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Author Topic: Phantom power ok feeding back into mixer outputs?  (Read 5041 times)

Mark Wilkinson

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Phantom power ok feeding back into mixer outputs?
« on: November 18, 2015, 02:16:54 pm »


I'm using a UMC 404 for Smaart I-O.   Phantom power is either on or off for all 4 of the unit's inputs.

So if I use Input 1 as the reference channel with a line level signal coming from a mixer or a processor,
and use the remaining channels for measurement mics with +48v engaged,
aren't I also sending +48 v back into the mixer's or processor's output?


It looks like it must not hurt the mixer or processor based on the Smaart I-O devices I see people are using....
....but it it completely harmless, and if so, how so?   

Many thx.......continue to realize how little I know.......!
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Steve M Smith

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Re: Phantom power ok feeding back into mixer outputs?
« Reply #1 on: November 18, 2015, 03:22:34 pm »

Yes, but there should be capacitors in line with the outputs which will not pass the dc.


Steve.
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John Roberts {JR}

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Re: Phantom power ok feeding back into mixer outputs?
« Reply #2 on: November 18, 2015, 04:00:03 pm »

Most well engineered professional products will tolerate several kinds of abuse, in general it is not a good practice.

JR
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Keith Broughton

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Re: Phantom power ok feeding back into mixer outputs?
« Reply #3 on: November 18, 2015, 04:05:49 pm »

I'm using a UMC 404 for Smaart I-O.   Phantom power is either on or off for all 4 of the unit's inputs.

So if I use Input 1 as the reference channel with a line level signal coming from a mixer or a processor,
and use the remaining channels for measurement mics with +48v engaged,
aren't I also sending +48 v back into the mixer's or processor's output?


It looks like it must not hurt the mixer or processor based on the Smaart I-O devices I see people are using....
....but it it completely harmless, and if so, how so?   

Many thx.......continue to realize how little I know.......!
I am using the same device and I send the signal in on a TRS 1/4 connector instead of the XLR.
The TRS is a line/instrument level input.
While the phanton may not be a problem, in this case, I have had problems with other devices getting phantom on an output.
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Rob Spence

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Re: Phantom power ok feeding back into mixer outputs?
« Reply #4 on: November 18, 2015, 07:16:52 pm »

My LS9 goes a bit crazy with awful noises if I put phantom into an omni out. I don't do that anymore and, at least for me, nothing got damaged.


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Mark Wilkinson

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Re: Phantom power ok feeding back into mixer outputs?
« Reply #5 on: November 19, 2015, 09:39:08 am »

I am using the same device and I send the signal in on a TRS 1/4 connector instead of the XLR.
The TRS is a line/instrument level input.
While the phanton may not be a problem, in this case, I have had problems with other devices getting phantom on an output.

Thanks all,

Keith, great!
 
I always pictured  XLR/1/4 combination connectors  as simply having the TRS's tip-ring-sleeve  in parallel with XLR pins 2-3-1.
It's nice to finally realize that the TRS is just for line level and doesn't connect. phantom.

Is this generally true for all XLR/1/4 combo connectors, other manufacturers?
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Arthur Skudra

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Re: Phantom power ok feeding back into mixer outputs?
« Reply #6 on: November 19, 2015, 01:41:27 pm »

Likewise, going the other way I discovered that the line output of my Roland Octacapture is *not* happy when phantom power is present on the connection, it goes into a really weird oscillation.  So if you are plugging the output of some measurement interfaces either to a mic input on a mixing console, or a DSP input, make sure the phantom power is turned off for that input.  YMMV.
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Steve M Smith

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Re: Phantom power ok feeding back into mixer outputs?
« Reply #7 on: November 19, 2015, 03:59:40 pm »

A properly designed piece of equipment with both XLR and TRS inputs on the same channel should not have the phantom power appear on the TRS input.  It's quite trivial to use the internal switching contacts within a jack socket to accomplish this.

However, that's not to say that it never happens.  There is most likely equipment around with TRS just parallel connected to the XLR.


Steve.
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Primoz Vozelj

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Re: Phantom power ok feeding back into mixer outputs?
« Reply #8 on: November 19, 2015, 07:00:06 pm »

Mixed a show with X32 rack on stage sending LR to XLR inputs of analogue house console with global phantom power switch turned on. No problems.
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Lyle Williams

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Re: Phantom power ok feeding back into mixer outputs?
« Reply #9 on: November 20, 2015, 04:43:14 am »

In one application where I don't want 48v, I have a bit of plastic jambed into the circle of the XLR combo jack to prevent accidental insertion of a connector that would carry 48v.
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Re: Phantom power ok feeding back into mixer outputs?
« Reply #9 on: November 20, 2015, 04:43:14 am »


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