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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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In Reply to: Re: Bipolar vs MOSFET vs J-FET posted by tomservo on January 26, 2007 at 18:06:33:
>Are you saying that nowadays a good polypropylene cap (I mean electrically good, not boutique) still has a signature (aside from what ever change its reactance imposes)?<I measured inexpensive mass produced PP caps that on a good HP LCR meter at several freqeuencies. Had very little ESR, accurate capacitance, low inductance at higher frequencies. Then I measured a "boutique" cap against it that also was a PP, with the same capacitance and voltage rating. It measured worse. Higher ESR, higher inductance at high frequency.
I tried both caps in my amps that used no NFB. This makes the sound of the caps pretty audible if there's a sonic signature to them. The mass produced caps sounded harsh and the boutique cap sounded smooth and detailed. Maybe what you need is the right amount of "non-cap" performance in some circuits to make it sound tolerable. Or was there some interaction of PP distortion and something else in the construction of the boutique part? Don't know, but I was disappointed that the expensive part worked better.
Luckily, the best bargain in caps today are the Russian military surplus teflons. They sell for about $2 apiece for a 0.056 uF 400V one and they sound close to direct coupling. No harshness at all where the ordinary PP failed. I never measured the teflon cap, though. I should try that some time. I have tried a boutique teflon at great price. It was marginally better. Now I think that teflon is the right dielectric to go with here no matter the price.
Other things not measured on an LCR meter - dielectric hysteresis distortion, dielectric saturation effects of Vbias. That should affect the sound. But it's not usually measured. I bet teflon performs best in these areas.
Kurt
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- Re: Bipolar vs MOSFET vs J-FET - kurt s 22:08:08 01/28/07 (0)
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