Ground Loop Hum?

[P-Dub]

I just noticed a ground loop hum coming from my subs, which are being powered by a Sampson S700. My whole setup is plugged into one large surge protector. As far as I can tell, if I shut off the TV, the hum goes away. I don't notice it during movies.

So should I just leave it be, or try and fix it? Will it do any harm to my equipment? I'll be connecting my Sampson through my BFD, would that any differnece?




Paul

There are three kinds of people in this world; those that can count, and those that can't.

[Kevin P]

If the hum stops when you shut off the TV, it's probably not a ground loop. Instead, it's noise being picked up from the TV.

To rule out a ground loop, try using a cheater plug (one of those adapters that lets you plug a 3-prong plug into a 2-prong outlet) on the BFD or the amp, and see if the hum goes away. If it goes away, you have a ground loop. If it doesn't, take the cheater plug out and try relocating cables or equipment away from the TV.

KJP




Official Computer Geek and Techno-Wiz Guru of HTGuide - Visit Tower of Power
My HT Site

[Andrew Pratt]

Do you have a coax cable plugged into the TV? If so it could be that the coax cable isn't grounded properly. You might be able to ground it better or have the cable company come out and do it for you....or you can use a cheater plug but I'd frist try to fix the problem before resorting to a cheater plug.

[David Meek]

Paul,

Absolutely stay away from the cheater plug! Use it to identify if it is a ground loop hum and then take it out of the circuit. If it turns out to be the cable, and if you have cable it probably is, get the cable company to come out and fix it pronto. They may have used a separate ground and not used the "house" ground. This could lead to real problems if that is the case.

If it's not a dual ground problem, come to think of it, Burke has a little black box from Mondial that got him out of a hum problem. Burke, you out there?




David - HTGuide flunky
Our "Theater"
Our DVDs on DVD Tracker

[Burke Strickland]

1) The reason we are advising against long term use of a "cheater plug" (beyond very careful temporary use to test whether the hum is a ground loop problem) is because the thrid prong on the power cord is a safe path for shorted electricity and if it is defeated by using the cheater plug and there is a short which passes current to exposed metal surfaces of your components., you can become the circuit path for the electricity with potentially lethal results.

2) If your ground loop hum is the result of ground differential between the cable feed and and the rest of the systemm, it might possibly be corrected with some do-it-yourself techniques using inexpensive parts from Radio Shack (essentually two 75 ohm to 300 ohm transformers faced back to back) -- but since that didn't work effectively enough for me, I moved up to the Mondial Antenna Ground Isolation Circuit (aka MAGIC box) which completely silenced the sum for an investment of about $100.

For more info about the Mondial product: http://www.klipsch.com/mondial/index...line=mondial&1

Burke

[Wayne A. Pflughaupt]

This subject comes up a lot, so I thought is might be time for:

WAYNE’S COMPREHENSIVE GUIDELINES FOR TROUBLESHOOTING SYSTEM NOISE AND GROUND LOOPS


CATV Related

• There should be a
  <a href="http://www.partsexpress.com/pe/showdetl.cfm?&User_ID=7395190&St=4498&St2=-87762043&St3=83922387&DS_ID=3&Product_ID=2245&DID= 7" target="_blank">RF grounding block where the CATV service enters the house . There should be a thick wire (10-12 ga.) between the grounding bock and the house electrical ground stake (generally at the main breaker box). The ground wire must be securely screwed down and/or clamped at both ends.
• If the ground wire appears corroded or frayed, replace it with a new one.
• The ground wire should go directly from the ground block to the ground stake. If is routed elsewhere (like into the breaker panel) replace it. (I’m always suspicious of ground wires that “disappear” into the breaker box.)
• If the ground block is covered in layers of paint, replace it with a new one (the paint could be preventing good electrical contact).
• Once you are certain your RF ground issues have been addressed, disconnect the CATV service from the ground block. If the hum in your system goes away, the problem is not in your house, but somewhere in their feed, and they should fix it.

Last chance remedies:

• A pair of 75- to 300-ohm matching transformers, spliced together and connected in-line, will usually isolate and eliminate persistent CATV ground loop problems.
• I’ve heard more than once (primarily from Burke) that the Modial Magic Box will work when other ground isolation devices fail.

DSS Related

• Both the antenna and the coaxial feed should be grounded with a heavy-gauge ground wire to the house electrical ground stake. If your installer did a “quick and dirty” ground to the nearest water pipe (or similar), you have the potential for a ground loop.
• The coaxial feed should be properly grounded before it enters the house, per guidelines in “CATV Related,” above.

House Electrical Related

• It’s generally accepted that a dedicated circuit is a good way to insure reliable, noise-free operation of a home theater system. To further insure isolation from ground loops, multiple dedicated circuits should be connected to a single electrical leg (aka “phase”) at the service panel.
• There should be no light dimmers or electric motors sharing a circuit with home theater electronics.
• Dedicated circuits using Romex should not use 12-3 or 10-3, where the home theater circuit shares the same cable as another circuit (which is typically connected to the opposite phase). Due to proximity, any noise or interference from the non-HT circuit sharing the cable can be transferred directly to the HT circuit via inductance. Therefore only single circuit 12-2 or 10-2 Romex is recommended.
• Upgraded commercial or industrial outlets are recommended over cheap residential-grade devices. There is no good reason to use orange isolated ground (I.G.) circuits or I.G. outlets in a home theater. Also, “dedicated circuit” does not mean “single outlet.” A dedicated circuit can generally have as many outlets as needed within reasonable amperage limitations, without fear of inducing a ground loop.
• If a dedicated circuit is not in use, make sure all equipment is plugged into the same circuit. A remote sub plugged into the nearest outlet, for instance, might well be on a different circuit from the rest of the equipment. Even worse, that “different circuit” could be on the opposite electrical leg or phase. If it is not verifiable that other outlets are on the same circuit, make sure all the equipment is plugged into the same outlet.

Connections/Equipment Related

• For CATV, DSS and broadcast antenna signals, make sure only good quality coaxial cables are used throughout. Do not use the cheapie cables with push-on F-connectors that come with the equipment.
• If possible, bypass all splitters for testing purposes, and add them back one at a time to see if equipment elsewhere in the house is causing the problem.
• Amplifiers can induce noise into other electronics that are too close to them. Therefore make sure any and all other electronics – VCRs, cable boxes, external crossovers and equalizers, etc. – are at least six inches above or below a receiver or amplifier.
• Double check all system audio cabling, especially between the receiver and any outboard amplifiers. This is best done by disconnecting everything in the system, and then re-connecting one component at a time, noting if the noise starts when a particular piece is added. If you find a suspicious component, replace the cables with a known good set, to verify if the problem is with the component or the cables.
• Make sure your are using good-quality, well-shielded cables. Some “tweak” audiophile interconnects that do not use a shield, but rely on independent twisted conductors for noise rejection, which I expect is inferior to shielding if EMI is bad enough.

Regards,
Wayne A. Pflughaupt




My Equipment List

[Andrew Pratt]

Great reply as usual wayne!

[David Meek]

Hi Wayne! Glad to see you posting here.

The ground wire should go directly from the ground block to the ground stake. If is routed elsewhere (like into the breaker panel) replace it. (I’m always suspicious of ground wires that “disappear” into the breaker box.)

Amen, brother!




David - HTGuide flunky
Our "Theater"
Our DVDs on DVD Tracker

[P-Dub]

Great responses.

I actually moved my VCR down a few shelves, so maybe that's the problem.

Looks like I've got a nice list to go check though.

Thanks guys. :T




Paul

There are three kinds of people in this world; those that can count, and those that can't.

[P-Dub]

Okay, I've checked the amp with a cheater plug, the hum goes away. So if this is the case, would I still have a cable problem as well?

For a cable fix, what am I going to do with this part?



I need two, but am I just connecting the two loose ends together and feed my cable through one end and out the other?

Oh for my cable situation, I have it running out of the wall, into a splitter amplifier, then it goes to my surge protector, then through that and to the vcr and TV. Should I simplyify this setup first to see if it make a difference?

Okay, Wayne, I'm in way over my head when you talk all house connections.

Let's see if I can make some sense here.

Dedicated circuit - I have no idea, I'm sure some lights and other stuff is connected onto the same circuit. I don't think there's much I can do about that.

No light dimmers, no eletric motors.

What's a Romex and would that even apply to me if I don't have a dedicated circuit?

Outlets are pretty much as is, home grade.

All my gear is plugged into the same surge protector, which is plugged into one socket.

All CATV cables are the screw on type.

Hmm, I got some splitters, so I'll dump those and see what happens.

I've moved my Sampson amp to the top of the rack. No difference. I've even tried plugging it into different sockets on the same surge protector, and also the free socket on the wall. No change.

Most of my cables are of the okay variety. I'll switch some around, but I don't think replacing okay with okay is going to make a difference.




Paul

There are three kinds of people in this world; those that can count, and those that can't.

[P-Dub]

Okay, just for fun, I've hooked up my sub through my HK PA5800, a 5 channel amp which doesn't come with a 3 prong ground plug. No more hum from the subs, but now I hear a hum from the amp. :?: Too bad Andrew's away or I'd ask him if he has s hum coming from his amp.




Paul

There are three kinds of people in this world; those that can count, and those that can't.

[Wayne A. Pflughaupt]

Paul,

I'm headed out of town for the rest of the week. I'll drop in a reply on Monday, if no one has helped you by then.

In the meantime, if you can get brucek's attention he can put you on the right track.

Regards,
Wayne




My Equipment List

[Lex]

Great effort guys. Looks like your in capable hands Paul. This time, I am not sure I have a clue short of changing electrical circuits on some of your gear.

Or perhaps it's 1 cable that isn't shielded properly acting like a big antenna.

Lex

[Kevin P]

Paul, if you disconnect your CATV cable, does the hum stop? If it does, then you have a grounding problem with your CATV cable. If not, try disconnecting/unplugging other components, one at a time, and see if the hum stops. If all else fails, there are devices that will isolate the ground to eliminate ground loops.

If a hum is coming from the amp itself (not the speakers), this isn't a ground loop. This is the transformer in the amp being noisy.

KJP




Official Computer Geek and Techno-Wiz Guru of HTGuide - Visit Tower of Power
My HT Site

[David Meek]

What's a Romex

Paul,

Romex is the generic name for electrical wiring that is sheathed in a heavy rubberized plastic that is use in house construction. It is safe to use without running in conduit.




David - HTGuide flunky
Our "Theater"
Our DVDs on DVD Tracker

[brucek]

Paul,

Well, since you have discovered that the hum in your sub is eliminated when using a cheater plug, it would be safe to assume you have a ground loop.
And since you are using a single circuit to power all your equipment, it would also indicate that the CATV coaxial cable is introducing the difference from the safety ground potential.

To establish this fact, as Kevin says, simply remove the CATV cable as it initially enters your system at the "surge protector". The surge protector is the first point of contact with the house safety ground, so remove it there. If the hum is eliminated, you have found the culprit.
As mentioned, there are two ways of dealing with this. The first is to ensure the CATV is properly grounded with a grounding block at your service panel area and the second is to remove DC continuity in the CATV shield with a transformer. You can buy the Modial device or any of the other equivalents, or you can make your own (as Wayne mentioned) with two back to back impedance matching transformers.

There are a couple problems with these home made kind though.
A lot of the transformers of this type have DC continuity on the shield side of the 300 ohms through to one lead of the 75 ohm wire to preserve the ground path. They are designed that way and as such won't solve the problem. In the case where the ground potential of your cable is different than that of the safety ground at your equipment, you'll experience the "humming" ground loop problem. If the DC continuity of the transformer is preserved, then the problem will still exist. This is why this trick doesn't work for some people. A simple check with an ohmeter will reveal this problem. You want to use the kind that have no DC short through the device - then they'll work. And yes, you just hook the wires on the 300 ohm side together with whatever means you like and hook your cable CATV into one end and carry on with another cable on the other side. It is an in-line device.

The other small problem is one of insertion loss. These transformers will introduce a small insertion loss, so two together will marginally reduce the signal - no big deal.

These "fancy" premade cable hum reducers are simply a 75 ohm to 75 ohm transformer with no DC continuity, sold for ridiculous prices......but they do work.
Be sure to insert your transformer before the CATV cable enters your system at the surge protector.

Of course, as already mentioned, you have to first ensure that the cable coming into your home is grounded, or you'll have trouble for sure. But many people still experience ground loop hum with a completely and properly grounded system. The culprit is usually through the cable shield potential, so the transformer may also be neccessary.

On another note, I would suggest loosing the CATV splitter amplifier unless you paid in excess of $100 for it, because it will be introducing more noise into your cable signal than is really acceptable. It is far better to use a simple passive splitter and suffer the 4dB loss per split than to use one of those RS splitter amps....

You said you moved your VCR around and then you noticed the hum. Be sure it isn't something as simple as a bad cable with an open shield introducing this hum into the system - not likely, given the symptoms you've reported..

Anyway, you seemed confused by Waynes mention of a dedicated circuit. If you haven't installed one yourself, you likely don't have one.

There's nothing magic about dedicated circuits. It just ensures a single electrical run of cable from your service power panel to a wall receptacle, with no interconnections between and nothing else plugged into the circuit except your system. Many HT'ers and audiophiles install these dedicated circuits to ensure a clean low impedance path back to the loadcenter.

The receptacles in your room now may have up to 12 lights and receptacles on the same circuit. At each receptacle that the wiring runs through, there is a set of twisted connections inside covered with marrettes (wire nuts) that may be presenting a small resistance. The more of these connections, the more possibilities of poor, high resistive joints before the circuit reaches the receptacle that you are using for your HT system.
Not to mention the myriad of things like motors, fluorescent lamps, and computers that may also be plugged into this same circuit besides your system.
All this can result in a loss of power and increased noise at the receptacle you're using for your system.

There's also a large possibility that if you are using more than one receptacle, that they may be on a different leg of the loadcenter.
These things are a recipe for problems of ground loops and other interference. This is the reason many like to install one or two dedicated circuits direct from the power panel to behind their system.

When you use a dedicated circuit, and noise is introduced on a different circuit in the house, even though they return to a common point at the loadcentre, this noise tends not to travel down your dedicated circuit because of the extremely low source impedance of the mains at the panel. It acts like a pass filter to this induced noise.

Ground loops are sometimes a difficult task to track down and remove because there are a million reasons for them to exist. The loop is caused by a difference in the ground potentials in your system. Breaking the safety ground almost as often clears the problem, and that is why it goes away with the use of two prong power cords or with the use of cheater plugs. This easy fix is obviously tempting, since it's so easy, but it's extremely dangerous and not recommended unless you enjoy getting a shock.

The safety ground is a cold conductor designed to provide a path to ground for safety protection against internal shorts inside your equipment. This safety ground is attached directly to the metal case of your equipment (through the third prong) and if the hot 120 volt shorts to the metal case because of a fault, a breaker will trip and protects you against a shock.

Generally, a ground loop can be tracked down to its source, but removing the problem can sometimes be a little more difficult.

One of the other major culprits in creating ground loops is the use of more than one circuit in an HT system. You don't have this problem since you're using a single circuit, but maybe in the future as your system gets larger you might move to two circuits. The larger systems demand more power, so several circuits (dedicated or not) are sometimes needed. Actually, even using a single circuit with different receptacles can cause a ground loop.
Residential houses use 240 volt "single phase" three wire power. The two "hot" legs are 120 volts and are 180 degrees out of phase. The loads in your house are balanced between these two legs at the service panel. It is advisable, if you do have two circuits powering your HT system, to ensure you are using a common leg.

Let me explain a bit about ground loops.......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.

When I plug a power amp into one receptacle and a preamp into another receptacle, the metal cases of these two units can have a small potential difference in their safety grounds which means that this equipment's metal cases are at a slightly different potential. When I connect a single ended (RCA) cable between these two devices, a small AC current can flow in the shield because of the potential difference. This signal is in the signal loop circuit and can cause a hum. 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. Breaking the safety ground of one of the two devices removes the potential and the path for the unwanted signal flow...

Exactly the same situation can occur, except usually worse, when you introduce a new ground into the system from cable TV or a satellite. Their ground on the shield may possess a different potential than the ground in your system and current will flow in all the interconnects. Usually by centralizing and bonding all external grounds to the common house ground you're at least giving yourself the best chance of reducing this problem.... Sometimes to locate a ground loop you have to start with a minimal system and build it up cable by cable to find the cause. It won't be necessary in your case.

Anyway, that's a few thoughts on the whole issue. Hope it helps...

BTW. don't be concerned about the mechanical transformer hum coming from the 5800 amp. They are notorious for doing that. I have one in my second system and the toroid hums once in a while - crappy transformer..

brucek

[P-Dub]

Wow, great info!

So if I left things be, ie live with the hum. Will that damage my equipment?




Paul

There are three kinds of people in this world; those that can count, and those that can't.

[brucek]

So if I left things be, ie live with the hum. Will that damage my equipment?

No - but you still have to tell us if the hum goes away when you pull the cable from the surge protector.... :?: :roll:

brucek

[P-Dub]

When I pull the cable, most of the hum goes away. If I'm up close to the sub, I can still hear a faint hum.

Just picked up a couple of those RS dohickies and will try that out.




Paul

There are three kinds of people in this world; those that can count, and those that can't.

[David Meek]

If I'm up close to the sub, I can still hear a faint hum

Paul,

Is your sub a servo-controlled design, ie. Velodyne FSR or HGS? If so, the faint hum is normal for those units. I had the same concern when I first got my FSR-15, but found out from Velodyne and also from owners of other servo-controlled brands that this is not cause for concern. Now, in a quiet room, I can generally hear this hum from about 2 feet away and no more than that, so it is a very faint noise - is your's about that level?




David - HTGuide flunky
Our "Theater"
Our DVDs on DVD Tracker

[P-Dub]

David: Nope, I've got a dual SVS passive setup, and they are being driven with the Sampson amp.

Good news, I put together those transformers into the loop and I've all but eliminated the hum. The results are the same as if I had pulled the cable connection. I still hear a faint hum, but nothing that would get me worried.

I spliced this deviced as the cable exited my surger protector, so I may try to bypass the surge protector all together.




Paul

There are three kinds of people in this world; those that can count, and those that can't.