[sdiy] Fet to short pedal input?

[brianw]

Ah, I'm going to make a few guesses here. Looking at the schematic would help a lot, so let me know which ARP synth you're talking about, and where the schematics are, if you know.

First of all, I assume that the portamento slider resistance is 0 Ω when there is "no" portamento, and increasing resistance as the portamento time increases. If this is the case, then I assume that the portamento pedal will basically short the slider to 0 Ω when the pedal is "up" and then simply go open-circuit when the pedal is pressed down.

Instead of resistance, portamento might be a CV signal, where 0 V is "no" portamento, and increasing voltages represent longer portamento times. If this is the case, then the portamento pedal probably shorts one pin to ground (0 V) with the pedal is "up" and then passes through the slider voltage when the pedal is pressed down. This seems less likely, though, because voltage-controlled portamento would probably be more expensive circuitry than a simple RC network using the portamento slider and a capacitor (with the pedal shorting out the slider when attached).

You should probably use the Gate output of your Frostwave Quad MIDI to CV Converter. The Gate should output 5V for all notes, regardless of velocity. You'll have to select the correct trigger mode, though, since the Frostwave supports Roland mode as well as the S-trigger of Korg and Moog. The manual that I found for the Frostwave seems to be missing a lot of important information.

I would not use the Velocity voltage to power an external circuit. You'd be better off powering your circuit from the Frostwave wall wart. Just put two jacks on your device so you can daisy-chain the power to the Frostwave.

Brian

p.s. I guess I should ask, "Are you wanting to use Velocity to engage Portamento, such that soft playing is without portamento and harder playing has portamento?" - I guess I'm curious how the Frostwave comes into the picture - is it a power source or a MIDI source? Why not use the standard MIDI Control number for Portamento (which I assume exists)?


On Nov 27, 2025, at 6:14 PM, el macaco wrote:
> Thanks Brian,
> 
> The portmento pedal jack disconnects the portamento slider from the circuit via jack normal.  The pedal connects the slider back in when pressed.
> 
> I have everything to try it, so I will.
> 
> My Frostwave Quad midi to CV converter has a velocity output jack per channel but it only outputs a 5V gate signal when velocity is over a threshhold.
> 
> I’m wondering if that is enough to power a circuit to engage the portamento.
> 
> Thanks,
> 
> Ed