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A portable PA system I'm looking at provides 4 XLR inputs and switched phantom power... But this is switched on all 4 not per-channel.

If I have a mix of powered and non powered mics could this be a problem? Can phantom power be damaging to microphones that don't require it?

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  • Hm... I have a tube pre-amp with a VU meter that always used to red-line when I plugged phantom into the output, although it didn't seem to affect the sound, and I'm still on the same tube some 20 years later... Mar 7 at 22:21
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    @AndyBonner VU Meters work by rectifying the signal to DC and smoothing it. Most likely your VU meter is measuring one signal line with respect to ground. If the VU meter were connected differentially between hot and cold signal lines, it would be phantom-immune.
    – Theodore
    Mar 8 at 18:03

3 Answers 3

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The existing answers are correct, but just to simplify a bit into a 'common rule'.

If your mic was made any time in the past 50 years or so & you use standard XLR>XLR cables, there is no problem at all.
Mics that don't need phantom just ignore it. They don't even know it's there.

Old ribbon mics are known to be 'not safe' for this - but if you owned one, you'd probably already know this.

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As long as you don’t have a ribbon microphone then it will not damage your other microphones.

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    It's worth mentioning that unplugging/plugging in an XLR cable without muting the channel is more likely to result in a bang/pop from the speakers if phantom power is on. (Of course you should mute the channel before unplugging anyway.)
    – Ian Goldby
    Mar 8 at 12:10
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It depends on how your microphone is wired. If your microphone is wired symmetrically the two +48V contacts will just sit on opposite sides and create a 0-potential. This is why it is called phantom power, as you do not see it if you do not need it. If you microphone is NOT wired symmetrically it definitely can. E.g. if you have a microphone on a Mono jack and use some XLR-Jack converter you might give that microphone quite a bad time.

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    It's not so much about being "symmetrically" wired as it is about not providing a return path for the phantom current passing through a sensitive component. "Phantom-immune" microphones (like typical dynamics) have their coil floating with no connection to ground.
    – Theodore
    Mar 8 at 15:11
  • @Theodore To be totally correct: You do want to connect both +48V pins to anything that does not require a potential. This will result in a 0V potential.
    – Lazy
    Mar 8 at 17:35
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    I think you're using "symmetrical" where typical English usage is "balanced" or "differential". But some older microphones have a balanced transformer with a center tap connected to ground. This is still "symmetrical" by a reasonable reading and will still burn up with phantom power applied. The key is that ground return path. I think the details belong on electronics.stackexchange.com, not here.
    – Theodore
    Mar 8 at 18:07

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