[sdiy] CMOS as voltage variable resistor

[Steve Ridley]

The ARP Omni 2 (model 2470) bass voice is full of 4007s 
in a variety of roles.

The main section of interest is the VCF, which is a 2 pole
job, each stage using a 470R in series with an N stage of
the 4007 and a 0.068 cap to ground.  The interesting bit is
the initial cut-off control signal, which uses a third N stage 
from the same 4007 in the feedback of an opamp.

Another 4007 is used as an ADR envelope generator and
a third for enabling the bass voice.  In these stages the
4007 is only switching, not behaving as a VC resistor.

I can't scan the schematic it at the moment, but if anyone's 
interested, email me in a couple of weeks when I've found
my scanner.  Just moved house...



Steve Ridley