[sdiy] Silvered mica caps in VCO core integrators

Ian Fritz ijfritz at comcast.net
Fri Apr 15 06:10:10 CEST 2016


I managed to dig up the old Pease article I remembered:
http://www.datasheetarchive.com/files/national/htm/nsc03883.htm

He found different behavior for different devices of the same material. 
  So it's not too surprising that I found PPE inferior wrt soakage in 
the quick tests I did.

There is a curve for mica in that article.  Looks pretty bad.  I vaguely 
remember some old lore that the early synth manufacturers tried mica, 
but it had too much soakage.

Remember, mica caps are made from natural mineral materiel (as in dug up 
out of the ground).  So there is a lot of variability among batches, 
which could explain any discrepancies.

Ian



On 4/14/2016 8:47 PM, David G Dixon wrote:
> 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?
>>>>       > >
>>>>       > > _______________________________________________
>>>>       > > Synth-diy mailing list
>>>>       > > Synth-diy at dropmix.xs4all.nl
>>> <mailto:Synth-diy at dropmix.xs4all.nl>
>>>>       > > http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>>>>       >
>>>>       >
>>>>       >
>>>>       > --
>>>>       > Quincas Moreira
>>>>       > Test Pilot at VBrazil Modular
>>>>
>>>>      _______________________________________________
>>>>      Synth-diy mailing list
>>>>      Synth-diy at dropmix.xs4all.nl
>> <mailto:Synth-diy at dropmix.xs4all.nl>
>>>>      http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>>>>
>>>>
>>>>
>>>>
>>>> _______________________________________________
>>>> Synth-diy mailing list
>>>> Synth-diy at dropmix.xs4all.nl
>>>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>>>>
>>>
>>
>> _______________________________________________
>> Synth-diy mailing list
>> Synth-diy at dropmix.xs4all.nl
>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>
>


-- 
ijfritz.byethost4.com



More information about the Synth-diy mailing list