Hum problem solved.

[ojc123]

I just wondered if anyone with more knowledge than me could tell me why this problem is solved.

 

I have a 6 way XLR socket stage box which is part of a permanent install. It's been there for over ten years and has worked fine with dynamic mics and other sources. For the first time a phantom powered condenser mic was used a couple of weeks ago. The result was a significant hum. The mic worked well enough but the hum was obvious and annoying. The hum was present on all of the sockets on the box but not on the other boxes which go down the same main multicore. It was present whether or not any other sources were plugged into the box. None of the other sources caused any hum.

 

Today I set out to identify the problem. I tested each socket in turn and it turned out that one socket had the connections to pins 2 and 3 reversed. I sorted that out and tried the condenser mic again. Problem solved.

 

In my relative ignorance I was a bit surprised when it worked. Can someone enlighten me about this?

Thanks in advance.

 

System Configuration

Mixer A&H PA28

Speakers RCF722A.

No outboard used on this occasion.

Mic Audio Technica Pro49Q.

All interconnecting cables tested.

[mervaka]

in theory, swapping pins 2 and 3 shouldn't have affected the phantom power. They should have a common DC potential, 48v above pin 1.

[ojc123]

They were both at 48V relative to pin 1 which is why I was surprised.

[mervaka]

that's normal. they should both be 48v above pin 1, and therefore 0v relative to each other (in DC terms)

[c.cam108]

There may have been a grounding issue between sockets that you dislodged when dismantling the whole thing.

 

Colin C

[ojc123]

Probably was a grounding issue, stray strand of wire or something. I had thought of the possibility but wondered if there was something I didn't understand. Thanks anyway.