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Carvin Phantom Battery (or killing my warranty)

Discussion in 'Pickups & Electronics [BG]' started by bassbenj, Jul 9, 2012.

  1. bassbenj


    Aug 11, 2009
    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!
  2. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    Very cool mod! Thanks for sharing.
  3. mech

    mech Supporting Member

    Jun 20, 2008
    Meridian, MS, USA
    Nice project and well done.

  4. colcifer

    colcifer Esteemed Nitpicker Supporting Member

    Feb 10, 2010
    A Galaxy Far, Far Away
  5. DiabolusInMusic

    DiabolusInMusic Functionless Art is Merely Tolerated Vandalism Supporting Member

    You sir are awesome... I am more of a hippie than I like to admit so I don't like using batteries, I was wondering why somebody hadn't used phantom power to run their active basses before, it was always the perfect way to run my D.I.
  6. Jazzdogg

    Jazzdogg Less barking, more wagging!

    Jul 29, 2006
    San Diego, CA

    I've been looking for a compact, lightweight, doubler's A/B box that would provide switchable 48v phantom power to an XLR jack (for a condenser mic) and switchable 9v phantom power through a 1/4" jack for an electric bass.

    Out of curiosity, is there a reason you decided to mod your amp (and void your warranty) instead of adding a small external black box to provide the same functionality?
  7. bassbenj


    Aug 11, 2009
    I actually built the box first!


    And then I modded my Laney combo because it was old and out of warranty and had lots of room inside for new stuff.

    No question the box works, but the amp mod is just SO much more convenient! No bunches of wires and plugs and boxes and crap. And then there's only one cord (the amp's) going to a plug instead of a big battle over who gets to plug what or power strips or the like. No extra wall warts to find plugs for etc.

    The amp mod was just plain HANDY! You plug the amp in. You take a TRS cable and plug the bass into the amp. If it's an active bass you flip the phantom power on. If it's passive or if it's an active bass that is still using an internal battery, you flip the phantom power off. If you are using a pedal board (I especially like my optical volume pedal but it takes power) you take the power cord and plug it into the back of the amp. No batteries to worry about, no extra plug spaces for power wall warts. It ALL runs off one line cord!

    After using this system for a while I was just plain SOLD. Now I am thinking about one more "box" mod. And this would be similar to my original box only instead of the box I'd like to somehow cram it all into one of those large diameter speaker phone plug bodies. In this case, you'd have a "special" guitar cord that was TRS on the bass end and had a large diameter mono phone plug on the other. Out of that mono phone plug (which goes to the amp) would come a long power wire to the 1 spot that you'd plug in for power. This would minimize all the extra wires, boxes and plugs. I want it for those times (like at jams) when I'm using one of my active basses on someone else's amp. So in this case all I'd need to bring is the "special" cord. But I haven't built that yet so for now I have to use the box.
  8. Jazzdogg

    Jazzdogg Less barking, more wagging!

    Jul 29, 2006
    San Diego, CA
    Fascinating! Thanks for the link to the other thread. :)
  9. colcifer

    colcifer Esteemed Nitpicker Supporting Member

    Feb 10, 2010
    A Galaxy Far, Far Away
    Is there a way to do this so that you can keep a battery hooked up inside the bass as a backup?
  10. bassbenj


    Aug 11, 2009
    You can always pop out the shorting plug and put in a battery at any time. Which is what I am using as my "backup position".
    I've not had the AC fail yet, but I do like backups. And of course the OTHER backup position is for basses that have a passive bypass. On my Laney combo I actually installed an AC switch on the Wall wart supply so I could turn it off. The idea was that if it should suddenly start smoking, I could just flip it off and turn the bass to passive or at worst, slap a 9 volt battery in it and keep playing. The Carvin doesn't have that feature because I felt is was unnecessary. There I'm presuming that the "1 spot" has a fuse and if it blows up the fuse will blow turning it off. If not, then I'll have to pop the Carvin lid and clip the power wires to it. Since I have two Carvin Amps all I need to do is just turn the bad amp off, anyway. So that is an additional backup.

    It's always good to think about these things BEFORE disaster strikes!

    But if you'd like to keep a battery in the bass ready to go and still use the AC power, you need to have two things: The first is you have to have a bass where the preamp runs on 18 volts. This is because power is applied through the ring terminal which is usually used as a switch to ground. Hence if you put 9 volts on the ring terminal and have an additional 9 volts from the battery to give a total of 18 volts on the preamp. That may or may not be OK with it.

    The second thing is that bass preamp must also work fine with only 9 volts. This is common with 18 volts just giving more "headroom" over 9 volts. So in this case if the AC power quits you simply turn off the phantom power and the bass works just like any 9v active bass would

    Of course with this method the battery is actually supplying the bass with half the 18 volts so it isn't exactly sitting in reserve.

    You could do a "reserve battery" thing but you'd have to put a switch on the bass to go between AC and battery power. In that case the battery wouldn't run down in the AC position. And you wouldn't need an 18 volt preamp.

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