[sdiy] Polyester or Polypropylene for VCO?

[harrybissell]

Simon Brouwer wrote:

> In this circuit you have a capacitor of 150nF in series with one of 1000pF.
> The bigger capacitor hardly contributes to the combined capacitance, so the
> same is true for its tempco. So in this case it probably doesn't matter much.

Nope. These capacitors are NOT in series. There are two capacitors here. One
is reset (?) by Q10, the other couples a sync pulse into the VCO.

If they were in series, you could remove the larger one (you are correct, the
smaller capacitor will dominate the value and tempco)

> Without more data, I would go for polypropylene, see e.g.
> http://www.americancapacitor.com/Diel.htm

without more data, that is an excellent choice. I would use the polypropylene
over polyester.  Polystyrene is not a real viable choice anymore for such a large

value cap... but it is possible.

> Of course it's always a good idea to read the data sheet of the component
> in question.

excellent advice as well. :^P

H^) harry