Envelope - A Looping ADSR module for Eurorack

Constructional Difficulty: Easy to moderate with surface mount parts

The 6HP wide Oakley Envelope is an easy to use four stage envelope generator with switchable looping mode.

The ADSR is operated by a traditional gate signal, but can also be triggered by slow rising CVs too due to the built in schmitt trigger function. No additional 'trig' input is required.

Although the panel does not imply a voltage controlled design, the internal electronics uses a voltage controlled slew generator at its core. This allows very fast minimum attack and decay times. And yet, the controls with their true exponential response, allow you to accurately adjust faster times with ease.

Two LEDs are provided. One gives a visual indication of the output level of the internal ADSR waveform, and the other shows the status of the gate input lighting up when either an active gate signal is present or the unit is in looping mode.

Loop Modes

The Oakley Envelope incorporates a looping mode. Looping means that the output will rise to the attack peak at the speed determined by the attack pot and then fall to 0.5V at the speed determined by the Decay pot. It will then rise again to the attack peak and then fall back to 0.5V and so on.

NORM - the module behaves as a standard ADSR.

GATED - the output will loop only when gate is high. As soon as gate arrives the output will rise up at the attack speed and then decay at the decay time and repeat. If the gate is removed at any point the output will then fall at the release time.

LOOP - The module's output will loop continuously in AD mode. The Gate input has no effect in Loop mode.

In both looping modes the position of the sustain pot can be used to turn the looping on or off. At values above 10% the looping will stop.


Attack times: 0.18 milliseconds to 25 seconds (fast) or 1.4 ms to 200 seconds (slow). Charging voltage +10V, internal attack peak +5V. Pseudo linear ramp.

Decay/Release times: 0.35 milliseconds to 30 s (fast) or 2.8 ms to 240 seconds (slow). Time measured from 90% of sustain value to 10% of sustain value. Exponential decay slope.

Sustain levels: 0.0V to 5.0V

Current draw is approximately -22mA and +33mA.

The PCB set

The Envelope module comprises of two printed circuit boards (PCBs) connected together with six 0.1” (2.54mm) single in line (SIL) headers and sockets. The main board on the rear of the module houses the power input and conditioning, and the ADSR core. The pot board has the pots, switch, and sockets that are attached to the front panel, as well as the gate input, LED drivers, and output circuitry. The main board is a four layer design, while the pot board is a two layer design. Each board is the same size; 29 mm x 107 mm.

The majority of the components are surface mount parts. The ICs are SOIC, while the resistors and surface mount capacitors are 0805. The two transistor arrays are SOT457. All components are standard parts.


Click here for ordering details.

ADSR (Euro) main board issue 1 PCB........................................... 10GBP

ADSR (Euro) pot board issue 1 PCB ............................................... 5GBP

Both boards are required to build the Oakley ADSR for Eurorack project.

All other parts can be purchased from your usual electronic component supplier.

All prices include VAT at UK rates. Shipping is additional to these prices. See also the FAQ page.

Project Downloads


Construction Guide Our handy guide to building Oakley DIY projects

Parts Guide Our handy guide to buying parts for Oakley DIY projects

Schematics are only available to purchasers of the PCBs and will be sent via e-mail when the boards are shipped.

Front Panel database

A Schaeffer front panel can be made for this module. The database can be found by downloading the following link:

6HP Eurorack format in natural silver

To read, edit and print these files you will need a copy of 'Frontplatten Designer' from Schaeffer. Panels can be ordered via the program using its secure online ordering system.

Schaeffer are based in Berlin, Germany and can send panels to anywhere in the world. Delivery to the UK normally takes around ten days. For North American users you can also order your Schaeffer panels from Front Panel Express.

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Copyright: Tony Allgood.
Last revised: March 14, 2023.