - is the following:
If you connect mimimum-phase blocks in series then the result is also mimimum phase.
If you split your signal path into serveral different mimumum phase paths and sum them together again later on your overall response is most probably not minimum phase anymore.
Regards
Charles
Hi Vladmirk,
Note that I have shown results for those sorts of measurements in my book, "Designing Audio Power Amplifiers". Those results and effects are real, although they are often quite small and must be put in perspective. Take a look at my results for relay contacts and banana plugs. I also show very detailed measurements for thermal distortion in resistors.
While cables can make a sonic difference (often the connectors in my view), there will always be lots of debate and argument about cables for several reasons. First and foremost, there are many snake oil cable claims out there that are simply ridiculous and have no merit. This does not mean that cables make no difference, but is a reflection on that part of the industry. Secondly, there are some cables out there that make a sonic difference because they depart from accuracy. In some extreme cases, certain amplifier-cable combinations can result in amplifier instability.
Cheers,
Bob
WladimirK
It is typical, that persons speaking about tiny audible effects, are being attacked and proposed to demo the effects they speak about.
What is attacked is not hearing tiny effects or claims of hearing them.
There are claims about technical behaviour of amps but, to the insisting demands for proofs of this behaviour, there is only reiteration of the same claims.
Is is quite understandable that this attitude may upset some people when, on the other hand, numerous analyses show that the allegated facts are irrelevant for audio signal or, even, that they are pure fallacy.
It is typical, that persons speaking about tiny audible effects, are being attacked and proposed to demo the effects they speak about.
What is attacked is not hearing tiny effects or claims of hearing them.
There are claims about technical behaviour of amps but, to the insisting demands for proofs of this behaviour, there is only reiteration of the same claims.
Is is quite understandable that this attitude may upset some people when, on the other hand, numerous analyses show that the allegated facts are irrelevant for audio signal or, even, that they are pure fallacy.
I came to this conclusion when I changed the opamps in my cd-player. I had a thread about it
http://www.diyaudio.com/forums/digital-source/172114-opamp-change-now-some-disappointments.html
The people there were also arguing. Unfortunately I have no equipment and knowledge to research it. The pity was no-one at that forum wanted to research how it happens. One person an engineer gave the hint that it could be the transients.
I think we should also discuss how soundstage and imaging is heard physically and mentally.
http://www.diyaudio.com/forums/digital-source/172114-opamp-change-now-some-disappointments.html
The people there were also arguing. Unfortunately I have no equipment and knowledge to research it. The pity was no-one at that forum wanted to research how it happens. One person an engineer gave the hint that it could be the transients.
I think we should also discuss how soundstage and imaging is heard physically and mentally.
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My 2 cents. An increase in sound stage may be caused by distortion (phase anomolies ( actually used in recording studios to simulate a wider stage)), so I believe a lot of people mistakenly believe a system with more distortion is better. Just because a person (or 100 for that matter) likes one system better than another doesnt mean its more acurate (ideal: wire with gain).
Really, the only "equipment" you need is a soundcard and a computer. Doing a listening test is pretty easy as well- if it were me, I'd capture the output in an uncompressed .wav format, make use of Diffmaker (and/or the ABX function in foobar) and see if there's anything real there- it is FAR too easy to get false positives when you don't use ears alone for sonic evaluation.
Nothing ugly about opamps. I am working on a Turing test for opamps, will open new thread when the thinking is done.
If you can't expect much of a sound stage from CD-players there is precious little left.
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