hello Rob,
just to know before buying will the Midi Expression work with the Ernie Ball Vol Jr 6181? It's the active version with the 25k pot. I tried to connect it as exp pedal with other systems (KMI Softstep and Kemper Profiler) via a send return cable and the sweep of the pedal works only in the extreme latter part (almost near the end or the toe), but it works very well with Mission Engineering Expressionator.
...maybe I'm lucky and you already tested this with your product as it's a pretty common pedal?
Unfortunately, I haven't tested it. Because it has a 25k pot, I would expect it to work reasonably well. I've used other pedals with 50k pots, and while not perfect, they perform well enough. Keep in mind that it's a volume pedal, so you'll need to use the expression curve to make the response linear. If you do buy a MIDI Expression and you find that it's not working well with that pedal, you can always just mail it back to me and get a refund.
I have just received my Quattro and I have a Ernie Ball Jr 25K pedal hooked up to it and it's working very well. Note, though, that I also have a softstep and I am finding the same pedal works well with it too! That said, I like connecting it to the Quattro more because I can adjust the curve.