60 hz power hum on music and page

[jcw2]

I've just installed a BCM50 and the music and pages have a noticeable power hum. I have the BCM plugged into a UPS with the server(s), can this be the source?

The wire from the BIX strip to the paging amp and music source is in shielded wire and I hoped that might be the source. The music sounds clean at the point of attachment to the BCM.

The paging amp and music source were working fine on a CICS when I changed out the CICS for the BCM. I was wondering if I needed an impedance matching transformer for the music source which is one side of a stereo amp that should go to a 4-16 ohm speaker. They said it worked fine on the CICS though.

Any suggestions would be appreciated.

 

[curlycord]

Remove amp from page pins and test with butt set and see if same issue as well background music F86.
No way the BCM should be sharing a UPS unless it's big one.



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curlycord

http://www.curlycord.com

 

[jcw2]

I have tried the butt test with the feeds isolated from the switch. What I didn't think to try is each feed alone (with the other disconnected). ie. just the paging ckt on the switch with no music feed.

I also didn't closely check the UPS if some of the outlets were unfiltered power. It is a pretty big unit but maybe an old one.

As usual the problem switches are a 3 hour drive away. I think I will try to get the customer to try a different power source, even if they have to run an extension cord temporarily.

 

[DHRoger]

A little late with the reply, sorry.
You stated 'shielded wire'. How are the shields terminated?
The hum is possibly caused by a ground loop.
Best practice would have the shield grounded at one end only, to minimize the risk.
Back in my radio engineering days I always grounded at the 'source' end of the shielded pair and it served the purpose.