I have Ernie Ball's VP JR, the 250kOhm version. It does not work very nicely with KPA as expression pedal that controls volume. I have it connected in Pedal 1 input in back of the Kemper.
With this pedal the curve is weird, and I got this reasoning from Facebook's KPA users group for it:
"The problem is almost certainly due to the fact that the volume pedal has a Log Pot (audio taper pot) but the KPA is expecting to see a Linear pot. For volume control the KPA already has a Log taper programmed in so you are doubling up the effect which will give strange results."
It really feels like that. Should I replace the pedal's pot into linear one? I also saw somewhere that the Ohms should be with a value between 10kOhm - 100kOhm. So is the 250kOhm part of my problem?