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I think I solved a ground loop issue with sound system. How do I make it code

I think I solved a ground loop issue with sound system. How do I make it code

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  #1  
Old 01-20-21, 01:03 PM
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I think I solved a ground loop issue with sound system. How do I make it code

I have a ground loop hum in my system. I removed it by grounding the Xfinity cable with the same ground as my audio equipment (power strip). Although Xfinity is grounded outside my home (Xfinity tech came and confirmed this), the hum must be coming from somewhere inside....Anyway, my below HACK removes the hum. I grounded the cable splitter in this pic to the power strip ground.

Clearly I need a permanent fix that is code.

Again, see 1st picture of my test that solved this issue. 2nd picture is an item I may buy, but that looks rather weak.

Was thinking of taking a computer cable (3 prong, heavy gauge) cutting both ends off of it. On the plug end, buy a DIY plug but don't connect the power leads, only the ground. On the other end, strip back just the ground end and connect it to the splitter. No way for that plug to have power to the wires, only the ground.

Any better ideas out there?




Thoughts?

 

Last edited by MRTkH; 01-20-21 at 02:28 PM.
  #2  
Old 01-20-21, 02:50 PM
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Hi, what system are you talking about, I would start at the source ie. where is the equipment plugged in, is that receptacle properly grounded, the grounds in the power cords should be grounding the equipment, unless they are all 2 wire cords..
Geo 🇺🇸
 
  #3  
Old 01-20-21, 04:20 PM
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Did you try ferrite rings?
 
  #4  
Old 01-20-21, 05:11 PM
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Using a (single conductor) wire you may ground the body or chassis of anything you choose (including a coax splitter) to a grounded outlet box (or strung downstairs to a grounding electrode conductor). Different piec es of audio or computer or video equipment may be bonded to one another with such a wire whose far end is connected to the outlet box or other known ground.
 
  #5  
Old 01-20-21, 05:15 PM
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Well, here is my solution.

That's an inside wall wire with a DIY plug. I may replace that wire but it's kind'a nice cause it doesn't flop around.

I cut the black and white wires on both ends, so they are not exposed on the splitter and inside the plug they are not even there..thus not in use. Only connected the ground.



 
  #6  
Old 01-20-21, 05:26 PM
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I'm a pro sound engineer. I run into ground loop problems continuously.

You need to figure out where the errant ground is. If you have audio hum then you must be interconnecting low level audio sources. That means you have a difference of ground between units.

Most units don't have a ground pin..... three prong plug. It's units that do that are prone to problems.
Even grounded cables systems can cause problem. An easy but incorrect way to fix the hum is to open/cut grounds. That you don't want to do.

When I get high end home system where the cable system causes problems I use a 1:1 isolator. It safely couples the coax ground but stops the ground loop. I use Jensen Iso Max's but the one in the link does the same thing.

Coax isolator
 
  #7  
Old 01-21-21, 07:32 AM
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Thanks, PJMax. I have a follow up response and tell me what you think:

Here are the facts. Note all of these existed BEFORE I grounded the splitter.
- Subwoofer is a powered sub. It does NOT hum when just plugged in power. So I believe hum is signal generated and not the power line.
- Subwoofer does NOT hum when connected to AVR via RCA cable.
- Subwoofer does not hum when I add Blueray player to AVR (via HDMI).
- Subwoofer does not hum when I add Apple TV to AVR (via HDMI).
- Subwoofer DOES hum when I connect Xfinity box to AVR via HDMI.

Xfinity tech came out and confirmed their cable wire is grounded at the home connection (outside wall). I visually could see their ground wire (green) going to the metal electrical pipe that goes into the ground.

More facts:
- Powerstrip that runs all units is shows "correct" when i use my plug test light. The light that shows if I have an open ground, reversed, etc.
- Xfinity box is a 2 prong plug.
- AVR receiver is a 2 prong.
- Subwoofer Amp is a 3 prong plug, so it gets ground.
- When testing I was plugging in subwoofer to same power strip.

Since I isolated the sound to only happen when I remove Xfinity receiver HDMI to AVR, it must be coming from Xfinity. Is my solution to simply ground the splitter ok? It stopped the noise, so that works. I realize I need to twist the copper wire around the nut and I will remove the other leads from the wire entirely--even though they are not connected to anything hot.
 
  #8  
Old 01-21-21, 11:32 AM
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Yes, ground the splitter if that works. I do not understand a need to remove the other leads.

The green wire going to the electrical pipe that goes into the ground may or may not be sufficient to ground the cable wire.

That pipe would be an adequate ground for lightning purposes if it ran underground for eight feet. It would be an adequate electrical ground if it continued to a properly grounded panel or junction box. (There is no such thing that protects from direct or near direct lighting strikes)

It is a good idea to connect the cable company coax shield to the house electrical ground at or before the first piece of your own equipment.Equipment with a three prong plug into a properly grounded receptacle normally does this although a separate wire connected to the equipment chassis or to the shell of an input or output jack and run to the house ground will also do. (For this purpose house ground stands for anywhere along the network of equipment grounding conductors e.g. going to outlet boxes or anywhere along the network of grounding electrode conductors e.g. going to ground rods.)

 
  #9  
Old 01-21-21, 12:03 PM
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It is a good idea to connect the cable company coax shield to the house electrical ground at or before the first piece of your own equipment.
Generally correct, but I've had that backfire-

Comcast ran the cable tv line through a spruce tree. Over time the branches wore away the insulation on the cable and the branches were touching the metal coax shield. Generally not a problem.
However, the spruce tree's branches grew until they were long enough to occasionally tap the powerlines.

So, during a gusty downpour thunderstorm, the wet spruce tree branches managed to touch BOTH the 15kv line AND the Comcast cable sheath ground. Took out every Comcast cable box on the block.

I was watching tv when it happened, bright flash, and a pencil-lead sized hole melted in the metal cable box where the cable ground jumped to the electrical ground.
 
  #10  
Old 01-21-21, 07:58 PM
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Unfortunately shorting of the 15 kv or so primary line at the top of the utility pole with other things will have bad not always predictable consequences. Comparable in nature although usually less in magnitude to lightning strikes.

Hopefully the cable company has since developed maintenance and other strategies to prevent a recurrence,

The ideas I have given are not against code.
 

Last edited by AllanJ; 01-21-21 at 08:37 PM.
  #11  
Old 01-22-21, 10:14 AM
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Originally Posted by AllanJ
-Unfortunately shorting of the 15 kv or so primary line at the top of the utility pole with other things will have bad not always predictable consequences. Comparable in nature although usually less in magnitude to lightning strikes.
-Hopefully the cable company has since developed maintenance and other strategies to prevent a recurrence,
-The ideas I have given are not against code.
You're right. I meant that "things fail in ways you never expected".

TANGENT- Following up on "a tree killed all the Comcast cable boxes on the block" had THIS:
-One summer during college the rest of the family went to the Jersey shore, I was taking summer classes and so was enjoying a long weekend of the house to myself. A Summer thunderstorm rolls through in the early evening, windy and rainy.
-And then around 9 pm, a local police cruiser slides to a stop in front of the house, slams into reverse, then barrels into the driveway, and rushes to the door, pounding loudly. I walk over -
"Hello officer, what's up??!"
"SHOW ME SOME ID, WHY ARE YOU IN THIS HOUSE?!"
"Uh, I live here, hold on, (rummaging around) here's my driver's license.
WHO ELSE IS HERE, WHERE ARE THEY?!
"Nobody else is here, it's just me."
THEN WHO DIALED 911?!
"Um, nobody dialed 911, I didn't."
WE GOT A 911 CALL FROM THIS HOUSE
"I'm the only person here, I didn't dial 911."
And then I get the bright idea to check the phone. Turns out, the insulation on the phone line had been worn away by a tree branch, and the phone had a dial tone, but was "clicking" every time the wind slapped a tree branch against it.
(Officer Listens to the clicking on the phone)
OK KID. SORRY IF I SCARED YOU.
DAMN, HOW DO I WRITE UP A REPORT EXPLAINING HOW A TREE DIALED 911?!
 
  #12  
Old 01-22-21, 11:12 AM
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If grounding the splitter solves the problem, it makes me think that the ground they used outside the house isn't properly bonded. Can you follow that ground rod/ground wire back into your electrical panel? I'm thinking a loose connection at the ground rod maybe.

Of course, ground loops can be caused otherwise too, but they are much more likely in a large venue with different panels and are rare in a residential environment.

If you stick with your grounding solution, the only change I'd make would be to replace the NM cable with a single strand of THHN or similar wire from the plug to the splitter. Same concept of course, but doesn't 'look' as potentially 'wrong'.
 
 

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