15 Apr
2008
15 Apr
'08
8:16 p.m.
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
positions.)
--
tsch??,
Jochen
Homepage: http://www.unixag-kl.fh-kl.de/~jkunz/