after installing some DiMarzio ultrajazz pickups in my Jag a couple of months ago, and not being extremely thrilled with the Jag's kinda loose, and boom/sizzle stock preamp (treble and bass controls) i just modded mine by installing an EMG BTS system in it. the EMG's treble and bass controls have center detents (as a reference to flat), 4 selectable treble frequencies, a better bass boost/cut frequency as well as a cleaner, more punchy circuit. (the fender circuit was just about all boost). i didn't want to route or modify the body in any way, so in order to use the jag's stock thumb wheels, i had to order some 50K linear pots with a shorter threaded mounting shaft that still had a center detent. here's a pic of the EMG pots: here's the new pot as compared to the EMG one: i also had to bend the 5 pin connector 90 degrees so it would fit underneath the switch in the upper control plate cavity. here's a pic of the new (bass control) pot wired to the EMG's main pcb: here's a pic of the new treble pot (left) and EMG treble pot mounted to it's pcb: and here's a pic of the new treble pot wired to the pcb: i used very thick 3M heavy duty clear double stick tape to mount the main pcb in the cavity, and the small one on the control plate: and finally, i used the old preamp's cavity under the pickguard to add another 9V battery in series to the original one, so the system runs on 18V for better performance and maximum headroom: the test results: well, first i had to reverse the outer wires on the new pots since the controls worked backwards (easy one minute fix). once i got them running the same way as the original controls, i gave it a listen. this preamp is TONS better. it's still completely bypassable (with the switch on the upper control plate), but i actually prefer to always leave it on. in the center detents, the tone does not change, but a very slight rise in gain occurs, i suppose due to the buffering. when you roll the volume down, it's tone stays pretty much the same in any position (the highs don't roll off near as much as in the passive mode). the dimarzio ultrajazz bass pickups in this bass sound great and are extremely quiet. when the preamp is kicked in, there is no additional hum, but there is a very slight amount of hiss added, which is normal for any preamp that is buffering/boosting signal and frequencies, and is much quieter than the fender preamp that it replaced. i have an EMG VMC (variable midrange control) on its way to me and i'm going to experiment with replacing the jag's passive master tone with the EMG's mid control. it has concentric pot (freq on the ring and center detent boost cut on the upper) so i also ordered the fender stacked knob kit that looks like a regular jazz bass non-stacked knob (not a conventional jazz bass stack knob) fo it. i'm generally a passive bass guy, but after using my EMG JV/TBC jazz bass at the last gig, and loving it, i thought it might be cool to have treble, sweepable mids, and bass controls all on board at least one of my fender basses. i mean, the way i see it, i might as well take advantage of all the knobs and switches that they put on that thing.