[sdiy] Polymoog resonator question

[Donald Tillman]

> On Oct 4, 2018, at 9:57 PM, David G Dixon <dixon at mail.ubc.ca> wrote:
> 
> I did have one other question, though...
>  
> What is the significance of "V_CH" which seems to play the role of ground almost everywhere in the schematic?  Is this some specific voltage which is not 0V?

Indeed, V_CH is 4.85 V.

That audio section uses CMOS CD4000 series chips for audio switching.  Those max at 18V.  So the Polymoog runs the CMOS at 0 to +15V, and biases the audio signals up a little to fit in there.

The alternative would be to leave the audio centered around 0V, and run the CMOS at something like +/- 5V.  Then all the logic lines would have to be shifted.  Which is a drag, but would have been better for audio quality.

  -- Don
--
Donald Tillman, Palo Alto, California
http://www.till.com