[sdiy] Silvered mica caps in VCO core integrators

Michael E Caloroso mec.forumreader at gmail.com
Mon Apr 18 02:20:26 CEST 2016

Many vintage polysynths with CEM VCOs used mica caps for the charge core.

Not every VCO design can work with mica caps if the soakage impacts
reset time of the ramp core.  Other designs work fine.


On 4/17/16, Ian Fritz <ijfritz at comcast.net> wrote:
> Tony --
> Thank for your thoughtful response.  A couple of comments.
> What is the relevance of something working as well as it did 17 years
> ago?  Why wouldn't it? And what does that have to do with using a mica
> cap?  I have lots of circuits built 40 years ago that still work fine.
> I'm glad that you brought up FM applications, as this is one area where
> good tracking and stability have a big advantage.  And actually, going
> by message board traffic, there has been a fair amount of interest in FM
> recently.
> "If it works for you, it works." Well, obviously.  But if you are
> talking about manufacturing something would't you be more concerned
> about your customers' needs? Hmmm..., use a more expensive inferior
> part. Doesn't seem like good business sense to me.
> But after all is said and done, this really isn't rocket science.  It's
> basically trivial to achieve the level of performance I mentioned.  I
> demonstrated it many years ago (1998).  It only requires careful choice
> of a few critical components. I never considered mica timing caps,
> because I had read that they have soakage issues and that everyone
> prefered polystyrene. The Bob Pease work certainly confirmed this.
> But you still haven't told us exactly how well your mica VCO works.
> Would you by any chance have some data you could share with us?
> Thanks for your interest.
> Ian
> On 4/17/2016 12:29 AM, Tony Clark wrote:
>> tl;dr
>> I wouldn't hesitate AT ALL to use Mica's for VCO's.  I used Mica caps
>> for the VCO circuits I designed 17 years ago and they still work just
>> fine.
>> Unless you are Mr. Chowning and have some new fangled retro analog
>> bent, I wouldn't be too concerned about your VCO meeting some silly
>> "modern standard" (and is it IEEE?).  If it works for you, it works.
>> If it doesn't, pick a different part.  It's not hard to swap out a
>> silly cap.
>> Tony
> --
> ijfritz.byethost4.com
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