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From: firstname.lastname@example.org (A.Iakovlev)
Subject: Re: Need 2SC3326 Transistor for an Audio Mute circuit
Date: 21 Dec 2002 02:55:42 -0800
NNTP-Posting-Date: 21 Dec 2002 10:55:42 GMT
"Phil Allison" wrote in message news:...
> "Teece" wrote in message
> I am building an audio mute circuit which effectively short circuits
> the audio to ground. It works pretty well except that there is
> distortion in the audio when the mute circuit is not active. I built it
> with a garden variety 3904 as the switch and I suspect that when this
> part is turned off there is enough junction capacitance in the collector
> to cause distortion at audio frequencies.
> ** More likely the base collector junction is still able to
> conduct the audio into your drive cct. Try a 2.4 volt zener or a few
> diodes in series with the base.
Yes, that is an important point.
Tom, you need to ensure that in the mute off state, the base of the
muting transistor is at a potential ensuring that the base-collector
junction is not conducting (for the purpose of the application; also
assuming that emitter goes to ground) even when the signal is at its
lowest instant value.
I.e. if the signal is 2V peak-to-peak, ground-centered, then you might
apply -2V or lower (more negative) to the base. If you don't have a
negative power rail, you might try to leave the base "floating": take
a look at http://perso.wanadoo.fr/a-i/mute1a.png - you use your
control circuit instead of DA1.
How do you measure the distortion? For a circuit I am currently
designing I am going to use ZTX1051A - but haven't tested it yet.
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