DIY mini expression pedal

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Miza
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DIY mini expression pedal

Post by Miza »

Threw this mini expression pedal together this afternoon.
20211107_184049.jpg
20211107_184049.jpg (2.88 MiB) Viewed 2207 times
Keen to try out the expression inputs on my Alter Ego X4 and Neumaber EXP. This one has a 10k pot for the TC. I've got a 25k pot for another one for the neunaber.

Am I right that no audio signal runs through the cable? I used a 3.5mm TRS jack and smaller cable, with an adapter at the pedal end just to save space.

It seems to work, but the sweep from 0 to 100 is a long way rotating your foot left to right!

Do they make pots with shorter sweeps??
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Re: DIY mini expression pedal

Post by PaulWD »

I'd be tempted to try a log pot in there to see whether the sweep feels more betterer.

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Re: DIY mini expression pedal

Post by Mattallica »

Yep try a different taper first. Linear vs log vs reverse log

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Re: DIY mini expression pedal

Post by Miza »

PaulWD wrote: Mon Nov 08, 2021 8:45 am I'd be tempted to try a log pot in there to see whether the sweep feels more betterer.
I guess the log pot would allow for a bigger difference in the "sweet spot" of the taper. From little to lots. Good suggestion.
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Re: DIY mini expression pedal

Post by Miza »

Would still be good to have a pot with a short sweep/throw. About 90 degrees would be ideal. A quick Google search reveals they're not common. Or cheap.
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Re: DIY mini expression pedal

Post by jeremyb »

Miza wrote: Mon Nov 08, 2021 12:16 pm Would still be good to have a pot with a short sweep/throw. About 90 degrees would be ideal. A quick Google search reveals they're not common. Or cheap.
Just use a higher value pot and then you could fabricate some kind of stop for the movement, hmmmmm dot of solder on the inside to stop it going past a point?
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Re: DIY mini expression pedal

Post by Miza »

jeremyb wrote: Mon Nov 08, 2021 12:45 pm
Miza wrote: Mon Nov 08, 2021 12:16 pm Would still be good to have a pot with a short sweep/throw. About 90 degrees would be ideal. A quick Google search reveals they're not common. Or cheap.
Just use a higher value pot and then you could fabricate some kind of stop for the movement, hmmmmm dot of solder on the inside to stop it going past a point?
Thanks JB - that's where my electrical knowledge starts to get limited. What would a higher value pot do to the effect? Would it reach 100% sooner in the sweep?
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Re: DIY mini expression pedal

Post by NippleWrestler »

100% is still 100%, you're just changing the value of what that 100% is.

Hes saying that if you have a 100k pot and use all the travel, use a 500k pot and only use 1/5th of the travel you'll get through 0-100k quicker (using a perfect sweep taper as the basis for the logic).

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Re: DIY mini expression pedal

Post by Miza »

Ok, let's see if I've got this correct. At 100%, it's like an open tap? So the value at full right turn will always be the same? And as you turn the pot anti-clockwise (towards 0) it's adding resistance, therefore the higher the pot value, the more resistance you're adding in a much shorter amount of sweep?
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Re: DIY mini expression pedal

Post by calling card »

I made some crude thing back in my musical odyssey infancy. It was two pieces of wood and a hinge & spring with a slider type volume control gutted from an old home stereo attached between base and pedal. It worked.
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Re: DIY mini expression pedal

Post by NippleWrestler »

Miza wrote: Mon Nov 08, 2021 1:59 pm Ok, let's see if I've got this correct. At 100%, it's like an open tap? So the value at full right turn will always be the same? And as you turn the pot anti-clockwise (towards 0) it's adding resistance, therefore the higher the pot value, the more resistance you're adding in a much shorter amount of sweep?
The value is determined by the pot. The effect that pot has is determined by the circuit.

It sounds like what you're looking for is some kind of pot stopper so the pot doesn't go around it's full 270 degree rotation but rather stops at 90 or 180.

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Re: DIY mini expression pedal

Post by Miza »

NippleWrestler wrote: Mon Nov 08, 2021 2:23 pm
Miza wrote: Mon Nov 08, 2021 1:59 pm Ok, let's see if I've got this correct. At 100%, it's like an open tap? So the value at full right turn will always be the same? And as you turn the pot anti-clockwise (towards 0) it's adding resistance, therefore the higher the pot value, the more resistance you're adding in a much shorter amount of sweep?
The value is determined by the pot. The effect that pot has is determined by the circuit.

It sounds like what you're looking for is some kind of pot stopper so the pot doesn't go around it's full 270 degree rotation but rather stops at 90 or 180.
Yeah I guess so, as long as the upper and lower values of that sweep are useable. 0% effect (off) would be useful, and probably up to 50%, but I'd never turn the feedback of a delay up to 100%, so I yeah i can probably stop the pot early. I need to go back and do some experimentation with pot values and tapers to see what works.
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Re: DIY mini expression pedal

Post by Optical »

Pot value and tapers aren't going to get you anywhere, i dont think.
An aggressive antilog taper is just going to move the 80% output voltage to about halfway on the pot, then the remaining 20% will be spread over the remaining pot rotation. That might be something useful but it's about as close as you're going to get.

The pedal is expecting 0v input for 0%, 2.5v for 50%, and 5v for 100%, and everything in between obviously.
The only way you're going to reduce the rotation range of standard 270 degree pot is to get the pot to output 5v at halfway/50%, which means feeding 10V into it. But that' s not practical as it would require another power supply and then some kind of regulator on the output to prevent sending too much voltage into the unit. Ordinarily you'd remap the input in the pedal software so 2.5v = 100%, but that's not an option either.

I'm not really sure what option you have apart from building a customised power supply that makes the pot output the way you want. Or changing the mechanical aspects of the control to move the pot quicker (like a wah pedal).

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Re: DIY mini expression pedal

Post by NippleWrestler »

Yeah if it's anything to do with voltage you've got a headache. I ignorantly presumed it was just a variable resistor mounted externally.

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Re: DIY mini expression pedal

Post by Miza »

Thanks for the replies. I was just reading up on expression pedals and voltages here:
https://missionengineering.com/understa ... on-pedals/

I will keep experimenting. I definitely don't need the pot at 100% on the Alter Ego cos that's just too much delay.

For the Neunaber, when you insert an expression pedal, the knob sets the max value, so for that I will need 100% if I want to reach where the knob is set.

A proper wah-style foot controller will be on the cards I'm sure.
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