[sdiy] Fet to short pedal input?

[Michael E Caloroso]

The dark resistance of any LDR is always going to be in parallel with
the 1M pot, which will reduce the max portamento rate.

You really need a control element with infinite resistance (open circuit).
That element needs to have open circuit and short circuit states and it's
hard to beat a relay controlled by a Darlington BJT.

Routing MIDI note velocity to Portamento enable is a neat expression tool -
it's a trick I use on choir patches on my Andromeda.  Pitch glides only at
high velocity, and you don't need an extra hand to toggle it.

MC

On Fri, Nov 28, 2025 at 9:26 AM Oren Leavitt via Synth-diy <
synth-diy at synth-diy.org> wrote:

> Looks to me like a simple LDR (LED/photocell) may do the trick here.
> Given the LDR has sufficiently high "dark" resistance.
>
> - Oren
>
> On 11/28/25 5:47 AM, Tom Wiltshire wrote:
> > I've checked the Arp Odyssey schematics (since it has one of these
> > inputs). The relevant part is attached below.
> >
> > The Portamento input jack is a TRS jack connected across the ends of the
> > 1M audio-taper portamento pot. So shorting the Tip and Ring connections
> > disables the portamento. It's not a simple short-to-ground action as I
> > had thought it might be, but any bidirectional switch should work in
> > this position.
> >
> >
> >
> >> On 27 Nov 2025, at 20:34, el macaco via Synth-diy <synth-diy at synth-
> >> diy.org <mailto:synth-diy at synth-diy.org>> wrote:
> >>
> >> Hi all,
> >>
> >> The portamento pedal input on arps has me thinking of using my midi to
> >> cv converter's velocity output (+5V) to activate a fet with the two
> >> pedal contacts on the source and drain.
> >>
> >> Can it be this simple?  The only power coming from the velocity 5v?
> >>
> >> Thanks,
> >>
> >> Ed
> >>
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