Weird voltage controlled Digisound VCF idea

[Matthew S. Padden]

Hi..

	The recent thread about the Digisound VCDO made me remember an idea I had 
for the Digisound 80-7 VCSVF (the one based around the SSM2040). It uses a 
2-pole 7-way rotary switch to choose the filter response (2pole LP, BP, HP, 
4pole LP, BP, HP, and notch). I thought: Why not have voltage controlled 
selection of the filter type?

	Off the top of my head, this would need each pole of the switch replacing 
with a CMOS switch array (4016, 4066) with one side of all the switches 
commoned. To drive the switches, rig up an AD converter (say, 8bit) which 
receives the CV input, and then fires the assorted CMOS switches which are 
wired to the AD digital outputs. By playing around with the digital wiring, 
you could make a steadily increasing control voltage step through 4pole HP, 
2pole HP, 2pole BP, 4pole BP, 2pole LP, 4pole LP and notch (or whatever 
sequence you desire).

Is this useful or bonkers?

--
Matthew S. Padden
Computer Music Research Group
Room M2/08, Music Dept.
Huddersfield University
Queensgate
Huddersfield
England HD1 3DH
p: +44 1484 422288 x2402
f: +44 1484 472656
e: mattp at mindless.com
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