Just purchased a used Tribbie L2500 sight unseen and have some wiring issues. Bass works perfectly fine passive, but when I engage the active preamp, i get very low output and when I dig in REALLY hard, the preamp LOUDLY distorts. I checked all the wiring and it seems to be correct and I checked all wires for bad connections or shorts and I could not find any. I'm thinking that the OpAmp is bad or biased incorrectly so I ordered a new OpAmp since it was only about a buck. Any ideas on if my preamp is totally toast and biased incorrectly or am I on the right track here? BTW, bass sounds absolutely awesome in passive mode.
I know it's stating the obvious but have you checked/changed the battery? If you leave your cord plugged in the battery continues to be drained even if you go passive. My Dingwall generates a high pitched whistle when the battery is dying and my Yamaha TRB would lose tone, volume and sound distorted. If you get in the habit of unplugging your bass every time you put it down (even on breaks) you'll get at least 6 months out of a regular Alakline 9 volt. If you don't unplug it, it will likely drain overnight.
I should have mentioned that I tried multiple batteries. Sorry about that one, that was my first test though. Thanks!
You mentioned that you checked the wiring, but if you haven't also checked the wiring going to the battery connector, I'd do that. I don't what kind of connector the L2500 has, but I've had another active setup where the wires on the battery connector itself had come loose, so even good batteries didn't really power the circuit very well.