DIY mini expression pedal

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FuzzMonkey
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Re: DIY mini expression pedal

Post by FuzzMonkey »

You are correct. No audio signal is passing through the cable.

It is a digital pedal (the Alter Ego X4 that is) so an expression pedal (a 25k linear pot is recommended in the user manual) will no doubt be acting as a simple voltage divider. There will be a reference voltage coming into one side of the pot; 3.3-volts no doubt with the other side tied to ground. The middle lug of the pot being the output. I assume that's how you have it wired?

If so, it makes sense that it is a TRS cable; one section of the jack for each signal. The incoming reference voltage, the outgoing divided voltage, and ground. The pot simple divides the voltage up and down depending on its position. The DSP reads that voltage and adjusts to the parameter in question in accordance with the new voltage reading. For example, 0-volts might set the delay time to a minimum while 5-volts sets to maximum and everywhere between depending on the position on the pot i.e. 2.5-volt would be halfway. As Optical explained earlier.

This is how I assume it is working of course as I have had the pleasure of playing around with an Alter Ego X4 so it is best my educated guess.

Changing the value of the reference voltage to say 2.5-volts as, again, Optical suggested earlier would cut the maximum delay time in half but that half would still be spread out across the entire rotation of the pot. It would probably give you finer control over the available delay time but it doesn't solve your problem in terms of your limited foot rotation in order to turn the pot to the desired setting. You, of course, could mount the pot on the side of the enclosure instead of the top so you are rolling it with your foot rather than twisting it. Or as you say, got the way of the wah.
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Re: DIY mini expression pedal

Post by Miza »

Thanks FuzzMonkey - yeah that all sounds right from what I've read. I used alligator clips and trial and error to test if the tip or ring connected to the wiper.

Yes the TC requires a 25k pot, and the Neunaber a 10k pot. Both use a TRS jack (sounds like only some Line6 stuff uses a TS jack).

Read the manual for the Alter Ego X4 last night, and when you plug in the expression pedal you need to set the min and max values of the knob(s) you want to manipulate, so I wasn't doing it properly when I first tried it out! Also I was using the 10k. Lesson learned.

I've started putting the 25k one together as well, so will test it out properly when I get a chance.

The other thing I could do is add a second pot (a trim pot) to set the minimum value of the expression pedal, like some of the commercial ones have. I think it goes between ground and lug 1?
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Re: DIY mini expression pedal

Post by Optical »

The pot value doesnt matter. Just needs to be more than 5k and ideally less than 500k.
The value does matter for the L6 stuff which uses only half the pots function.

Adding another pot or resistor from ground to the first pin will set a minimum offset adjust. 5v to the third pin will be a max offset adjust.

Maybe read this and it will be less mysterious https://en.wikipedia.org/wiki/Voltage_divider

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Re: DIY mini expression pedal

Post by FuzzMonkey »

As Optical said, the value of the pot doesn't matter too much as long as it is a linear taper so you get a linear response to the pot's rotation. I'd stick with 25k because that's what is recommended and you've got that value. But as you've discovered, 10k will also work.

If you decide to go down the wah enclosure route, adding another pot to set the minimum value is a good idea. A lot of volume pedals have that feature so you can set the minimum volume. It sits between the expression pot and its connection to ground. Like this:

Image

The wiring is no doubt slightly different to what you might be using at the moment as the orientation of the pot changes inside a wah enclosure. Rather than turning the pot clockwise to turn it up like in your current arrangement, inside a wah enclosure turning it up will be counter clockwise if you want to have the toe down position as the maximum speed.
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Re: DIY mini expression pedal

Post by Cdog »

Because Ohm's law! 🤓 (Or Kirchoff's voltage law?) 😜

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