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.
Buy kit or PCBs in my storeKey features#
- envelope generator
- controls for attack, decay, sustain and release
- trigger input
- CV output
- LED indicator
- easy to build, all through hole components
- 6HP
Video#
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.
Assembly#
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.
See the Component Basics guide for help identifying parts.
BOM#
Link to interactive BOM of the component board
| Reference | Value | Footprint | Description | Qty |
|---|---|---|---|---|
| C1, C2 | 10n | Capacitor_THT:C_Disc_D5.0mm_W2.5mm_P5.00mm | ceramic | 2 |
| C3 | 4.7u | Capacitor_THT:CP_Radial_D5.0mm_P2.50mm | electrolytic | 1 |
| C4, C5 | 100n | Capacitor_THT:C_Disc_D5.0mm_W2.5mm_P5.00mm | ceramic | 2 |
| C6, C7 | 10u | Capacitor_THT:CP_Radial_D5.0mm_P2.50mm | electrolytic | 2 |
| D1-D6 | 1N4148 | Diode_THT:D_DO-35_SOD27_P7.62mm_Horizontal | 6 | |
| J1 | CONN1 | Connector_PinHeader_2.54mm:PinHeader_1x06_P2.54mm_Vertical | 1 | |
| J2 | CONN2 | Connector_PinHeader_2.54mm:PinHeader_1x06_P2.54mm_Vertical | 1 | |
| POWER1 | Conn_02x05_Odd_Even | Connector_IDC:IDC-Header_2x05_P2.54mm_Vertical | IDC 10-pin | 1 |
| R1 | 10k | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | 1/4W 1% resistor | 1 |
| R2, R7 | 100k | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | 1/4W 1% resistor | 2 |
| R3, R4, R8 | 100 | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | 1/4W 1% resistor | 3 |
| R5 | 47k | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | 1/4W 1% resistor | 1 |
| R6 | 1M | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | 1/4W 1% resistor | 1 |
| R9, R10 | 10 | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | 1/4W 1% resistor | 2 |
| U1 | TL074 | Package_DIP:DIP-14_W7.62mm_LongPads | 1 | |
| U2 | 7555 | Package_DIP:DIP-8_W7.62mm_LongPads | 1 |
Link to interactive BOM of the control board
| Reference | Value | Footprint | Description | Qty |
|---|---|---|---|---|
| D1 | LED | LED_THT:LED_D5.0mm | 5mm LED | 1 |
| J1 | CONN1 | Connector_PinSocket_2.54mm:PinSocket_1x06_P2.54mm_Vertical | 1 | |
| J2 | CONN2 | Connector_PinSocket_2.54mm:PinSocket_1x06_P2.54mm_Vertical | 1 | |
| J3 | IN | Connector_Audio:Jack_3.5mm_QingPu_WQP-PJ398SM_Vertical_CircularHoles | Thonkiconn 3.5mm jack sockets | 1 |
| J4 | OUT | Connector_Audio:Jack_3.5mm_QingPu_WQP-PJ398SM_Vertical_CircularHoles | Thonkiconn 3.5mm jack sockets | 1 |
| Q1 | 2N3904 | Package_TO_SOT_THT:TO-92_Inline_Wide | NPN transistor | 1 |
| R1, R3 | 1k | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | 1/4W 1% resistor | 2 |
| R2 | 10k | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | 1/4W 1% resistor | 1 |
| R4 | 4k7 | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | 1/4W 1% resistor | 1 |
| RV1 | ATTACK 1M | Potentiometer_THT:Potentiometer_Alpha_RD901F-40-00D_Single_Vertical | linear, vertical, threaded, 6mm | 1 |
| RV2 | DECAY 1M | Potentiometer_THT:Potentiometer_Alpha_RD901F-40-00D_Single_Vertical | linear, vertical, threaded, 6mm | 1 |
| RV3 | SUSTAIN 10k | Potentiometer_THT:Potentiometer_Alpha_RD901F-40-00D_Single_Vertical | linear, vertical, threaded, 6mm | 1 |
| RV4 | RELEASE 1M | Potentiometer_THT:Potentiometer_Alpha_RD901F-40-00D_Single_Vertical | linear, vertical, threaded, 6mm | 1 |
Schematics#
References#
https://www.schmitzbits.de/adsr.html
https://yusynth.net/Modular/EN/ADSR/index.html
https://www.tinytransistors.net/2021/04/24/the-555-timer
https://www.circuitbasics.com/555-timer-basics-monostable-mode
