Mic Power supply's a hummin-OK to use a ground lift adapter?

Discussion in 'Electronic Repair Modifications DIY' started by Bejeeber, Feb 25, 2005.

  1. Bejeeber

    Bejeeber Guest

    So there's one and only one thing in the studio here that introduces ground hum.

    A power supply for a tube mic.

    Everything's on one isolated circuit BTW.

    A 3 to 2 prong ground lift adapter will silence this nutty piece o' hummin gear, but is it safe? (This mic will be used for a D/I'd electric guitarist who will be simulaneously playing and singing).

    If it isn't safe are there any good alternatives? Rewiring the mic cable? using one of those isolation transformers?

    Is this common or is the power supply potentially wired wrong?

  2. tubes4tone

    tubes4tone Guest

    Does the preamp that the mic is connected to have a ground lift? Many do, but check it out to be sure. This will lift the ground on the mic-level signal and not on the power supply (a much safer proposition). I would try this or a mic cable with pin 1 disconnected at one end.
  3. Bejeeber

    Bejeeber Guest

    No ground lift on the mic pre - it's an FMR RNP, and the guitar is actually D/I'd into it's second channel.

    BTW, I've tried a power supply that's for another tube mic I have, and it's dead quiet.

    So now I'm wondering whether a hum eliminator like this one would be something to try:

  4. TeddyG

    TeddyG Well-Known Member

    Jan 20, 2005
    Could you maybe send the "humming" supply somewhere to be fixed - or try to teach it the words?

  5. Bejeeber

    Bejeeber Guest

    The retailer sent me a replacemnet power supply and it hummed just the same, so I'm not sure if there's something actually defective about the power supply or not.....

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