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Old 8th March 2011, 02:56 AM   #11
SY is offline SY  United States
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Quote:
Originally Posted by stratus46 View Post
More curiosity. Would the 'islandy' nature of the film mimic DA?
No. It's a pure resistance and a damn small one. With a high DA, you can charge up a cap, discharge it, then open circuit it, and you'll see voltage build back up- memory, as it were. It's mostly a function of dielectric. ESR is just a simple resistance, on the order of milliohms.
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Old 8th March 2011, 07:02 AM   #12
Elvee is offline Elvee  Belgium
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Originally Posted by TomHinton View Post
Resistance, either internal or external, is not the same as DA. Distortion analysis will reveal the difference. Internal resistance would add to external resistance and alter the RC time constant of whatever circuit is being used. DA would still be the same.
DA in itself is a linear phenomenon, and doesn't cause distortion.
It is true however that dielectrics having a high DA often happen to be non-linear, but that's incidental and another story.
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Old 8th March 2011, 11:58 AM   #13
DF96 is offline DF96  England
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DA might be linear, but is it good for an audio circuit to remember the signal which was passing through a few seconds ago? Or does DA just remember the signal average, which will normally be around zero?
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Old 8th March 2011, 01:45 PM   #14
Elvee is offline Elvee  Belgium
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Originally Posted by DF96 View Post
DA might be linear, but is it good for an audio circuit to remember the signal which was passing through a few seconds ago?
Probably not, but I was just correcting the assertion that "distortion in capacitors is caused by DA".

The effect is to alter the phase and frequency responses.

But this effect has to be put in perspective too: it can only manifest itself where the capacitor is used as a reactive element, which is not the case in coupling or bypassing applications, that is over 90% of capacitors in audio.

In filters, it does matter, but in general, the effect will be very small compared to the "normal" filtering action of the network, and even in high Q active filters, it is normally sufficient to simply include it in the generic losses, the tan delta.
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Or does DA just remember the signal average, which will normally be around zero
It does a bit of both, short term and long term.
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Old 8th March 2011, 07:33 PM   #15
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Originally Posted by Elvee View Post
Probably not, but I was just correcting the assertion that "distortion in capacitors is caused by DA".
If not DA, what phenomenon causes distortion in capacitors?
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Old 8th March 2011, 07:36 PM   #16
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In what use? Different applications have different requirements and different distortion mechanisms.
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Old 8th March 2011, 09:42 PM   #17
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In what use? Different applications have different requirements and different distortion mechanisms.
All audio applications. Other than DA effect, how can distortion be generated?
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Old 8th March 2011, 09:47 PM   #18
SY is offline SY  United States
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That's a way overbroad question. A power supply cap is not a coupling cap is not a crossover cap is not an equalizer cap is not a servo cap is not a Zobel cap... It's a category error often made.
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Old 8th March 2011, 09:48 PM   #19
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Originally Posted by TomHinton View Post
All audio applications. Other than DA effect, how can distortion be generated?
External vibration. self excited vibration, wire to foil connection contamination, moisture contamination, changes in value due to applied voltage, tribo electric effect, and of course the best known external fields the outside foil.
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Old 8th March 2011, 10:01 PM   #20
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Originally Posted by simon7000 View Post
External vibration. self excited vibration, wire to foil connection contamination, moisture contamination, changes in value due to applied voltage, tribo electric effect, and of course the best known external fields the outside foil.
I have never observed ill effects from the above sources. Most caps manufactured today no not suffer from these maladies, especially film caps.
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