[sdiy] Updating the Tau 1010 VCO

[David G. Dixon]

> C0G (NP0) caps are quite good, but available (usually) in 
> small values. I'd switch to polystyrene once you need a value 
> that is hard to get. Polystyrene caps would be larger, have 
> more parasitic inductance, and be sensitive to soldering 
> temperatures and some solvents. C0G ceramics are pretty 
> indestructable.

For most VCO (and VCF) integrators, caps in the 100pF to 2.2nF range are
typically best, and this is the perfect range for C0G.  I use 205pF 1%
silvered mica caps in all my 2164-based filters (although 220pF C0G caps
would be just as good), and have settled on 680pF caps for my 2164-based
tricore oscillator.  I generally try to design based on optimum performance
of the 2164 over the frequency range of interest, and then select the
nearest standard cap size.  If I really need to make any adjustments beyond
that, I typically make them to the associated resistor values, which are
much easier to source.