[sdiy] op amp based filter

[JH.]

> Sure, check here: http://www.national.com/ds/LM/LM101A.pdf

Oh, I thought there was some extra application note you were referring to.
The data sheet was the first place I looked. But where is that Eventide LPF?

> Given that there are two compensation inputs, I wonder if you couldn't
> even make a 4-pole filter. Just a silly idea.

How many poles do you think the Eventide filter has?
That was the whole point of my mentioning it: How steep a response they 
squeezed out of a single-opamp filter, combining two-pole compensation and 
an external circuitry reminiscent of a 3-pole LPF topology.

My PSpice istn't running anymore, and I don't recall if it was closer to 
4pole or 5pole response, but it sure was impressive.

JH.