Humming in Power Amps!!

Will,

PLEASE don't remove the ground. If anything ever went wrong with the amp and you touched it. You would become the point of least resistance. Without a ground on the amp you'll become the ground. You could have a problem with amp and not know it until you touched it. You could get a jolt that could kill you. As I'm sure you already know amps have lots of power in them. Cheater plugs solve the humm, but expose you to a great risk.

To get rid of the ground loop hum. Try bonding all your gear together with speaker wire. Pay real close attention to the satellite or cable box(these are usually the cause of ground loops). Try connecting a speaker wire to a screw on the sat or cable box. Then connect the other end to the amp. This will tie the grounds together. In my case I ran a speaker wire from my Sat box, then to my vcr and then another one from my vcr to the amp. Totally eliminated my 60 hz humm.

Legairre

 

Will,

 

If you have cable TV anywhere in your system, I would unplug that first thing. Almost all cable systems cause some hum.

 

Wow, finally fixed my hum problem! I always knew it was from the cable television but never knew what to do to solve it, I would just unplug the cable when watching a dvd. I tried what Legairre recommended and wired the cable outlet to the receiver and the receiver to the vcr. Got rid of all of the hum. Thanks!

 

If the source of the hum is your cable TV connection then you may want to try using a ground cable block. The idea here is to "ground" the incoming cable to your local ground. You see the cable company's ground might be different from yours (don't ask me how that could possibly happen, but that's how I understand it) and therefore you must ground the cable to yours. This is done with a ground loop block you can find at any RadioShack. It's a simple little adaprter that you "splice" into your cable. It will have a third connector for a grounding wire which you will connect to your plumbing. I had some nasty humming and I eliminated it with the help of the ground loop.

For more info on this do a search for "ground loop hum".

- Mike

 

I had the hum on my system due to cable as well. Called up the cable company and had a tech sent out. He didn't believe me when I told him I thought we had a grounding problem with the cable but he did agree to check it. Turns out it wasn't grounded.

Five minutes later I was set. No hum. All grounded.

Maybe try giving a call to your cable company. . .

Regards,

Mike

 

Will,

If plugging in a 3prong cable makes a difference, then you have been using the wrong kind of poweer cords: you should *not* be using any two wire cords. Your amps are designed to have the case grounded. You are living on borrowed time. Literally.

You need to fix the ground loop, not hide from it.

Besides the cable company grounding problem, the other major cause of hum is powering your equipment from two different electrical phases. Most houses are serviced with two of the three phases used to transport electrical power. They are 120/240 degrees out of phase with one another. At any given time, there is a large voltage difference between the two phases. This translates into a much smaller difference in the ground voltages on their receiptacles. This causes small currents to flow along the reference grounds of the signal cables interconnecting the equipment that's powered from the different phases. This is heard as hum.

The easiest fix is to use a power strip and power everything from the same outlet. If you have many Class-A amps, though, this may oveload the circuit breaker.

The second fix is to use separate power runs back to the same phase of input power at your power distribution panel. In this case, you also have to be careful to use about the same amount of power on each of those runs. Otherwise the voltage drop in the power cabling will be slightly different, again causing current to flow between the equipment and causing a slight hum. It should be almost inaudible, though: much less than when using different phases.

Finally, sometimes hum is caused by failing filter capacitiors in the equipment. This doesn't seem to be your problem however.

I hope this helps a little.

 

Will,
Let me try and clear a few things up....
If a device has a two prong power cord, it is not connected to the safety ground in your house.
The two prong plug has a one of the two "blades" of its plug wider than the other. This is the neutral return - not a ground.
If a device, designed for a three prong plug, is modified by removing the safety prong of the plug or by using a cheater (which effectively removes the third prong), then you have created the unsafe condition I mentioned in my post above.
If you have a hum from an amplifier caused by a ground loop, then removing the safety ground connection to amplifier (and perhaps other devices as well), can clear the resultant effect of the ground loop, but creates the safety issue. It's more advisable to try and clear the condition causing the ground loop than to mask its effect by applying unsafe practices.
In that regard, 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. I hesitate to say that sometimes it's the only thing in the end that works on some troublesome equipment, ensuring that cheated piece of equipment is hidden away from anyone touching it.
Generally a ground loop can be tracked down to its source. Removing the problem can sometimes be a little more difficult.
You have to first ensure you have a ground loop situation by completely removing the offending amp and while using its proper three prong power cord, disconnect everything but its speakers and see if it still hums. If it does - you don't have a ground loop - fix the amp.
One of the other major culprits in creating ground loops is the use of more than one circuit in an HT system. The larger systems demand more power, so several dedicated circuits are sometimes needed. But 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. It is fairly easy to establish this.
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....
Anyway, getting back to your problem. You have to start with a minimal system and build it up to find the cause.
If you have no hum with the single amp and its speakers, then you can hook your preamp up with a single set of interconnects, ensuring the preamp has no source components connected to it and that its plugged into the same receptacle as the power amp. If it doesn't hum, then add a single source component to the preamp with the same conditions. If this minimum system has no hum, and you usually plug the devices into different receptacles, then you can try and plug the preamp or source component into a different and check for hum.
Well, you can see where this is going. You must rebuild your entire system, starting with the noisy amp, until the hum reappears and then figure out why that happened. This requires you to rip apart your entire system and rebuild it. You will find the source of the problem this way.
Do you see why people use cheaters......
brucek

 

Will, before you start disconnecting all of your equipment, just disconnect your cable/sat from your system.
I would bet that is the source of the problem. As was said before, you can buy a ground loop isolator at RS or Jensen makes isolators also. They cost a bit more however. Mondial designs sells what they call "The Magic Box" That will also fix it. Good luck!

 

Will,

 

Will,

Try tying them all together. My 2 prong receiver never hummed, but my 3 prong amp did. I tied them all togehter and the amp no longer hums.

ArmenK,

Glad it worked. I hate the ground loop hum. It's an evil beast that must be destroyed.

 

Why not just remove the outside ground on the cable? It seems like a pretty useless item and

apparently is the cause of many of these hum problems. You still have your normal household

electrical ground, who needs the cable t.v. ground?

 

Will,

You do not hear a hum when you use the two prong plug because you are no longer grounding the amplifiers. As such, you are then introducing the potential to shock yourself stupid.

In each post you have written how you are defeating your ground loop problem by effectively not grounding your system. Effective, but not wise. Get three prong grounding plugs for all your amps and fix your ground loop - for your safety, not ours.

 

As an aside, I have never had a ground loop hum.

BUT, my cable and eletrcial service use the same ground spike. The cable box outside is 10 feet from the eletrical service and is connected by what looks like a 12 gauge solid copper wire.

So, if you cable or SAT tv system is grounded well can you eliminate most sources of ground loop hum?