What solution do folks use for the dreaded BFD hum? - Page 12 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #111 of 330 Old 11-18-07, 09:00 AM
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Re: What solution do folks use for the dreaded BFD hum?

If it is not grounded at or near the entry point it would be a viloation of electrical codes in the USA, and could be the source of the problem. Unfortunately, grounding problems are all too common.

http://www.hometheatershack.com/foru...html#post62267




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post #112 of 330 Old 11-18-07, 09:19 AM
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Re: What solution do folks use for the dreaded BFD hum?

Thanks for the quick response.

I'm not familiar with Jensen Transformer products. I don't mind ordering online but I would like to grab one locally if possible so I can get the hum sorted out today if possible. Can you typically find their products at any type of local store or are they usually only available online? What kind of local store would you usually find them, it they were to be found locally?

-Rich


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post #113 of 330 Old 11-18-07, 09:20 AM
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Re: What solution do folks use for the dreaded BFD hum?

Wayne,

Its so strange that this thread was just resurrected after all this time - I was just getting ready to post an update to where we last left off based on some testing from last night!

As you may recall a bit earlier in this thread you helped me understand how to create one of these XLR adapters to solve my hum problem.

This worked great for several months, but recently I started getting this VERY slight hum from my subwoofer that was only noticeable when a source (such as my HD DVD player or STB) was outputting a signal AND it wsa in a silent passage. Nonetheless its been driving me crazy.

So in other words if the source was not sending a signal, such as if a HD DVD was stopped and my AVR showed not bitstream or PCM signal, then there was no slight hum. But once I hit play, during silent passages I could hear the hum - and if I hit mute on the AVR the hum would go away. And I know this is not the HD DVD player as the same thing would happen with other sources.

I rechecked all my connections and things looked fine. Eventually I became suspicious over my home made RCA female to XLR plug with the wiring change to isolate the ground loop. And that's indeed what turned out to be causing the slight hum.

I verified this by temporaily putting a cheater plug in and removing my custom adapter, connecting it instead with a standard Radio Shack female RCA to male Phono plug. Violia, no hum whatsoever.

Now I don't think that my custom XLR plug has gone bad (or at least not completely), because if I wire things direct without my XLR plug and without the cheater then it hums badly. And then if I insert my home made XLR plug then the hum stops completely - except for when the AVR is sending an active signal, in which case the hum returns. Again, with the cheater plug in and no custom XLR, I get no hum whatsoever at any time.

What do you think may be going on here? I don't think this is the typical grounding loop hum, because it only happens when there is an active source.

I really hate the idea of sticking with the cheater plug and would like to solve this once and for all.

Any ideas what may be going on here and how it can be definitively solved without the cheater plug? Apparently my custom XLR approach was not the full solution (either that or it has gone bad, at least partially)?

Thanks!
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post #114 of 330 Old 11-18-07, 09:30 AM
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Re: What solution do folks use for the dreaded BFD hum?

Quote:
lcaillo wrote: View Post
If it is not grounded at or near the entry point it would be a viloation of electrical codes in the USA, and could be the source of the problem. Unfortunately, grounding problems are all too common.

http://www.hometheatershack.com/foru...html#post62267
Great information. Thanks for the link. What should I be looking for to ensure the cable feed is properly grounded to the ground rod? I'm not sure what the ground rod looks like or where it would be located. I'm assuming it is outside the house, perhaps close to where the electric, phone, and cable lines enter the house. Is that correct? Is there any danger in grounding the cable feed to the ground rod once I find it? I'm assuming it isn't connected to the ground rod or the connections isn't good since I obviously have a ground loop causing the hum.

I'm going to see if I can get under my deck and try to fix the actual ground problem when I get back from church this morning. I know I will need to remove a section of the lattice from the lower portion of the deck but I'm not sure I will be able to get far enough under the deck to access the ground block or the grounding rod. We'll see...

BTW, I am repeatedly blown away by how much great information is available on this site and the amount of help you guys are willing to offer. It is very much appreciated. Hopefully, I will be knowledgeable enough to contribute to the helping others someday.

-Rich


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post #115 of 330 Old 11-18-07, 01:48 PM
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Update: The hum is gone and it didn't cost any $

I just finished eliminating the hum so I thought I'd post an update on what I did to eliminate it.

I took off a small section of the lattice where the cable ground block is located and I also had to remove a couple of the planks above to gain enough access to the ground block. To my surprise, there was a ground wire (loosely) attached to the ground block but the other end wasn't attached to anything. I attached the other end of the wire to a clamp that was already on the main power ground wire which was connected to the ground rod. I tested my system to see if I had eliminated the hum and discovered it was still there.

My next step was to use my Dremel with a soft wire brush to remove the corrosion that had built up on the ground wire from the CATV ground block and the main ground wire. I reattached the ground wire from the CATV ground block and retested. The hum was still there. That is when I noticed the screw on the ground block was loose. Next step...

I decided to clean the end of the ground wire connected to the CATV ground block and snug it up. This wasn't as easy as you would think because the deck was built in a way that one of the joists obstructed the ground block. I had to use a small 1/4" wrench to sloooooowwwwwwly loosen the ground block from the wall just so I could get to the screw that applies clamping force to the ground wire. I cleaned this end of the ground wire and snugged it down. Hum test number 3: The hum is gone. Woohoo!!! I went back out and mounted the ground plate in a new location that is easier to access and put the two planks back in place. I will need to put the lattice back at some point but I think I will tweak the sound a bit now that the hum is gone.

I'm glad I was able to get the hum problem resolved and without shelling out $ makes it even sweeter.

I think the cable TV picture actually looks better now too but this could just be a placebo effect. One thing that was also resolved which I know isn't just in my mind is a hum in our phones that was getting worse and worse over the last year...

Thanks for all the information and tips guys. You ROCK!

-Rich


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post #116 of 330 Old 11-20-07, 07:27 PM
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Re: What solution do folks use for the dreaded BFD hum?


Congrats on your success, Rich!

lovingdvd,

There’s nothing wrong with your cables. The clue is here:

Quote:
Now I don't think that my custom XLR plug has gone bad (or at least not completely), because if I wire things direct without my XLR plug and without the cheater then it hums badly.
This tells me that the problem is that severity of your ground loop has become worse than it was.

Reviewing a couple of pages back, I noted that you said there was a grounding block for the cable service (post #89). Looking at that post again, this looks a little fishy:

Quote:
lovingdvd wrote: View Post
Here's a quick update... I check outside and there is a grounding block that is grounded into a cooper pipe. Looks like the telephone is also tied into this pipe. The cooper pipe runs inside the house and into the electrical panel. So it sounds like the cable is grounded properly.
This ground looks suspicious. There should be a copper ground stake somewhere for the electrical service, drove into the ground. I don’t really trust grounding to pipes.

Aside from that, in light of Rich’s success by cleaning up all the connection points of the ground connection, I’d try that first. In light of the fact that further corrosion of the ground’s connection points would make the hum increase in volume over time, I strongly suspect that this is where you’re going to find the problem to be.

Is it possible to get the wire from the ground block to the breaker panel directly?

Regards,
Wayne



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post #117 of 330 Old 11-20-07, 09:16 PM
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Re: What solution do folks use for the dreaded BFD hum?

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Wayne A. Pflughaupt wrote: View Post
This ground looks suspicious. There should be a copper ground stake somewhere for the electrical service, drove into the ground. I don’t really trust grounding to pipes.

Aside from that, in light of Rich’s success by cleaning up all the connection points of the ground connection, I’d try that first. In light of the fact that further corrosion of the ground’s connection points would make the hum increase in volume over time, I strongly suspect that this is where you’re going to find the problem to be.
Thanks Wayne! I definitely think you are on to something here. It appears that my "ground" is not grounded at all!

Here's what I mean - I just went and took another look outside. Basically there is about a 1/4" copper pipe that is mounted along the side of the house. The pipe is not in the ground at all!

It actually starts about 18" off the ground and runs for about 2 feet along the side of the house where it then gets routed into the house. From the inside of the house I can see where it comes in from outside and runs inside my electric breaker panel where I assume it is connected in.

On the outside of the house there is a metal-like wire that runs from the cable TV line and attaches to the copper pipe via a basic little metal terminal block (the wire is pinched to the pipe via this block/screw). Similarly the telephone outside line has a wire that runs from the phone box to this copper pipe.

So again, the pipe runs from the electrical panel, outside the house and then stops way short of the ground, with cable tv and telephone attached to it. As I examined the pipe closer, I noticed that it is very sharp on the bottom edge as if it had been broken off.

I am not the original homeowner so who knows what went on way back when. I'm thinking that perhaps something outside the house caused the copper pipe to break off. Then again I don't see the other half coming up from the ground either, so who knows, maybe it was never put in right in the first place.

Am I correct to assume then that based on this my electric panel is not really grounded at all?? And I suppose this has implications beyond just my home theater?

Now as far as fixing this thing goes - what is my best option? I am NOT very handy at all (still a miracle I managed to make my own XLR cables ) . And there's no way I'm cracking open the electrical panel. Sounds like I need an electrician to come out and fix things up. Do you agree? I just want to make sure that's really needed - don't want to pay their fee only to have them come out and say its grounded properly already.

Quote:
Is it possible to get the wire from the ground block to the breaker panel directly?
Not sure what you mean by this... ? I think the answer is no, because a) currently I have nothing that really runs literally to ground, and b) it doesn't look like I can get to anything in the panel without cracking it open and that's the last place I want to mess around!

Thanks again!!
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post #118 of 330 Old 11-21-07, 08:14 PM
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Re: What solution do folks use for the dreaded BFD hum?


Good detective work there, lovingdvd!

How does this copper pipe attach to the breaker box? Typically if it’s conduit, it’ll be with an EMT box connector (I think that’s what they call them):




But I’ve never seen copper pipe used for anything electrical.

I’m wondering, how old is your house? Does it have grounded outlets?

Quote:
Not sure what you mean by this... ? I think the answer is no, because a) currently I have nothing that really runs literally to ground...
I meant from the cable TV ground block to the panel, but I see now there is no reason to do that.

Quote:
...and b) it doesn't look like I can get to anything in the panel without cracking it open and that's the last place I want to mess around!
Hmmm... Well, I guess there isn’t much more that we can do.

Have any friends with some electrical knowledge that might be up to tackling this?

Regards,
Wayne



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post #119 of 330 Old 11-22-07, 02:05 PM
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Re: What solution do folks use for the dreaded BFD hum?

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Wayne A. Pflughaupt wrote: View Post
How does this copper pipe attach to the breaker box? Typically if it’s conduit, it’ll be with an EMT box connector (I think that’s what they call them):
Not sure - as it goes into the panel and disappears. When I open the door where the breakers are, you only see the breakers. The pipe actually runs into the panel underneath that.

Quote:
But I’ve never seen copper pipe used for anything electrical.
The best way to describe the pipe is that it is a hard flexible material. In other words its not completely rigid like a water pipe. Instead it can be bend - not easily but it can. In fact that is what they do to curve it to turn it into the house and then route it into the panel.

Quote:
I’m wondering, how old is your house? Does it have grounded outlets?
Less than 10 years old and yes all outlets are grounded. I believe my UPS battery powered backup devices I have (several) have a built in warning if you plug them into an improperly grounded circuit, and I've never seen that warning come on FWIW.

Quote:
Have any friends with some electrical knowledge that might be up to tackling this?
I'll ask around. Also I've called an electrician that does work for us. Hopefully he'll come out and take a look at it soon.

UPDATE: I just took a look at my neighbors house which is built by the same builder. From the outside his telephone and cable is grounded in the exact same way as me. Same copper-like "pipe", and just like mine it is NOT attached literally to (into) the ground.

Is it possible to have a properly grounded electrical panel when the other end is not literally steaked ito the ground?

I just had another thought - perhaps the electric panel is grounded by some other means, and the copper pipe leading outside the house is for the sole purpose of grounding the cable and telephone. If the panel was grounded some other way, then it would make sense that they could send this pipe out to connect other things to ground... ?

Also am I correct to assume that an electrician has the tools to be able to determine whether outlets in the house are grounded properly? If such a tool shows the ground is indeed ok, then where is my hum coming from???
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post #120 of 330 Old 11-22-07, 07:31 PM
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Re: What solution do folks use for the dreaded BFD hum?


Quote:
The best way to describe the pipe is that it is a hard flexible material. In other words its not completely rigid like a water pipe. Instead it can be bend - not easily but it can.
Wow, that sounds like the stuff they use on my water heater, between it and the wall!

Quote:
Not sure - as it [the copper pipe] goes into the panel and disappears. When I open the door where the breakers are, you only see the breakers. The pipe actually runs into the panel underneath that.
You only see breakers because there is a cover in place. Four bolts will remove it and let you see the “innards.” It’s perfectly safe to remove the cover – just don’t go sticking your hands in there!

Quote:
Is it possible to have a properly grounded electrical panel when the other end is not literally steaked ito the ground?
Not if it’s up to code.

Quote:
I just had another thought - perhaps the electric panel is grounded by some other means, and the copper pipe leading outside the house is for the sole purpose of grounding the cable and telephone. If the panel was grounded some other way, then it would make sense that they could send this pipe out to connect other things to ground... ?
That did occur to me, that the electrical ground stake is not readily available, so this was a means to provide a ground for the phone and cable TV.

I was thinking about attaching a wire to the CATV ground and using that pipe as a conduit to get the wire to the breaker panel, where it could be connected to the proper ground. If you pull the cover on the breaker panel, it should be easy to see the ground cable connection. I’m guessing that since it’s inside, the breaker panel is flush-mounted in a wall?

Quote:
Also am I correct to assume that an electrician has the tools to be able to determine whether outlets in the house are grounded properly?
You don’t need an electrician for that. This cheap gizmo from any hardware store will tell you if your outlets are wired correctly and are properly grounded:




Quote:
If such a tool shows the ground is indeed ok, then where is my hum coming from???
The cable TV ground is not consistent with the electrical ground – i.e., the two have separate paths to ground. If that’s not the problem, then the problem is in the feed itself, and the problem is “upstream,” and it would be their responsibility to fix it. But we need to make sure your ground is proper and secure before we start throwing rocks at the cable company.

Regards,
Wayne



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