I'm out of ideas - ground loop buzz.... (1 Viewer)

[Gary Thomas]

I've been battling an annoying ground loop problem caused by my satellite connection. Here's the background:

Dish satellite properly grounded, along with phone ground and house ground at 1 point on grounding rod.

RG6 cable from outside box to satellite receiver. When I disconnect the cable, the buzz goes away. When connected to satellite reciever, buzz is present even w/ unit turned off.

I have tried disconnecting every other plug, one at a time, with no effect on the buzz.

1/2 components plugged into a Panamax surge protector, other 1/2 into a Belkin surge protector. Both plugged into dedicated 20 amp outlet. I tried plugging the Belkin into the Panamax w/ just 1 plug going to the outlet...no effect on the buzz.

When satellite cable is run through the Belkin surge protector, 50% of buzz goes away.

I tried a Jenson ISO Max, but discovered it is not compatible with satellite.

No other grounds in house...with the exception of a plumbing ground - basically it is a 2' long ground wire connecting a pipe on either side of a valve.

I do have a Lutron dimmer in home theater room, but it is not on the HT outlet. It controls track and rope lighting on the ceiling & in a tray. The track lighting hums a bit when on, but is silent when off.

What am I missing??? Are there any ground loop eliminators for satellite? Any other ideas?

Thanks!

Equipment List:
Echostar Satellite Receiver
Panasonic DVD Player
Denon Receiver
Samson Amp
Behringer EQ
VCR
IR Repeater

 

[John Robert]

Gary:

I just went thru the exact same problem with my satellite cable; when I unhooked it hum went away. I solved problem by purchasing inexpensive quad shielded cables and running the connection thru my Monster Power 2600. Does your Panamax have cable in/out???

P.S. What a relief to get rid of that hum! I was hearing it in my sleep...

 

[Gary Thomas]

John:

Yep, I am running it through the Panamax...which reduces the buzz. Also, it seems as though the Panamax eliminated the buzz from the main speakers, but left it in the subwoofer.

Interesting suggestion about the cheap cable...I actually tried a better quality cable & the buzz got louder!

 

[Matt_Doug]

Run your satellite cable through the belkin surge protector and plug your sampson amp and any other component with a 3 prong plug into it also. If you still get significant hum its your dimmer or a component with a noisy rf modulator like your satellite box, tv...etc

 

[brucek]

Dish satellite properly grounded

Can you be more specific here?

Is the dish 'antenna' itself grounded, and to what?

Are the one or two RG-6 feeds from the horn passing through a grounding block outside and where is the block located in distance from the horn and what is it grounded to?

If there is a grounding block outside, how long is the run of RG-6 from there to the sat receiver?

Describe what audio and video cables leave your sat receiver and where do they go?

brucek

 

[Gary Thomas]

There are 4 cables going about 10 feet from the dish to the grounding block. 1 of the cables has an attached ground wire that goes from the arm of the satellite dish to the grounding block. The grounding block has a ground wire that goes about 8 feet to the house grounding rod. Also attached at the rod is the house ground and the phone ground. The 4 cables go from the grounding blocks to 4 locations inside the house. The run to the HT in question is pretty long...about 50 feet.

The receiver has the following cables attached:

S-Video + Audio From VCR
Toslink + S-Video From Dish
Toslink + S-Video From DVD
6 Audio Cables from DVD for DVD-A
S-Video Out to TV
Sub Line Out to EQ, then to Amp.
Plug "in" from Panamax Surge Protector

Thanks!

 

[Parker Clack]

Gary:

If you unplug the satellite feed does the hum go away, in particular to the sub?

Parker

 

[Gary Thomas]

When I unplug the satellite feed, the hum goes away in all speakers, including the sub. It is dead silent!

 

[brucek]

When I unplug the satellite feed, the hum goes away in all speakers, including the sub. It is dead silent!

When you say this, do you mean unplug the RG-6 that feeds the sat receiver, or unplug the cable that goes to a surge device from the antenna?

If you bypass the surge device and go directly into the sat receiver, does the hum go away or stay the same or increase?

If you leave the RG-6 hooked to the sat receiver (while it causes the hum) and unplug the other 3 RG-6 cables in the house from their devices, does the hum go away?

Sorry for all the questions..... brucek

 

[Gary Thomas]

I may have hit on something...

I previously unplugged every other component one at a time w/ no improvement. I didn't think to unplug both the subwoofer amplifier and the subwoofer EQ. That did the trick. The hum stays gone when I lift the ground (using a 3-2 plug adapter) on the plugs of the amp & eq.

Since I don't want to lift the ground permanently...what can I do to fix it safely?

Bruce:

The hum disappears when I disconnect the feed to the satellite receiver. If I don't go through the surge protector the hum is much worse.

It seems as though the hum is a result of problems between the satellite ground and the subwoofer amp & eq ground.

 

[brucek]

Since I don't want to lift the ground permanently...what can I do to fix it safely?

I would guess that if you only '3-2 cheated' the EQ and not the amp it would also cure the problem. If it's a BFD feedback destroyer, I hate to advocate cheating it permanently, but the BFD is a bugger for that problem. I admit to having mine cheated, relying on the fact it gets its safety connection through the interconnects and I have it set back in a shelf.

Short of that you have to correct the slight sat ground difference.

Your satellite system as you've described appears correctly installed. Actually better than most. Many installations 'only' put a ground rod outside (near the antenna) and then ground the dish and 'cabling grounding block' to that rod - and that's it. No attachment to the house system. You appear to have it connected to house ground - that's good.

The grounding block should be bonded to the house ground with at least a #6 wire. This bonding will lower the shield ground potential of the RG-6 cables to the same as the house safety ground (third prong). This greatly lowers ground loop problems.

A number of problems can occur that allows the shield potential to be slightly different on the RG-6 from the satellite in comparison to the safety cold ground of your electrical system at your HT receptacles. Any small potential difference between these two grounds will start current to flow and usually ends up flowing in an interconnect shield in your HT. An interconnect circuit has a loop path (completed circuit) that flows through the centre conductor of the interconnect cable and back on the shield. If there is an AC signal on the shield flowing because of the ground difference potential, you'll hear a hum.

You definitely appear to have a potential difference between the sat cable shields ground and the house safety ground at the HT receptacle. You have identified the source and now you have to fix it. There are some possibilites.

1. The ground cable that bonds the satellites grounding block to your house ground is not of sufficient gauge. The higher resistance of this cable doesn't allow the shields to drop to the house ground potential.

2. The shield itself of the RG-6 from the outside grounding block to the receiver is resistive either by poor connection at the termination ends or damaged somehow, and so raising its potential.

3. One of the 3 devices that the other RG-6 cables are attached to are not properly grounded or are somehow raising the ground potential and passing this level through all the RG-6 shields.

4. The house ground is insufficient. Usually a ground is chosen such as the plumbing directly as it exits the house and then the load center is attached to that spot once the safety and neutral are bonded in the main panel. Offtimes supplementary ground rods are added because of external plastic plumbing. They used to allow you attach this ground at any spot in your house plumbing and then put a jumper wire at the water meter to make continuity, but they don't allow this any more. The jumpers would become resistive and not provide a low impedance path to ground. Now you have to attach to the exit side of the water meter as it enters the earth - no jumpers allowed. Ensure these wires and clamps etc are all in good shape.

5. Even bad interconnect cabling in your HT can cause hum that may be falsely blamed on electrical ground problems. A single ended connection requires it's shield for a completed circuit, but if a shield is broken, the signal will usually find another path through another shield or interconnection. The broken shield in this case is not revealed, but a hum begins when an outside influence like a sat or cable tv potential is attached.

Even if you do all this, problems do occur for no apparant reason. They're tough to find. Even though the safety ground is a cold conductor, it can, and usually does, develop a small potential, through mutual inductance, wire resistance and various other reasons that can be different at each receptacle in your house, particularly in long runs from the loadcenter. The long run increases the overall resistance of the safety wire and it can develop a small potential. Then if you bring another ground into the same area from a different route, it can be different than the safety.

Anyways, that's just a few ideas.......................... or you can just cheat your BFD (although I'm of course not recommending it)

brucek

 

[Gary Thomas]

Fantastic Post Bruce!! It will take me a little while to digest it...

The ground wire from the satellite block to the house ground is, I believe, 8 gauge. The 8 barely fit into the hole in the grounding block...I'm not sure if a 6 would fit!

The ground from the dish to the block, however, is very thin...probably 21 gauge. Should I replace that with the 8?

The EQ is a BFD. The equipment rack is located under stairs in an unfinished part of my basement. I use IR repeaters to control the system. The BFD is on the bottom shelf...no one should really go near it for any good reason. Cheating the BFD would do what kind of damage...shock, destroy the component... and what would cause such a problem?

I will definately check the cables from the satellite block to the satellite receiver...I used a connector to go from the original location to my equipment rack. I may replace the original cable (from the block to the basement) just for the heck of it...I've got some good quality RG6 laying around.

Thanks again!

 

[brucek]

Cheating the BFD would do what kind of damage...shock, destroy the component

The "third prong" is the electrical safety ground and is there to protect you and anyone who uses your equipment from electrocution. The safety ground is a cold conductor designed to provide a path to ground for safety protection against internal shorts inside your equipment when equipped with the three prong plug.

The third prong connects back to your service panel (where it is bonded to the neutral wire), and from there is connected either or both to your house plumbing or external ground rod.

On equipment with a third prong, the metal case and external metal parts are all connected to this safety ground when you plug the electrical cord into the wall. If a component fails inside a piece of equipment and the 120 volts shorts to the equipments case, then that case is now live and can electrocute you. If the safety ground was attached, then a breaker would trip to indicate you had a fault.

On equipment with two prong plugs, they are internally insulated from the external case to provide this protection without the third wire.

If a piece of equipment is cheated, but is connected to equipment that does have its ground connected, the cheated equipment is generally safe through the shield on the interconnects. But this is not accepted practice or even wise because one day you could forget and unplug the interconnects and the cheated equipment could shock you............but in a pinch as with the BFD, especially when its hidden away......well it's up to you.
Some people will only safety ground one component and rely on the interconnect cables to spread the ground to all the other chassis. This definitely rids you of any ground loops - but very dangerous practice.

brucek

 

[Parker Clack]

Gary:

You can also try putting a group loop isolator in the line between your satellite feed and your receiver. One such device, that a lot of members have used, is the Mondial Magic Box. It is a bit pricey but I have heard that it actually improves the picture quality too.

Parker

 

[brucek]

Since a satellite horns block amplifier receives its DC power from the receiver through the RG-6, you are not allowed to break the shield with one of these transformers....

 

[Matt_Doug]

Gary tried a line level isolator (jensen catv isomax ) anyway and he found it incompatible with his satellite receiver. I belive for 2 reasons: as Bruce mentioned passive rf amp/splitters draw their DC over the shields of coax connections from the receiver. Lift the ground, block the dc, no amplification of the sat signal. Also there is an insertion loss with the catv isolator which worsens the attenuation of the unboosted sat signal. This doesn't happen in cable cause their signal is boosted. But wouldn't adding an active rf amp allow the catv isolator to be used? more money I know. Also, why wouldn’t grounding everything with an earth ground reference at one point (the belikin surge protector) work also? As long as all safety grounds are established, secondary at site equalization of ground potentials shouldn't be a safety issue. Bruce laid out so many possible reasons for the potential difference you may never find it.

 

[brucek]

Bruce laid out so many possible reasons for the potential difference you may never find it.

Yep, ground loops can require a lot of investigation. They are illusive for sure.

brucek