[sdiy] VCO Integrator cap/resistor selection

[David G. Dixon]

Bigger caps take longer to discharge, so could create HF tracking problems,
particularly if your JFET's on-resistance is on the high side.  I typically
use 1nF, and probably 1nF to 2.2nF is somewhat typical, but I don't think
there is any particular drawback to using a larger cap.  I guess it depends
on where you want your VCO to oscillate at zero volts CV, and whether you
want very long times at the low range for LFO purposes.

One thing which factors in my decision is that I have taken to using C0G
multilayer ceramic caps (of the pretty little blue EPCOS variety) for this
application, and the largest value I can conveniently obtain (read: get for
free from the EE department) in this format is 2.2nF.

The gurus may have other ideas...

> As a general rule, in the integrator of a VCO, is there any advantage to
> going for the smallest capacitor possible (and bigger input resistors) to
> get the frequency range you're after?
> 
> I've noticed that my 10nF cap - while working fine - is looking kind of
> fat in comparison to just about every other design I've seen.
> 
> Just curious.
> 
> Oh - thanks again to those who helped out with the DC summing questions.
> Much appreciated.
> 
> Cheers,
> 
> Justin
> 
> 
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