I was never invited in the first place. I have no problem with passing jobs off to those more qualified. Get that concession from some of the others here.
I assume we all know this. However, I know numerous examples when the output relay was unable to interrupt DC power arc (because it is much more difficult to extinguish/blast DC arc than AC arc which crosses through current zero) and it ended with expensive speakers like BW800 damaged. It was a well known amplifier brand, DC coupled. Potentially the DC coupled amplifier is much more dangerous than the amp with input coupling capacitor. And 1uF coupling polypropylene cap would do absolutely no harm to the sound.
The idea or concept of using a dc servo was because WJ had a high gain RIAA phono stage that I suggested he go direct coupled. Such high LF or DC gain will have large dc offset and drift.
Line level and power amps not so much. My little low gain headphone amplifier doesn't use nor need a dc servo. And it is very stable with normal room temp variations also.
It isn't always needed.
THx-RNMarsh
Pffft. Right. There are journals for academics, its not necessarily a panacea. There is a lot of volunteer work that has be done by the reviewers. They read an article, send it back the editor with comments and questions, it gets revised by the author and sent back for more review. Repeat until published or declined. I don't know if audio has enough PhDs that have the time and interest to do it.
I would agree though there there should be some quality control. Don't know the best practical way.
So, what?
Zero crossings are not uniformly spaced in music either. Why pick on averages rather then zero crossing uniformity?
Philosophical conjecture, or science?
I don't think we are on the same page any more.
I shifted from caps and DA to CM signals and the many undiscussed (here?) ways CM signals manifest them selves. And, some solutions.
?
Where are we?
THx-RNMarsh
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I've been invited on a few occasions to review (in decent journals) after my MS but before finishing my Ph.D, both with my advisor (aka doing it then having him sign off), and solo. I've felt both qualified and unqualified as I've continued through my training but, in general, it has been in realms of what I have previously published. In that vein, I would very definitely agree that vetting of the reviewers is ever-important.
If I'm trying to distill something, it's definitely that it's less about the degree and more about the bona fides. Sadly tons of crap gets published everywhere. E.g. Science/AAAS/Nature/NEJM/IEEE/(EI-EI-OHHH)
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Regarding academic publishing, some problems are well known:
Academic publishing doesn't add up | Technology | The Guardian
https://www.economist.com/blogs/economist-explains/2017/03/economist-explains-23
Academic publishing doesn't add up | Technology | The Guardian
https://www.economist.com/blogs/economist-explains/2017/03/economist-explains-23
To cut to the chase, it's not clear to me why there are two sides on the issue of test waveforms, and what we can infer from tests about performance with music waveforms. Sure music is not a single tone sine wave. But we have other tests, such as multi-tone tests. We can now measure some things down to -150dB or so. Why can't we agree on test methods and how they work? It seems like a scientific problem, not a philosophical one at this point in time.
yes, OK
I don't know how to separate the listening experience from the subject.
It was the listening - that I was first made aware- by Peter Moncrieff (Berkeley Calif) who had substituted different dielectrics in cap and noticed a change and he thought to invite me over and asked if I knew what about a capacitor dielectric might cause the sound changes. I didn't know, of course, but after researching caps, his audible and that of others descriptions fell right in line with DA. Others, notably WJ and JC also listened and so on and so forth.
The same person, PM, did double blind tests on caps. Many various tests (music sampling comparisons) etc. I don't care to go over every step of the way but PM published his listening experiences and test in IAR. He also started selling caps also so others could try a high quality film cap in their equipment/speakers etc. This is where the popular idea started.
I can tell you that i cant hear in DBLT differences in small DA changes but in other ways I do. Having said that. I will no doubt have to explain it, sometime.
But lets pretend what occurred almost 40 years ago was all wrong... and no one had then or now heard any differences in cap's ...... well, it led to the dc servo and better topologies - and that is a good thing IMO.
THx-RNMarsh
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PMA, if you want to use a 1uf polypropylene cap, be my guest. 40 years ago, I designed in a 1uf Mylar cap that passed all my distortion measurements into a preamp output and my employer discovered that it was audible, to my embarrassment. THEN I had to go to DC coupling or servos. I chose servos mostly. PP was not popular back then, as it was just being introduced.
I know of at least one member here who was (is?) a reviewer for the AES. It is generally a well-kept secret to avoid undue pressure; sometimes the (emotional) stakes are high.
Jan
As long you design a protection, better it protect both speakers and power devices of the amp in the same time. There is no problem to chose a relay able to cut the power rail voltage under a 4 Ohm load and with a low enough 'on' resistance to be neat totally transparent. Can be a Mosfet switch as well, to be faster.
False problem.
BTW, one of the advantages of the Servos is you can set with little caps the FC low enough that you will see no phase switch at 16* or 41**Hz.
*For J.S. Bach fans
** For Led Zepp. fans.
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A series relay.... So you would need some sort of bybee enhanced relay, to avoid any quantum / sonic effects from the closed contacts, no doubt. And no doubt some would say the contacts are directional.. or need burn in... Just sayin'...
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