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  • Ground Loop isolator question

    I built my sister some Overnight Sensations a while back, run from the venerable Lepai 2020 amp. When i connected the amp to her new TCL 50" TV yesterday using an RCA-to-3.5mm cable, there was a pretty loud hum. When not plugged in to the TV, it's dead quiet. I'm assuming it's a ground loop hum. If so, is this the correct thing to get?

  • #2
    That should work fine. Here are a couple things to do to make sure it's a ground loop:
    Check the TV outputs directly, into headphones or another device if possible
    Check the Lepai amp directly, is there noise when sourced from your phone?
    Try a different outlet for the Lepai power supply, preferably on the same power strip as the TV. - Subquestion: does the Lepai power supply and / or the TV have a grounded plug? Does the TV have other inputs that are grounded, such as the HDMI inputs or a Coax cable?

    You may be able to cure your problem by lifting other grounds instead of adding the isolator. If all else fails.. add the isolator.
    Electronics engineer, woofer enthusiast, and musician.
    Wogg Music
    Published projects: PPA100 Bass Guitar Amp, ISO El-Cheapo Sub, Indy 8 2.1 powered sub, MicroSat, SuperNova Minimus

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    • #3
      Originally posted by wogg View Post
      That should work fine. Here are a couple things to do to make sure it's a ground loop:
      Check the TV outputs directly, into headphones or another device if possible
      Check the Lepai amp directly, is there noise when sourced from your phone?
      Try a different outlet for the Lepai power supply, preferably on the same power strip as the TV. - Subquestion: does the Lepai power supply and / or the TV have a grounded plug? Does the TV have other inputs that are grounded, such as the HDMI inputs or a Coax cable?

      You may be able to cure your problem by lifting other grounds instead of adding the isolator. If all else fails.. add the isolator.

      Yes, if the Lepai's PS has a ground prong in the plug. Many switching PSs tie their negative output to the ground prong. Easy to check with one of those 2 prong to 3 prong adapters at your nearest dollar store. Just don't attach the ground terminal to the outlet center screw.

      1mTyz.jpg

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      • #4
        Originally posted by Millstonemike View Post
        Easy to check with one of those 2 prong to 3 prong adapters at your nearest dollar store. Just don't attach the ground terminal to the outlet center screw.
        You can test it with that, but don't leave it there, it's a shock hazard. OP, the most common source of ground loop noise is the TV cable. That's what you need to transformer isolate. That's easy enough to test, disconnect the cable and see if the hum stops. The best way to get rid of ground looping between the TV and amp is by using the optical out, if the TV has one. You can't get a ground loop if there's no wire connection.

        www.billfitzmaurice.com
        www.billfitzmaurice.info/forum

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        • #5
          +1, My ground loops have been traced back to the cable box. Even with the TV off and the cable box off, I have to unplug the connection to the TV from the cable box
          John H

          Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

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          • #6
            Maybe you guys can help me. All my sockets have an open ground and have 2 or 3 prongs and no ground wire. My speakers buzz pretty loud so I borrowed a power conditioner and when I plug it into the 3 prong outlet it's almost gone but that outlet is across the room. If I put a GFCI outlet will that solve my problem?

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            • #7
              Originally posted by Ranis View Post
              Maybe you guys can help me. All my sockets have an open ground and have 2 or 3 prongs and no ground wire. My speakers buzz pretty loud so I borrowed a power conditioner and when I plug it into the 3 prong outlet it's almost gone but that outlet is across the room. If I put a GFCI outlet will that solve my problem?
              I think you'd need to provide additional details on what is in your system and how it's connected. Meanwhile..

              This part seems confusing:
              All my sockets have an open ground and have 2 or 3 prongs and no ground wire.
              A 3 prong plug and outlet is grounded, what do you mean there?

              If I put a GFCI outlet will that solve my problem?
              Nope. A GFCI outlet is a safety measure and has nothing to do with power conditioning or filtering.
              Electronics engineer, woofer enthusiast, and musician.
              Wogg Music
              Published projects: PPA100 Bass Guitar Amp, ISO El-Cheapo Sub, Indy 8 2.1 powered sub, MicroSat, SuperNova Minimus

              Comment


              • #8
                Assuming your 2 pin sockets are correctly wired you do have a ground wire, but it's only attached to the outlet frame. The so-called 'cheater' plug pictured above isn't intended to lift the ground, it's intended to provide it. The screw holding the cover plate to the outlet is removed, the plug inserted, then the screw is inserted through the lug on the side, connecting the third pin socket to the grounded outlet frame. However, if the ground wire is present as it should be you can just swap in a 3 pin outlet anyway.
                However, don't assume that this will fix a ground loop. Ground loops aren't caused by the lack of grounding, they're caused by too many ground pathways. This explains:
                http://www.rane.com/note110.html
                www.billfitzmaurice.com
                www.billfitzmaurice.info/forum

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                • #9
                  Originally posted by Ranis View Post
                  Maybe you guys can help me. All my sockets have an open ground and have 2 or 3 prongs and no ground wire. My speakers buzz pretty loud so I borrowed a power conditioner and when I plug it into the 3 prong outlet it's almost gone but that outlet is across the room. If I put a GFCI outlet will that solve my problem?
                  Does you PS have a 2 or 3 prong plug? If it is a 2 prong plug are the prong widths different forcing the plug into the socket in only one orientation? If not, try reversing the plug in the socket.

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                  • #10
                    If your receptacles are wired with romex, then you should see ground wires attached to the receptacles. If your house is piped in EMT conduit, then the metallic conduit and boxes provide the ground path and separate grounding wires are not required.

                    WOGG is correct about the GFCI. It can be used as a safety device in the absence of a ground wire or conduit system, but it will do nothing to remediate your ground loops.

                    Marv

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                    • #11
                      In my apartment I have both 2 and 3 prong outlets. I used a tester and all of them show open ground. I asked the landlord and he said there is no ground wire run to the outlets. My power conditioner is 3 pronged. The outlet where my stereo is only has a 2 prong outlet so I have to use an adapter and when I do my stereo hums a lot. The power conditioner has a long cable so I plugged it into the opposite wall that has a 3 pronged outlet and there is very little hum but was told by my girlfriend that no wires would be going across the room so that's out. Originally I thought getting the outlet grounded would solve the problem but after reading that article from Bill I am not sure. Looks like tonight I'll look up to see how the apt is wired ie if it has Romex or something else.

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                      • #12
                        My system
                        optical from TV >> smsl M8 dac with the smsl linear power supply >> Jolida hybrid integrated amp JD 1701 (iirc, I'll look it up tonight) tube pre amp with power amp >> Amigas

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                        • #13
                          Originally posted by Ranis View Post
                          . I used a tester and all of them show open ground. I asked the landlord and he said there is no ground wire run to the outlets.
                          I wouldn't trust him to know what he's talking about. Most two pole socket wiring has a third wire connected to ground, a much smaller gauge than the conductors, which might not have been connected to anything in the outlet box. Even old BX was grounded, by the metal sheath. One true two wire arrangement was post and knob, which was in my circa 1938 house. Even that can be wired to a 3 pole socket, connecting the neutral and ground. That's totally not to code, but not because it doesn't work. It's because if the ground lug is connected to the hot wire rather than neutral you've got a major shock hazard.

                          www.billfitzmaurice.com
                          www.billfitzmaurice.info/forum

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                          • #14
                            Originally posted by billfitzmaurice View Post
                            I wouldn't trust him to know what he's talking about. Most two pole socket wiring has a third wire connected to ground, a much smaller gauge than the conductors, which might not have been connected to anything in the outlet box. Even old BX was grounded, by the metal sheath. One true two wire arrangement was post and knob, which was in my circa 1938 house. Even that can be wired to a 3 pole socket, connecting the neutral and ground. That's totally not to code, but not because it doesn't work. It's because if the ground lug is connected to the hot wire rather than neutral you've got a major shock hazard.
                            I'm in an older house with lots of grounds via the BX sheath in metal boxes. Drives me nuts .. much prefer when I was in new construction with Romex throughout. And I've had a home with aluminum wiring - uuuggghhh

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                            • #15
                              Aluminum wire wasn't a problem, it was the hardware it was used with. https://www.carsondunlop.com/home-in...ring-part-one/
                              Aluminum wire is still commonly used by power companies, with compatible hardware.
                              www.billfitzmaurice.com
                              www.billfitzmaurice.info/forum

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