[sdiy] RC filter questions + SPICE RC filter simulation questions

[Neil Johnson]

Hi,

cheater cheater <cheater00 at gmail.com> wrote: 
> Hi guys,
> I have been playing around with pspice today, simulating and analyzing
> some very simple circuits.
> 
> I analyzed a simple RC filter: AC voltage source goes through R=1kR
> and C=1uF to ground. I analyzed it and got the familiar curve.
> 
> Then I stuck some more stages like that on it: there's a series of
> four 1kR resistors and after each one there's a 1uF cap to ground. I
> analyzed it and got the expected curve at the last stage, but the
> first stage has a distinctive bump. Additionally the cutoffs of all
> the stages are much lower. Where does the bump come from? Is there a
> specific law that defines this?

You're analysing intermediate stages in the whole circuit so expect the responses to be different from single circuits.  In your extended circuit =

R1 + (C1 || (R2 + (C2 || (R3 + (C3 || (R4 + C4))))))

(where '||' denotes parallel connection and '+' denotes series connection).

As for the bump... on this website:

http://www.logbook.freeserve.co.uk/seekrets/index.html

look at the picture of the back cover and have a go at simulating that circuit.

That should entertain you :)

> I am trying to find a way to filter a .wav through the filter and look
> at the voltage output. Is this possible to do in pspice? If not, do
> any other spice packages allow that?

LTSpice.  Can do both wav in and wav out.

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