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-   -   Improper Grounding causing Sub woofer noise (http://www.diychatroom.com/f18/improper-grounding-causing-sub-woofer-noise-149721/)

HarleyP 07-09-2012 06:50 PM

Improper Grounding causing Sub woofer noise
 
So I have a sub woofer connected to a stereo receiver, which is connected to a Cox Communications cable box via HDMI. At the old house I had no issues at all. At the new house, the instant the metal on the cable line contacts any metal on the cable box, the sub begins producing a loud tone.

After several hours of the cable company troubleshooting it, they came to the conclusion that the grounding on my home must have an issue. THey said since the cable coming from their plant is already grounded, and the circuit/home is not properly grounded, so the sub ends up using the cable line as the ground causing the line noise. To prove this, they ran an extension cord from the generator on their truck to power my sub. I was able to connect the cable line and the sub produced no extra noise, so their diagnosis seems accurate.

A buddy of mine suggested I check the voltage on the circuit the sub is using to check the ground. I get the exact same reading from Hot to Ground that I get from Hot to Neutral, which seems correct.

Anyone have any ideas as to how I can troubleshoot and fix exactly where my issue is coming from?

andrew79 07-09-2012 06:51 PM

check and make sure there is actually a ground, how old is the home.

HarleyP 07-09-2012 07:00 PM

I'm pretty sure there's a ground, but maybe not a good one? There is a wire that I believe runs from the main box down to a clamp around the metal pipe that comes out of the ground running up to the meter. I can't remember the exact configuration of it off the top of my head.

The home was built in 1991

andrew79 07-09-2012 07:12 PM

Quote:

Originally Posted by HarleyP (Post 961804)
I'm pretty sure there's a ground, but maybe not a good one? There is a wire that I believe runs from the main box down to a clamp around the metal pipe that comes out of the ground running up to the meter. I can't remember the exact configuration of it off the top of my head.

The home was built in 1991

it's got a ground then, probably just a lose connection, any number of things could be causing interference on a speaker. You could even have a power cord too close to the subwoofer signal wire. get yourself a plug tester and see if it shows an open ground on the plug with the cable unhooked.

stickboy1375 07-09-2012 07:40 PM

Is the Cable company grounded to the electrical grounding system, meaning, did they drive their own ground rod?

AllanJ 07-09-2012 08:05 PM

What you need to do is get a length of #12, #14, or #16 bare copper wire and connecting it to the "ground" of each piece of equipment. Start by disconnecting the cable TV cable and setting that aside. The connection of the new bare wire is usually done by holding the wire onto the equipment using one of the screws that penetrates to the equipment metal chassis, or fastening the wire to the shell of one of the input or output jacks. (For equipment with a metal body you can fasten the new wire to any exterior screw.) Daisy chain the wire from one piece of equipment to the next. Include the cable box. Connect the far end of the wire (splice on additional length if needed) to the fat ground wire that comes out of your electric panel box and goes to a ground rod or a water pipe.

Before reconnecting the cable TV cable, measure the voltage between its screw on cap and the shell of the jack of the TV or cable box or VCR it screws onto. If you measure 120 volts here, don't connect it but call the cable company back.

HarleyP 07-10-2012 11:51 AM

Quote:

Originally Posted by andrew79 (Post 961813)
it's got a ground then, probably just a lose connection, any number of things could be causing interference on a speaker. You could even have a power cord too close to the subwoofer signal wire. get yourself a plug tester and see if it shows an open ground on the plug with the cable unhooked.

Yeah I have a small outlet tester with the 3 lights, it shows everything as 'correct' in all the outlets i've tested so far.

HarleyP 07-10-2012 11:54 AM

Quote:

Originally Posted by stickboy1375 (Post 961834)
Is the Cable company grounded to the electrical grounding system, meaning, did they drive their own ground rod?

Not sure, they specifically said 'the line is grounded at the plant'. Unless there's something hidden in their locked up box in the yard I have no idea if there's an onsite ground.

HarleyP 07-10-2012 11:59 AM

Quote:

Originally Posted by AllanJ (Post 961865)
What you need to do is get a length of #12, #14, or #16 bare copper wire and connecting it to the "ground" of each piece of equipment. Start by disconnecting the cable TV cable and setting that aside. The connection of the new bare wire is usually done by holding the wire onto the equipment using one of the screws that penetrates to the equipment metal chassis, or fastening the wire to the shell of one of the input or output jacks. (For equipment with a metal body you can fasten the new wire to any exterior screw.) Daisy chain the wire from one piece of equipment to the next. Include the cable box. Connect the far end of the wire (splice on additional length if needed) to the fat ground wire that comes out of your electric panel box and goes to a ground rod or a water pipe.

Before reconnecting the cable TV cable, measure the voltage between its screw on cap and the shell of the jack of the TV or cable box or VCR it screws onto. If you measure 120 volts here, don't connect it but call the cable company back.

So you're saying with the cable line disconnected, create a new ground connecting the metal chassis from all of my devices to the existing ground outside, then check to see if I'm getting voltage between the outer/threaded part of the cable line to the outer/threaded part of the cable box jack?

What if there is little or no voltage? Just connect the line and see if the sub still makes the noise?

AllanJ 07-10-2012 12:16 PM

Quote:

Originally Posted by HarleyP (Post 962334)
So you're saying with the cable line disconnected, create a new ground connecting the metal chassis from all of my devices to the existing ground outside, then check to see if I'm getting voltage between the outer/threaded part of the cable line to the outer/threaded part of the cable box jack?

What if there is little or no voltage? Just connect the line and see if the sub still makes the noise?

Yes, connect the cable line back up and try out the subwoofer.

Did you say that the cable company put in an additional ground rod near where they mounted some equipment outside your house or where the cable enters? If you stilll have problems you could run a wire (best #6 gauge copper) from that rod to the fat ground wire coming out of your panel headed for a water pipe or another ground rod.

HarleyP 07-10-2012 12:36 PM

Quote:

Originally Posted by AllanJ (Post 962344)
Yes, connect the cable line back up and try out the subwoofer.

Did you say that the cable company put in an additional ground rod near where they mounted some equipment outside your house or where the cable enters? If you stilll have problems you could run a wire (best #6 gauge copper) from that rod to the fat ground wire coming out of your panel headed for a water pipe or another ground rod.

They haven't put any rods in the ground since I've had the place, so if there's any kind of pre-existing ground rods dedicated to the cable line I'm not sure. I'll try to look around for something when I get home today.

stickboy1375 07-10-2012 04:37 PM

Here is what I would try, just to rule out the circuit feeding your sub, I would run an extension cord to a receptacle closest to the electrical panel and see if the noise still exist, if the noise goes away, then you know you have an issue with the existing circuit, if it does not, you have an issue with the bonding of the cable company to the electrical system....

At that point I would go outside and look for where the coax enters the home from the street, look for the grounding block on the catv and follow the ground wire, it must be tied to the electrical grounding system.

I've seen guys bond the coax to a water spigot that was fed with plastic water lines... :no:


Here is an example of proper bonding of utility systems.
http://i171.photobucket.com/albums/u...9ecmCQfig1.jpg

HarleyP 07-10-2012 04:41 PM

Hrm alright, I have already tried running an extension to the bathroom GFCI outlet which I'm pretty sure is on a separate circuit, but it didn't stop the noise. There are some outlets in the garage that would be the closest to the panel, so I'll try those as well.

stickboy1375 07-10-2012 04:44 PM

Quote:

Originally Posted by HarleyP (Post 962510)
Hrm alright, I have already tried running an extension to the bathroom GFCI outlet which I'm pretty sure is on a separate circuit, but it didn't stop the noise. There are some outlets in the garage that would be the closest to the panel, so I'll try those as well.

Take some pics of the outside where the cable tv is located, might make it easier for us to give you an idea of what is going on.

HarleyP 07-10-2012 08:02 PM

Hrm ok so this is the first time I've really looked closely at how everything is setup at the electrical panel, what I assumed was the ground for the electrical panel is actually the ground for the catv.

http://i.imgur.com/6A7GF.jpg

I don't see anything going from the Electrical panel. You can see 1 unused clamp at the top, and then 3 wires further down that are bonded to the 'pipe' that goes up to the meter. The bottom 2 are the old phone ground, and the old cable ground, which are no longer used. The top and clean one, is the new one actually going into the catv box and bonding to the splitter inside. (here's a shot inside the box: http://i.imgur.com/pspah.jpg)


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