[sdiy] Polymoog Resonator virtual ground

[Dan Snazelle]

that sounds like a very simple way to do such a thing...any real drawbacks??

Sent from my iPhone

> On Aug 15, 2014, at 1:40 AM, "Donald Tillman" <don at till.com> wrote:
> 
> 
>> 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
> 
> 
> 
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