simple question, R//C

[fuzzo]

Hi guys,

I'm sorry to open a thread for that simple question but I didn't find answer.

What does a resistor associated with a cap in parrallele ? like used in preamp design :

http://www.runoffgroove.com/thor.html

(I speak about the 470K R with the 470pf cap with the bright switch).

[alanlan]

There are a couple of things to think about.

Firstly, the impedance of the resistor capacitor combination:  At low frequencies, it looks like a 470K resistor and at high frequencies it looks like a short.  I won't go into phase differences as it probably not that important in this case.

The second thing to ask is how will this affect the response of the circuit.  You can only answer that by looking at the circuit.  In this case, it feeds a very high input impedance FET input so considering the FET input to be like the bottom half of a potential divider, it won't have much overall effect.  I think even with the low input capacitance of the FET, there will be no appreciable effect.

I'm sure someone will put me right if I'm mistaken.