Hi Tom,

> i just bought a wasp filter module. it sounds very cool.
> i am curious if anyone could explain to the principle it operates
> upon i dont fully understand how electronics work. i understand
> that op amps are basic circuits that are in many electronics. i

see

> a lot of op amp ICs when i go to a local store that sells

electronic

> parts.

Filters can appear complex and hard to grasp for a newcomer to
electronics (certainly did for me!). However the Wasp filter is in a
standard configuraton, called a 'state variable filter', only as you
know, uses digital inverters rather than op amps. (The state variable
filter generally uses three op amps: one as an inverter, and two as
integrators.)

> how does this circuit use "digital inverters" as analog op amps,

and

> why won't it self oscillate

On their own, with no feedback, op amps generally have very high
gain, around 200,000 times, which is 'tamed' by using negative
feedback to bring it back down to reasonable levels (say unity to 100
or so). A digital inverter is essentially the same: as the input goes
from high to low (say), the output will (very suddenly) switch from
low to high - if you draw this out, the slope of the output would be
very steep, which translates into a high gain. Using digital
inverters rather than op amps makes it hard to use the negative
feedback to tame the high gain, and so to bias the outputs to keep
them swinging around the mid-point, without shooting off either to
the high or low state, and I suspect this has a lot to do with why it
won't self-oscillate (I've been trying to work this out myself, off
and on when time allows, for some time).

the res all the way up does create a

> very grotesque and fantastic sound. my understanding of filters is
> that the resonance is feeding the filter back into it self, thus
> oscillating at the tuned frequency (cutoff).

This is correct, and is called positive feedback - the signal fedback
gets bigger and bigger, eventually bursting into oscillation (and
controlling the amplitude then becomes a real problem). If you search
the web you'll should find some tutorial-type sites, but when it
comes down it, some studying will be necessary to properly understand
how and what filters do!

Tim