Building the A/R EG

PCB  and Schematic:


Later revisions have an integral Gate to Trigger converter (middle jack) that shortens a gate to about 10ms trigger and then uses that to generate the envelope. This is useful if the Gate signal is an entire note-length long to give the RELEASE control time to do something before the next note.

The latest revision (labelled Rev: D on PCB) uses A100K pots instead of A1M. This version uses two 10u 0805 capacitors instead of a single 1u capacitor.

Whichever revision you have, use the components as labelled on the PCB (except the 48K/50K resistors as shown above).


Source 1
Source 2
4Capacitor100n0603NOTE PACKAGE!
2PotentiometerA1M9MM SNAP-IN9mm vertical snap-in pot, Alpha / Panasonic style with 6mm built-in knob. Audio taper.
3Diode1n4148DO214ACSwitching diode
1Zener Diode5Z1SOD123Footprint on PCB too big, need to use more solder
23.5mm socketTHONKICONN3.5mm socket for Eurorack modular synths
2DiodeM7DO214AAPower diode
1Tile Tail"Futaba J" Tile Tail.
1OpampTL072SO08Almost any dual Opamp can be used


  1. Clean the PCB with Isopropyl Alcohol.
  2. Solder the surface-mount components to the PCB.
    1. Begin with resistors and capacitors.
    2. Note the 47K resistor changes in the PCB diagram above if using that PCB version.
    3. The small unlabelled footprints (0603 size) are 100n capacitors.
    4. The two large unlabelled footprints near the power header are M7/1n4007 diodes. A 1n4148 and 5.1V Zener are beneath the opamp. Make sure the polarity is correct.
    5. Finally, add the opamp, making sure it’s in the correct position (pin 1 is by the large white dot).
  3. If using hot-air or an oven to solder the surface-mount components then do this now.
  4. Inspect all of the soldered components for solder bridges between pins and components, especially around the opamp.
  5. Solder the Tile-Tail power lead. Trim the exposed front-side ends if they interfere with the pot.
  6. Solder the front components (pot and jacks). It’s a good idea to put the panel on before soldering to make sure they are aligned. Some pots have a metal support underneath — check that it doesn’t short the power lead pins. Cut the leads flush to the PCB if they are.
  7. Again inspect all of the soldered components for solder bridges between pins.


Check that there’s no continuity between the red, white, and black wires on the power lead. If there is continuity then for shorts between the components around the power lead and diodes.

Check that there’s no continuity between the both ends of each of the small 0603 capacitors, located near the OpAmp. If there’s continuity then check all of the soldered connections for shorts.

Plug the module in and test all functions. With the Attack control full left, and the Release control full right, the Envelope output should go to 5V at the start of a Gate input, then drop to 0V over several seconds when the GATE ends.

A long gate signal on the middle jack and the Attack and Release control turned full-left should result in a single pulse about 10 milliseconds long on the Envelope jack. Turning the Release right should result in the pulse slowly dropping back to 0V.