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Eurorack ADSR

Eurorack Modular Adsr Envelope Utility Easy-Build Through-Hole

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.

The PCBs are available in my store

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 RenĂ© 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.


The build is pretty straight-forward. The module only consists of through-hole components and is easy to assemble. There are three boards: a front panel, a board for controls/jacks, and a board for the circuit.

First, solder all parts on the component board. Keep the jacks and potentiometers for the end. Begin with the components with the lowest profile and work your way up. Screw the jacks and potentiometer to the front panel before soldering them. All components have a fixed designator and a component value printed on the board. Additional information on the parts can be found in the BOM below.


Link to interactive BOM of the component board

C1, C210nCapacitor_THT:C_Disc_D5.0mm_W2.5mm_P5.00mmceramic2
C4, C5100nCapacitor_THT:C_Disc_D5.0mm_W2.5mm_P5.00mmceramic2
C6, C710uCapacitor_THT:CP_Radial_D5.0mm_P2.50mmelectrolytic2
POWER1Conn_02x05_Odd_EvenConnector_IDC:IDC-Header_2x05_P2.54mm_VerticalIDC 10-pin1
R110kResistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal1/4W 1% resistor1
R2, R7100kResistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal1/4W 1% resistor2
R3, R4, R8100Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal1/4W 1% resistor3
R547kResistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal1/4W 1% resistor1
R61MResistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal1/4W 1% resistor1
R9, R1010Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal1/4W 1% resistor2

Link to interactive BOM of the control board

J3INConnector_Audio:Jack_3.5mm_QingPu_WQP-PJ398SM_Vertical_CircularHolesThonkiconn 3.5mm jack sockets1
J4OUTConnector_Audio:Jack_3.5mm_QingPu_WQP-PJ398SM_Vertical_CircularHolesThonkiconn 3.5mm jack sockets1
Q12N3904Package_TO_SOT_THT:TO-92_Inline_WideNPN transistor1
R1, R31kResistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal1/4W 1% resistor2
R210kResistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal1/4W 1% resistor1
R44k7Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal1/4W 1% resistor1
RV1ATTACK 1MPotentiometer_THT:Potentiometer_Alpha_RD901F-40-00D_Single_Verticallinear, vertical, threaded, 6mm1
RV2DECAY 1MPotentiometer_THT:Potentiometer_Alpha_RD901F-40-00D_Single_Verticallinear, vertical, threaded, 6mm1
RV3SUSTAIN 10kPotentiometer_THT:Potentiometer_Alpha_RD901F-40-00D_Single_Verticallinear, vertical, threaded, 6mm1
RV4RELEASE 1MPotentiometer_THT:Potentiometer_Alpha_RD901F-40-00D_Single_Verticallinear, vertical, threaded, 6mm1




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