[sdiy] Hand-matching capacitors for filter stages

[David G. Dixon]

> David,
> I'll let others more technically informed than I chime in on which
> parameters of polystyrene make them desirable for audio. My knowledge
> here extends to trying various types in filter circuits, on my
> breadboard and in my synths. This is where you get into subjective
> "by ear" testing, and each to their own and all that.
> Example: I replaced ancient ceramic caps in the CEM3020 filter in my
> Pro-One with polystyrene and it made an immediate and significant
> difference. The sound which previously I would have described as
> "biting" or even "brittle" became much rounder and fuller. In short,
> polystyrene caps sound good. Are they worth the extra money? You decide.

OK, now we're gettin' somewhere!  Of course, "ancient ceramic caps"
definitely falls well outside of the margins of what would be considered
"acceptable" for VCF timing.  Did you happen to measure the capacitance on
any of those old caps, and if so, was it anywhere near the advertised value?
Some of them could have become seriously degraded, to the extent that one or
more of the filter stages might not have been contributing significantly.
Perhaps the "brittleness" you heard was actually a loss of cutoff slope.

You have definitely piqued my curiosity, to the extent that I might actually
have to lay my hands on some polystyrene caps and try a little experiment.