Silvered Mica or Polystyrene Cap for VCO

[eventi]

I don't know from capacitors, but I'm getting my parts order together for my first VCO, and I need a Silvered Mica or Polystyrene Cap for C6 in this schematic: http://musicfromouterspace.com/analogsynth/VCO200604REV01/vcoschematicpage1.gif

How important is the capacitor type? I can find other types in that value, just not silvered mica or polystyrene

[druish]

Siver mica and polystyrene have very good temp stability. ie. capacitance changes little with temp changes. So you would use these in a circuit where the capacitance is critical to the circuits behavior (like in an oscillator).

Certain cap material is better depending on the application.

polystyrene and silver mica have good temp stability

ceramics are cheap but good in non critical circuits and distortion effects

most audiophiles like polypropylene or polyester film because they are smooth sounding and reliable.

people go nuts over caps but i've learned that you should always go the most economical unless the effect you are looking for calls for a better cap.

[eventi]

Thanks druish -

Can I use a polypropyleme or polyester instead of the mica? Do they have the same temperature stability? I really don't get what that cap does in the schematic I linked - some sort of cleaning of the raw wave, i guess

[druish]

No, you should use the polystyrene or silver mica in that part of the circuit. It affects the frequency of the oscillator.

[eventi]

Thanks for the help

[diablojoy]

rush on line www.rush-on-line.co.uk/cap_forums.html
they have the cheapest silver mica and polystyrene caps
available that i can find
good to deal with and no mininum
also they have good low tolerance values
go for f or even better d values if in stock
great for VCO's and Sample/hold ccts