[sdiy] Polymoog resonator question

David G Dixon dixon at mail.ubc.ca
Sat Oct 6 07:16:56 CEST 2018


Splunge. 

> -----Original Message-----
> From: Ian Fritz [mailto:ijfritz at comcast.net] 
> Sent: Friday, October 05, 2018 12:21 PM
> To: David G Dixon
> Cc: Donald Tillman; synth-diy at synth-diy.org
> Subject: Re: [sdiy] Polymoog resonator question
> 
> Will this be a commercial product?
> 
> > On Oct 5, 2018, at 12:54 PM, David G Dixon 
> <dixon at mail.ubc.ca> wrote:
> > 
> > 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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