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Discussion Starter #1
I've a FBQ1000 in my home theater installation for the sub. It works fine but since all my equipment is remote controlled except th FBQ, I wanted to use a remote controlled power switch to turn on and off the unit. The FBQ power switch left at the ON position and the remote controlled relay switches the power to the unit.
The problem is that when the remote controlled switch if OFF the FBQ generates a loud mains hum.

Im wondering if it's because the remote controlled switch is only single pole, so one side of the mains supply is always connected to the FBQ. I don't have a schematic for the FBQ100 so I can't verify whether it has a double pole mains switch and I don't feel like opening it up yet.

Anyone any ideas on this?


Thanks
 

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Discussion Starter #3
It's generating the hum through the sub but only when the FBQ is connected to the relay switch which is in the off position so one pole of the power supply is still connected.
 

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Discussion Starter #4
I found the cause.
There were spark suppressors across the relay contacts of the IR switches. Removing them cured the problem but I'm not sure why they caused hum. The same type of switch is used with the power amp and it works fine. It might be related to the type of power supply used in the FBQ.
Everything is earthed correctly.
 
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