In message <c42bac49.17e26%[email protected]>, dated Wed, 16 
Apr 2008, Ken Javor <[email protected]> writes:

>Caps used to be used in series in audio amps to block dc from being 
>amplified. Caps are used in series in ac-coupled o'scopes. In that 
>sense, a cap can be a high impedance decoupler.

No, those were, and are, called, for obvious reasons, 'coupling 
capacitors'. Besides, the coupling only works as intended (unless 
differentiation is intended) if the value of the capacitor is low enough 
that its charge does not change appreciably during one cycle of the 
lowest frequency of interest. If not, loss of gain and waveform 
distortion (other than of a sine wave) result. So the capacitor is LOW 
impedance compared with the source and load impedances in series.
-- 
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
Murphy's Law has now been officially re-named The Certainty Principle
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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