We've had plenty of situations where we just can't seem to get rid of the hum, especially with high efficiency subs, like sunfires. We've used these and they perform very well in many situations, even video ground isolation problems:
[Link: jensen-transformers.com]

I can't get the hang of all this fantasy about lifting grounds and having this immediate shock hazard. Why doesn't every component have a 3 wire plug if that is so?

I think shock is pretty unlikely. Where's Larry when we need him?

Especially the "main" component, the A/V receiver. Does any current brand of A/V receiver have a grounded 3 prong plug?

What on earth did we do in the days before 3 prong plugs? Do we have only half the relatives we would normally have because they all were zapped and vaporized?

If you want a real eye opener, volunteer to be an assistant recording engineer in any significant recording studio. I was part owner in one for years and I cant tell you how often, and perfectly normal, it was to use a ground lifter/cheater plug to eliminate ground loop hum.

No one was ever electrocuted and we had numerous pieces of gear that just stayed perpetually hooked up thru ground lifter plugs and I'm not talking about junk gear either...Adcom amp's, Lexicon reverb proccessors, Yamaha effects proccessors...you name it. I had to use a gound lifter plug on my sub (an HSU VTF-2) to eliminate ground loop hum even though the sub and the receiver are on the same electrical feed and even with all other gear disconnected from the receiver.

Works fine. If it eliminates the hum...enjoy the music!

BTW....the electrical safety course I have to take every year defines the third prong ground as a "Green wire ground/Grounding" conductor. It's purpose is to insure that line voltage cannot be present on the frame of the machine. Neutral is defined as the "Grounded" conductor which, under code, should connect to building ground/a cold water pipe, at the main electrical box of the building.

In my studio day's the only time I ever got zapped was by a microphone with a bad phantom power connection.

My Marantz receiver has a grounded plug... and alas so did the DVD player (and I ended up with an instant ground loop).

Slimfoot, you either need a ground loop isolator for the cable TV system or an RCA analog isolator for the sub itself. Try disconnecting the cable TV from the system, if the hum goes away, get the coaxial isolator, if it does not go away get an RCA isolator. The best isolators I have used to date are made by jensen transformers

Just to allay fears of shock, the existence of the loop indicates that the components are grounded; the "cheater" merely eliminates redundancy.

To address the issues posted about why have 3-prong outlets, etc...

Devices which have a 3-prong power cord do so to provide an extra level of safety. In such a 3-prong device, the dedicated ground is usually connected to a metal chassis, so that if isolation fails, an adequate ground is still present.

Another reason for the 3-prong power cord has to do with the transformer you'll find in most equipment. All transformers, and even switching supplies, exhibit some amount of leakage current. This is current that leaks from the AC onto the chassis or ground of the device. If this leakage current is as little as 30 millionths of an amp, some people will begin to feel a "tingle" if they touch something grounded, and the chassis of the device. Even if the current is not enough to cause problems, this worries most people enough that the device manufacturer gets the product returned, or a service request to fix the problem. The fix for this is to better isolate the transformer or power supply (increase the isolation), or add a chassis ground. If a consumer device has a metal chassis, or exposed grounded contacts, and a 3-wire plug, it is almost always because the transformer leakage is high enough to cause some issues. Devices with two wire plugs are either double insulated, or have transformers or power supplies with very low leakage.

So, if the device has a 3-prong plug, I don't recommend defeating it.

To help address your hum issue:

If all the devices are grounded to the same point, you won't have a ground hum issue. (There are however conducted or radiated hum.) If all the devices are plugged into the same outlet or power strip, and you still get hum, check for other paths to ground. Control cables, component video, HDMI, DVI, etc that run across the room, or into other rooms can all cause grounding issues as well, as all these include grounds in the cables, and potential connection to other equipment with a different ground. Disconnect cables not absolutely necessary, and start connecting one at a time until the problem re-appears.

Ground on the coax is a primary offender. Disconnect the coax and see if the problem goes away. If it does, use one of the coax ground isolators on the market. If these don't fix the problem, the issue is not grounding.

If the issue is not grounding, the hum is being coupled through conduction or radiation. This might be a speaker wire or other cable running in parallel with a power cord for some length. This can usually be fixed by crossing power and other cables at 90 deg. and no running them in parallel any closer than 1 ft apart. Remember that the power cord can be the Romex in your wall. I had a friend that neatly bundled his extra sub cable, and tacked it up on the wall at the same height as the outlet! You can imagine his surprise as I pulled his neatly bundled cable off the wall, and the problem disappeared.

If the issue is radiation, the hum will exhibit itself, and disappear when something is energized or powered down. Culprits include any device that transmits RF. These include cell phones, cordless phones, Wi-Fi connections, etc. The easiest fix is usually to move the transmitter further from the device being disturbed by the RF energy.

If these don't fix it, you've got a nasty combination of several of the above, that is causing you to make the wrong assumptions. If you have hum through grounding of a cable, and through a parallel run of a audio and power cable. Fixing either alone won't fix the problem, you will have to fix both before the problem will go away!

Good Luck...

Well I plugged all devices, including the sub, into the same surge protector and the hum went away. Unfortunately, the sub is to be located in a remote location, away from the equipment and surge protector.

Hey slimfoot,

Do you know where the earth is located on your house? I found that by placing a metal stake next to the existing earth (5 ft long and leaving about 6" above the ground) and patching the two together removed any hum that was in my system!

BTW.........I definatlety would mot recommed bypassing the ground plug on your sub......it is expensive when it does not work <---past experience :(

Matt

Slimfoot,

This is good news. We now know what the problem is. This is the first step toward solving it. We need to get the ground potential of the location the sub is at, as close to the same as that of the equipment.

Are you comfortable with working on outlets? You might also want to try changing the breaker if they both are not on the same phase of the electric service. If you are comfortable with doing these things, follow on. If not, you'll need to get an electrician and have them check that all the grounds in your system are good.

!!!CAUTION!!!
This is dangerous if you don't know what you are doing. There are voltages and currents present that can easily kill you if you make a mistake. If you don't want to spend the money... find a friend or neighbor who knows what they are doing. If you have to pay for this... Consider that you are buying Life Insurance guaranteed to keep you alive through this task!

From both the location of the Sub, and the equipment, check the ground leads, and power leads. Check every connection the electrician has made. (Of course you want to do this with the power off.) Pull the outlet from the wall, and check the power and ground connections. If bundled into a pigtail, make sure they are securely twisted together, and that the wire nut isn't what is holding them together. If the wires look dirty or oxidized, clean them well, and make new connections. Twist them together with pliers, and once they are securely held together, put on the correct size wire nut. Do this on every outlet in the circuit, as it is likely the circuit daisy chains through several outlets.

When I'm having this problem, I usually won't use the push in connection on the back of the outlet. I'd rather use a wire nut in the box with a pigtail from the wire nut to the screws on the outlet.

After doing this, did this fix the problem? If not, you'll need to open your breaker box, and check for correct grounding of the dedicated ground and neutral wires in the box.

!!!CAUTION!!!
We are starting to get out of average do it yourselfer territory. You should turn off the main breaker if you do this! Please don't attempt this unless you know what you are doing. Be sure you know where the main feed comes into the box, and when plugging and unplugging the breakers, that a slip will not result in accidental contact to the main service wire.

Last, if all else fails, are both circuits on the same phase? Different phases should be ok, but can ocassionally cause issues. If both breakers connect to the same hot buss bar in the box, they are the same phase. Boxes are arranged so that if you put one breaker directly below another, the breakers are on different phases. (This is done to balance the load for 220V devices like AC, etc. A dual wide breaker is taking two positions in the box, and has one side on each phase.)

Hope this helps. If after the above, you still have hum, you'll need some electronic solution to solve your problem by adding isolation to the cable to your sub. I'm not really up on the solutions present for this. I've always been able to fix these issues by cleaning up ground connections.

Good Luck!

I've had the same issue with the NHT subs as they have a 3 prong plug.Changing it to 2 prong with the adapter always works for us.

I would recommend holding the side of the metal service panel while placing your other hand on either of the 2 large wires in the center of the service panel and standing in at least 2 feet of water when doing this. Try to have as much metal on your person as possible, especially silver rings, belt buckles or bracelets. NOT!

If you are nervous about potential dealth or fire try purchasing an isolation transformer [edited from amp as I must have been in a daze ]. More money but less hazzardous.

The first part was a joke, the secod serious, in case it was not obvious.

Alan

This message was edited by Audible Solutionns on 03/03/05 12:30 ET.

not a good idea big fella, that ground is there for a reason, use an isolator.