Here's the scenario: I've got several different 3 band on-board preamps (Aguilar OBP-3, Bart NTMB and Nordy 3 band) mounted in pedal style boxes with bypass footswitches so I can do direct comparisons and also use them with passive basses that I don't want to modify. I've been running them each on their own 9v battery and everything works fine. I recently put them all on a makeshift pedalboard and wired them to a common 9v supply, so that I can leave them all wired up without running the batteries down. Here's the problem: They all work fine in that configuration, but for some reason the Nordy preamp has a lot of hiss and noise on the output, even with the preamp gain trimmer and the EQ pots on minimum, but only when it's running on a 9v supply. It's well below the bass signal level, but very noticeable when I'm not playing. It's nice and quiet on a battery. I've tried two different supplies, various value filter caps on the 9v line to the preamp board, checked my wiring several times and called Nordstrand. The guy I talked to had no idea what would be causing it because they've always run them on batteries. They're very busy getting ready for NAMM, so Carey wasn't available and I didn't want to be a pest over relatively minor problem that's probably being caused by me using it in a configuration for which it wasn't designed. Like I said, it's a minor problem, but it's bugging me that I can't correct it. Anyone have any ideas on what could be causing it and what could be done to correct it?