AR or AD generators that will fire on a trigger or a gate, giving envelopes up to approx 25 seconds

These are AR or AD generators that will fire on a trigger or a gate, giving envelopes up to approx 25 seconds. A single gate to input 1 will fire all 3 envelopes, when nothing is plugged into inputs 2 & 3.

SMD chips and resistors, but a very easy build with minimal components.