AD/AR

envelope generator with manual button based on a 555 timer

The AD/AR is a Eurorack envelope generator based on a 555 timer. It’s simple to use, cheap and easy to build.

The AD/AR is named after the primary feature: a switch between attack-decay mode and attack-release mode. Your envelope can be held high with a gate input, or switch it to engage a gate-to-trigger conversion circuit so your gates become plucky stabs.

The button on top is a manual gate/trig so you can test or play it directly. The gate/trig switch on top has a center position for mute, so you can smoothly deactivate parts of your music without clipping any notes. Outputs are available as 0->10V in both positive and negative for modulating anything. It’s buffered but has a 1kOhm output limiter.

The length of the envelope is set with two knobs, ranging from 0 to ‘full’. The Full length is defined by how long it takes to fill or empty some capacitors. The module uses four 10uF caps for this, two in parallel for a 20uF effective, and two in series for a 5uF effective. The fast envelope has a max time of about 4 seconds. The slow envelope is about double that; 4 seconds lit and ten seconds overall. When building your own you could replace these with other values.

https://karltron.com/ad-ar/