Wiardgroup

For the technically inclined, have a look at

http://www.musicsynthesizer.com/Circuitry/Multi-Function%20VC
F.htm

The opening block diagram is practically a schematic for the 
Boogie filter with A,B,C and D being the 6,12,18 and 24 dB per 
octave outputs. The mixing is done externally by YOU. The 
resistors shown are actual Vactrol resistors in the Boogie 
design, instead of a shorthand symbol for the OTA's in a 3372 
chip.

That eliminate about 100 transistors from the signal path, and 
should be much quieter. Plus the mixer can be VCA based like 
the Blacet Quad VCA. So a sequencer or 4 envelopes can be 
used to mix the filter "poles" for filter mode sequencing or 
envelope morphing.