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Author Topic: XLR Mic Cable Splitter - Phantom Power  (Read 1508 times)

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Offline djphrayz

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XLR Mic Cable Splitter - Phantom Power
« on: July 16, 2017, 07:03:24 PM »
I recently purchased a Zoom H6, and I was disappointed to learn that the safety recording feature only works on the L/R channels (microphone capsule add-on which does not support phantom power).  I wondered if splitting the signal from one pair of phantom powered SDC mics into two pairs of inputs would:

1. be electrically feasible - I do not have a solid understanding of how phantom power works.
2. pose a risk of shorting out something in the recorder?

My thought here is that I could run lower gain on the 2nd pair of inputs to create a safety track.

Thoughts?

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Offline DSatz

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Re: XLR Mic Cable Splitter - Phantom Power
« Reply #1 on: August 02, 2017, 11:31:05 PM »
It's not generally a good idea to split a microphone signal simply by using "Y"-cables, because then each microphone has to drive two inputs, and the load (burden) on the microphone is doubled; it has to produce twice as much signal current.

(Another way of saying the same thing: The two inputs are in parallel, thus their combined impedance is roughly half what each one's impedance would be separately.)

Whether the phantom powering from one input might damage the other one, and/or whether the presence of the second input would pull the phantom powering out of spec and make the microphones not work (or not work well), depends entirely on the circuit design of the two inputs. Again, not a risk worth taking IMO.

On the other hand, if you are strongly motivated--there are "mic splitters" (with transformers inside) that do this kind of thing without introducing the risks I've described. But if you decide to use them, test the whole setup before the recording; depending on the splitters you use, the phantom powering may require special attention (e.g. many splitters will pass phantom powering through only one of their outputs, while blocking it on the other one or ones, so you need to make sure to power the one output of the splitter that will pass the powering along to the microphone).

--best regards
music > microphones > a recorder of some sort

Offline F.O.Bean

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Re: XLR Mic Cable Splitter - Phantom Power
« Reply #2 on: August 05, 2017, 12:03:32 AM »
Well, first and foremost, I have NEVER owned or run a Zoom deck of any kind, so I have zero experience with the Zoom H6. That said, Ive done a "poor man's" mic comp by using simple "Y" XLR Splitters after the mics, and using Phantom Power on only ONE of the two decks! If you apply Phantom Power to BOTH decks supplying Phantom Power, you greatly raise the risk of damaging something! However, it sounds like you want to split the signal into the SAME deck/recorder[Zoom H6 correct?], which Ive never done, since the last time I did splits like that, I was only running 2 channel stuff back then for Phish, so I never had to worry about splitting Phantom Power to the SAME device :( I usually ALWAYS agree with DSatz, and this is no exception. If you are trying to split a signal into the same deck with Phantom Power only on 2 of the Channels, I personally wouldn't want to risk my gear trying that!

And if you PROPERLY want to split a mic source with Phantom Power involved, I'd suggest saving up and buying real Mic Splitters that are MEANT to handle that particular task, especially if you plan on running that way in the future! I only did that "Y Split" a few times just to comp some different preamps back in the day, but if I planned on doing that on a more regular basis, then I would've definitely gotten some nice Mic Splitters ;)

Hope this helps in some way, and as always, Happy Taping 8)
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Re: XLR Mic Cable Splitter - Phantom Power
« Reply #3 on: August 05, 2017, 06:46:53 PM »
A simple passive split will probably cause 48v phantom to be applied to the inputs of the other connected channels- I bet you get some insane DC offset if you try it (and nothing catches fire)

Here's a discussion on Gearslutz about buffered and isolated splits with some good info.
https://www.gearslutz.com/board/so-much-gear-so-little-time/448371-best-xlr-splitter-duplicator.html

If you don't have phantom power issues, you will still have potential "gain fighting" from the two inputs. When I've used a passive split on a dynamic mic, and one output increases gain, it causes the gain to drop on the other output.  I don't know why that is, but perhaps it's Ohm's law at work... Like Dsatz said, "The two inputs are in parallel, thus their combined impedance is roughly half what each one's impedance would be separately."


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