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Old May 17th, 2006, 11:12 PM   #1
Fred Retread
 
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Dynamic mics immune to phantom power

Am I correct in assuming that dynamic mics are free from harm and any kind of performance degradation with phantom applied?

Our high school auditorium seems to be miswired. At the XLR jacks in and around the stage, phantom power is applied only between pins 1 and 3 as opposed to between 1 and 3 and also between 1 and 2, which I confirmed is the way the XLR jacks are powered at the board itself. Dymanmic mics work when plugged in at the stage but my AT3031 condenser mics don't. Before I propose rewiring the jacks I wanted to be able to assure the music staff that nothing would change for them.
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Old May 17th, 2006, 11:48 PM   #2
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Quote:
Originally Posted by Fred Retread
Am I correct in assuming that dynamic mics are free from harm and any kind of performance degradation with phantom applied?

Our high school auditorium seems to be miswired. At the XLR jacks in and around the stage, phantom power is applied only between pins 1 and 3 as opposed to between 1 and 3 and also between 1 and 2, which I confirmed is the way the XLR jacks are powered at the board itself. Dymanmic mics work when plugged in at the stage but my AT3031 condenser mics don't. Before I propose rewiring the jacks I wanted to be able to assure the music staff that nothing would change for them.
The board should also have the ability to shut off the phantom power to the outputs. If you intend to use a dynamic mic on a certain channel, make sure its phantom power is off.

-gb-
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Old May 18th, 2006, 01:01 AM   #3
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The patch points around your school auditorium will probably just be cables that go from one point to a control room or biobox where the mixing desk is located.

I doubt that the wiring in the walls has been installed incorrectly, but you can use a multimeter or cable checker to confirm.

Depending on the desk, you may be able to turn phantom power on for ALL channels or INDIVIDUAL channels. If your desk only supports "PHANTOM ON/OFF" (ie. you cannot turn it off for individual channels), then, I guess tough. In THEORY phantom power SHOULD NOT hurt microphones that do not require phantom power. I have never personally seen a microphone hurt by sending phantom to it, although I have heard others say that they have.

Hope this is of some help.
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Old May 18th, 2006, 05:41 AM   #4
Fred Retread
 
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My board is either "phantom on" or "phantom off" for all inputs.

My thinking is that dynamics apply their signal across pins 2 and 3, so if both of those are at +48 with respect to pin 1 then they are at zero potential with respect to each other and everyting should be fine.

Does anyone have confirming or contradictory information? TIA.
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Old May 18th, 2006, 06:59 AM   #5
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I've got the situation where my mixer is either
all phantom on or all phantom off, and I've used
dynamics with the phantom going to them and
haven't noticed any problem from doing so.
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Old May 18th, 2006, 07:40 AM   #6
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Dynamic microphones are typically not damaged by phantom power, and if everything is wired properly, nor will there will be any effect on the sound. I've used dynamic mics with mixers that don't have individual on/off for phantom power and thus had no choice but to feed them phantom power, and have had no problems. That said, it depends on the specific mics and a dynamic mics could be damaged if the cables were incorrectly wired, you don't want to run power across the delicate coil in the mic, that will damage it. Be safe, only power mics that need the power. Here are three situations where a mic and/or the power supply can be damaged:

(1) T-power is another scheme for powering microphones and T-power microphones only work with T-power supplies. If you connect a T-powered microphone to standard +48 volt phantom power supply, it's likely you will damage the microphone, and the same is likely true the other way around. Some mixers, for example my Sound Devices 302, offers a choice of no, Phantom, or T power, so when using any kind of professional audio gear, get in the habit of checking the position of all settings prior to plugging in any microphones, and,

(2) Plugging a ribbon microphone into phantom power can damage the ribbon element, in theory phantom power will not damage then, but any difference in the potential voltage between pins 1&2 and pins 1&3 turns the ribbon into a fuse and it will go sizzle. Since these are mostly found in studios it's not something you're likely to come across in video applications, and

(3) I'm told there are some battery powered microphones that don't play well with the application of phantom power with the possibility of damage, this is not the case with most contemporary battery powered condenser mics which are designed to co-exist with phantom power, so if anyone has a specific example, I'd like to know about it.
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Old May 18th, 2006, 07:52 AM   #7
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Quote:
Originally Posted by David Tames
(3) I'm told there are some battery powered microphones that don't play well with the application of phantom power with the possibility of damage, this is not the case with most contemporary battery powered condenser mics which are designed to co-exist with phantom power, so if anyone has a specific example, I'd like to know about it.
I think Audio Technica says that their AT822 battery-powered
mic could be damaged if phantom is applied.

I've also heard -- don't know if it's true -- that applying
phantom to a modern ribbon will not hurt it, so long
as the phantom is not powered on when the mic is plugged
in.
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Old May 18th, 2006, 08:59 AM   #8
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Thank you, gentlemen.

I Googled T-power to rule out that this might have been done deliberately to our stage jacks. Nope.
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Old May 18th, 2006, 09:13 AM   #9
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T-power was developed for field applications, so it's unlikely you will find it as an option on a stage mixing board. You will find some mics like the Schoeps CMC 4 that only works with T power, but you will probably not come accross T power except in professional video and film sound work. Some professional sound recordists prefer T-power because it offers better performace than +48V phantom power for very long microphone cable lengths. By the way, A-B is the old term for T powering.

For those who are interested in the technical details down to the circuit diagrams, I found this very comprehensive article: http://www.epanorama.net/circuits/mi..._powering.html that explains everything from the plug-in power used in camcorders to power mics through the 1/8" mini-jack connectors to the details of phantom powering and beyond.
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Old May 18th, 2006, 09:27 AM   #10
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Quote:
Originally Posted by Dave Largent
I've also heard -- don't know if it's true -- that applying
phantom to a modern ribbon will not hurt it, so long
as the phantom is not powered on when the mic is plugged
in.
The problem comes in with incorrectly wired cables, or when a connector is plugged in or unplugged and for a split-second power is not evenly provided to both pins 2 and 3 and ZAP, the ribbon becomes flashpaper. Thus the rule of thumb is: don't use ribbon mics on lines with live phantom power, as can create a riskly situation and these mics are expensive.
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Old May 18th, 2006, 10:49 PM   #11
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Good balanced dynamic mics will not be efected by phantom power. Un-balanced mics can be efected or damaged.

Not all mics with XLR connectors are balanced, All non XLR mics are un-balanced.

Danny.
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Old May 19th, 2006, 05:24 AM   #12
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Quote:
Originally Posted by Danny Natovich
Good balanced dynamic mics will not be efected by phantom power. Un-balanced mics can be efected or damaged.

Not all mics with XLR connectors are balanced, All non XLR mics are un-balanced.

Danny.
ALMOST all non-XLR mics are unblanced. I have seen balanced mics that used 1/4 TRS connectors instead of XLR but I admit it's a rarity.
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