[sdiy] clickless muting

[David G Dixon]

>  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.