I'm fully aware that film caps may well cause unwanted high-frequency oscillation, when used as "reckless" bypasses in power supplies, but... is the same risk present when using them as described earlier, in a feedback situation?
In case anyone was curious, the amp in question is Mike Bittner's Symasym.
In case anyone was curious, the amp in question is Mike Bittner's Symasym.
I've used a 220uF/6.3v Nichicon ES type bipolar and I've never had any problems...
but the amps probably never see any hard use. I would use a higher
voltage in the future though just to be safe.
I recommend using a bipolar cap instead of a polarized cap with
protection diodes because the diodes will have leakage current that
may affect the sound quality.
but the amps probably never see any hard use. I would use a higher
voltage in the future though just to be safe.
I recommend using a bipolar cap instead of a polarized cap with
protection diodes because the diodes will have leakage current that
may affect the sound quality.
outright oscillation would be unlikely, the esr of the electro provides some damping and even a Q of 20-30 from a ~1 Ohm impedance would still only look like 30 Ohms at the peak - not much change in β with >>100 Ohm fdbk resistor, still if I knew the resonance was there I would add series R to the film damp it
Shouldn't be any problem with low esr at all, since you'll likely have a couple hundred ohms in series with it. The Q becomes so low it can't resonate with anything. My measurements of bipolar electrolytics led me to the conclusion that they shouldn't be used anywhere in an audio system if any halfway sane alternative is available. A large enough standard electrolytic won't have significant voltage across it and can be ok, but getting rid of it is the reason for going to an active servo, though admittedly the design of that has more pitfalls than the simple cap method.
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