At the bass gear review archive site, there is a link for a page that has information reprinted with the permission of Mr. dave King. There he offers advice on different preamps that can be used in his custom built instruments. He says that the Aguilar OBP-1 can handle from 9 to 48V. That is 5 9volt batteries wired in sequence. What kind of benefit would this offer? My Alembic only uses one 9 volt and it is EXCELLENT!!!! Why would a preamp need any more than 18 V? What advantage would 3 or 4 batteries give my tone that one or two wouldn't?