Wall outlet AC hum

Discussion in 'Home Theater and Stereo' started by pillatier, Jul 7, 2019.

  1. pillatier

    pillatier Well-Known Member

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    I have positively traced the problem to the outlet. I am assuming it is grounding problem. How to chase down the problem? Is it the outlet, the switch (outlet is on a wall switch), or the breaker or the wire in between?
     
  2. Phil A

    Phil A Well-Known Member Top Poster

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  3. pillatier

    pillatier Well-Known Member

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  4. pillatier

    pillatier Well-Known Member

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    I found an article how to use a Multi-meter to check for ground problem, I will try that. Also, I decided to go ahead swap out the outlet for a hospital grade for improved contacts and also the wall switch for a commercial grade. They are each less than $5 at HD. If that does not solve then do further testing.
     
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  5. Barry_NJ

    Barry_NJ Well-Known Member

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  6. pillatier

    pillatier Well-Known Member

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  7. Barry_NJ

    Barry_NJ Well-Known Member

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  8. DYohn

    DYohn Bronze Member Donor Top Poster

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    Is the hum coming from your speakers or from the equipment?
    If you turn off the circuit breaker supplying the outlet, what else in your house loses power?
     
  9. pillatier

    pillatier Well-Known Member

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    The sound is from the speakers it's a 120Hz buzz sounds like the one in the PS audio link in Barry's post above. I have for now plugged system into another outlet on the wall that is from a different circuit altogether and the speakers are dead silent. Since I have a temporary solution I have put this problem in the back burner for now. If I recall correctly the breaker cuts off power to all the outlets and lights in the family room only. I had this other circuit put in to power my TV through a double conversion UPS in the basement. The UPS batteries died and the TV is ancient so I simply by passed the UPS.
     
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  10. Pete Mazz

    Pete Mazz Active Member

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    LED lights can introduce noise in the circuit.
     
  11. DYohn

    DYohn Bronze Member Donor Top Poster

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    LEDs and light dimmers. Are the lights in the room on a dimmer? Also try unplugging everything else in the room and if the hum is gone, plug them in one at a time until you locate the culprit.

    120Hx is an odd frequency for a ground loop or DC offset hum, so it's definitely coming from some other device on the circuit is that is an accurate estimate.
     
  12. pillatier

    pillatier Well-Known Member

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    I have LED bulbs in the recessed lights above the fireplace, but no dimmer. I noticed the buzz during the day when the lights are off. The only other source could be the gas fireplace main power switch, if it got accidentally turned on. I completely turned off the fireplace including the manual gas valve two winters back. There is nothing else connected in the family room.
    All the audio equipment is plugged into a Trickle Star surge protector power strip, which is then plugged into the wall outlet. The receiver is plugged to the control plug of the strip. Plugging the Trickle Star has silenced the system. In fact my first thought was to blame the Trickle Star.

    Tier 1 Advanced Power Strips - Tier 1 APS | TrickleStar
     
    Last edited: Jul 13, 2019
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  13. DYohn

    DYohn Bronze Member Donor Top Poster

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    Sounds like you have a DC offset issue not a ground loop and your power strip isolates it. That's good. Something on that circuit is causing a differential DC on either the neutral or ground or both. If you want to try troubleshooting further let's talk, but since your strip has solved it then you are set.
     
  14. pillatier

    pillatier Well-Known Member

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    The audio system has been on the strip for nearly ever. So the strip is likely not the source. When I thought it was the strip I first plugged in the receiver and the power amp directly to the suspect bad outlet, heard the buzz. Then I disconnected the receiver the buzz was still there - eliminating the receiver. Then I plugged the power amp to the good outlet buzz gone, plugged in the receiver no buzz. Now while writing this I thought of another test - the TV has been on the good outlet all this time and the rest of the system on the suspect outlet. I should plug in the TV and the system both to the suspect outlet and if the buzz is still there I can eliminate the TV. Turning off the TV turns off the display but some circuits in the TV are always on.
     
  15. Barry_NJ

    Barry_NJ Well-Known Member

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  16. pillatier

    pillatier Well-Known Member

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    Okay I did the test for the TV today. Starting condition - Trickle Star strip (with all the audio equipment) and the TV plugged to the "Good" outlet on the wall using up both plug in points - Silence.
    Test 1 - Trickle Star connected to the "Good" outlet on the wall - moved the TV plug to the Trickle Star always ON outlet - No Buzz. For clarity - TV and audio both now connected to the Trickle Star.
    Test 2 - Moved the Trickle Star strip with both audio and TV to the "Suspect" outlet on the wall - No Buzz
    Test 3 - Moved the TV from the Trickle Star strip to the "Suspect" wall outlet - No Buzz.
    Test 4 - Moved the Trickle Star to the "Good" outlet on the wall with the TV on the "Suspect" outlet - Buzz.
    Test 5 - Moved the TV to the "Good" outlet on the wall and the Trickle Star to the "Suspect" outlet - Buzz.
    Note - Test 5 condition was the original condition when I detected the buzz.

    Summary - when both TV and audio are on the same wall outlet either the "suspect" or "good" - No Buzz.

    So where is the problem? The TV or the problem is between the two wall outlets? Difference in ground potential perhaps? One more point the "Good" outlet is on a circuit that also has GFCI.
     
    Last edited: Jul 15, 2019 at 5:00 PM
  17. Barry_NJ

    Barry_NJ Well-Known Member

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    There is a difference in ground potential between the two outlets/circuits, so if everything is on a single outlet/circuit, you're good.
     
  18. DYohn

    DYohn Bronze Member Donor Top Poster

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    And again, the difference in ground potential is being caused by something else on the circuit. It could be your LED lamps. It could be a large motor like a refrigerator. It could be a dimmer. It could be nearly anything that uses a switched mode power supply.
     
  19. Barry_NJ

    Barry_NJ Well-Known Member

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    David, I'm confused now, is this DC-Offset or Ground Potential difference? I thought the Fridge, LED, etc could cause DC Offset on the AC circuit, and that a single system powered via multiple circuits would be Ground-Potential difference causing the hum(?) In this case, putting everything on a single circuit resolves the issue, so I thought Ground Potential. It was noted earlier that the different outlets are on different circuit breakers.
     
  20. DYohn

    DYohn Bronze Member Donor Top Poster

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    DC offset can cause ground potential difference because it carries the voltage on the neutral leg, which in a house is also the ground leg. "Putting everything on the same circuit" may have solved the issue because the issue is being caused by the TV.
     

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