One of the great tricks of volume pedal is that you can use it as an expression pedal. Ernie Ball VP Jr is one of the most popular volume pedal models. However, when you hook up Ernie Ball VP Jr volume pedal with Line6 HX Stomp (or any other Helix product I guess), one problem comes up: when you roll the pedal from heel to toe, the position shown in HX Stomp goes from 0% to 100% and to 0% again. Based on my testing, this is because the resistance of VP Jr’s potentiometer is too big (250kohm). After switching to 25kohm, the issue is solved.

1. Typical Method of connecting volume pedal as an expression pedal
   • Use a split cable: 1xTRS connector to 2xTS connector. plug TRS into master effect, 2xTS go to the volume pedal’s IN and OUT.
2. HX Stomp Method of connecting volume pedal as an expression pedal
   • Use a TS to TS cable, connect volume pedal’s OUT to HX Stomp’s EXP1/2.
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3. “0%-100%-0%” Issue
   • when you roll the pedal from heel to toe, the position shown in HX Stomp goes from 0% to 100% and to 0% again.
   • Root cause is the 250kohm pot that VP Jr comes with. 50kohm pot solves this issue.
4. Change Jr VP’s pot
   • where to order pot. (https://www.amazon.com/dp/B001FWYB1G?smid=ATVPDKIKX0DER&ref_=chk_typ_imgToDp&th=1)
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   • Steps
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5. During the process i found a small switch on PCB, after looking at it closely, it is just simply paralleling a 222ohm fixed value resistor with the potentiometer. After flipping the switch up, the resistance curve (red below) is not linear anymore. It seems this switch is designed to make the sound more “gradual”.
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Appendix

*TRS, TS: Tip, Ring, Sleeve.