i use ampeg myself
if you don't mind jazz pickups, you could try the RBX4 A2. It's very lightweight and very yamaha.
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i guess lightweight BB are out there. i see some 8lb weights advertised after a quick internet search. unfortunately i haven't run across them personally. Yamaha sort of advertised lighter weight and smaller bodies with the recent BB234,434,734a,P34 series but from what i've seen, it's only about half a pound or so, bringing a 9-10lb bass down to 8.5-9.5lb range. i guess there are some that are a little lighter due to the wood density.
you probably know this, but the 734a and P34 have an interesting alder/maple sandwich construction. how that affects weight and would be affected by chambering would be interesting to know.
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