Can phantom power pass through a patchbay?
A question from a Audio Masterclass website 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.
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 (even though it doesn't need phantom power), but I would have to worry about magnetic saturation of the core of the transformer, and maybe even 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 patch cord 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 normalled (or normalized) so you don't need to use a patch cord to make commonly-used connections, then you cannot always rely on the switch contacts to pass phantom power.
The switch contacts are very small in area. 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 and in particular I have spent many a working day with phantom powered mics connected through a patchbay (using patch cords) without ever there being a problem. (Delicate ribbon microphones, that in my opinion should not be recommended for professional use, are an exception and you should consult the manufacturer on whether it is OK.)
I haven't seen any formal study on passing phantom power through normalled connections but it's something I have avoided for the reasons stated above.
Also, this would have to be a patchbay with full-size quarter inch jacks. I've never used the smaller bantam jacks myself but I have heard plenty of complaints from people who have, even for line-level signals.
So there you have it, connecting microphones through a full-size quarter inch patchbay passing phantom power is fine, if you use patch cords to connect rather than relying on normalled connections.
P.S. XLR patchbays are great for mics in smaller studios, and are well worth considering. Phantom power - No problem!