Signal path electrolytic capacitors

[überfuzz]

I have an application that calls for some high valued capacitors ≈1000uF. Are there good and bad ones, or is it all snakeoil?

Edit, the voltage strain is less than 1 V.

[km6xz]

1000ufd in signal path? Must be a very low Z circuit to be willing to add that much inductance to the signal path. These are coupling caps?There is polarization of 1 volt? Then the signal must be in the 100s of millivolts or less. I doubt I have a signal path that required 1000ufd for a low level stage coupling cap. Can you upload the schematic?

[magnus0re]

Avoid old ones. Google "Capacitor plague" .
if this is a DC blocking capacitor or a High-pass capacitor (I'm guessing), make sure to keep the -3dB point way out of audible frequencies. This way you add minimal distortion, because all capacitors have different impedance at different frequencies. having the impedance of the capacitor "work" outside of the audible band is then a good thing.

Don't buy the cheapest ones you can find.

Also a book I have has a good quote on this:
Quote from D.Selfs "Small signal audio design" :
"My view is that electrolytics should never, ever, under any circumstances, be used to set
time-constants in audio. There should be a time-constant early in the signal path, based on
a non-electrolytic capacitor, that determines the lower limit of the bandwidth, and all the
electrolytic-based time-constants should be much longer so that the electrolytic capacitors can
never have significant signal voltages across them and so never generate measurable distortion.
There is of course also the point that electrolytics have large tolerances, and cannot be used to
set accurate time-constants anyway."

[Mark Hammer]

My own rule of thumb is that if the signal path is carrying a wide-bandwidth multi-source signal (e.g., a symphony orchestra or entire mixdown of a track), then you probably want to pay attention to cap quality. If it's just a bloody guitar through a fuzzbox, going into speakers that roll off above 6khz, then you have much less concern with things like phase alignment across the spectrum, and your requirements for cap quality are greatly reduced.

The challenge is that, when you have multiple sound sources (like an orchestra or band) all passing through the same electronic path, and coming out the same speakers, a huge challenge is posed to the human nervous system of "assigning" all that harmonic content to the "right" sound source. Is that stuff at 14khz a harmonic of the cymbals, the snare, the violins? Does it go with the stuff at 7khz, or is that 7khz content coming from something else? Only two ears, and a whole lotta frequency content. The phase alignment of fundamentals and harmonics is part of what permits the brain to sort out all that frequency content into the right "piles", so that what you hear is easily heard as identifiable sources, instead of a mish-mash.

Where the musician is playing a single low-to-medium bandwidth instrument through their own equipment, and nothing else comes out of their amp speakers besides what THEY play, the mental sorting of harmonic contentis largely taken care of. If it was a stereo amp for listening to recorded music, or was a studio mixer, you can bet your bottom dollar I'd want to use a higher-quality cap.