Quad VCHADSR

This voltage controlled envelope generator is based on a circuit developed by Jürgen Haible. It has voltage control for attack time, decay time, sustain level and releas time. In addition to this, there is a hold feature, that holds the gate for a voltage controlled amount of time. I have added two more features to the circuit:

The Punch Feature

With punch activated, the envelope immediately jumps to the maximum level, and stays there for the time set by the attack CV. So the latter now contols the duration of a sustain segment, instead of the rise time. After the time set by the attack CV has elapsed, the Decay, sustain and release functions exactly as a normal ADSR.

Voltage controlled trig level

There is a CV input to control the threshold voltage that triggers the envelope. This is useful if you trigger several EGs from a ramp or another EG. If you set the level differently, they will fire in succession.

Some performance measurements

Hold time: 0,5 ms -- 45 s
Attack time: 0,5 ms -- 35 s
Decay time: 1,0 ms -- circa 90 s
Release time: 1,0 ms -- circa 90 s
Trig level: 0,5 -- 10,2 volts
With punch activated, the attack time is 0,3 microseconds.

Module construction

My module contain four separate envelope generators. The size of the module is 150 x 132 x 50 mm. I designed a printed circuit board with two envelope generators. Two such boards are used for this module. A third circuit board acts as a backplane and also holds eight of the jacks.

Circuit board layout (PDF-file)

Component placement (PDF-file)

Schematics and circuit theory (link to Jürgen Haible's site)

My additions to the schematics

Instead of redrawing the complete schematics, I have made the above schematic, that cover just the additions to JHs design.
In addition to this, I omitted all trimmers and changed the following resistors:

R16: 82k
R58: 82k
R59: 82k
R54: 56k
R50: 56k to + and 47k to -
R53: 470k
R15: 270k

All changes are reflected in the circuit board layout and component placement view. I matched the transistors in the exponential converter.
If you are going to contol the parameters from knobs (potentiometers), you should use 10 k lin pots and feed them with a stabilized 10 volt supply. You can simply use an op-amp for this. I used an NE5532 dual op-amp, which feeds all 24 potentiometers on my module. The NE5532 has a higher output current capability than most other op-amps.
Because the control inputs are truly exponential, the resolution is very high at the short end of the attack, decay and release times. This might create the impression that nothing happens before "5" on the knobs. You can improve this somewhat, by connecting an 8,2 k resistor between the wiper of the pots and the 10 V supply. Do this only on the pots for attack, decay and release.
The power consumption for the entire module is 78mA from the negative supply and between 140 and 180 mA from the positive supply, depending on the knob settings.

This picture shows the back of the completed VCHADSR module

The two dual EG boards are connected by means of a backplane, that also holds one row of jacks.

Here we see the module with the two boards removed. The IC on the backplane board is an opamp that provides 10 volts for the pots.

The module looks like this from the side. Note the compact construction.