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  • Help with ground issue

    I need some help with a ground loop problem.

    Background: last spring my wife and I bought and moved into a new house. The house was built between the World Wars, but the electrical system (originally knob and tube!) was renovated in 1998 with modern Romex and a modern circuit breaker. (I had our inspector make sure that all the living room and study outlets were connected to the new circuit panel with Romex during due diligence, and I personally verified that at least the outlet behind the equipment cabinet is connected to 3-conductor Romex. Shortly after we bought the house I had a 20A circuit installed in the basement for the multisub amp.

    Long story short, the living room audio wiring (18 speaker channels total - seven main channels with biamp capability for the LCR, four sub channels, four height channels, and an 8-channel signal snake going from the living room to the basement for the sub amp, along with a HDbaseT line to the TV over the mantel) was completed about two months ago. I hadn't had time to really dial anything in due to long work hours + new baby + etc., so I just hooked the seven main channels up to my AVR so we could have surround sound until I got things going. With a major matter at work winding down, I took the day off today to take measurements and set up the multisubs, run ARC, etc.

    Well...not so fast: ground loops galore! I get hum when I connect my AVR (an Anthem MRX300) to my mains amp (an ATI AT2007 in the same equipment cabinet), and when I connect my AVR to my multisub controller and amp (8x8 miniDSP feeding an ElectroVoice CPS8.5 in the basement, with a CL2X rated Mogami 8-channel snake feeding signal and the 12V trigger to the basement.) I've tried swapping power cords, running the AVR and amp both straight into the wall (no power strip), and nothing really changes the hum issue.

    I also tried troubleshooting by running signal cables directly from my iPhone to the mains amp and miniDSP. No noise. Then I tried from the analog outs of my Oppo BDP-83. Noise - until I disconnected the HDMI line from the AVR. Then no noise. Then I tried from the analog outs on the cable box. Same result. Disconnecting the cable didn't do anything.

    I do have another AVR (a Sherwood Newcastle R-972) but it's in a storage unit that I haven't had time to reach.

    And, here's the kicker. My MacBook power supply is plugged into an outlet on the other side of the room, but on the same circuit as the outlet into which everything but the sub amp is plugged in. The powersupply is always plugged in, because I'm lazy. I plugged my MacBook in to charge it, and the hum got much worse.

    So, do I need to send my AVR back for warranty service (I have I think 3-4 months of warranty left, thankfully), do I call an electrician to sort out the house ground, or both?
    --
    "Based on my library and laboratory research, I have concluded, as have others, that the best measures of speaker quality are frequency response and dispersion pattern. I have not found any credible research showing that most of the differences we hear among loudspeakers cannot be explained by examining these two variables." -Alvin Foster, 22 BAS Speaker 2 (May, 1999)

  • #2
    Re: Help with ground issue

    What happens when you unplug everything from the outlets and just have the receiver connected and only the LR channels connected?
    If nothing happens, then add your Oppo player with HDMI, if that works fine, then slowly start adding different components?

    You may also have to go through and check each outlet and make sure that everything is wired correctly and that there are no loose wire nuts or connections. You might also want to check your breaker box to see if the grounds and common are separated. I know that some electricians just wire the common and the grounds on the same leg and call it good, so that could also be an issue.

    Good luck
    If we all reacted the same way, we'd be predictable, and there's always more than one way to view a situation.
    What's true for the group is also true for the individual. It's simple: Overspecialize, and you breed in weakness.
    It's slow death.

    //Burn n' Die//Dream Weaver//Maximus//ABC Bookshelf Speakers//Dayton Twin Towers

    Comment


    • #3
      Re: Help with ground issue

      Originally posted by Thumper Tom View Post
      What happens when you unplug everything from the outlets and just have the receiver connected and only the LR channels connected?
      It works fine until I try to connect anything to the preouts. No hum when running the speakers off of the AVR. Connect a separate amp on the same circuit (and I tried a couple), noise. Connect the sub amp on the dedicated circuit in the basement, noise.
      --
      "Based on my library and laboratory research, I have concluded, as have others, that the best measures of speaker quality are frequency response and dispersion pattern. I have not found any credible research showing that most of the differences we hear among loudspeakers cannot be explained by examining these two variables." -Alvin Foster, 22 BAS Speaker 2 (May, 1999)

      Comment


      • #4
        Re: Help with ground issue

        Do you have a way to connect a ground from your receiver to your sub amp and see if the hum is still there.
        If we all reacted the same way, we'd be predictable, and there's always more than one way to view a situation.
        What's true for the group is also true for the individual. It's simple: Overspecialize, and you breed in weakness.
        It's slow death.

        //Burn n' Die//Dream Weaver//Maximus//ABC Bookshelf Speakers//Dayton Twin Towers

        Comment


        • #5
          Re: Help with ground issue

          Sort of, but not with much copper. The snake going between the AVR and sub amp has 3 unused balanced lines (1-4 are used for signal and 8 for the trigger.) Snake is the CL2X-rated variant of Mogami W2932 so that means 6 25AWG connectors, 3 shields, and 2 ??? AWG drain wires.

          However, my external mains amp is about 4' away from the AVR, and has the same problem. (I would prefer to use the ATI monstrosity rather than the AVR's internal amps to power my "top seven.") So literally just run a wire (say, a speaker cable) between a screw on the AVR and a screw on the amp chassis?

          Lastly, the AVR has a 2-prong IEC plug.

          Does that matter?
          --
          "Based on my library and laboratory research, I have concluded, as have others, that the best measures of speaker quality are frequency response and dispersion pattern. I have not found any credible research showing that most of the differences we hear among loudspeakers cannot be explained by examining these two variables." -Alvin Foster, 22 BAS Speaker 2 (May, 1999)

          Comment


          • #6
            Re: Help with ground issue

            try removing cable television signal from the system.
            craigk

            " Voicing is often the term used for band aids to cover for initial design/planning errors " - Pallas

            Comment


            • #7
              Re: Help with ground issue

              Originally posted by craigk View Post
              try removing cable television signal from the system.
              My first step, if only because everything worked without a hitch in my old loft, and the only new component is the cable box.

              Did not affect it at all. The one broken connection that did matter was when I ran two interconnects from my BDP to the amp. With the HDMI line from the AVR connected there was noise. Unplug the HDMI cord, no noise. Plug it back in, noise.
              --
              "Based on my library and laboratory research, I have concluded, as have others, that the best measures of speaker quality are frequency response and dispersion pattern. I have not found any credible research showing that most of the differences we hear among loudspeakers cannot be explained by examining these two variables." -Alvin Foster, 22 BAS Speaker 2 (May, 1999)

              Comment


              • #8
                Re: Help with ground issue

                any chance of changing the HDMI cord ? could it be bad ?
                craigk

                " Voicing is often the term used for band aids to cover for initial design/planning errors " - Pallas

                Comment


                • #9
                  Re: Help with ground issue

                  Originally posted by craigk View Post
                  any chance of changing the HDMI cord ? could it be bad ?
                  I swapped out all of the HDMI cords, alas. And swapped them out for different types. (I bought a bunch of the newish thin PE ones with an end about the size of a USB cord, to get my last order up to free shipping, and had my old ones still.)

                  The hum happens happens basically any time I hook an amp up to any preout on the AVR, or the BDP when it's connected to the AVR over HDMI. (And yes, I swapped all the interconnects as well for known good ones. That was annoying because I cut my interconnects to length and combine them in a Techflex sleeve to make a snake, but it did show me the RCA cables weren't the problem.)
                  --
                  "Based on my library and laboratory research, I have concluded, as have others, that the best measures of speaker quality are frequency response and dispersion pattern. I have not found any credible research showing that most of the differences we hear among loudspeakers cannot be explained by examining these two variables." -Alvin Foster, 22 BAS Speaker 2 (May, 1999)

                  Comment


                  • #10
                    Re: Help with ground issue

                    Originally posted by Pallas View Post
                    It works fine until I try to connect anything to the preouts. No hum when running the speakers off of the AVR. Connect a separate amp on the same circuit (and I tried a couple), noise. Connect the sub amp on the dedicated circuit in the basement, noise.
                    This explains the source of ground loops, and the fixes for them.
                    http://www.rane.com/note110.html

                    They're not caused by lack of grounding, they're caused by devices being connected to ground via multiple pathways. Unbalanced connections are the worst to deal with, as they mix AC and signal grounds. Transformer isolation of the interconnects is the usual best method to fix them. That includes transformer isolation of TV cables.
                    www.billfitzmaurice.com
                    www.billfitzmaurice.info/forum

                    Comment


                    • #11
                      Re: Help with ground issue

                      Check, with a voltmeter for ground shifts between problem equipment.
                      I didn't try to follow your description of the house wiring fully, but are
                      you comfortable following them all back to the box, then checking how
                      the grounds are handled in the box? Don't go in, obviously, if you don't
                      know what you are doing.
                      Wiring is often sloppy, with loose connections and often much worse.
                      I've done house wiring since I was a kid, and had a summer job working
                      with an electrician at one of the major food brands.

                      Comment


                      • #12
                        Re: Help with ground issue

                        Originally posted by billfitzmaurice View Post
                        ***They're not caused by lack of grounding, they're caused by devices being connected to ground via multiple pathways.
                        That's why I'm confused why I'm getting hum from an AVR and a mains amp plugged into the same outlet. Including when they're the only two things plugged into to said outlet.

                        Originally posted by billfitzmaurice View Post
                        Unbalanced connections are the worst to deal with, as they mix AC and signal grounds. Transformer isolation of the interconnects is the usual best method to fix them. That includes transformer isolation of TV cables.
                        Any recommendations for cost-effective isolation transformers? The Jensen ones will end up costing about as much as my AVR for 8 channels + cable!

                        Also, even with isolation transformers there will still be a connection between the gear from the 12V trigger. Trigger setup is AVR to Emotiva ET-3 trigger box, mono 3.5mm cable to mains amp in equipment cabinet, mono 3.5mm cable hacked up and run down the 8th channel of my snake, connected to a Panamax M4000 20A surge protector And yes, I've taken the trigger box out of the equation. I've also plugged the sub amp into an "always on" outlet in the surge protector and run the trigger directly to the "power remote" terminals on my sub amp.
                        --
                        "Based on my library and laboratory research, I have concluded, as have others, that the best measures of speaker quality are frequency response and dispersion pattern. I have not found any credible research showing that most of the differences we hear among loudspeakers cannot be explained by examining these two variables." -Alvin Foster, 22 BAS Speaker 2 (May, 1999)

                        Comment


                        • #13
                          Re: Help with ground issue

                          I would also look at the circuit panel. is the 120 volt 20A breaker next to a 220 amp circuit ? this can cause noise. also is the neutral L1 and L2 really grounded like they should be or are they running to the same bus ?
                          craigk

                          " Voicing is often the term used for band aids to cover for initial design/planning errors " - Pallas

                          Comment


                          • #14
                            Re: Help with ground issue

                            Same outlet, that is odd, still I would open it and have a look, if there is a way
                            to screw it up some worker will make it happen.

                            Comment


                            • #15
                              Help with ground issue

                              Originally posted by Pete Basel View Post
                              Same outlet, that is odd, still I would open it and have a look, if there is a way
                              to screw it up some worker will make it happen.
                              I did, to verify that it was new wiring and not knob and tube. Now, I'm anything but an expert, but the three poles looked correct, and were tightly secured.

                              I'm leaning toward an issue with the AVR. Any combination of the stuff I on hand to test works fine...except anything that involves an avr preout to an external amp. I'll try to grab my Sherwood R972 from storage soon to verify, and have something to use if the Anthem needs to go for warranty service.

                              I'll also take a look at the panel and the grounding outside in daylight tomorrow. Assuming I get out of the office while it's still light...
                              --
                              "Based on my library and laboratory research, I have concluded, as have others, that the best measures of speaker quality are frequency response and dispersion pattern. I have not found any credible research showing that most of the differences we hear among loudspeakers cannot be explained by examining these two variables." -Alvin Foster, 22 BAS Speaker 2 (May, 1999)

                              Comment

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