[sdiy] Circuit purpose?

[Neil Johnson]

Ove Ridé wrote:
> A non-polarized electrolytic capacitor is really two polarized ones
> connected back to back internally, so it's really two components, even
> if you can't see it. :)
> I'm guessing those weren't made, or at least weren't cheap enough when
> the circuit David is looking at was produced.

ALL electrolytic capacitors comprise two capacitors in series - see
the excellent series by Cyril Bateman (RIP) on capacitor sound.  The
difference between polarised and non-polarised electrolytics is the
size of the cathode capacitor: in polarised caps this is huge (so has
minimal effect on the final capacitance value) as the aliminium oxide
dielectric layer is very thin and therefore goes pop very easily.  In
non-polarised capacitors it has the same (thickness) value as the
anode capacitor, and so the capacitance is halved (or, conversely, for
a given capacitor the size is doubled).

The biasing scheme Ove mentioned is a bit of a red-herring and just
complicates matters.  See Cyril's articles.

Neil
--
http://www.njohnson.co.uk