I'm unclear about active pickups. I have an Ibanez Sr 300X with a p-bass style split coil in the neck position and a jazz style single coil in the bridge position. The bass has a 9-volt battery inside. Are the pickups themselves active or is there preamp that makes the bass active? I'm thinking of upgrading the pickups and want to make sure I understand what's what before spending the money. In otherwords, do I buy active pickups or passive pickups?