I have emailed /called Fender & Squier on this: Trying to find out where or who made the active circuit for Squier basses. No response. The tech dept & customer service is an infinite hold zone. Is it an active EQ or full on pre-amp type ? So I ask fellow TB'ers if they have any idea ? This was all prompted by my desire to change the p/u's in my active Jazz. In the past, 99% of my basses have been passive and I just threw Dimarzios in and off we went. The 1 % ? Well that was my Wal Pro II custom fretless, enough said on that one ! So I have been enlightened that active basses use Lo impedance p/u's therefore no Dimarzio pick up will work since "we do not make any Lo-Z pickups " as stated by one of their fine Techs, Who answered within 5 seconds of me calling ! The whole reason for a swap was thinking that the stock pick ups were inferior to what is aftermarket. The bass does sound very, very good once one dials in 'their' tone. So any further info or theory on whole active circuitry is very welcome. UPDATE : As I posted this, I just rec'vd this from Fender: "From what I can tell this is an active EQ system. I have included the wiring diagram for this Bass for your records. I do not have any specific specs on the pickups but they are a traditional passive setup and we do not have a parts list so I do not have a record of the manufacture of this unit." The .pdf schematic is pretty general, it is for a 5 string although I have the 4 string model.