[sdiy] Fet to short pedal input?

[brianw]

Hi Ed,

That seems promising. Now I understand what you're trying to do.

You might need an optoisolator, as has been suggested, because the transistor will be floating in the portamento circuit. Controlling the transistor (BJT Base or FET Gate) from a voltage outside the Odyssey will require that the voltage be relative to the Emitter or Source. That might be tricky.

I think your first hunch is correct: an FET would probably be easier to get working. I wonder if there are optoisolators with FET circuits instead of bipolar or Darlington pairs.

And you're right that it might be "max velocity no slide" unless you can insert a second transistor to invert the control logic (but that would probably require a power supply to feed the transistors).

Brian


On Nov 27, 2025, at 7:49 PM, el macaco wrote:
> Hi Brian & all,
> 
> The schematic indicates the pedal contact shorts the portamento slider out.  Gotta see the polarity of the pedal.
> 
> The idea was to use the 5v velocity voltage output to activate a fet/relay/etc to replace the pedal in function, so that notes with max velocity slide.  It’s a MK I Odyssey.
> 
> Of course it could be max velocity no slide, since velocity isn’t being used for volume or anything it just becomes a per note portamento on/off signal.
> 
> Ideally with no additional circuits or power.
> 
> Seems like it’s within the realm of possibility.
> 
> Ed