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View Full Version : adapter to remove phantom power?



Zach
08-05-2007, 07:02 PM
I've got what I think is a new one, apologies if it's been asked already but I couldn't find it.

I do live performance videography and have mics coming into a Mackie mixer, as well as a feed out of the house board. The mics need phantom power but the house mixer does not, and occasionally the phantom power causes buzzing or worse thru the house mix.

I'm wondering if there's a simple adapter I could put somewhere along the line to remove phantom power from the cable, or if I could make such an adapter myself. I know just enough to think this should be pretty simple, but not enough that I could actually do it.

Ideally I want an adapter that remains XLR, rather than going from XLR to quarter-inch. Any help is appreciated.


Zach

mumin
08-05-2007, 08:12 PM
but if you loose phantom power the mic wont power up. M 'I confusing something here?

Noiz2
08-05-2007, 10:59 PM
He wants to block Phantom power on specific channels. I didn't think Mackie allowed ballanced line in on the XLR's. It doesn't put Phantom on the TRS jacks.

Anyway yes all you need is an isolation transformer. You may find an in-line version but the balanced line "hum blockers" are the same thing. You could make your own also. You need some 1:1 audio transformers and a soldering iron.

However I doubt that phantom power has anything to do with the hum. You probably have a ground loop with their mixer. The hum blocker may solve that issue or you may have to lift some of your grounds.

ptalsky
08-06-2007, 04:09 PM
I think Scott has it right - it's not a phantom power thing, it's a ground loop.

Though, if you want to eliminate the phantom power through the board, why not pick up a Denecke (or other) phantom power adapter, turn the phantom off on the board and use that instead. In other words, rather than remove the phantom from selected channels, add it in via an external power supply.

Phil

Noiz2
08-08-2007, 09:58 AM
And if you want to go Phil's route I have a 4 channel Phantom power adapter I would sell cheap.

Zach
08-08-2007, 03:03 PM
I work at a variety of theatres w/ equipment of drastically different quality. Sometimes yes it's a ground issue and I've been able to fix that with a ground lift.

However in two specific situations, I'm pretty certain it's phantom power because when I turn off phantom power, the buzz that was going into the house speaker system disappears. Or, if I used adapters and changed from XLR over to TRS, it went away as well.

I'd prefer to remove phantom power rather than add it just on the lines necessary--it's one less piece of equipment I have to hook up when I'm pressed for time. Thanks for that suggestion though.

If anyone is aware of an in-line isolation transformer, I'd appreciate a link. I'll keep looking.



Thanks

Zach

TheDingo
08-08-2007, 03:40 PM
If anyone is aware of an in-line isolation transformer, I'd appreciate a link.

How about this one?

http://www.sescom.com/audio/il-iso.html

http://www.fullcompass.com/product/299962.html

Zach
08-08-2007, 04:55 PM
Will this work?

http://www.hosatech.com/hosa/products/GLT-255.html

I'm trying to avoid a $50 purchase...