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

[Aaron Lanterman]

On Apr 16, 2010, at 3:31 PM, Scott Nordlund wrote:

> If you're expecting a filter with 4 poles at 1/(2*pi*RC), that's not what
> you've built.  It's not 4 independent stages, it's all one circuit, and a 
> measurement taken at any point will be affected by the entire rest of the 
> circuit.  You've got 4 poles, but they're all at different frequencies, 
> resulting in a rather flaccid transfer function.

I worked out the transfer function of this sort of circuit a few years ago; it was a huge pain and took multiple pages. If I recall correctly, Tim Stichcombe did the same analysis, and fortunately my result matched his:

http://www.timstinchcombe.co.uk/synth/Moog_ladder_tf.pdf

See p. 34

- Aaron