[sdiy] Silvered mica caps in VCO core integrators

Simon Brouwer simon.o at brousant.nl
Fri Apr 15 12:56:34 CEST 2016


Hi, 

Why is soakage an issue in VCO's? 

My impression is that the time constant of the soakage effect is orders of
magnitude longer than the period of audio range signals. If that is correct,
soakage would not significantly affect the frequency stability of a VCO, or
would it?

Best regards
Simon

> On 15 April 2016 at 03:56 Ian Fritz <ijfritz at comcast.net> wrote:
> 
> 
> Mica caps have too much dielectric soakage for serious use in VCOs. 
> (See the famous Bob Pease writeups.)
> 
> My super S/H project was started to compare soakage and leakage in C0G 
> ceramics vs plastics.  I found that C0G and polystyrene had nearly 
> equivalent behavior.  Other plastics, including PPE, were inferior.
> 
> I'll say it again: C0G is the way to go for high-performance synth 
> circuits, especially given their small size and reasonable cost.
> 
> Ian
> 
> 
> On 4/14/2016 4:33 PM, Pete Hartman wrote:
> > Film caps generally seem to be preferred, but I can't say I've heard any
> > strong arguments for one type of film cap over another for that purpose.
> >
> > Thanks
> >
> > Pete
> >
> > On Thu, Apr 14, 2016 at 4:25 PM, David G Dixon <dixon at mail.ubc.ca
> > <mailto:dixon at mail.ubc.ca>> wrote:
> >
> >     Yves suggests either polystyrene or silvered mica.  I guess they're
> >     interchangeable...?  I think silvered mica are easier to use (and to
> >     get).
> >
> >      > -----Original Message-----
> >      > From: Quincas Moreira [mailto:quincas at gmail.com
> >     <mailto:quincas at gmail.com>]
> >      > Sent: Thursday, April 14, 2016 2:15 PM
> >      > To: David G Dixon
> >      > Cc: Sdiy
> >      > Subject: Re: [sdiy] Silvered mica caps in VCO core integrators
> >      >
> >      > I use polystyrene (as per Ray Wilson's instructions)  but I'm
> >      > willing to bet Mica will be perfect as well.  In fact I think
> >      > Yves Usson uses Mica for that in his VCO:
> >      > http://yusynth.net/Modular/EN/VCO/index.html
> >      >
> >      > On Thu, Apr 14, 2016 at 3:53 PM, David G Dixon
> >      > <dixon at mail.ubc.ca <mailto:dixon at mail.ubc.ca>> wrote:
> >      > > Hey team, what do we think about silvered mica caps in VCO
> >      > core integrators?
> >      > > I've used them in filters, and they work great.  Any hidden
> >      > dangers I
> >      > > should be aware of?
> >      > >
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> >      >
> >      >
> >      > --
> >      > Quincas Moreira
> >      > Test Pilot at VBrazil Modular
> >
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