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Thread: Unplugged mic before turning phantom power off

  1. #11
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    What is being overlooked is that it may not be the mic so much at risk...but your preamp input. Some are not as robust as others AFA protection circuitry.

    This really isn't as much a case of the "shorting to ground" thing...though it can happen with TRS plugs very easily.
    It's that when you "hot" unplug/plug into phantom power on, with mics that draw more considerable current...you will have large/fast voltage transient spikes at both ends of the cable. When power down/up with the switch, there is a more gradual dissipation, and no spikes.

    Now again...if that is NOT a concern, or it's just too much trouble to turn off the phantom power..then proceed with your preferred method!
    I find it amusing that anyone would argue in favor of a more risk approach...but I guess some folks like to throw caution to the wind.

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  3. #12
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    I done a few numbers. The maximum dissipation in a mic's internal transformer from phantom power would be some 85mW but only if the DC resistance of the winding was a very serendipitous 6,800 Ohms. Higher or lower than 6K8 and the power is less.

    To put that 85mW into context, a 32R headphone hit with 5V, +16dBu, a not unreasonable voltage, would dissipate some 780mW and headphone coils are pretty bloody wee! You do not however hear horror stories of cans getting burned out at all often?

    Damage to the pre amp inputs: The pre amp designer must know that 48V will be present. He/she will also know that 48V is above the input limit for many devices and will therefore fit protection diodes. "Ah but, what if they cheap out and DON'T fit the diodes? Not going to happen since the pre production models would fail all over the shop. B.U.T. They CAN get away with not fitting protection to other inputs! Line inputs for example and yes, in such a case, the accidental application of spook juice could certainly destroy the input IC (there will still be no smoke or twisted metal. 85 THOUSANDTH of a watt remember?)

    So, IMHO microphones and their pre amps are expected to meet and part with phantom powr and 't'appen and faults occur but if either suffers as a result that is shit kit*.

    Now I freely admiit I do not have the vast experience of many forum members of studios and their doings. I only have my own electronics knowledge but I really think the risks to mics and preamps is very low indeed. Moreover, if a huge corporation like the BBC do not see fit to switch 48V and plaster warnings on the kit I think they know there to be no risk worth speaking of (I just wonder how 'king many mic XLR outlets exist in all the BBC studios and OB vans?)

    Of course, turn off phantom power before connecting or disconnecting a microphone but if you forget, don't worry. VERY unlikely to cause any damage to anything.

    So, if I was given a 3000 vintage ribbon mic would I let it take its chances? Of course not! In fact I would almost certainly build a capacitor isolator box and attach it to a dedicated mic stand and Superglue the XLRs in!

    *I hold much the same view regarding 'power conditioners'. My view is that equipment should be designed to work to specification at mains voltage extremes, + and - 10% here and have reasonable internal filtering against RF and spikes. I do however understand that our colonial friends do not enjoy the same quality of mains power that we do?

    Dave

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  5. #13
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    Do it over and over again. Day in day out. For months. You won't hurt the thing unless it's already broken.

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    Quote Originally Posted by ecc83 View Post
    Of course, turn off phantom power before connecting or disconnecting a microphone but if you forget, don't worry. VERY unlikely to cause any damage to anything.
    This is the thing I'm saying...and my approach.

    I've done it too...pulled the mic and forgot it was still powered...and that nice "crack" in the speakers or the seeing the meters getting pinned for a moment is what made me realize what I've done.
    Nothing was damaged...BUT...there are people who have clearly stated on audio forums that they HAVE gotten damage to mics or inputs. Without getting into their specific cases and reasons why they had damage when most people won't suffer it...is irrelevant, and I don't think they were lying about it...so the point is there is a "possibility"...not a "probability".

    So with that in mind...people can do what they think is best.

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    The only mics that I have ever had to die were a pair of CAD 411 dynamics. I think they are sensitive to the phantom 48V. There's no other reason that both died (at different times but under similar circumstances). Luckily I found a couple on sale for about $20 each, so they were easily replaced. I kind of like them on guitar cabs, not unlike my Senn 835s. They also give snares a little more snap than a 57 without sounding like a condenser.

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    Oh Rob ! You're such a rebel !!

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    its all good to know

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