http://www.ernieball.com/faq_content.php?subjectcode=vol_pedalsQ: When would I use an active (25k) pedal as opposed to a 250k/500k "passive" pedal, and why?
A: Passive vs. Active: Whenever there is a passive signal leading into an EB pedal, the 250K or 500K pedal is recommended (mono VP & VPJR 250K and stereo 500K VP pedals available). Whenever there is an active signal (powered preamp in the instrument, effects loop, etc.) leading into an EB pedal, the 25K pot is recommended (stereo VP and mono VPJR pedals available). If an active signal is placed before a 250K or 500K EB pedal, or if a passive signal is placed before a 25K EB pedal, then the consequence may be that the swell of the pedal does not act as designed. Either way, as stated above, try whatever combination you desire, and determine if it works for you. All of our volume pedals are designed to be as transparent as possible in a signal chain. However, whenever you add any component to a signal chain, the signal will change whether it is audible or not. Keyboards are generally served best by the 25k pedals as well.
