Capacitor replacement question

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paulrichards7
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Capacitor replacement question

Post by paulrichards7 » Mon Jan 31, 2011 3:50 pm

Im trying to learn about DIY electronics
Now Ive notice that on most capacitor replacements for PSUs and mixer channels, the electrolytics are replaced
But on things like mics and FX processors its usually the square or disc caps
I know this is a fairly sweeping statement
But are the electrolytics swapped because they are usually within and between active(gain) circuits?
Ive read quite a few electronics books and it I dont seem to be quite getting the grasp
Ive read some of the stuff in the Tape op book, which talks about electrolytics in guitar amps and how they are kind of high pass filters and to filter out AC to ground or DC at junctions
But that is about the only book information that actually references audio electronics!
Thanks
Paul

PS There are no audio electronics courses anywhere near where I live in Bath England

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Scodiddly
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Post by Scodiddly » Mon Jan 31, 2011 4:24 pm

The electrolytics are able to have very high values in a small package, so they're used where you need a lot of capacitance. In general the higher the capacitance the less lows are filtered out, assuming it's a coupling cap between sections of a circuit. Where it gets tricky is that this is affected by the impedance of a circuit - lower impedances need higher capacitance caps to get the same results. Condensor microphones have much much higher impedances around the capsule, so much lower capacitance is needed.

Electrolytic caps don't tend to be very good with audio, so if you don't need one you use something better like a poly cap.

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Snarl 12/8
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Post by Snarl 12/8 » Mon Jan 31, 2011 5:22 pm

I'm pretty seat of the pants when it comes to DIY audio. Lots of blowing things up, not so much understanding, but I have a theory about your question.

The big electrolytics are replaced in old PSU's because the goo in them has dried out. They usually get replaced with something very similar in construction and quality to the original.

The channel strip and fx units are having perfectly working (for what they are) capacitors removed to make room for much better, hifi, more expensive caps in an effort to upgrade the sonics of the unit.

So, the issue of what gets replaced where, usually, is a separate issue from why what type of cap was there in the first place.
Carl Keil

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paulrichards7
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Post by paulrichards7 » Tue Feb 01, 2011 3:38 pm

Thanks for that guys
Still a bit hazy, but will have to get a grip on cappacitance and impedance
Paul

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