[sdiy] Silvered mica caps in VCO core integrators

Vinicius Brazil brazil.v at gmail.com
Fri Apr 15 18:16:17 CEST 2016


Interesting article.

Since the seventies I used mica capacitors in industrial equipment
operating in exigent conditions, temperature stability issues, among other
reasons.
Filters, modulators, demodulators, VCOs, etc.
Equipment operating all the time without being almost never turned off and
does not require calibration over time. I never had any problems caused by
this parameter.

The only problem is price.

On Fri, Apr 15, 2016 at 12:06 PM, Ian Fritz <ijfritz at comcast.net> wrote:

> You might want to look at the Pease article I linked to yesterday.  The
> earliest concerns about soakage centered on high voltages and long times,
> so that's commonly what you hear about.  But the effects can also be
> important for low level audio. In my S/H work I saw obvious soakage effects
> at msec times.
>
> Ian
>
>
>
> On 4/15/2016 4:56 AM, Simon Brouwer wrote:
>
>> 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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>
> --
> ijfritz.byethost4.com
>
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