Reply-To: "LY" email@example.com>
From: "LY" firstname.lastname@example.org>
Subject: Help needed with audio mute circuit
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NNTP-Posting-Date: Tue, 17 Sep 2002 01:01:13 EDT
Organization: Prodigy Internet http://www.prodigy.com
Date: Tue, 17 Sep 2002 05:01:13 GMT
Seems easy, but I've been wrestling with this for a couple of days now.
to call in the reinforcements :-)
I need a circuit that would mute the output of an audio circuit, upon power
on AND power off. Muting on power on is the easy part, but muting it during
the power off sequence is perplexing. Once the power is turned off, the
output IC hangs around for a while (10-20ms), then WHAM it crashes to ground
from its DC bias voltage, thus causing an annoying thump on the AC coupled
The ideal way to fix this is to use a relay and drive the coil with the
power. Thus when the unit is unplugged, it would just disconnect the output
(or short it to ground, depending on the flavor of the relay NC or NO).
Unfortunately, relays are too bulky and expensive for this consumer
I was thinking about connecting the output to ground with a JFET. The
problem is that I don't have the bias voltage necessary to drive it. Only
have 0-5V. Also, the idea of exposing a JFET to an output isn't very
appealing to me.
Hmmm..... am I missing something? Is there a really easy to way to get this
done with a few bjt's? Any help would be greatly appreciated!