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FOH issue. Playing Live might be damaging my Gear!

Discussion in 'Live Sound [BG]' started by chaak, Nov 19, 2017.

  1. chaak


    Apr 25, 2013
    now here

    I have this live gig once every two weeks at a very chill and wonderful venue on the beach (literally). The gig consists of two percussionists (both mic'd) a guitar player (mic'd combo amp) two singers ( on some tracks only one, and on others none). We play original music (Neo Soul, Funk, Rock Fusion, and the occasional blues when we are joined by a harmonica player).

    Not to drift too much from the main issue here, I am the only one using a D.I. and a monitor.
    I am using my active Five strings for that gig going through my pedal board (compressor>octave>envelop filter>) Radial JDI and into the mixer.

    And as I always do when i play live I specify and make sure the sound guy does not have phantom power on my channel. But that venue is different, it seems the mixer has only one phantom power switch and that provides all the channels with it. You cannot bypass a channel. And this is where I am really worried. I have high end gear down to the cables. I would like some help first in identifying if that phantom is damaging my gear and second how to solve that.

    Thank you.
  2. If the last component of your signal chain where you connect the XLR the sound guy hands you is a simple transformer type DI box, your equipment will be isolated from any DC voltage feeding out of the mixer. For example, a Radial DI box.
  3. walterw

    walterw Supportive Fender Gold Supporting Member Commercial User

    Feb 20, 2009
    from the FAQ on the radial JDI:

    "Will 48V DC phantom power harm the JDI?
    No. The transformers will block the DC without any concern."
  4. Mark Reccord

    Mark Reccord Supporting Member

    Yep as @walterw and @Hoochie Coochie Man said above, the JDI's transformer can safely handle phantom and will block it from getting into the rest of your gear. You're good to go with that setup.
    Gearhead17 and LiquidMidnight like this.
  5. BurningSkies

    BurningSkies CRAZY BALDHEAD Supporting Member

    Feb 20, 2005
    Syracuse NY
    Endorsing artist: Dingwall Guitars
    Also, if you're super paranoid, the phantom is on the ground of the XLR. Lift the DI ground if you can. I live with my DI ground lifted by default and only turn it on when there's a noticeable problem on the bass channel at FOH.
  6. You should not assume that lifting the ground on a piece of audio equipment will remove phantom power from the circuit.

    Phantom power is applied to pins 2, and 3 through current limiting resistors, with the return being on pin 1.

    While an isolating transformer will block the DC phantom power, lifting pin 1, (ground) in a non-isolated circuit, will not remove phantom power from the circuit if the XLR connector pin 1 on the equipment being fed is connected by some other path to a ground that is close to the same potential as the source of the phantom power source circuit return, (ground).

    A dynamic michrophone, like an SM 58, won't see the phantom power because it is connected to pins 2, and 3 only with no possible means to complete the circuit to pin 1.

    Equipment that contains a power supply derived from the AC mains supplied by a three wire grounding power cord, (like another mixer, electronic instrument or amplifier without some method to also lift pin 1, or block DC in the circuit) may have a low resistance from its XLR connector pin 1 to the same ground as the phantom power supply circuit. This is why you should take care when spitting signals from stage to two mixers via a splitter snake to record or create a monitor mix separate from the FOH mixer.
    Last edited: Nov 30, 2017

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