ground loop question

Discussion in 'AV Receivers' started by StanB, Jul 17, 2005.

  1. StanB

    StanB Agent

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    I have a rotel 1090 and a denon 5803. I use the 1090 to drive my two mains. I have very loud hum and I mean loud when I touch the interconnect from the denon to the 1090. Here's the thing I don't understand. When I unplug everything from the outlets (except the 1090) and also disconnect the cable line from the wall into my cable box, and then I plug in the interconnect from the denon to the rotel I still get the very loud hum. I would think with EVERYTHING unplugged from the outlets except the rotel and no TV cable connection, I would not be getting the loud hum just by connecting the interconnect from the denon. If I use a cheater plug, the probelm goes away. Any ideas?
     
  2. Wayne A. Pflughaupt

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    Stan,

    Maybe one of our more engineering-minded members can explain why, but it’s not unusual (and indeed quite normal) to get hum in the system when one of the components in the signal chain is not powered. That’s not the same as a ground loop, although it sounds like one.

    Regards,
    Wayne A. Pflughaupt
     
  3. Brad Wood

    Brad Wood Stunt Coordinator

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    Stan,
    My guess is that you have a grounding issue between the 5803 which uses a two pin AC power plug and the Rotel 1090 amp which is properly grounded utilizing a three pin power plug.

    In recent years, there has been alot of discussion in professional audio about the "pin 1 problem" and correct grounding techniques using the cable shield to chasis ground. I doubt chasis ground is of much help in consumer audio however, as pro audio components are usually mounted in metal racks that are bonded to the house ground.

    I don't have first hand knowledge of the grounding configuration of either the 5803 or the 1090, but my guess is that one of these (likely the Denon) is causing a grounding problem. Rather than using the "cheater plug", try lifting the cable shield on your RCA cable. Make sure that you lift the shield at the Rotel end. If you lift it at the Denon end, the shield just becomes an antenna and will route any extraneous noise or RF into the input of your amplifier.

    Give that a try, and see what happens. I'd be curious to hear from other Denon/Rotel owners to see if they had the same grounding issue.
     

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