[sdiy] Re: cap id question

[Ingo Debus]

harry wrote:
> 
> Capacitor parasitic elements (like inductance, resistance...) are usually small
> and low impedance circuits tend to swamp (overcome) them.

But why?
If I think of a coupling cap between two stages, the cap and the input
impedance of the 2nd stage form a voltage divider. The higher the input
impedance, the less a nonideal anything (resistance, inductance,
nonlinearity) in series with the cap will affect the signal, right? Like
with CMOS analog switches: the higher the impedance of the circuit, the
less the quality of the switch matters.

One could say, with higher impedances smaller caps are used. If the
ratio of capacitive and parasitic impedance of a cap is about the same
for different cap values the above effect is more or less compensated.
But how can get things *worse* with higher impedances? Am I missing the
point completely here? If the circuit impedance is so low that an
electrolytic has to be used, things are certainly worse.

(Using the term "worse" here regarding signal fidelity).

Ok, for parasitic things in parallel with the cap higher circuit
impedances are more critical. Are they important for good
non-electrolytic caps?

Ingo