chatterbox Posted October 23, 2011 Share Posted October 23, 2011 Just finishing an install. Have 2 powered tops and a powered sub. The speakers stay on all the time, as the speakers hibernate when they dont receive a signal for a certain amount of time. The audio equipment is in a rack on wheels. When it is plugged into the wall power - there is a dreadful buzz/huum coming from all of the speakers, but as soon as the power is switched on at the power point - the noise stops..... plugging or unplugging any inputs/outputs/sources etc make no difference...the minute the power is plugged in - the noise starts, but stops as soon as you turn power on at the plug. We are in Australia, where the power is not as clean as the UK, but have never had this problem before.... any thoughts????? Link to comment Share on other sites More sharing options...
timd Posted October 23, 2011 Share Posted October 23, 2011 Have you tried a transformer based, earth lift DI between the equipment racks and the speakers? Link to comment Share on other sites More sharing options...
David A Posted October 23, 2011 Share Posted October 23, 2011 Australian power is no different to UK power, you probably have an earth loop, I'm guessing your powered speakers are plugged in to a separate circuit.Removing the signal earth at the powered speakers should solve the problem. Link to comment Share on other sites More sharing options...
mallyJJ87 Posted October 23, 2011 Share Posted October 23, 2011 It sounds like a ground loop issue. Timd's suggestion above is spot on in my opinion; and there's a few other things you might want to try as well. If you've tried unplugging all of the rack cables one by one and the hum is still there then it's probably coming from a mucky power supply. If you're using a powered system is there an earth lift switch on the speakers? This could be an alternative to buying a DI to place between the mixer and speakers. Are you using balanced XLRs between the rack and the speakers? If not you might want to consider them as they're better at cutting out interference than unbalanced jack cables. Take a look at the wiring in the rack, and the equipment to see if any metal cases are in contact with one another; sometimes this can be an issue. It's debatable whether it's worth buying a power conditioner/ UPS (Uninterruptable power supply) at this stage; I'd try everything else first. Finally (and I'm sure you know this already) don't be tempted to disconnect any earth connections inside the mixer or speaker plugs. Good luck and let us know how you get on! Link to comment Share on other sites More sharing options...
Sound Man Posted October 23, 2011 Share Posted October 23, 2011 Do the speakers hum when the audio cables are disconnected from the rack and left floating? Have you got the rack and speakers connected to the same mains powerpoint? David Link to comment Share on other sites More sharing options...
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