Phantom Power and TT/TRS Patch Bays

If you're building a studio, this is a bad idea. Avoid it.

Use XLR connectors instead. Yes, they're not as high density as a TT bay. Don't hot patch microphones when the phantom powering is turned on. Turn the phantom power off first. Even this may not be sufficient.

The problem is that the tip of the plug can contact ground as the plug is being   With a transformerless input, this can discharge/charge the input blocking capacitors thru the microphone's output transformer. This could magnetize the core of the transformer, zap a ribbon microphone, or (remote possibility) damage a dynamic microphone.

With a transformer coupled input, you risk magnetizing the core of the console's input transformer, ruining its distortion characteristics.

If the microphone's output is transformer coupled, the microphone's output transformer could also have its core magnetized, ruining its distortion characteristics.

This is not good.

There are several ways to disable or turn off   phantom power in a mixer.

Disconnect the input to the rectifier/filter system in the phantom power supply. Mackie mixers with a global phantom power switch use this method. There should be a bleeder resistor somewhere within the supply to discharge the filter capacitors.

Break the feed to the 6k81 phantom feed resistors, either individually or in groups. In transformerless consoles, there should be a discharge path for the input coupling capacitors.

Using a voltmeter, or the console schematics, determine which method your console uses and how long it takes for the voltage at the microphone inputs to fall to zero volts after the phantom power has been switched off. If you can't do this yourself, get someone who can and have them explain it to you until you understand it. Have them read this article.

When patching microphones through a patchbay, either turn off the phantom powering first, and/or unplug the sensitive microphones (ribbons) before repatching any of these lines.

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Copyright © 1999-2009 by Rick Chinn. All rights reserved.

Last modified 04/14/2011. 18:27:16