[sdiy] Silvered mica caps in VCO core integrators

[David G Dixon]

I found the page in Bob Pease's book where he says that the dielectric
absorption of silvered mica caps is unexpectedly bad.  I still don't know
what (if anything) this is going to mean in a VCO circuit, especially a
tricore (no sudden change in voltage on the cap).  If it is truly
intolerable (like, it won't track, or the triangles look all wobbly), I'll
suck it off and replace it with C0G (shoulda used sockets).  However,
something tells me that it's going to work just fine.


> > -----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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