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I'm trying to connect a mixing console to a videoconferencing equipment, to send the audio out of the console to the mic input of the videoconferencing unit. We are talking about a Yamaha MG166cx console and a Tandberg 990 MXP VC unit. The user manual of the VC unit says that the mic input provides a phantom power of 24V and a echo canceling functionality (in which I'm interested). The mixing console manual says that the Aux send is a balanced output and provides these images about it.

"Aux send" jack configuration of Yamaha MG166CX: Aux send jack configuration of Yamaha MG166CX

"Aux send" block diagram of Yamaha MG166CX: Aux send block diagram of Yamaha MG166CX

Back of the VC unit showing the XLR mic inputs: Back of the VC unit showing the XLR mic inputs

The question: is it possible to connect the "Aux send" output to the phantom powered mic input of the VC unit without harming the console?

The manual of the VC unit does not provide details about circuitry.

  • It depends. If there are adequate output coupling caps and/or protection on the outputs of the mixer then you shouldn't fry the mixer outputs, but it's hard to know for certain without trying. BTW if you fry the mixer this way you might also hurt the mic inputs. Your best bet is to find another way to do what you want to do (I'm guessing have more than two mics hooked up with echo cancellation) or to get into the Tandberg and disable phantom power. Or, "dumb" idea: use TS cables on the mixer out into transformer DIs with the ground lifted. – Todd Wilcox May 14 '15 at 13:42
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I decided to make my dumb idea an answer. Get two direct injection boxes - they could be active or passive but they have to have ground lifts. Connect the TRS out on the mixer to the DI boxes using just TS cables. You'll be grounding out half of the mixer outs but the mic inputs probably have a good amount of gain on them. Then make sure ground is lifted on the DI boxes and plug them into the mic inputs.

The ground lift will ensure that the phantom power is not flowing to the mixer and a side benefit is you'll have better impedance matchinng overall.

  • Actually, according to Cadu's image, a TS plug in that particular type of output is just fine. There's only one driver for hot, instead of one each for hot and cold, and both wires have equal impedances even though cold just connects to ground via that impedance. Equal impedance makes a balanced output as far as noise rejection goes, and this particular design allows for anything to plug into it without stress, except for a T-S short or phantom power. I like DI idea also, with the caveat of making sure it's ground-lifted. – AaronD Jun 3 '15 at 22:44

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