[sdiy] clickless muting

David G Dixon dixon at mail.ubc.ca
Mon Oct 29 01:25:10 CET 2012


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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