[sdiy] Capacitors questions

[Magnus Danielson]

From: Ryan Williams <destrukto at gmx.net>
Subject: [sdiy] Capacitors questions
Date: Sat, 10 Apr 2004 04:25:29 -0500
Message-ID: <4077BD89.6040607 at gmx.net>

> hi all,

Dear Ryan,

> I've got a simple question here about electrolytic capacitors. I 
> understand that the positive side has to have a greater voltage than the 
> negative side or else it will explode, but I don't understand how they 
> work with AC signals when blocking the DC part of the signal. like this:
> 
> module_input----||-----module
>                    +
> incase it doesn't show up right, the '+' side is on the 'module' side.
> 
> how does this work? I've seen this on many synth diy schematics, but all 
> the capacitor tutorials I've seen do not talk about this. It just 
> doesn't make sense to me since the signal is AC.

First of all, recall that a DC offset will move the signal, so that the
instantanious voltage of the full signal can be all on the positive side of
things. However, for large signals or low DC offsets you may never the less
have the capacitor in reversed polarity for a short time. There is naturally a
time limit for which it can survive this reverse polarity. With a DC reversal,
that time limit passes quickly, for AC it is a bit more complex. Also, how
strong is the drive for reversed polarity?

Never the less, try to avoid it. Usually it isn't those caps that blow up
anyway. They do age like all others.

Personally I don't like polar capacitors as DC blockers for many reasons, but
there is allways times when nothing else can be motivated. IMHO you should try
to avoid it by propper design.

Cheers,
Magnus