Re: gEDA-user: capacitors

[sdb@xxxxxxxxxx (Stuart Brorson)]

> Probably what you want is a ceramic, but watch out.  I've measured 
> some audio circuits where the dominant distortion mechanism was the 
> ceramic caps.  Replacing them with paper caps dropped the distortion by 
> at least 20 dB, maybe more.  Of course that will depend on what you're 
> using them for.  Ceramics in an audio filter or oscillator are more 
> critical for linearity than in an AC coupling application.

Just to riff on Dan's post -- For high linearity (important in audio
stuff and in filters) you are often best off with polypropylene or
polystyrene.  They are physically large, but come in the capacitance
range you (Marc) want (0.01uF).   

NPO ceramic caps are also very linear, but they only range up to a few
hundred pF in value.  Other cermaic caps like X7R and the like can be
quite non-linear.  Fine for decoupling, but bad for audio and signal
filtering applications.

Also, as Dan asks, why use a polarized cap for 0.01uF?
Polypropylene caps are non-polar, as are ceramic.   The polarized caps
(Ta and electrolytic) tend to have larger values (i.e. > 1uF) , and
are used for bulk decoupling and bypassing.   What's your application? 

Stuart