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Old 8th March 2011, 10:15 PM   #21
SY is offline SY  United States
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If you're talking about standard film caps from major manufacturers (e.g., Wima, Panasonic...), then that's largely true. When you bring in boutique caps from "audiophile" sources, then many of these problems can appear.
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Old 8th March 2011, 10:58 PM   #22
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If you're talking about standard film caps from major manufacturers (e.g., Wima, Panasonic...), then that's largely true. When you bring in boutique caps from "audiophile" sources, then many of these problems can appear.
My definition of distortion is the introduction of frequencies that were not present in the original signal. Capacitors are in the signal or feedback path. What source of distortion is greater than effect of DA?
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Old 8th March 2011, 11:12 PM   #23
SY is offline SY  United States
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Could you please give an example of the distortion you're talking about?
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Old 8th March 2011, 11:27 PM   #24
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Getting back to the original question.

With respect to coupling caps I don't think you can make a blanket statement that one type is superior to the other. The general assumption is that film and foil are superior; but I have certainly heard some pretty good metallised caps and some pretty dire foil ones.

I think the outcome is more due to materials selection, manufacturing processes and QA.
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Old 9th March 2011, 12:27 AM   #25
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Could you please give an example of the distortion you're talking about?
The distortion that results from using caps with high DA (electrolytics - ceramics), as opposed to using low DA caps like polypropylene film in signal or feedback path.
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Old 9th March 2011, 01:36 AM   #26
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Well, that's what's used in the signal path of my sound card (input cap, output cap, feedback cap), but the distortion is below 0.001%. Ditto the nice solid state power amp I use in my lab (an old school Adcom 555, not quite 0.001, but down there).

So can you give a different example?
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Old 9th March 2011, 02:26 AM   #27
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Well, that's what's used in the signal path of my sound card (input cap, output cap, feedback cap), but the distortion is below 0.001%. Ditto the nice solid state power amp I use in my lab (an old school Adcom 555, not quite 0.001, but down there).

So can you give a different example?
Absolute distortion measurements can be misleading; did the distortion change when you replaced high DA caps with low DA ? Did the sound character of the equipment change?
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Old 9th March 2011, 02:57 AM   #28
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At those ridiculously low levels, I doubt that I could measure or hear a change. In any sort of practical amplifier circuit, the caps are rarely the limiting factor in distortion- tubes and transistors are highly nonlinear devices in comparison.
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Old 9th March 2011, 07:02 AM   #29
Elvee is offline Elvee  Belgium
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My definition of distortion is the introduction of frequencies that were not present in the original signal. Capacitors are in the signal or feedback path. What source of distortion is greater than effect of DA?
Then, you're talking about non-linear distortion.
DA does not belong to that category.
Non-linear effects are caused by a change in permittivity as a function of the applied electric field, and they depend upon the absolute level of tension applied to the capacitor. DA remains the same at 1mV or 1KV.
If you use a 50V mylar capacitor at AC voltages of several volts, some non-linear effects will be noticeable, but if you use a 1000V part in the same conditions, the effects will practically vanish.
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Old 9th March 2011, 08:09 AM   #30
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Walt jung's article Picking Capacitors part II has a description of how DA causes "distortion" of audio signals. Certainly to a layman like me it seems to be plausible. The attachment is just a small extract from the article. Both part one and part two are available on Walts site, where he gives quite a thorough (I thought) coverage of why you would want to use various types of capacitors in preference to others.

I've yet to read Cyril Batemans Understanding capacitors articles.

Tony.
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File Type: png DA_effect.png (57.9 KB, 113 views)
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