Hello there guys, I wanna ask you all very serious and important questions, because I really need big help and I hope you can help me. So I’ve got an discontinued very cheap 2007 British made Vintage V800BK bass with small body and P/J pickup configuration, the only thing I wanna do is to upgrade and change the pickups and the electronics to sound completely passive and loud without using active preamp, because the original passive ones have a very low output. I have another Squier P bass which have a more large body then the Vintage and more high output, so I made a test by taking out the P/J pickups from my Squier and put them on my Vintage and the result is the same low output quality actually. So does that mean if the body is large the output is high because the wood is resonating more when is large, and if it’s small the output is too low because the wood is not resonating much when it’s small size?
if it’s that should I buy a high/hot DC resistance pickups to get high passive output from bass with small body, or putting A500k instead of A250k logarithmic pots, can you tell me what I should do to solve the problem please? Thank you 
Output from the instrument itself is calculated by the pickup output itself (number of windings/resistance ohms) and the distance of the pickup pole pieces to the strings. How far away are the pickups from the strings on your small bass? If it’s outside of spec (like 6/64 when fretted at the final fret) you’re always going to have volume and output problems regardless of the winding output. If you have a spare 3/4” jack and a multimeter that will read resistance you can cut and strip the wire and hook each lead to the +/- of your multimeter and check the output of each pickup with the pickup selector.
Pickups do not care about the wood, they are a transducer that senses the movement of the strings. If you’re getting low output it’s likely either something else in the electronics or the distance from the pickup poles to the strings.
This is almost assuredly just pickup height and action height.
Ok @BasistaFunky what’s the reason for hotter pickups?
Are you using headphones amp? Small amp?
What sort of sound/ tone are you looking for? What kind of musicology you play?
Easy answer is to get a relatively affordable high output set and get your volume, but it’s
There are a lot of benefits in running low output pickups. I can understand that the pickups you have on the vintage is not high quality enough but you can switch it to another low output pickup.
Most lower end basses come with high output pickups mainly because most of the time they’d be paired with small (beginners) amp the high output pickups makes the combo easy to drive.
Personally, I think a harder to drive pickups offer better tonal package than the hotter ones.
On the side note; not all actives systems are equal. Many people misunderstand the “active tone”. That’s another can of worms altogether, lol