PS411 EnvAmp (Attack/Release Envelope Generator & Opto-VCA)

by Antti Pussinen

The Dynamics of synthesized sounds are controlled with a Voltage Controlled Amplifier, or VCA. In a classical subtractive synthesizer arrangement the VCA is controlled through an envelope generator, allowing more interesting dynamic possibilities than just the on/off of a note gate.

Vactrol based Opto-VCA add an Attack and Release time automatically due to the relatively slow turn on, and off times of the led-ldr pair inside a vactrol. The ”opto” part of our VCA is a fast and accurate AC-Optocoupler, which adds a tiny bit of Attack time and Release tail to the signal, but not so much as a Vactrol would. We Decided to go with the optocoupler since factory made Vactrols are getting more rare and expensive, and altho rolling your own is a good choice, the response varies due to led and ldr types and manufacture tolerances.

The Paper Synthesizer PS411 adds more control to the opto-VCA with Attack and Release control potentiometers. If both turned to zero, the module acts like a normal VCA, controlled by external CV. If Attack or Release are adjusted, it affects the input CV before it controls the VCA. If CV input is a Gate signal, the envelope generator works like a normal Attack Release generator. Created envelope can be used to also control other modules view envelope output connector. A led is used to visualize the envelope. A jumper in the board selects between long and short attack and release ranges.

The module comes also with an bipolar offset potentiometer for manually controlling the amplitude.



Paper PCB



  • Resistors:
  • 1x 68 Ohm
  • 1x 100 Ohm
  • 3x 1 kOhm
  • 2x 10 kOhm
  • 1x 1.5 kOhm
  • 1x 5.6kOhm
  • 5x 100 kOhm
  • 2x 470kOhm
  • Capacitors:
  • 1x 22µF (bipolar)
  • Diodes:
  • 5x 1N4148
  • 1x LED
  • Semiconductors
  • 1x TL072 OpAmp
  • 1x TL074 OpAmp
  • 1x H11F1 Optocoupler
  • Mechanical:
  • 1x IC socket, 8pins
  • 1x IC socket, 16pins
  • 1x IC socket, 6pins
  • 4x Thonkiconn 3.5mm jack socket
  • 1x pin strip 2×8
  • Trimmpotentiometer:
  • 1x 50 k
  • Potentiometers:
  • 2x 100k lin
  • 1x 100k log


The PS411 EnvAmp was designed by Antti Pussinen 2017.
It is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

Creative Commons License