[sdiy] Silvered mica caps in VCO core integrators

[David G Dixon]

I couldn't find any references to the dielectric soakage of mica caps.
However, mylar (polyester) caps seem to have lower soakage than C0G caps
(0.2-0.5% vs 0.6%), according to a table in the Wikipedia page on dielectric
soakage.  Polypropylene and polyphenylene sulfide caps had the best numbers
(0.05-0.1%), way better than C0G caps. I'm looking for info on silvered mica
caps now.



> -----Original Message-----
> From: Ian Fritz [mailto:ijfritz at comcast.net] 
> Sent: Thursday, April 14, 2016 6:56 PM
> To: Pete Hartman; David G Dixon
> Cc: Sdiy
> Subject: Re: [sdiy] Silvered mica caps in VCO core integrators
> 
> 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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