is this possible?

[Valoosj]

My bass player asked me to put a boost into his passive bass, since he has problems with volume differences if he switches to active.
I took a look into his bass, but there is no room for a 9V battery. So I was thinking I could put a stereo jack into his guitar, and have the 9v+ run through the extra wire, and the 9v- through the guitar ground wire. Can this be done, and if not, why then?

[CGDARK]

Yes, it can be done, but it's not practical. I think a better solution will be to build it in a small enclosure and place them on top of the amp so the cable going to the amp will be the shortest possible and it can be turn off when he switches to active.

CG

[Mark Hammer]

You don't HAVE to plan around 9V batteries.  There are plenty of other ways to get suitable power, and if the circuit you use requires minimal current, the options open up wider.

For instance, there are lithium "coin cells" that can be stacked to make 9 or 12V in a small space, and 12v batteries about the size of an AA.  The hard part would be figuring out a means to hold the power source in place.

Alternatively, some folks have used "phantom" power with a stereo cable.  So, the bass gets a stereo output jack, and the 3-conductor cable plugs into into a box containing a suitable power source.  And that could be as basic and bone-headed as a 1590A with a stereo and mono jack (for input and output, respectively) and a 9v battery.  The cable between bass and box carries ground and audio, and uses the third wire to feed 9v from the battery to the bass.

I might point out that the box itself could even be a little plastic unit that is velcroed to the strap.  For that matter, leave the mono jack on the bass, and install a mini (1/8") mono phone jack on the pickguard.  Then run a mini phone plug from the plastic box on the strap (and power source) to the jack and power up the circuit.  That way, your buddy has his onboard preamp but doesn't have to route anything, and can still just run a cable from the bass to the amp direct.

[Valoosj]

Alternatively, some folks have used "phantom" power with a stereo cable.  So, the bass gets a stereo output jack, and the 3-conductor cable plugs into into a box containing a suitable power source.  And that could be as basic and bone-headed as a 1590A with a stereo and mono jack (for input and output, respectively) and a 9v battery.  The cable between bass and box carries ground and audio, and uses the third wire to feed 9v from the battery to the bass.

This is what I meant to do. That way he doesn't have to use any batteries for his active bass either. So I should just install a stereo input on his bass, and let the 9V+ run through the extra wire, and have the 9V- goes to the ground (which is also used for the normal ground on a guitar). And have a little box on his pedal board provide the 9V in this stereo cable.

[Mark Hammer]

Correct.  It will work just fine.

[cobra94]

Just make sure nobody plugs a mono (regular) guitar cable into that box on the guitar side or you'll short out the battery.

[CGDARK]

My bass player asked me to put a boost into his passive bass, since he has problems with volume differences if he switches to active.
I took a look into his bass, but there is no room for a 9V battery. So I was thinking I could put a stereo jack into his guitar, and have the 9v+ run through the extra wire, and the 9v- through the guitar ground wire. Can this be done, and if not, why then?

Yes, it can be done, but it's not practical. I think a better solution will be to build it in a small enclosure and place them on top of the amp so the cable going to the amp will be the shortest possible and it can be turn off when he switches to active.

CG

This is what I meant to do. That way he doesn't have to use any batteries for his active bass either. So I should just install a stereo input on his bass, and let the 9V+ run through the extra wire, and have the 9V- goes to the ground (which is also used for the normal ground on a guitar). And have a little box on his pedal board provide the 9V in this stereo cable.

Correct.  It will work just fine.

Yes, it will works fine, but...

Just make sure nobody plugs a mono (regular) guitar cable into that box on the guitar side or you'll short out the battery.

That's why it's not practical, but possible (with a little care).

CG