This module is part of my Eurorack series. It is an envelope generator based on the 7555 timer integrated circuit. An envelope generator creates a control voltage that is usually used to shape a sound over time, e.g. in a voltage-controlled amplifier or filter. It sounds more natural than just turning a note on and off.

Key features

• envelope generator
• controls for attack, decay, sustain and release
• trigger input
• CV output
• LED indicator
• easy to build, all through hole components
• 6HP

How it works

The circuit is based on René Schmitz’s Fastest Envelope in the West. It is using the CMOS variant of the 555 timer, the 7555 IC.

I replaced the input section that is conditioning the trigger signal with my own variant to keep the component variety even smaller. The circuit detects a rising edge on the trigger signal and is sending a short pulse going from high to low to the timer IC.

The timer is set up as a monostable timer which is a one-shot application of the integrated circuit. There is a capacitor (C3) that is charged through the attack potentiometer when the timer’s output is high. The timer stops when the voltage on the threshold pin reaches 2/3 VCC. The capacitor is discharged through the other pots giving the control voltage output its characteristic shape.

This offering only includes the PCBs and front panel without components!

See https://polykit.rocks/adsr for technical details and assembly.