Kassutronics Precision ADSR with retriggering and looping modifications

This is an ADSR envelope generator synth module. Layout and panel are Kosmo format.

The main part of the design is from Kassutronics, who in turn based it on the YuSynth ADSR (version 2), which is similar to René Schmitz's Fastest Envelope In the West. The latter two, like some other envelope generators, have the problem that the voltage releases very slowly after reaching about 700 mV, taking several seconds or longer to drop below 100 mV. Kassutronics fixed this by replacing the decay and release diodes with precision rectifiers (op amp with diode in the feedback loop). Another modification was a clever way of combining the LED indicator with the inverted envelope output using a single op amp.

The present design adds the following features:

• Two switch selectable capacitors for slower and faster time scales (restoring a feature of the YuSynth ADSR, though without the two resistors in the attack path).
• Capacitors can be socketed for experimentation, soldered, or socketed at first and soldered later.
• Retriggering input, allowing additional attack/decay peaks on top of the sustain (inspired by but simplified from Benjamin AM's design).
• Looping mode, allowing attack-decay envelopes to repeat as long as a gate is present, or, if nothing is plugged into the gate input, indefinitely. This can be used as a sequence of envelopes or as a kind of odd LFO.

Current draw

12 mA +12 V, 10 mA -12 V

Photos

Documentation:

• Schematic
• PCB layout: front, back
• BOM
• Build notes
• How to use

Git repository

• https://gitlab.com/rsholmes/precadsr

Submodules

This repo uses submodules aoKicad and Kosmo_panel, which provide needed libaries for KiCad. To clone:

git clone git@gitlab.com:rsholmes/precadsr.git
git submodule init
git submodule update

Alternatively do

git clone --recurse-submodules git@gitlab.com:rsholmes/precadsr.git

Or if you download the repository as a zip file, you must also click on the "aoKicad" and "Kosmo_panel" links on the GitHub page (they'll have "@ something" after them) and download them as separate zip files which you can unzip into the aoKicad and Kosmo_panel directories.

If desired, copy the files from aoKicad and Kosmo_panel to wherever you prefer (your KiCad user library directory, for instance, if you have one). Then in KiCad, add symbol libraries

aoKicad/ao_symbols
Kosmo_panel/Kosmo

and footprint libraries

aoKicad/ao_tht
Kosmo_panel/Kosmo_panel.