[sdiy] Silvered mica caps in VCO core integrators

[David G Dixon]

That's what I wanted to know (but was afraid to ask).  Silvered mica caps
are more or less insisted upon in RF circuits.  What becomes so bad in AF
circuits? 

> -----Original Message-----
> From: Synth-diy [mailto:synth-diy-bounces at dropmix.xs4all.nl] 
> On Behalf Of Simon Brouwer
> Sent: Friday, April 15, 2016 3:57 AM
> To: Ian Fritz; Sdiy
> Subject: Re: [sdiy] Silvered mica caps in VCO core integrators
> 
> 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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