Tapped 4pole Filter

[WeAreAs1 at aol.com]

Hello Harry,

I f you are referring to the OBxa 2-pole filter schematic that I mailed to
you, the rest of the list has not seen it, as I sent it to you privately.  As
to whether anyone has ever sucessfully built one, I guess you could count the
thousands of Oberheim OBxa's as successful examples (since the schematic I
sent is their exact design), but I don't know anyone who has built one from
scratch.  

I'm guessing that it's possible that your problems with simulating the circuit
on Electronics Workbench may have something to do with Electronics Workbench
not really having an accurate model of the actual CEM3320 to work with (I
imagine that you're using generic operational transconductance amps to
simulate the 3320 gain cells, right?).  Maybe it's time to break out the
soldering iron?

I would like very much to see your tapped filter circuit for the Pro-One.
Please mail it to me when you have a chance.

Best regards,
Michael Bacich

In a message dated 3/18/99 9:09:57 AM, you wrote:

<<  Thanks for the schematic. This is exactly what I tried to simulate on
Electronics Workbench. My results showed that changing the resonant feedback
point didn't work. As you move to lower rungs (6-12db) the cutoff frequency
changes (higher) and the amount of resonance becomes less (and at a higher
frequency)  I kept the resonant feedback from the 4th stage, and used a second
diff-amp to "tap" the filter. This works well. Did anyone ever build this
filter as posted? I'd like to find out if my simulation agrees with reality
(often not the case...) I'll post my 3320 tapped filter later... for a Pro-One
its a really simple mod.  :-) Harry >>