I've got a couple of J basses with the Sadowsky preamp in it.Have not owned or played a passive bass in many years.I never turn the preamp off. Recently a recording engineer in a studio did ask me to turn off the preamp and in the studio the resulting sound was fine. But when I listened to the final mix on a different sound system, the bass sounded really dull and lifeless. I regretted switching off the preamp for the recording. So at home I did this test. Going through my board and my studio monitors, I turned bass and treble to zero and compared the active to the passive sound of both basses (Atelier Z and 74 Fender, Nordie and Ultra Jazz pickups) and there was a huge difference. It sounds like turning the pre off is not a bypass but it actually degrades the sound of the pickups to the point that there's a real drop in volume and all the overtones and some of the lows are missing. Is that possible or am I just so used to hearing the preamp that the real tone of the pickups sounds bad to me? Or does the preamp improve the sound even when it is set to zero?