[sdiy] CV inputs with bipolar "amount" knobs

[David G. Dixon]

> John Blacets "Mixer/Processor" module MX2040 uses center detent pots
> with trim pots such that you can get a null of -60dBv or better at
> the detent.
> 
> This is the best version of this type of module ever made. Period.
> 
> Any arguments, meet me behind the bar!

No arguments from me (I'm a very non-argumentative guy... NOT!).

So, which circuit does he use, the "differential amp" approach or the
"buffer and inverter" approach?  Also, what are the values of the pot and
the trimmer?  Has he tried to keep the response linear or to make it more
S-shaped?

I just put a "differential amp" style bipolar CV pot on my latest filter,
and it's sweet!  No trimmer, no detent; the response is linear and the
centre is calibrated by lining up the pot knob with a line on the panel
(real high tech!).  However, it adds loads of fun to a filter having this on
there (if I'd only known sooner...).  My next one will probably have a
detent and a trimmer.