I've been using a standard J/J Activator set (including the original 2x volume & 1x low pass filter pots that come with it) for 10+ years now. Since the instrument they should go into may make a difference, here's what mine have been sittin' on since August '99: 2-pce swamp ash J-body; 3-pce hard rock maple J-neck with rosewood fretboard and graphite inlays; Schaller bridge and tuners; graphite nut; satin finish; medium light GHS Boomers.
The sound? They're amazing! They make any J sound better, more hifi (no way keeping those harmonics hidden, not even with the filter closed all the way, so you'd better refresh your string-damping skills!!). Both volume pots offer output adjustment on the circuit board. This set is capable of pushing any (pre-)amp to its limits (I use a solid state class A pre, renowned for its huge headroom, yet it soft-clips wonderfully!).
Turn the filter all the way up, full neck PU and bridge rolled a little back, hit that open E and a certain guy named Miller comes to mind immediately, no matter how old your strings are! Or turn the brigde PU down a little more and tweak the filter down to the right hi-mid peak before rolling off. Sound familiar? That's Abe Laboriel's cutting P-sound, great for making those slides/vibrato's. Jaco? Stanley? Anthony Jackson in his Chaka days (add a little flanging..)? They're all living in your bass and all it takes to get them out is a 30-minute, solder free connecting job.
It takes some time to get used to the sheer endless combinations the 3 controls offer (just listen to what shifting the filter pot by as little as 1mm does!!), but once you've heard your bass with Activators installed, there's no going back to the (passive) stuff installed on regular J's (unless you're a huge Duck Dunn-fan and proud of using the original 1964 factory-installed strings: then these PU's may not be your cup o' tea). Hope this helps. Otherwise, feel free to ask.