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In Reply to: RE: ESR posted by Triode_Kingdom on August 23, 2014 at 08:58:16
Jack
When the 2700uf caps were used in my ALtec 1530s, the mids were compressed and the high end extension was 1300cps lower on measurement until I took those out and had gone to film caps..I understand that bypassing changes that narrative but at the voltages we are dealing with and these were series connected,1350mf is an overkill that most likley changed the output impedance of the power supply. The original capacitance after the huge choke was a total 20uf at 900v.I had put in a pair of 51uf at 1500v solens in parallel and the sonic character changed dramatically just from those two caps as opposed to the series connected 2700uf caps/
I had the same thing with my Cary/AES 811 SET amps..Dennis had used his typical 1200uf series connected caps in the supply rail and I had taken those out and put in a pair of 80uf motorrun caps in parallel and just that upgrade helped the high end extension and it made the amplifier quicker because it was inherently slow..I did a few other upgrades but the motor run caps did the most for it.
I cannot understand why anyone would put that kind of capacitance in an amp at 600 to 800vdc because we aren't talking massive amounts of current at those voltages where you would justify it... YMMV tho.
Honest amplification is better than excessive 2nd order distortion anytime.
Edits: 08/23/14 08/23/14 08/23/14Follow Ups:
"I cannot understand anyone would put that kind of capacitance in an amp at 600 to 800vdc because we aren't talking massive amounts of current at those voltages"
I agree with everything you've said, and I completely believe the improvements you heard from the caps you installed. I'm just skeptical that ESR is the culprit. 2,700 uF caps almost certainly exhibit a lot of hysteresis, not to mention their inductance at higher frequencies. As you say, it's just not an appropriate value for this application.
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...Shouldn't the term "hysteresis" be used with some set of parameters such as hysteresis of the B-H curve or hysteresis of the force-displacement curve etc.
This...
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...in that "test". It seems to be voltage coef of cap but he never states it outright. Do you know for sure what he's measuring?
I don't understand your statement, the article explicitly states what he's measuring and how he's measuring it.Short version: he's using an analogy to estimate the ratio of field strength to applied voltage.
Mark Kelly
Edits: 08/25/14
...and if it isn't, then surely the ratio you describe must have a common physics or industry designation or name, esp if it has any practical relevance in electronics. Then there's the question of the parameter's relevance to audio.
"Short version: he's using an analogy to estimate the ratio of field strength to applied voltage."
Yes, provided that by "field strength" you mean the displacement field, D, and not the electric field E. The current flowing through the capacitor is proportional to dD/dt rather than dE/dt, and that's why he gets a D vs. E curve.
I'm not sure why you say "analogy." Seems like the real thing here?
Chris
It's an analogy because he's not measuring D directly, he's measuring an analogue of it.
Mark Kelly
"It's an analogy because he's not measuring D directly, he's measuring an analogue of it."Hmmm...I suppose it comes down to semantics, really. By the same token, one could say that he's not measuring the current directly, but an analogue of it, since he is actually measuring the voltage drop across a resistor, and then using Ohm's law.
In one case Ohm's law is used, in the other case, a Maxwell equation.
If one starts on that path, then in the end all of life and existence is just an analogy, with the only "measurements" being our conscious perceptions in the mind...
Chris
Edits: 08/25/14
"If one starts on that path, then in the end all of life and existence is just an analogy"
You're lucky Ayn Rand is no longer with us. :)
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"Do you know for sure what he's measuring?"
No, not in the terms you're asking about. I've always assumed this to be an artifact similar to the "memory" that large caps exhibit. It's a little out of my field though, so I just take Steve's work at face value as demonstration of a non-linearity in the caps. Maybe "hysteresis" isn't the best terminology, but it seems to describe the phenomenon being portrayed in the tests.
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Pretty sure "memory" in a cap is more conventionally known as "dielectric absorption" and Bench is definitely not testing for that. Additionally, since DA is important in real world applications, there are well defined, standardized, objective test protocols to characterize it. No need to reinvent the wheel.
As an aside, I believe it's always wise to be a bit skeptical regarding claims for something when all the facts aren't clearly presented...or the claims haven't been verified independently.
It is not very clearly explained in that Steve Bench article in the link. But I suppose the essence of it is that he looks at the equation I= C dV/dt for the current passing through the capacitor, and relates that to the rate of change of the electric displacement D (as per the Maxwell equation curl H -dD/dt ~ J). So he has something proportional to dD/dt on the left-hand side of his equation, and something proportional to dE/dt on the right-hand side (since at constant plate separation, the electric field in the capacitor is proportional to the voltage). His "technical note" at the bottom of the article seems to suggest he is integrating the current to get D, and plotting versus V, which gives E. Thus his plots are supposed to be D versus E, I suppose, which would then be indicative of the constancy, or otherwise, of the dielectric constant as the applied voltage varies. A kind of analogue of the B versus H hysteresis curves in the magnetic case.Another way of putting it would be that by plotting the integral of I against the voltage V, his plot is showing how the capacitance C depends on the applied voltage (straight diagonal line = no dependence on voltage).
Chris
Edits: 08/24/14 08/24/14 08/24/14 08/24/14 08/24/14
"Another way of putting it would be that by plotting the integral of I against the voltage V, his plot is showing how the capacitance C depends on the applied voltage (straight diagonal line = no dependence on voltage)."
So yes, voltage coef of capacitance is what he's measuring (actually just displaying...no numbers involved).
The next question is how audible a large and variable V coef of C could be. Maybe spice has a C=f(V) capability so it could be simulated.
I just want to add that statements regarding the audible improvement of replacing power supply caps always bother me when there's no measurement data confirming a change. For example, what was the THD/IM before and after? Did frequency response change?
Just as important, if capacitors have been changed, did it result in a difference in the amplitude/frequency of signal components present at the output of the supply? It has always been my contention that when those components are zero (a theoretical concept only), the supply represents a perfect, zero-impedance voltage source, and in such a case, the capacitors can have no negative impact on sound quality of the amplifier. Derived from this, I also believe that the deficiencies of the supply, including whatever tonal inaccuracy is contributed by the capacitors, can be quantified by artifacts present at the top of the last capacitor.
Unfortunately, very few people take the time to make such a measurement, so there is virtually no data available with which to make comparisons or draw conclusions. Nevertheless, if the spectral content produced at the top of the last capacitor while the amplifier is in operation does not change when power supply components are replaced, I do not believe the amplifier can sound different.
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