[sdiy] CV mixer trouble

[Neil Johnson]

Hi Tom,

> I'm having  spot of bother with an oscillator's CV mixer. The circuit
> is:
>
> http://www.electricdruid.net/images/CVMixer.png
>
> I've got a Note CV coming in to one end of R6, 0-5V, and I'm
> expecting to get 5V-0V out of the other end. The Offset trimmer
> adjusts the -5V offset that gets fed to the mixer. Seems simple
> enough on paper.

As Veronica says, your "1v/oct" trimmer adjusts the gain of your summer, 
which will affect *both* inputs (CV and offset).

If you just want to adjust the CV gain then I suggest getting rid of PR2 
and making R6 your adjustable "1v/oct" trimmer.  You might want to 
fiddle with some of the values, and DO NOT use the supply rails directly 
for references - heck, even a zener would be better than all the crap 
coming in from the supply rails.

Neil
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