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Phantom Power

Discussion in 'Electronic Design' started by HardySpicer, Nov 11, 2007.

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  1. HardySpicer

    HardySpicer Guest

    What's the best way to provide 48V phantom power for a portable
    battery operated microphone device. Obviously a dc-dc convertor of
    some sort. Let's assume the power supply is dc 9V.If I were doing it
    from scratch I would make an oscillator - step up the voltage then
    rectify.

    Hardy
     
  2. Eeyore

    Eeyore Guest

    Be careful about getting the switcher noise into the audio ground.

    Graham
     
  3. Bruce Varley

    Bruce Varley Guest

    If you haven't checked the actual voltage requirements already, it would be
    worth doing. I have a phantom powered mike for which the rated voltage is
    48v, but speced minimum is 9v. It works fine at 8v as well.
     
  4. Barry Lennox

    Barry Lennox Guest

    Try it at 9 volts. Most still work fine. I use a Behringer ECM8000
    measurement mic at 9v, but the spec says 48v I believe they mean that
    to be a maximum.

    Barry
     
  5. Eeyore

    Eeyore Guest

    48V is one standard but many mics work on as low as 12-15V. I've yet to meet one
    which works as low as 9V myself.

    The phantom power resistor value may need reducing from 6k8 with the lower
    voltages.

    Graham
     
  6. I was thinking of one of those tiny class D speaker amps, wired as a
    wien bridge osc, with suitable lightbulb (fet stabilisation should
    obviously never be used for audio :) into a little step up tranny
    and a rectifier. Might work quite nicely


    Martin
     
  7. Speedskater

    Speedskater Guest

    What happens the day you need to use a microphone that requires most of
    the 48 Volts ?
     
  8. Barry Lennox

    Barry Lennox Guest

    Duh, it won't work.

    That's not conceivable in my setup. The only decent mic I own, and
    use, is the ECM8000.
     
  9. I once had a U87 connected to a phantom supply that was turned off
    accidentally during a performance. The sound quality didn't change
    noticably, but it just got quieter and quieter over several seconds as
    the supply voltage died. I had the faders on the desk up full to
    compensate before I realised what had happened.

    It's kinda obvious when you consider how that sort of condensor mic
    works. The gain of the preamp remains roughly constant but the mic
    element itself has a gain that's proportional to the bias voltage.


    Not all mics work that way though, e.g. an FM mic doesn't bias the mic
    element with the supply voltage.

    Regards,
    Allan
     
  10. just LTspicified a little P48 generator, simply to try out this
    http://schmidt-walter.eit.h-da.de/smps_e/spw_smps_e.html
    Not optimised at all, made most of the component values up

    I've stuck a zip of it here
    http://es.geocities.com/mart_in_medina/p48.zip.
    Include a FFT because it took a long time to run, noise tends to be
    below -90dB wrt 1V, not bad for a quick bodge


    Martin
     
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