Out of the box, my OLP Tony Levin was a nice bass straight away. It played well, had loads of bottom end, but just lacked a little top end sparkle. Compared to my Musicman Stingray the build quality wasn't brilliant in some places, but for the price I was very happy.
Then I gigged it. Again, nice playability although the strings are a bit close together at the nut for comfortable slapping, but I adapted to that no problem.
The big issues were 1: a horrendously cut nut, 2: an awful hissy treble pot, and 3: the lack of top end.
So I decided to pimp it, because the EQ was pretty poor, and I couldn't live with that pathetic nut, I did the following;
Nordstrand 5.2 pickup, John East 3 band EQ, Brass nut, Musicman battery box (the OLP one was terrible), 3 way switch fitted.
It cost a bomb to do, but as I've said in other threads, the bass was a gift from the Mrs, so I don't mind.
The Nordstrand was a luxury rather than a necessity, but the other upgrades were vital IMO. Having said that, the Nordstrand has transformed the tone immeasurably.