Is it important for the phantom power to be turned off when attaching a mic? at DVinfo.net

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Old November 18th, 2006, 10:49 PM   #1
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Is it important for the phantom power to be turned off when attaching a mic?

I never bother, but a friend of mine warned me today that it might damage the mic otherwise.
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Old November 19th, 2006, 07:48 AM   #2
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I think that some mic manufacturers recommend this. I always have phantom off when I connect a capacitor mic. Can't hurt.

Regards,
Jerry
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Old November 19th, 2006, 08:20 AM   #3
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When making or breaking a connection, the contacts in the connector don't meet or separate at exactly the same instant. In the case of connectors with only two contacts that doesn't matter, because the opening or closing of the second one is no different than closing or opening a switch. But with connectors that have more than two, like XLR, then the order of closure could be important. Applying power to one circuit an instant before another circuit is "ready" could cause damage. The power circuit and the signal circuit have to share a wire in XLR condenser mics. My guess is that the two circuits are sufficiently isolated in most mics' electronics that damage won't result, but I'm not sure.

Making connections of all types with the power off is an advisable habit.
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Old November 19th, 2006, 10:22 AM   #4
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Related to that, I think. I noriced my Rode NT1a's pin 1 is slightly longer than the other 2. Was wondering if it was a QA glitch when I learned that it's done that way by design so the ground side of the circuit makes contact before the hot side when you plug it in. All in all, I don't think it's a good idea to plug or unplug any equipment while it's power is hot.
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Old November 19th, 2006, 11:00 AM   #5
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I know that you will never see someone in a sound studio plug in a mic when phantom pwr is already on.
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Old November 19th, 2006, 12:04 PM   #6
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Okay, okay, lesson learned. The mics are too expensive to lose to a power surge.
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Old November 19th, 2006, 02:22 PM   #7
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Quote:
Originally Posted by Emre Safak
Okay, okay, lesson learned. The mics are too expensive to lose to a power surge.
You betcha!

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Jerry
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Old November 19th, 2006, 09:37 PM   #8
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I have worked in and around audio studios for over 20yrs, and have never once heard this. Professional consoles do not typically have switches to turn their phantom power off that are easily controlled by the operator. I have never once heard of this being an issue, but I would like to hear input from other recording professionals.
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Old November 20th, 2006, 02:07 AM   #9
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I'm with Paul. I've worked in live event environments for years and not once has this been an issue. I can't see any real reason why connecting something with phantom on would damage a mic. The voltage is WAY too low for starters. However as others have said, it can't hurt!
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Old November 20th, 2006, 08:23 AM   #10
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I was reminded this morning by an associate, that if the mic is wired incorrectly - ribbons and some tube mics can fry if attached to phantom. These are remote incidents where the mics were refurbished by individuals who did so incorrectly. The internal wiring caused the issue. I guess it is better safe than sorry if you have antique mics of dubious history. You can use a transformer to buffer the phantom off only one channel.
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Old November 20th, 2006, 10:38 AM   #11
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Quote:
Originally Posted by Paul Schneider
I was reminded this morning by an associate, that if the mic is wired incorrectly - ribbons and some tube mics can fry if attached to phantom...
More specifically, a ribbon mic should never be sent phantom or T power or what have you ever, ever, ever, because chances are it will fry.
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Old November 20th, 2006, 10:56 AM   #12
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The reason for not disconnecting or connecting a mic with phantom supplied is a loudspeaker protection, not mic protection.

Most professional mixers I use, certainly do have phantom power buttons on the mic strip - a pretty esssential feature - look at Souncraft, A&H, Midas etc.

People often unplug a mic while the channel is live, and reconnect another. A huge thump/bang goes through the system as the mic power connects. As has been said, pin 2 and 3 will make contact at slightly different times, producing a voltage spike for the fraction of a second until the other pin makes contact - this spike can easily take out the HF drivers, or if at sufficient level, pop the coil out of the slot in the LF driver - over excursioned is the term for this kind of damage. Theoretically, you could prevent the spike by making contact at exactly the same time. Some mixing desks have a simple two pole switch for applying phantom, and these operated very close together, minimising the problem. Even if you could do the powering exactly at the same time, you'd still get a low frequency thump as the pre-amps power up and stabilise.

It is true that some delicate ribbons can be damaged by a 48V phantom line that has been accidentally unbalanced by shorting one leg to ground - the ribbon physically jerks and some of the little corregations are deformed, affecting frequency response and sensitivity.

So, pulling the fader down and connecting the mic with or without the phantom being on is normally quite ok. Just watch for cable problems if you have expensive ribbons (some are immune anyway, depending on their tranformer configuration)

In 30 odd years of connecting mics, I've never damaged a single one - but I have wrecked a few loudspeakers.

Some studios are very pedantic about phantom switching. If you work in these, it will be fader down, mute on, phantom off, swap mic, phatom on, mute off, open fader every time
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Old November 20th, 2006, 11:29 AM   #13
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Quote:
Originally Posted by Bennis Hahn
I know that you will never see someone in a sound studio plug in a mic when phantom pwr is already on.
I was reading this same topic of discussion on
another forum and a guy came on and
said he has operated a pro sound studio
for 10 years and the phantom has
*never* been turned off that whole time.
He said he had not noticed any problems
with connecting mics where the
phantom power is on.

There was also mention that the BBC
headquarters building always leaves
phantom "on" to all their connections.
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Old November 20th, 2006, 11:48 AM   #14
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ehh, it's the way I have been taught. Paul J said it, that it is more for the sound system protection then the mic's.

Either way, it is such a small thing to do that takes all of 2 seconds I feel it is better safe then sorry.
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Old November 20th, 2006, 12:31 PM   #15
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Quote:
Originally Posted by Seth Bloombaum
More specifically, a ribbon mic should never be sent phantom or T power or what have you ever, ever, ever, because chances are it will fry.

I've heard that this is actually only true for a
very small group of vintage ribbons. The problem
is not that the affected mics are "a ribbon"
per se, but the problem is the way these
particular ribbons were wired.
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