Thanks for yours messages
I'm gone this morning in the shop to try a preamp : the Hartke
VXL Bass Attack (xlr direct out put, harmonic control).
It gives more volume with the fonction sharp, this fonction sharps the medium sound 80 hz to 1khz(with the preamp i have the same volume as with my bass without preamp).
The preamp has a little equalizer (bass, treble and brite). The sound was correct but not ideal and the problem is thath it gives the rubbing sound of my fingers under the strings

(scratchhhh, scratchhh, scratchhh) but i think this comes from the piezzo fishman bp 100. I don't know the double-bass material, but i read a lot of bad review for this pick up under internet. This is the most sold but it isn't the best.
I see thath a amp marshall isn't a good amp for doublebass, a gallien krueger would be better. Marty, i don't understand what you want to say when you tell : Is that a
PA system? (escuse my english).
I don't know what to do, buy a new pick up or the preamp hartke. I have not a lot of money and i just play doublebass with friends and make little concert with my music school. I can buy a pick up like kk bass max or sd system lcm 100 with one preamp lp (pick up active + preamp for 300 euros) or buy the preamp hartke (130 euros) with i can play with my bass and my double bass.
Is it any one who have a sd system lcm 100 ? what's the sound ? do you think is it normal to have rubbing sound with piezzo, is it different with active pick up ?