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Controlling Oberheim TVS-1 / SEM 1A with midi-CV
Old 23rd May 2020
  #1
Controlling Oberheim TVS-1 / SEM 1A with midi-CV

Hi Friends
Having trouble controlling my Two Voice via CV/gate in. This is the older TVS-1, not the new reissue. For what it's worth it's also the older circuit, the 1080 B.

When playing a midi sequence, the SEM's envelope doesn't re-open until there's a more extended gap in the notes. The notes aren't triggering the envelope as I'd like. The result is no attack from note to note, just more faint sustain.

The signal's coming from a Kenton pro solo, I tried it from another Kenton (pro 4) and got the same result.

Playing the same sequence, using the same midi-CV, sounds as I'd expect into say an ARP avatar or Korg Monopoly. The notes are distinct, the envelope re-opens. I should also say that using the TVS-1 keyboard, without any CV/gate plugged in, the envelopes open as they should but it does take a pretty clear staccato-like keystroke if that makes sense.

I've tried the different gate (And even s-trig) settings on the Kenton, doesn't fix it.

I know there are envelope jumpers in the SEM circuit board. I think/hope this can help me but I'm confused. I looked at mine and they appear to be set up as the manual shows for "Gate". It looks like the factory setup just guessing from looking at the solder. There is another setup for Trigger+Gate... maybe that's the ticket?

Does anyone have experience with the envelope jumpers? Any similar problems overcome?

I'm out of my studio for a little bit but next step is to try switching to that trigger+gate jumper wiring.

THANK YOU
Old 25th May 2020
  #2
bump... hoping anyone out there has experience with the envelope jumpers in the old SEM...

THANKS
Old 29th May 2020
  #3
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.
Old 29th May 2020
  #4
Oh, sort of related, this valuable bit from CZ Rider, from another thread, helped me and I think is useful to remind:

Quote:
Originally Posted by CZ Rider View Post
Have to remember the SEM uses Switchcraft Tini-jax. These are .141" and about 3.58mm in metric. Best to use Switchcraft 750 (plastic end) or 780 (all metal) ends. Otherwise connection could be intermittent.
This is totally true and can give you pitch issues on the CV input if you use the slightly smaller 3.5mm. You can definitely hear it if you wiggle a 3.5mm plug while playing a note. Maybe a new performance trick though.
Old 5th June 2020
  #5
Got the switching set up with 4PDT to switch between the Gate versus gate-trigger on both envelopes for both SEMs to have that option for sequencing. Added switch to have the single external CV2 be able to control SEM 1 (TVS-1 stock wiring has the SEM 2 VCOs only controlled by keyboard or mini-sequencer).

Super pumped. dual SEM unison sounding amazing.

Thanks to Dave Brown at modularsynthesis.com for his amazing resources on his site and for answering my questions on the SEM triggering.
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