FAQ: Ground Loop nightmare!

[bootman]

Use the cheater plugs and invest in some good surge protection for your gear.
You will finally have some peace and your gear will be protected.

[hemster]

While of course cheater plug eliminate ground loops altogether, I do wonder about the stand an insurance company would take, if something untoward were to happen...

Maybe the legal eagles among us can chime in...

[bootman]

Why not use a good quality surge protector with cheater plugs.
Most of them have the MOV connected across hot and neutral anyway bypassing ground.

[Nemesis.ie]

I have a couple of those isolator things, one is the DTI in your link, I've not tried them yet though as I don't have a bad hum.

[selkec]

The insurance company does not have to know you use cheater plugs. if something were to happen

[fronesis]

I tested the AC wall outlet, and it's fine.

Also, I have a good quality furman surge protector/power conditioner. So I am probably OK with the cheater plugs.

But I have so many hours in this that I want to see it through, so I now have a series of items on order that may solve the problem more completely:

1. Hum X
2. "poor man's isolation transformer"
3. Directional RCA cables
(evidently these aren't just snake oil, because the shielding grounds them on only one end, thus breaking the ground path between my subwoofer and my amp --- oreilly.com/pub/h/4241)
4. I have the DTI isolator in my Amazon wish list

I'll report back.

[DYohn]

I am a bit unclear. Is the coax you are using (and that is causing the ground loop) supplying cable or DTV?

If it's cable, try one of these: Cable ground loop isolator

Driving a separate ground rod is not the answer as your cable/DTV and electrical service grounds should all be bonded together. As Selkec says, this is the responsibility of your building owner (or condo home owner's association.) If the grounds are not properly bonded, the building is not up to code.

Since your ground loop is only in the subwoofer and not the rest of the system it is possible your subwoofer amplifier has a bad power supply filter cap. Using an RCA cable with the ground lifted on one side (so-called "directional cable") might work.

Also, try connecting a wire between the RCA shield (outer ring) and the subwoofer amp chassis to see if the ground internal to the sub amp is defective.

Operating the sub amp using a ground lift "cheater plug" is fine and only dangerous to humans in the room should the sub amp short out and energize the ground plane. Not likely to happen. If using a cheater plug breaks the loop, use a cheater plug until the building owners repair their defective electrical grounds.

[fronesis]

Jun 8, 2011 10:22:48 GMT -5 DYohn said:

I am a bit unclear. Is the coax you are using (and that is causing the ground loop) supplying cable or DTV?

I have separate running service for both. Both buzz.

If it's cable, try one of these: Cable ground loop isolator

I had a special SAT version of one of these, and it seems to have failed. I already ordered another one.

Driving a separate ground rod is not the answer as your cable/DTV and electrical service grounds should all be bonded together. As Selkec says, this is the responsibility of your building owner (or condo home owner's association.) If the grounds are not properly bonded, the building is not up to code.

Agreed. And again, I am the owner.

I never said anything about driving ground rods. It's a very large building, with CATV and SAT running to lots of units. I am pretty certain that CATV and SAT ARE GROUNDED. The coax cable does NOT have AC on the line, so it is "properly grounded" according to specs.

But the building simply does not have one single, common ground for electricity and everything else. As selkec said in a later message, I think having two different ground potentials is a common occurence in a large condo building. It is a BRAND NEW building, all run professionally by direcTV and Comcast. They have a green grounding wire run into every unit's utility closet. But unlike a home, the coax ground is not bonded to the same single ground as the AC service. I think, now, that this is just how it works in new large MDUs.

Since your ground loop is only in the subwoofer and not the rest of the system it is possible your subwoofer amplifier has a bad power supply filter cap.

I have two subwoofers. Both buzz separately. The subs aren't the problem.

Operating the sub amp using a ground lift "cheater plug" is fine and only dangerous to humans in the room should the sub amp short out and energize the ground plane. Not likely to happen. If using a cheater plug breaks the loop, use a cheater plug until the building owners repair their defective electrical grounds.

I am using the cheater unit.

But I don't think I'm going to convince my condo board to try to recreate a single common ground for the entire building. That's not going to happen.

Having now studied this for days, I feel fairly certain that the problem is created by the difference in ground potential between my two prong Yamaha AVR and my 3 prong subwoofer amps. Once I connect the sub to the AVR with an RCA, then these two different grounds are competing. Once I then connect the coax, I have a second ground to run to, and the ground LOOP is completed.


I think the answers are:

- cheater plugs (working now)
- separate audio and video systems with optical audio (also works)
- ground loop isolator for video (if I can get one that's not defective)
- directional RCA, to prevent sub and AVR from seeing each others' ground
- audio isolator between sub and AVR
- hum X connection for AVR so that it effectively becomes a 3 prong ground.

[DYohn]

I'm glad you have solved your problem.

But your building is not to code and I am surprised you are the only one experiencing this issue. You really should bring it up to the home owners association.

[jedinite24]

Fronesis

Great you were able to track down where your ground loop came from. I currently have a ground loop issue but no patience to truly track it down. I do use the Ebtech Hum-X and for me it greatly reduced the hum coming from my speakers. Before the hum was really audible even from over 6ft away. With the Hum-X I now only hear the hum when I put my ear to the speaker. I've used the older squarish one as well as the newer rounded one.

[matt]

Jun 7, 2011 22:42:54 GMT -5 bootman said:

Why not use a good quality surge protector with cheater plugs.
Most of them have the MOV connected across hot and neutral anyway bypassing ground.

But not all of them avoid using the ground wire. I would place the cheater plug on the surge protector's outlet.

I am replacing all of my cheap surge protectors with Zero Surge 8R15T-I since MOV's accumulate damage and can fail in unpleasant ways. That model will dump the excess voltage to neutral and not wear out over use.

[matt]

Jun 8, 2011 10:44:41 GMT -5 fronesis said:

- audio isolator between sub and AVR

I like this one the best. It does not mess with the power or grounding.

I use a ART DTI Dual Transformer/Isolator, but not to prevent hum. I am using it to isolate the low frequency transducer amp's input from the sub's input / UMC-1's output. I just do not trust the low frequency transducer amp to be electrically connected to my more expensive equipment.

[fronesis]

Matt: you make a good point about the extra advantages of isolator for the signal. I haven't bought the ATI unit, but you have made me consider it.

Also, can you explain the differences between putting the cheater plugs on the sub cables (that are plugged into the surge protector) vs. putting one cheater plug on the surge protector cable itself? I think I just don't understand exactly how this works.


GENERAL UPDATES

1. The Hum X greatly reduces the hum.
Without the hum X, it is LOUD; with it, you have to put your ear to the speaker to hear anything at all. However, there is still some hum with it.

2. The directional RCA cables (from AVR to sub) didn't work.
Now, i tested these only with the Hum X already connected, so I was dealing with very little hum already. But it didn't remove that hum, and as far as I can tell it is not preventing the grounds from seeing each other. (Yes, I tried them both ways.)

3. The Poor Man's Isolation Transformer degrades the satellite signal.
It drops the signal strength from 99 to 77. Not a good choice.

4. The Satellite ground loop isolator leads to intermittent signal problems.
I had been using one of these successfully, and then the signal started break up. I ordered a new one, and it does just what the old one does. The signals strength measures OK, but there are all sorts of artifacts in the picture, and sometimes it goes out entirely.

Finally, then I see 3 (+1) overall options:

1. Leave the subs connected with cheater plugs (one way or the other).

2. Keep the audio and video paths isolated (and therefore give up on hdmi switching through the avr).

3. Use the Hum X and live with a tiny amount of hum.

4. Order an ATI signal isolator and see if it works better than the above.

[matt]

Jun 9, 2011 13:34:08 GMT -5 fronesis said:

...
Also, can you explain the differences between putting the cheater plugs on the sub cables (that are plugged into the surge protector) vs. putting one cheater plug on the surge protector cable itself? I think I just don't understand exactly how this works.
...

Most MOV surge protectors act like an open switch between hot and ground. When the difference between hot and ground is greater than a certain amount, it closes so that the huge difference does not make it into the appliance. Not all surge protectors work this way.

Note that a MOV is not exactly like a switch. It gets damaged every time it is used and the damage may lead to no protection or it closing during normal conditions (creating excess heat and hum on the ground wire).

electronics.howstuffworks.com/surge-protector1.htm

I disassembled a surge protector (do not try this at home) and found MOVs between hot and ground, neutral and ground, and hot and neutral. This design protects all 3 wires from a surge between any 2 of them or more. I am not sure of all surge protectors are this thorough. If your surge protector had this design, it could work with the cheater plug on either side. Although even if it could provide protection for your sub on either side, there may be a minor benefit to having excess current between ground and some other wire be shorted under surge conditions for the benefit other appliances connected to the circuit breaker. I am not sure about that thought.

[ausman]

sounds like a grounding issue with the rca plug rather than power..

[fronesis]

Thanks, Matt, for taking the time to reply. It makes a lot more sense now.

To Ausman: the RCA connection between the sub amp and the AVR is certainly part of the equation, but it is definitely not as simple as saying the problem is there and not in power. You don't have a ground loop problem if you don't have power, along with two different grounds with different potentials. The problem originates with having two different ground voltages in the AVR and sub amp; the problem is enabled when those two grounds "see" each other through the sub-out RCA connection; and the loop is completed, and the problem shows up, when the audio signal path is connected to the video signal path (when I plug hdmi into the AVR) and the voltage runs to ground through the coax cable.

What I've learned from this process is that a "ground problem" is never just one thing. It's a complex system, and it can be fixed at lots of different places.

In theory, my problem can be fixed by running a directional RCA between the AVR and the sub, but that doesn't work (I've got two subs and a dozen RCA cables that I've tested, and the problem is always there).

In my opinion, if you want to fix this sort of problem at its root, you start with power. Before I had a sub with 3 prongs and an AVR with 2, I had no problem. The fundamental source of the problem is in the ground voltage differences between those two devices. If you can't fix it there, then I think the next (closest to root) fix is in the signal path. And if that's not an option you fix it by eliminating the coax cable connection.

I could, of course, try out a line level isolator. And I may do that. But it's just not the case that the problem is simply an RCA connection. Of course, it's true that a BAD RCA cable can cause a hum in an otherwise perfectly fine system, but that's not what's happening in my case.

[dbster]

Have you tried
1) plugging some of the equipment into different outlets that aren't on the same circuit breaker ?
2) Connecting the chassis together with their ground connectors with a separate wire ?

[Nemesis.ie]

BTW, I connected my Behringer filter inline with my 2 rear (humming) subs and the hum went away.

[KeithL]

This may not seem helpful but..... GET A BETTER GROUND ISOLATOR.

Different isolator units have different capabilities and limits. There is no legitimate reason why the signal provided by your service CANNOT work through an isolator. Your symptoms there suggest that the isolators you have been using simply don't have enough bandwidth, and so degrade the signal. A better isolator, which isolates the ground, but doesn't degrade the signal while doing so should solve the problem. (You may need to pay more, and you may need to get some professional advice as to which one would work properly for you, but that is the direction you need to go in.)

Jun 9, 2011 13:34:08 GMT -5 fronesis said:

Matt: you make a good point about the extra advantages of isolator for the signal. I haven't bought the ATI unit, but you have made me consider it.

Also, can you explain the differences between putting the cheater plugs on the sub cables (that are plugged into the surge protector) vs. putting one cheater plug on the surge protector cable itself? I think I just don't understand exactly how this works.


GENERAL UPDATES

1. The Hum X greatly reduces the hum.
Without the hum X, it is LOUD; with it, you have to put your ear to the speaker to hear anything at all. However, there is still some hum with it.

2. The directional RCA cables (from AVR to sub) didn't work.
Now, i tested these only with the Hum X already connected, so I was dealing with very little hum already. But it didn't remove that hum, and as far as I can tell it is not preventing the grounds from seeing each other. (Yes, I tried them both ways.)

3. The Poor Man's Isolation Transformer degrades the satellite signal.
It drops the signal strength from 99 to 77. Not a good choice.

4. The Satellite ground loop isolator leads to intermittent signal problems.
I had been using one of these successfully, and then the signal started break up. I ordered a new one, and it does just what the old one does. The signals strength measures OK, but there are all sorts of artifacts in the picture, and sometimes it goes out entirely.

Finally, then I see 3 (+1) overall options:

1. Leave the subs connected with cheater plugs (one way or the other).

2. Keep the audio and video paths isolated (and therefore give up on hdmi switching through the avr).

3. Use the Hum X and live with a tiny amount of hum.

4. Order an ATI signal isolator and see if it works better than the above.

[Chuck Elliot]

www.jensen-transformers.com/datashts/vrd1ff.pdf

Solved my similar problem