[sdiy] clickless muting

[Barry Klein]

 When I worked at Music Man we had a few amp models with a relay that
switched between normal and effects channels.  This relay would produce a
pop in the audio depending on the signal amplitude and I was always looking
for an alternative.  I came across one of those design note articles in EDN
or similar that utilized I think a CD4007 - the part that had what was
termed Mickey Mouse logic capability  (discrete).  I tried it and it worked
way better than the relay.
Then I was canned and since I have lost the reference article.  Sure would
like to figure out what article that was.  I've looked through my reference
material at least 3 times and haven't come across it.  Way cheaper approach
than 2164...

Barry


-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of David G Dixon
Sent: Sunday, October 28, 2012 17:25
To: 'Tom Farrand'; 'synthdiy diy'
Subject: Re: [sdiy] clickless muting

Thanks for the excellent advice, Tom!  Lots of food for thought there.  I'm
liking the relay idea the most.

My 2164 Expo-Linear VCA (basically the Irwin design with a few improvements
and additions) attenuates at least 80dB when biased "off".  I know this
because if I feed a 10Vpp signal to it, the signal bleedthrough when "off"
is invisible on my scope set to the lowest voltage setting (2 mV graticule),
and visually below the noise floor -- i.e., all I can see on the scope is
noise at about 1 to 2mVpp, and no trace of the signal.  However, if I crank
my outboard mixer right up (such that a 10mVpp signal is pretty deafening),
the bleedthrough signal is clearly audible nonetheless.  Of course, for
everyday synth signal processing, this is completely acceptable.  However,
for a high-quality audio signal processor, the muted signal should be well
and truly absent, and this requires true disconnection of the input from the
output; hence, a switch of some kind.  The question is which kind, and a
PCB-mounted relay would seem to be more or less ideal.

I'll keep you posted!

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