15 Apr
2008
15 Apr
'08
8:57 p.m.
On Tuesday 15 April 2008 16:16, Jochen Kunz wrote:
On Mon, 14 Apr 2008 20:03:17 -0500
Jim Leonard <trixter at oldskool.org> wrote:
Not the way he described it being connected, across the speaker. If it'd
been between the speaker and whatever was processing the signal subsequently,
I'd have to agree, but that's not what was described.
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.)
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin