Integrating Capacitor

[Steve Varner]

This question may have been asked recently, so if you want to email me
directly it's OK...

The current produced from the exponential converter in VCOs charges an
integrating capacitor. This cap is usually labelled "poly" (for
polystyrene capacitor). Now, these circuits were often layed out in the
late 70s and early 80s (such as the Electronotes VCOs). Some designs
were based on even older schematics from commercial synths. Back then I
don't think there were so many alternatives to polystyrene. Ceramic and
the older "mylar" caps would not be acceptable because of their specs I
think. Modern caps (20 years later) have much better specs than those
available in 1980 (temperature, tolerance, etc.). Some of the newer
ceramic caps and the polyester film caps have great specs. Is there some
other reason that polystyrene is important? They are listed as having
"excellent electrical characteristics, high reliability and stability,
low temperature coefficients, and small dissipation factor." I have a
feeling it is the low dissipation at high frequency (<0.1% at 100kHz)
that makes them good. Right? I bought some anyway, so I'll probably use
them in my VCO design. I just want to know why, and why I can't use some
other cap.

SV