Some time ago I ordered a sample set from Alfa’s CEM clones for which I build 4 separate modules. A VC ADSR, a dual VCA, a VCO and a Synthex VCF clone. This is the voltage controlled ADSR based on the AS3310 IC, which is a clone of the CEM3310. It outputs a nice 10vpp envelope. This schematic is based on a combination of several designs I found on the internet.