Beginner's capacitor question
jkunz at unixag-kl.fh-kl.de
Tue Apr 15 15:16:33 CDT 2008
On Mon, 14 Apr 2008 20:03:17 -0500
Jim Leonard <trixter at oldskool.org> wrote:
> While I have read the wikipedia entry on capacitors, I'm missing
> something obvious. My question: Why the 4.7uf capacitor? Does it
> serve to limit the signal? Reduce it's voltage? (or increase it?)
> Filter the signal in some way?
The capacitor simply eliminates the DC offset on the signal. Most likely
the speaker is connected to a digital (totem-pole) output that switches
between 0 V and 5 V. So you get a squere wave signal from 0 V to 5 V.
I.e. a squere wave signal with 5 V amplitude peek-to-peek with 2.5 V DC
offset. A large DC offset can drive a line input out of range.
Therefore you add a capacitor in series to filter out any DC on the
signal. Also: If your amplifier chain is completely DC coupled you will
end up with considerable DC current on your speakers. This can damage
the speakers. (Overheat, drive the moving parts to there extreme
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