Regarding what John's been saying about thinness in the PJ config, I've got 4 PJ's with different pickup configs, and just went through them all listening with headphones.
The SX with the stock vintage style pickups had a definite loss of balls on the upper notes when in full PJ mode and only slightly less when you rolled off the J pickup a little. The 76 Precision with the 62 CS P and the DiMarzio Ultrajazz fared way better. It did the standard phasing/volume cut thing with both full-on, but it was still a pretty ballsy tone. And backing off the J pickup, I didn't notice any lack of balls at all. The parts P with the DiMarzio Model PJ's, ditto, only with more output and less highs. The P Lyte with EMG PJ's is seemingly bulletproof against phasing out with both on full, and has no lack of balls, either.
Too bad it's not as simple as humbucker vs single coil, though. I used to run the Ultrajazz (humbucker) in my P Lyte along with a Duncan Quarter Pounder P (humbucker), and hated the Ultrajazz because both pickups on full made the high notes noticeably phased out and weak. I replaced the Ultrajazz with a QP J (single coil), and while it wasn't bright enough for my tastes in that bass, it sounded much better and much fuller. And it looks like getting matched PJ sets may help, but not always since the SX "matched" set didn't do so well, and the Ultrajazz that sucked the life out of one bass made the other pop.
So apparently luck is the biggest factor in getting a set of PJ's to pop.
The SX with the stock vintage style pickups had a definite loss of balls on the upper notes when in full PJ mode and only slightly less when you rolled off the J pickup a little. The 76 Precision with the 62 CS P and the DiMarzio Ultrajazz fared way better. It did the standard phasing/volume cut thing with both full-on, but it was still a pretty ballsy tone. And backing off the J pickup, I didn't notice any lack of balls at all. The parts P with the DiMarzio Model PJ's, ditto, only with more output and less highs. The P Lyte with EMG PJ's is seemingly bulletproof against phasing out with both on full, and has no lack of balls, either.
Too bad it's not as simple as humbucker vs single coil, though. I used to run the Ultrajazz (humbucker) in my P Lyte along with a Duncan Quarter Pounder P (humbucker), and hated the Ultrajazz because both pickups on full made the high notes noticeably phased out and weak. I replaced the Ultrajazz with a QP J (single coil), and while it wasn't bright enough for my tastes in that bass, it sounded much better and much fuller. And it looks like getting matched PJ sets may help, but not always since the SX "matched" set didn't do so well, and the Ultrajazz that sucked the life out of one bass made the other pop.
So apparently luck is the biggest factor in getting a set of PJ's to pop.

