The preamp may be of some value if you are running into a PA (using your bass rig or not). I ran into this a while back. Wasn't getting any volume when I ran through a direct box into my rig and out to the PA. I plugged in an MXR Micro Amp I happened to have in my bag and it solved the problem. I posted videos in the first part of this thread, but so you won't need to search, here you go. Not the greatest quality(iPhone video) but you may get the idea. From that night:
ManicDepression Cover By Fatso LIVE KALA U-BASS - YouTube
Fatso- Sara Smile - YouTube
ManicDepression Cover By Fatso LIVE KALA U-BASS - YouTube
Fatso- Sara Smile - YouTube
