I patched up a complete emulation of the Quad VC Envelope Generator. I believe it is faithful to the hardware from a functionality standpoint. I did indeed use two Venom Envelope Factories per EG as you suggested, so the architecture is fairly close to the hardware as well.
Do not use this version 1 patch - it is seriously buggy! Instead use the corrected version 2 or the much simpler version 3 found in later posts. Or use a bare Envelope Factory for one envelope generator as described later in this post.
Buchla 284 Quad VC Envelope Generator.vcv (10.1 KB)
Here is the user interface and patch bay that represents the complete module:
And here is the functional internals that should not be touched:
It was a little tricky to get everything working properly. I had to introduce a sample delay for one of the controlling gates. It also takes some logic to properly block retrigger actions while an envelope is active. I use an AD/ASR to convert the gate into a trigger for when Sustain is off. If Sustain is on I pass the incoming gate directly to the 1st Envelope Factory and I also send -10V CV to the Duration time (1st EG release) to effectively set it to 0 so the Decay stage starts immediately after the gate is released.
But I think there is a much simpler solution that only uses one Envelope Factory per envelope generator. Simply create 4 copies to get full Quad functionality.
Buchla 284 Single VC Envelope Generator.vcv (3.5 KB)
The patch is configured for Sustain OFF, as shown below.
Any control voltage should be patched to the V/Oct input, except the Envelope Factory doesn’t have an attenuverter for that input. You will have to provide your own.
All the controls and ports have been renamed in the tooltips to show what their function is in context of the Buchla 284. Most of the controls are locked so you can’t accidently corrupt the functionality.
To turn sustain ON, simply change the 3rd stage action (the Duration stage) to Sust, and make sure to set the Drift knob to 0, as shown below. In the hardware this knob would be ignored when sustain is enabled, but here it must be manually set to 0.
I recommend saving the Envelope Factory configuration in the patch as a preset so you can conveniently create a Buchla style EG at any time.