I built this 218r V2 keyboard for a Serge system. I adapted the power supplies to +/-12V only, separated the pulse output into a 5V trigger and a 5V gate, and set the preset control range and pressure range to 5V.

This is an older EMS board which had tarnish. I cleaned it as best I could and did 5 coats of satin clear. You can see just a bit of delamination along the side edges. The last two 218r old stock boards that I made had this problem. I spent a lot of time cleaning these PCBs and the delaminations on this one are a bit less than the previous. I never had this issue with PCBs when they were relatively new.

The left has the +5V modification and the right has the 5V trigger and gate modification. I added a third trimmer to adjust the maximum portamento time to work with this particular vactrol.

I replaced the 13.5V regulator for the Preset controls with a 78L05. I ran the 3.3V regulator from the +12V which operates within the temperature safe area..

I added a LM319 Dual Comparator with a threshold of 2V for the gate and 8V for the trigger.

This was a bit of a challenging hand modification.

The rising edge of the stock pulse circuit is slow so the trigger is slightly delayed from the gate.

The second key trigger in operation.

The falling edge of gate is well defined.

The trigger width is 750 µS.

The gate to trigger delay is only 277 µS which shouldn't be an issue.

I adjusted the maximum portamento time to 80 mS.

I used a Bud boat and added a short Serge-style power cord and a signal ground banana jack on the rear.

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