Sat Jan 8 18:15:47 EST 2011

No analog synths without OTAs!

Too bad they're a dying race.  I just received the LM13700 dual OTA
from Futurlec at $1.50 a piece.  That's not bad, but if you compare it
to TL074 quad opamp at $0.27 there does seem to be some scarcity at
play.  Similar price on eBay.  To compare, not an OTA, but the SSM2164
VCA is $10 on eBay.

Since the hacked ramp -> exp envelope generator doesn't seem to be a
good idea, it seems the only real option is to implement the circuit
as a cutoff-parameterized linear filter responding to a step function.