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phantom power supply

Discussion in 'Question of the Day' started by tenor_singer, May 10, 2006.

  1. tenor_singer

    tenor_singer Active Member

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    Good morning everybody,

    I encountered a problem yesterday with our new sound system that has me baffled. I need to set the stage, though, so bear with me.

    We have four hanging microphones on our stage that are hard wired to our patch bay, but not hard wired to our board. Whenever I use them I patch them through whatever channel is available. They need phantom power to operate and work well.

    Yesterday I set up for a little kiddie musical. The risers were set up well in front of our upstage hanging microphones and the down stage ones wouldn't cover any kids standing in front of the risers. I dug out our old AT boundary microphones (which also require phantom power). When I set them up, they wouldn't work. I tried to change different channels and still nothing. I finally put an AA battery in the power module of the mic and they worked perfectly.

    My question... Why would these channels operate the hanging microphones requiring phantom power but not the boundary microphones? The only thing that I could come up with is that there is some loss of voltage from the booth to the stage (about a 100' run) and that the hanging microphones (being a newer technology than my 10 year old boundary microphones) may still function with this lower voltage. Does this sound plausible?

    I am thinking about purchasing a phantom power supply to keep on the stage for these cases.

    Thanks for any input.
     
  2. AVGuyAndy

    AVGuyAndy Active Member

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    Are you sure the AT mics accept phantom power? I have a few old AT lavs which require AAs, and they will not work on phantom power.
     
  3. tenor_singer

    tenor_singer Active Member

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    They are phantom power microphones. They worked at our old school, which sent a phantom voltage, but at a much smaller run.
     
  4. audioslavematt

    audioslavematt Active Member

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    Grab a shorter mic cable, maybe 20ft., and plug them directly into the back or your console. If they don't work then, we'll go from there.
     
  5. cutlunch

    cutlunch Active Member

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    What mixer do you have? If I have it right is it a Midas? Also what model number microphone are they? This will help us check specifications. Some mikes need the full 48 volts while others will work with a range from 9 - 48 volts.

    Please forgive this question you probably have checked but was the Phantom Power switched on for each channel you were using? I ask because you say that you may use different channels each time.

    You could put a multimeter on the end of the run. If you measure the voltage between Hot - Gnd and Cold - Gnd they should read close to 48 Volts unless there is to big a voltage drop.

    The other thing to check is if there is any shorts on the phantom supply. This can happen through faulty leads. Also if you used an unbalanced to balanced lead that plugs into the XLR mike input this will short the phantom supply and may drag it down enough to stop operating. I had this happen on a rack of wireless mikes I hired once. They had taken the unbalanced output from the receivers and wired it to the XLR's on a rack panel. When I plugged them in they shorted out the phantom. I had to patch directly to the XLR balanced outputs to get around it.

    It may also be the run distance but what I would check first would be to disconnect them all but one ( leaving them in their normal positions at the end of the run) and test whether it works. If it does keep adding mikes to see whether it is a loading problem. If it is then add a power supply at the stage. You can buy commercial supplies or have an electronics person make one up for you.


    Hope this helps.
     
    Last edited: May 11, 2006
  6. Peter

    Peter Well-Known Member

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    I have run into this problem with several mixers and even a dedicated pre-amp unit. If you plug more the a certain number of devices into it, they do not each get the full power they are supposto. A good friend of mine has two sampson C03 mics which have a blue LED to indicate they are getting enough power, and he has a 2 mic preamp unit. No matter what he does, it cannot supply enough power to run them both, he ended up going out and buying another preamp unit and just using one channel on each. I really have never had enough time to measure the voltages, but I realy dont think it's a cable run issue in my case because the runs are really short (<20ft).

    The only other thing I can suggest is that you try a bunch of different combos of channels, or try one mic, and then another and another and so on until you find how many it can handle.
     
  7. Chris15

    Chris15 CBMod CB Mods Premium Member

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    The overloading of the supply does seem like a probable option. Were all the mics plugged in simultaneously? The pother thing is that on some boards, I believe that phantom is supplied to blocks of channels seperately, eg. ch 1-8 have one supply and 9-16 have a different one. Balancing the mics out over all the supplies might help or it might not.

    As far as tolerance for low voltage, as has been said, it may be that the mic needs a full 48 volts but these are rare. If anything, newer technology is less tolerant of low voltage.
     
  8. Willy Wonka

    Willy Wonka Member

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    The mics may not require phantom power. There is a possibility they require AA batteries.
     
  9. Chris15

    Chris15 CBMod CB Mods Premium Member

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    This has already been noted,
    and answered:
     
  10. cutlunch

    cutlunch Active Member

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    Tenor Singer have you found out what the problem with the microphones were?
     
  11. avkid

    avkid Not a New User Fight Leukemia

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    I doubt that the distance should be a problem, something posiibly may have happened to the ground shield(s) which carry the phantom power. I would try to test the cables before doing anything else.

    How long have you been using that patchbay?
     
  12. Dillon

    Dillon Active Member

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    The last facility I worked at had some bugs in their patchbay when it came to phantom power. The voltage would make it through the patchbay (from the console) to the microphone (we could verify this by voltage testing), but we got a very slight buzz in the system whenever phantom power was turned on to a source through the patchbay. The solution was to use some external phantom power supplied which we plugged in on the stage deck at the mic jack. No more buzz. I've heard that the reasoning for this was that patchbays, in particular, are very fickle -- if everything is not electrically perfect, phantom does not always agree with it.

    As far as your problem goes... Phantom power typically does not degrade on a cable, solely due to a distance of 100' (as others have already noted). It sounds to me like your patchbay is the culprit.
     
  13. pacman

    pacman Active Member

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    If you must use a patchbay, the recommended way to provide phantom power is to use a an external power supply on the stage end or somewhere between the stage but before the patchbay. Most sound contractors strongly advise against running phantom power through a bay because the small sparks generated by the 48 volt power when you plug & unplug patchcords will eventually degrade the contacts in the bay to the point they will not reliably conduct the signal. Yes, you lose the console's built-in phantom power supply & have to buy an external source, but you retain your ability to re-route signal inputs to the console.
     
  14. mbandgeek

    mbandgeek Active Member

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    This may sound stupid but have you tried turning the gain up.

    I have found myself doing that.
     

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