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

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.


Scope



Schematic



Paper PCB

Faceplate



Parts

  • 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