Without seeing the way you play, how you have your bass set up and how old and thick your strings are, it's not really possible to say what's going on with your playing. I'm guess that Larry's sound was either direct into the board, or a mic'd ampeg - something like that. The sound was in his hands, not his gear - it's a cliche but it's true, sadly. If only you could buy a 1U rack of Larry's sound, we'd all get one! :o)
Old school sounds are normally got with old school gear - passive musicman and fender basses through ampeg and fender amps seemed to be the order of the day in the 70s.
a compressor will 'squash' you sound - it takes the loud notes and softens them, and the low notes and makes them louder. With a slap sound it can make it sound slightly crisper, but it depends on what controls are available on the compressor in question - if you have control over the attack, release, the 'knee' and the ratio, you can shape a slap sound with that. If it's a two control job, you might struggle...
experimentation is the key... :o)
Steve
www.steve-lawson.co.uk
