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Phantom power ??

Discussion in 'Live Sound [BG]' started by vinny, Jun 8, 2011.


  1. vinny

    vinny

    Apr 3, 2006
    Las Vegas, NV.
    My board (Mackie 1604 VLZ III) has phantom power which the girl singer needs for her microphone. My bass amp (G-K 1001 RB II) can't have phantom power, according to the manual. For this reason I can't line out from the head to the board. Can I safely use a Radial JDI between my bass & the amp to DI to the board without any consideration for the phantom power? In other words, will the JDI isolate the bass amp from the board's phantom power?
     
  2. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Yes, a passive transformer DI like the JDI will isolate the amp from the phantom power.
     
  3. vinny

    vinny

    Apr 3, 2006
    Las Vegas, NV.
    Thank you.
     
  4. teleharmonium

    teleharmonium

    Dec 2, 2003
    Typically phantom power on the board is only available at the XLR mic inputs for each channel - if there is a separate 1/4 inch line input for the channel, as there is on many mixers, it's probably not seeing the phantom power.

    You can verify this with the manufacturer, but if so, and if you have a line level output from the amp, you could go in through that input without needing to buy anything else.

    (With the possible exception of an XLR to 1/4 inch cable in the event the amp DI output is on an XLR connector.)
     
  5. vinny

    vinny

    Apr 3, 2006
    Las Vegas, NV.
    That's good to know too. I was XLRing in, but I don't have to. I'll check the manuals to see if they're separated on my board. Thanks again.
     
  6. MNAirHead

    MNAirHead Supporting Member

    over the years.. I've learned it's much more prudent to have external phantom power boxes for these applications.. permanently disable it on the board.

    I always send out of a transformer DI box to ensure phantom doesnt' knock something out.
     
  7. Medford Bassman

    Medford Bassman Supporting Member

    Aug 8, 2007
    Medford, Wisconsin
    The Allen & Heath MixWizard that I use has selectable phantom power for each individual channel. So much nicer than our old board where either every channel had it or not.
     
  8. JohnMCA72

    JohnMCA72

    Feb 4, 2009
    I'm pretty sure Mackies are "all-or-nothing" regarding phantom power on mic. channels vs. per-channel.
     
  9. teleharmonium

    teleharmonium

    Dec 2, 2003
    Right, but I'm asking if it has separate 1/4 inch inputs for each channel that don't see phantom power. If so, using one of those makes phantom power a non issue regardless of whether it is on globally.
     
  10. vinny

    vinny

    Apr 3, 2006
    Las Vegas, NV.
    The Mackie manual does indeed say that the 1/4" inputs on each channel don't share the phantom power. Thanks for prompting me to look up an answer for which I didn't know the question.

    Also, the G-K manual says nothing about phantom power, so I don't know where I got that idea from.
     
  11. I've never heard of anyone running DC power through 1/4" connections. Phantom power is used on XLR inputs of all signal levels and impedances, but not 1/4" inputs. Though 48V at a couple of milliAmps should not be dangerous, it is not a good idea to have DC power live on a 1/4" male connector. The connections are completely open. Also, the connections briefly short when you insert and remove 1/4" connectors.

    If you don't want phantom power, add an isolation transformer as inductive coupling to block the DC.
     
  12. teleharmonium

    teleharmonium

    Dec 2, 2003

    That's exactly my point with respect to mixer inputs, which as you can see by reading the thread, has now solved the issue for the OP.

    In other applications, there are indeed uses for sending DC on a 1/4" TRS cable. For example, my upright bass uses a piezo and a mini electret condensor, and low voltage phantom power from the preamp as well as both audio signals share the same cable.
     
  13. Interesting. I guess I'm not familiar with uprights. :hyper:

    Btw, there are several applications in which a short-protected DC power source is applied to the ring terminal, with an unbalanced signal at the tip. The Line6 Variax guitars, for example, can be powered on 9V at the ring terminal. (AFAIK, their current consumption is quite high.)
     
  14. georgestrings

    georgestrings Banned

    Nov 5, 2005

    You sure about that??? - I ask because I just looked in my 700rb-II&1001rb-II Owner's Manual, and can't find that anywhere in it...


    - georgestrings
     
  15. vinny

    vinny

    Apr 3, 2006
    Las Vegas, NV.
    Yeah, I checked it again too & it isn't there. I don't kow where I got that from. Maybe bad info from th G-K forum.
     

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