[sdiy] clickless muting

Barry Klein barryklein at cox.net
Mon Oct 29 05:16:37 CET 2012

What I remember about this design was that the gates took advantage of the
virtual ground of the negative input of an opamp as well as another gate
being in the op amp feedback loop.  It thus eliminated the usual signal
distortion as well as supported signals up to the supply rails - which a CD
series chip would normally not do.
Where are the "figures" you refer to?


-----Original Message-----
From: David G Dixon [mailto:dixon at mail.ubc.ca] 
Sent: Sunday, October 28, 2012 21:10
To: 'Barry Klein'; 'synthdiy diy'
Subject: RE: [sdiy] clickless muting

>  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...

That would have been the "transmission gate" approach.  This works well, but
I think I'm going to use the series-shunt approach with two JFETs in current
mode, as illustrated in Figures 16.34 and 16.35.  The beauty of JFETs is
that their control voltages can be lagged for a "fast crossfade" to
eliminate clicks.  The circuit is a little bit more complex than some
alternatives, but it will work well, and is apparently a favorite in
high-end mixing desks.

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