A passive bass uses a potentiometer ( or a couple )to roll of treble for tone giving you limited E.Q options as. This I understand. I've heard of 3 things active pickups , active E.Q and basses with preamps. Active E.Q lets you boost treble and bass by adding gain via power supply ( ie. 9 volt battery ) My bass has a bartolini pre-amp which has switchable e.q , besides added gain what does this do for me... can I plug a bass with an onboard pre-amp into a power amp and play? Active pickups.... is there such ( well yeah ) a thing and how do they work?