[sdiy] Simple LPF Schematic ?

[Oakley Sound]

 > Ok, what's with those +12 / -6 volt supplies in the Moog modulars?

Indeed. Something historical no doubt, but its before my time. :-)

 > Would any resistor values need to be changed to use a "normal" 
bipolar supply?

Not in the filters.

 > Also, why 2 different types of op amp?

I don't know for sure, but perhaps its a stability thing. Neither 
circuit is protected for cable capacitance.

Personally, you can replace both op-amps with a decent audio op-amp like 
a OP275, or even a TL072.

 > Is R32 ("HPF DC") there to cancel out what would be a +3 volt DC bias?

No there is no 3V offset here. The circuit AC coupled with reference to 
ground and the outputs are mostly symmetrical about zero. The offset 
control is a design feature of this module in that you can set the 
output offset of the HPF output from the front panel. Its not needed if 
you want standard HPF functionality, simple miss off those bits and 
connect the rev log to ground at one end [pin 5].

Rev log pots can be got from Banzai or New Sensor. Most guitar places 
have them too - perhaps Small Bear??

Tony

www.oakleysound.com