Sometimes you don’t need a full ADSR, you just need a simple decay. For example, when creating percussive sounds, stabby chords, or short notes. That’s exactly where this circuit comes in handy.
Because it only requires a small number of components (nothing fancy: just resistors, capacitors, a diode, and a couple of classic TL074 or TL072 op-amps) it feels like a a perfect first project if you want to build a very simple envelope generator.
This project is originally based on a design from Bartone Musical Circuits, a graat website filled with a lot of different DIY modules. It’s definitely worth exploring ! There’s a lot of great material, including detailed PDF documentation explaining each part of the circuit.
Because it only requires a small number of components (nothing fancy: just resistors, capacitors, a diode, and a couple of classic TL074 or TL072 op-amps) it feels like a a perfect first project if you want to build a very simple envelope generator.
This project is originally based on a design from Bartone Musical Circuits, a graat website filled with a lot of different DIY modules. It’s definitely worth exploring ! There’s a lot of great material, including detailed PDF documentation explaining each part of the circuit.
This is the second time I’ve built a module based on this design. The first one was a quadruple decay generator, closer to the original. I added an attenuator with a buffered output for each decay, as I prefer placing attenuation on the emitter/output stage. It's my module, I do what I want ! :)
For this module, I decided to pack two decay generators together and wire them to the same gate input. This way, a single trigger can generate two envelopes. This is perfect for generating synced envelope for both a VCA and a VCF simultaneously.
By experimenting I also replaced some values from the original :
I also included an attenuator for each decay output. If you want to simplify the build, this stage can be omitted by removing the final op-amp, potentiometer, and associated resistor.
By experimenting I also replaced some values from the original :
- I changed the 10µF capacitor by a 2.2µF one, which results in a snappier, more immediate response.
- to maintain a similar maximum decay time, I increased the potentiometer value from 100k to 500k, and chose a logarithmic potentiometer, which feels also more natural.
- I also changed the 220Ω resistor to 1kΩ. Since this resistor defines the minimum decay time, the original value felt too short for my needs.
I also included an attenuator for each decay output. If you want to simplify the build, this stage can be omitted by removing the final op-amp, potentiometer, and associated resistor.
Component List
1× TL0741× TL072
2× 100kΩ potentiometer
2× 500kΩ log potentiometer
8× 1kΩ resistor
4× 100kΩ potentiometer
2× 10nF capacitor
2× 2.2µF capacitor
4× 100nF capacitor
2× 10µF capacitor
2× 1N4148 diode
2× LED
3× Jack socket
I probably could have reduced the component count by merging both decay paths after the gate-to-trigger stage (the first op-amp in the circuit). Keeping them separate could be useful later if I decide to give each decay its own input.