[sdiy] Polymoog resonator question

David G Dixon dixon at mail.ubc.ca
Fri Oct 5 20:54:25 CEST 2018

Thanks, Don.  That's what I figured.  I have removed CD4000 switches from
many designs and replaced them with DG400 switches for that very reason.

I'm going to redesign this Polymoog Resonator, using 2164s for the R's,
putting the stages under voltage control, and changing the output switching
situation a fair bit.  I'm still not sure what I'm going to do about the
loop gain situation.  I'm deriving the transfer function right now to get a
better idea of what it actually does.


> -----Original Message-----
> From: Donald Tillman [mailto:don at till.com] 
> Sent: Thursday, October 04, 2018 11:04 PM
> To: David G Dixon
> Cc: synth-diy at synth-diy.org
> Subject: Re: [sdiy] Polymoog resonator question
> > 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

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