[sdiy] Another new module: 4 pole multimode filter

[Scott Bernardi]

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