[sdiy] Polymoog Resonator virtual ground

[Donald Tillman]

On Aug 14, 2014, at 10:13 PM, David G Dixon <dixon at mail.ubc.ca> wrote:

> I was just looking at some Polymoog Resonator schematics, and noticed that
> the virtual ground is not 0V, but is about 5V.  Why?  Does anyone here know?

I don't have the inside scoop or anything...

But my guess would be that they chose to use CD4000-series CMOS switches, which have a maximum voltage of 18 V, and chose to string them between +15 V and ground.  They probably thought it would be easier to bop the audio up to 5 V than to run the CMOS at +/- 7 V and level-shift all the logic signals.

  -- Don

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