For anyone following along! My personal diary here. Well I figured out how to do this. A lot of this has to do with how the TVS-1 is wired.
The TVS-1 keyboard (and mini sequencer) only sends gate + CV. The trigger inputs on the SEMS are not connected to anything in the TVS-1. Instead, the gate is used for both the trigger and gate signals, per the default setup of the envelope jumpers.
This is okay if you're playing the keyboard, you just have to play staccato. The mini-sequencer must be able to send super short gates.
But when you're controlling it externally, especially with busy notes that aren't necessarily staccato, the gate stays true/open and never closes to re-engage the envelopes. So you need an external trigger input (along with the gate and CV), and you need to configure the jumpers to include the trigger+gate.
But if you set the jumpers to gate+trigger, well then the keyboard doesn't work right because there's no separate trigger in the TVS-1 circuits.
So if you want to be able to have the "stock" two voice keyboard functionality, and at other times use an external sequence input (which as wired only controls SEM 2), you need a switch, DPDT, to toggle between gate and trigger on both envelope jumper sets on the SEM 2.
This way worked for me.
Next I want to put in another switch to have a single external gate+trigger+CV control both SEMS in unison. So it can work as a standalone playable TVS-1, or either a 2 or a 4 oscillator single/dual SEM module. And also follow this envelope jumper switching but now on both SEMS (which I think will actually require a 3rd switch, or a 4PDT??). Will need to chill before I think that hard though.
Hope this helps someone one day.
Last edited by error_trials; 30th May 2020 at 12:00 AM..
Reason: revised for clarity.