Carvin BX 500 Phantom Battery Carvin had a sale and I bought two BX 500 Carvin light weight heads to put together a new rig. So far they seem pretty nice although the new rig is not done yet. One reason was that my old rig uses "phantom power" to run most of my active basses. I wrote that system up here before. So the new heads needed modded to allow me to run my active basses. To review the way it works is you use a TRS cable instead of a standard guitar cord and the "ring" terminal supplies 9 volts from the head to the bass. The 9 volts is supplied by a "1 spot" pedal board supply wall wart. [WARNING: turning phantom battery on when bass still has a 9v battery will put 18 volts on the bass preamp which it may or may NOT like! ] Thus Modifying the Carvin heads involves, mounting the "1 spot" inside the box and wiring the 9 volts to the input jack "ring" terminal. An LED and mini switch is added to the front panel to turn phantom power on and off with the LED as an indicator. When power is OFF the Ring terminal is grounded so a normal active bass with a battery can be used even with a TRS cable where the switch grounds the bass battery to turn the bass on. Each active bass needs the battery replaced with a shorting clip as shown below. The modded Carvin front panel looks like this with new phantom power switch and LED. Phantom power from the wall wart is ALSO run to a back panel jack which can be used to power a pedal board from the head. NOTE that pin here is positive while Pin on "1 Spot" is negative. Thus a cord wired "twisted" needs to be used. Here are the wiring details and parts list: And here is how I mounted the "1 spot" inside the case: The Wall wart is stuck down with double sided sticky foam but also has a mechanical clamp just in case. And here are a few mechanical details. I really LOVE this system. Note that not just ANY "wall wart" will work! The "1 spot" has short circuit protection that is VERY necessary when the jack is removed with power on (not recommended!) I think this kind of phantom battery is a new era (game changer...heh!) in bass. The reason being that NOW one isn't limited by battery current as to what you can build into your bass. For example one of the first things I'm going to add is LED fretmarkers for all fretless basses. I can use tons of current and not worry about batteries! And just one thing. These Carvin heads are brand new and obviously I just trashed my warranty on them! So you had better be sure they are working right before you start! And be SURE to keep metal drilling chips OFF the circuit board!