I have two passive 4-string Jazz basses: Fender Standard Jazz (MIM) and my backup Jazz clone (ash body). When moving 3 different sets of pickups back and forth, I noticed a big change in sound. Jazz clone has much more bottom than Fender with same pickups. Difference is really noticeable. It could be because of the strings: I didn't move them, they are different brand but same gauge. Next time I change strings, I will put heavier gauge on Fender jazz. It could be pots, but it shouldn't affect low freqs, right?