[sdiy] Polyester or Polypropylene for VCO?

[Simon Brouwer]

Hi Michael,

At 20:57 31-7-2005, you wrote:
>I am putting together a parts order for my VCO and trying to decide on the 
>cap for the integrator. As you can see in the schematic 
>http://frankentron.freezope.org/source/REV4-2.gif there are 2 caps in 
>series - 1000pF and 0.15uF. This is from the JH linear detune mod. I have 
>already aquired 1000pF 1% polystyrene caps but I'm unsure what to order 
>for the larger cap. On my PCB layout I have made a  0.25" lead space 
>location for this cap. From the Mouser catalog it looks like my only 2 
>options that will fit is the MKP2 series Metalized Polypropylene or the 
>Xicon Metalized Polyester axial round body if I mount it on end. I know 
>the polypropylene are primarily used in switching power supplies but is 
>there any reason it wouldn't perform well in a VCO?
>
>Thanks in advance!
>
>M. A. Ruberto

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.

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

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

Vriendelijke groet,
Simon Brouwer.

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