paper_synth:ps411

PS411 EnvAmp (Attack/Release Envelope Generator & Opto-VCA)
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- Schematic
- Paper PCB
- Faceplate
- Parts
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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.