Phantom power mic causes hum on stage box but not local

[yorkshirepuddingParticipant]

We have a Qu-24 mixing desk with an AR168 stage box. We have a pair of Sontronics STC1 condenser mics that seem to be causing a hum when connected and phantom power activated on the stage box but not when connected locally to the desk. We have another condenser mic connected to the stage box without issue and also 3 DI boxes without issue.

I tested with the same cable and I plugged in and routed to local on the desk and it worked with phantom power. When I plugged in to the stage box with the same cable and enabled phantom power, a hum started to build.

Any suggestions?
Thanks

[Mike CParticipant]

Are you plugging the mic and cable directly into the stage box and mixer for your testing or are you going through a snake cable on one or both of the connections?

Check that the cable / cables do not have pin1 ground tied to the shell of the XLR connectors.

I’m assuming that the stage box and the mixer are in two different locations, could there
be some source of hum pick up for the mic in the location of the stage box?

[yorkshirepuddingParticipant]

Thanks for your suggestions
In both scenarios, I’m plugging directly into the mixer and the stage box. The mixer and stage box are probably about 10 metres apart. If pin1 ground was tied to the shell of the XLR connectors in one cable, would that produce different results in mixer and stage or would I expect the same result in both? Do you need to dismantle the plug to check if tied or is there a code on the cable that would distinguish one type from another?

In the vicinity of the stage box, but not really close, are drum kit with two mics, electric piano, monitor/foldback speaker. Writing that, I’m wondering if the monitor speaker could be the problem? The channel that the mic goes into does not go into the foldback as its for drums, so it won’t be feedback but could it be interference?

Gives me a few ideas to check anyway.

[Mike CParticipant]

To check the connectors you could take a multi meter and check between pin 1 and the out shell for continuity, it should read as open, or open up the connectors and look for a jumper between pin 1 and the screw or connection that mates with the outer shell.

When you switch between the stage box and local mixer inputs or you using the same physical channel on the mixer so all the processing and routing remains the same?

[yorkshirepuddingParticipant]

Yes – using the same channel on both; just changing the source from local to dSnake. Will take my multimeter on Sunday to check.

[Author]

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