AW: vc adsr

[Haible Juergen]

	>I like the idea of using OTAs as current sources (maybe CA3080,
beacuse
	>it's cheaper than the LM13600), the problem is that to use it as a
	>general vc-resistor (floating) it needs 2 opamps, so the circuit
could
	>be too complex (and expensive).

You don't need 2 opamps, really. You can build a VC RC lowpass
(i.e. floating resistor connected to grounded capacitor) with just
1/2 LM13600 and a JFET. See my homepage for a complete
VC ADS (easy to expand to ADSR with a couple of CMOS switches).
The only (well known) problem with cheap OTAs in envelope
generators is offset voltage. But it works nicely on VCFs and 
cheap pseudo linear VCAs nevertheless.

If you want an OTA solution withoutout offset problems, Joachim
Verghese is your man - he's on the list, too.

JH.