Adventures In Audio

Can phantom power pass through a patchbay?

by David Mellor
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You could connect your mic lines directly to your mixing console. Or you could connect them through a patchbay so you can easily rearrange the channels if necessary. But will it work?

A question from a Audio Masterclass visitor...

I have an issue I need to resolve.

It concerns connecting my 12 channel XLRf to XLRm snake, coming from the recording booth, to a Behringer PX2000 unbalanced patchbay.

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Considering that I have my mic preamps also connected a patchbay, I'm wondering how would it be possible to send phantom power thru the patchbay to the mic in the booth.

Can phantom power travel through TRS-XLR cables/connectors?

P.S. The patchbay is unbalanced 1/4" jacks.

David Mellor responds...

Unfortunately, the simple answer is no. It is not possible to send phantom power through an unbalanced patchbay. Well it might be, but you would be putting 48 volts across the output pins of the microphone. A capacitor microphone will not work. A dynamic mic just might work, but I would have to worry about magnetic saturation of the core of the transformer, and possible damage.

Phantom power can be sent via any balanced connection. So an XLR - XLR cable passes phantom. A 3-pole jack to 3-pole jack cable will pass phantom power too. Naturally an XLR to 3-pole jack cable will also work.

A balanced patchbay can also be used to pass phantom power, but here we have an issue...

If a patchcord is used to connect the mixing console input providing the phantom power to the microphone, then all will be well and phantom power will pass. However, if your patchbay is normalized so you don't need to use a patchcord to make commonly-used connections, then you cannot always rely on the switch contacts to pass phantom power.

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The switch contacts are very small in area and many people doubt their ability to pass mic-level signals anyway. Any oxidization of the contact surfaces will result in an intermittent connection, and perhaps distortion due to partial rectification of the signal.

Passing phantom power through the contacts seems to accelerate the deterioration.

These are my observations from personal experience. I haven't seen any formal study of this, but I would say that connecting a mic via a patchbay, using patchcords rather than normalized connections, seems to be OK.

Also, this would have to be a patchbay with full-size quarter inch jacks. I don't personally rate the smaller bantam jacks for any purpose.

Image: Phantom of the Opera

Tuesday November 15, 2005

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David Mellor

David Mellor

David Mellor is CEO and Course Director of Audio Masterclass. David has designed courses in audio education and training since 1986 and is the publisher and principal writer of Adventures In Audio.

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