[sdiy] Another new module: 4 pole multimode filter

[Grant Richter]

Congratulations, you have reinvented the Wiard Omni-Filter!

You will be wanting to add another set of switches to invert the feedback
phase for bandpass mode.

And no doubt adding allpass (phase shifter) mode when you realize it's just
half the LP switches on with the HP switches, which puts a variable
resistance in parallel with the cap... (don't ground the cap for this mode
of course).

Robert Rich complained because it didn't sound MORE like a CEM3320...


> Just what we need - another filter circuit. Anyway, I've always liked
> the CEM3320 filter chips, which has 4 transconductance stages which can
> yield any of the standard filter response (HP, LP, BP, and All Pass) in
> 4th order, depending on how you interconnect the stages.  I hit on the
> idea of using analog switches to do the interconnecting and build a
> switchable (not simultaneous) multimode filter. I previously built one
> with a CEM3320 that yielded BP and LP functions.  The  new circuit
> contains no CEMs but is built with LM13700 OTA's and MAX413 analog switches.
> The HP and LP functions work perfectly, just as I expected. The BP
> however doesn't seem to respond to the resonance settings as well as it
> should (and certainly not as well as the CEM3320 BP).
> Maybe some of you geniuses can take a look a make suggestions (make
> suggestions even if you don't consider yourself a genius!).
> I've got to break down and build me another case. I've got a box full of
> loose modules without a home.
> 
> http://home.comcast.net/~sbernardi/elec/og2/og3_4pmultimode.html
> 
> -- 
> Scott Bernardi
> sbernardi at comcast.net
> 
> 
> 
>