So after being fed up with replacing the batteries on my bass, I've had a little idea for a kind of 'phantom power' box for powering an active instrument from an external pedal, without having multiple cables going to the instrument: Basically a stereo cable connects the 'active in' to an active bass, guitar or just about any active instrument (so long as it has a stereo jack). The tip and sleeve connect to the hot and ground as usual, while the ring carries the +9v signal. It has a passive input too as I intend to use this at the start of my pedalboard (so I can use an active or a passive bass), and there is a footswitch to toggle between the two (no option for both at once though), the LED is there to indicate when the active signal is in use. The +9v would just come from a regular power supply, and could even be +12v or +18v depending on what's required by the instrument (could even be a mod to a keyboard for example). The project does involve modding the bass itself - so if a battery is required at some point, it wont disconnect from the circuit when no jack is plugged in like a regular active bass (the negative terminal on the battery would have to solder directly to ground), so that would be a potential downside to this project. Some extra considerations: 1. Make sure a stereo lead is used. Also make sure the pedal is switched to the passive input when plugging stuff in to prevent damage to electronics. 2. An XLR cable, or any similar 3-conductor cable could potentially be used instead of a 1/4" stereo lead. 3. Try a resistor on the 'active in' to reduce the input so that an active signal will match a passive one. Also remember that, depending on the kind of LED used, a resistor is usually needed in front of it, otherwise you'll blow up the LED with the 9v signal (trust me, I've done this). 4. A passive input is not required. Removing the passive input means you wont need a footswitch & LED (just make sure you don't turn on the power supply until you instrument is connected to the pedal). 5. This would be particularly handy when converting a passive instrument to an active one, and would mean that you don't need to worry about routing out space for a battery. If I have missed something, or if I'm just plain wrong here, please let me know, as I'm still only an amateur when it come to this stuff, and would hate to be unintentionally misleading people (and myself).