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EnvyLope V3

Voltage Controlled ADSR, LFO, and Glide

Courtesy/Thanks to: Aaron Cram

Description: I set out to design the ultimate multi-function envelope generator circuit. I think I came close, for my needs anyway. With nothing plugged into the gate input, the circuit is locked in sustain mode. You can use this as a voltage controlled glide by patching a signal into the sustain input. The attack/decay voltages will then control the up and down glide speed. If the sustain knob is turned all the way down, the circuit re-triggers itself and becomes a voltage controlled triangle LFO with separately adjustable up and down ramp times. If the gate input is connected, it becomes a gated LFO, and will only run when the gate is high. The trigger input resets the cycle, and can be used as a sync. Of course, the main function of the circuit is the ADSR. This is implemented with the envelope starting out at zero and going up from there, allowing you to send the envelope output through a VCA to control the overall amplitude. This is important when, for example, you want the velocity control from your MIDI keyboard to properly modulate the loudness of a tone. Note also that the sustain point can be set “below ground.” However, in this configuration, you lose the separate release slope and the envelope returns up to ground at attack speed. The slope of all envelope ramps are exponential with respect to the control voltages.

The ramps themselves can be either linear or R/C. There are actually three modes to the EG, which can be controlled from the front panel by an on-off-on DPDT switch. Mode 1 is linear for all stages. Mode 2 (center position) is linear attack and R/C decay and release. Mode 3 is R/C for all stages.

The trigger input resets the envelope, from wherever it may be in the cycle, and if a gate is sent at the same time it will start the cycle over. This reset happens smoothly so that you don’t hear a “pop” when the trigger is fired. Finally, you’ll notice that there is a separate LED that shows the current state the envelope generator is in. There is a sustain gate output, which is low except when the EG is in the sustain state. This allows cascading multiple EGs together to make more complex contours. It could also trigger other modules on the synth. Or it could simply be used as a timer.


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   Schematics and description of the EnvyLope version 3
Parts used
   High speed Switching Diode
   PNP switching transistor
   NPN switching transistor
   High Conductance Fast Diode
   JFet-input Operational Amplifier
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