Author Topic: Boss GT1 exp input modulation  (Read 248 times)


Boss GT1 exp input modulation
« on: March 09, 2021, 03:54:00 AM »
I'm wondering if I could plug something in to the expression input of a GT1 that could modulate values in sequence.

Anyone know what kind of input it is expecting? I read that boss devices send out a control voltage and the expression pedal is basically a variable resistor that decides how much cv is returned.

So does the EHX Sequencer pedal play nice?

I have a Beatstep Pro but I'm afraid I would fry the Boss if I plugged that into it!

If I just need a sequence of variable resistors maybe I could do something with an arduino?


Re: Boss GT1 exp input modulation
« Reply #1 on: March 09, 2021, 10:49:29 AM »
The beatstep has a CV output, right? Maybe you could do something with some kind of optocoupler to get a variable resistor out of it?


Re: Boss GT1 exp input modulation
« Reply #2 on: March 09, 2021, 01:28:49 PM »
The EXP socket the GT-1 is expecting a stereo/TRS jack, so I'd start by putting a stereo/TRS lead in the socket and then testing the other end of the lead with the multimeter. My guess is:

Sleeve: Ground
Ring: +5V
Tip: CV input

This is only an educated guess, might be completely wrong. Might be 3.3V on the ring.Might be different arrangement. But you're probably looking for something along these lines. The key part is to find out what voltage range it's expecting, which I notice Boss are surprisingly reluctant tell us.


Re: Boss GT1 exp input modulation
« Reply #3 on: March 13, 2021, 03:17:28 PM »
I have taken readings from a TRS plugged in.

Sleeve = Ground
Ring = 3.18v
Tip = 2.16v

I have a Roland EV-5 expression pedal. I tried measuring the resistance but my cheapo multimeter probe snapped off and I couldn't get a good reading pressing the tiny strand of copper wire to the jack.

As the Boss is definately putting out voltage, am I right to conclude that if I somehow manged to design a circuit that sequenced through different resistor values then it probably would do what I want?


Re: Boss GT1 exp input modulation
« Reply #4 on: March 13, 2021, 06:43:35 PM »
Does the voltage on the tip vary when you waggle the pedal? Given the other two readings, we're expecting to see 0V to 3.2V or so.

If it does, it looks like if you had a sequencer that output various voltages in the right range, you'd just feed that in with the sleeve and tip connected (so ignoring the +V feed on the Ring) and treat the expression socket as a CV input. It should work. Note that it's looking for a *voltage* not a *resistance* though - assuming I'm right, which is by no means guaranteed. The Beatstep Pro CV output should work, but you'd either have to make sure you keep things within a 3.3 octave range (and therefore within a 3.3V range) or you'd have to add a couple of resistors to the output to scale it down a bit.