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For devices that support mic input on the XLR and line level input on the 1/4" parts of one of those Neutrik combo jacks, do I generally need to worry about phantom power being sent to my line-level device?

We have an assortment of digital recorders with this style of input. I always tell folks to turn off the phantom power when they don't need it, but I am unsure if I need to take extra precautions, in case they forget.

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It really depends on your equipment. The Neutrik combo connector has separate connectors for the XLR and TRS pins, so it depends on whether the digital recorder in your setup feeds phantom power to both the XLR and the TRS pins. For such instances, this thread might be of help, although I've never tried it myself and you'll have to open your device and get busy with a soldering iron (i.e. break your warranty). I suppose you could fashion a very short cable with a male XLR or TRS and another Neutrik female if you're worried about soldering inside your equipment.

My audio interface only supplies phantom power on the XLR pins. I've accidentally left on phantom power while connecting several synthesizers using XLR cables without any apparent damage, so at least with my own equipment I've become less worried.

I suspect leaving phantom power on is a common mistake, so hopefully most equipment manufacturers put in safeguards. Of course that doesn't help you the day you connect a device that isn't protected...

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+1 - the only equipment I've ever seen damaged by phantom power are oldschool ribbon mic's. –  Mark Henderson Dec 16 '10 at 4:56
    
Ah, I didn't realize all the pins were separate on the jack. Thanks for the input Kim! I think I will get my meter out and check our records to see how they might be hooked up. –  Brad Dec 16 '10 at 14:43
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I've fried the motherboard on my android tablet by connecting the headphone jack to a mixer with a 1\8" to xlr cable by leaving phantom power on. DO NOT DO THISWITH A PHONE TABLET OR COMPUTER u will send 48v into ur headphone jack which is cpnnected to ur logic board

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Of course your tablet was fried. You connected it specifically to a microphone jack with phantom power on. My question was referring to the Neutrik combo jacks, and whether or not the TRS pins had phantom power, in addition to the XLR pins. But, thanks for your answer anyway. –  Brad Sep 18 '12 at 13:39
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On an XLR cable, pins 2 and 3 carry the same voltage, just 180 out of phase, while pin 1 is the ground.

Wiring this up to a TRS connector, pin 2 is tip, pin 3 is ring, and pin 1 is the sleeve.

XLR to TRS image linked from here

So, if you're using balanced TRS connections in your combo jack, the answer is, it should be fine. The voltage present on the tip and ring "is seen by equipment as “common mode” noise and rejected, or ignored, by the equipment." source

A caveat, however...

As the jack plug is inserted into the jackfield its tip will momentarily connect with the ring contact in the socket, while the ring of the plug touches the sleeve contact. This short-circuits the phantom supply, bridging the +48V line straight to the earth return and, although the phantom supply should cope, the resulting voltage spike can cause irreparable damage to the input circuitry of the mixer channel. The mic input stage can be destroyed outright (particularly with older types of electronically balanced inputs) but it is more usual to find a gradual degradation in performance as various circuit components deteriorate. source

The quote above is not exactly related to your situation, but close enough to give you some useful tips to avoid damage.

Having said all that, I suppose in the end, it depends on how the Neutrik connector is wired on the back side. If there are only three leads (which are just split to connect to both the XLR and TRS contact points) There would be phantom on the TRS. If, however there are six leads, it could go either way. I suppose the only way to know for sure would be to test with a DMM or contact Neutrik :)

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