[sdiy] Another new module: 4 pole multimode filter

[Scott Bernardi]

Hah! I should have figured it wasn't a new idea.   Looking at the 
features of theOMNI filter, yours is a lot fancier - like the voltage 
controlled "morph" feature.
I'll try inverting the BP feedback, thanks.

Grant Richter wrote:

>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
>>
>>
>>
>>
>>    
>>
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>  
>

-- 
Scott Bernardi
sbernardi at comcast.net

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