Hi there, i was wondering what kind of amp / preamp / effect i can use to mimic the classic 70s P Sound (for instance the sound of Roger Waters in Another Brick on the Wall or the sound of the very early Steve Harris). I own a 83 P Bass with maple neck, but it doesn't have the classic crispy highs and high-mid frequencies of a 70s bass.
Try rotosound strings ,valve ampeg,hiwatt /70smosfet amps( accoutstic,trace Elliot & boosting the mids!
They both used Rotosound 77 strings for their classic tones, I'd start there(Keep in mind that Steve used a new set for every gig). You could look into different pickups as well, like the Seymour Duncan Antiquity(Very vintage) or the SPB-2(What Steve Harris uses, very crisp and clear in the upper mids with a HUGE mid-bass/low-mid presence). An Ampeg or Hiwatt all tube amp would bring you closer to that 70s sound as well.
FWIW, I have a '76 P that came with the original pups, and IME Fender's '62 Original P pups sound nearly identical to my '76's original pups - Seymour Duncan's SPB-1's do also, with a tiny bit more lows... In your situation, I'd start with a set of either of those, and some strings like those players used, THEN think about amp changes... - georgestrings