[sdiy] Modified Juergen Haible's VC-ADSR and mono synths ADSR behaviour.

[Massimo Ischia]

Hi to all.

I've modified the well known Juergen Haible's voltage controlled HADSR 
(I apologies to Juergen !).
I chose a classic NE555 + 4052 configuration for feed the 2-quadrant 
exponential current generator and a differential
amplifier that compares the ADSR output voltage with the required 
reference voltage and servo loop the circuit.
The prototype works perfectly! A sligty more bulky 3310 but with all 
control voltages in range 0 +5v.
The attack peak match exactly the maximum sustain available (+5v) and 
the envelope shapes are true RC curves.

Schematic on demand, I've not yet a personal site.

I build the Jurgen's schematic too but, in my prototipe if I apply short 
gate pulses with release set at maximum, the
output voltage raise up the saturation of the op-amp U9D. My suspect is 
around the reset pulse applied on Q5 base
and the servo loop that "compares" current  from R3 and R42.
Opinions are welcome!

And now a question:
I've ever thought that in an ADSR for a monophonic synth the attack 
phase must to start always from 0V each time
the gate goes high, so some circuitry is needed in order to reset the 
release phase if still pending.
But all the schematics I found don't work in this way: each time i press 
a key the attak phase begins were the release
phase ends. The CEM3310 behaves the same.

Well, how behaves the perfect ADSR for a mono synth ? With or without 
the release reset when a key is pressed ?

Thanks

Massimo Ischia

Arco (TN)  Italy.