From: "Ban"
Newsgroups: sci.electronics.basics,sci.electronics.design
References: <6VTh9.107889$ub2.2283608@news1.tin.it> <9m7i9.1785$YE2.51348773@newssvr14.news.prodigy.com>
Subject: Re: Help needed with audio mute circuit
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2800.1106
Message-ID:
Date: Thu, 19 Sep 2002 06:39:21 GMT
NNTP-Posting-Host: 62.211.173.136
NNTP-Posting-Date: Thu, 19 Sep 2002 08:39:21 MET DST
Organization: TIN
"LY _y@mindspring.com>"
news:9m7i9.1785$YE2.51348773@newssvr14.news.prodigy.com...
> > a self-conducting jfet can shorten the output to gnd, but you will need
a
> > negative voltage bigger than the neg.output swing + Upinch-off to
reliably
> > put it into high impedance. Since there is not much current involved,
you
> > can do that with a voltage doubler circuit after your transformer. With
> this
> > arrangement the quality will not suffer, as the signal is not passing
> > through the fet.
>
> Yes. Do you think that having a JFET sitting at the output is a problem?
> e.g. ESD. The thought of generating a negative bias voltage makes me
> uneasy :)
>
> > Really the relays are not an expensive option, you need only one relays
> for
> > multiple channels if there are enough contacts and again you can power
it
> > with a separate rectifier from your transformer to switch before the
> > regulator starts to drop out.
>
> The problem is that this is a compact, low power design with a lot of
> outputs,
> so relay isn't really an option. Oh yeah, and price is a big issue as
well.
>
> BJTs on the other hand are less a cent a piece.....
> There has to be a way.... isn't there?
>
>
LY,
1. BJTs need a positive voltage to make them conduct, which will not be
available for long when the device is unpowered.
2. BJT have a small offset voltage, which will be less than the normal bias,
but still substantial (50mV)
3. for higher output currents there is a rectifying action
there are some schematics on the website of Rane, as far as I remember it is
an analog delay which has this kind of output mute.
--
ciao Ban
electronic hardware designer
http://thinkamove.com/