Just wondering what helps prevent or stop ground hum or loops in a surround system. I know this is a very broad question. So far, I'm aware of inproperly grounded cable and satellite feeds as a cause. Pulling the ground on a sub works sometimes, but is it actually dangerous or does it cause less power? The current system I am looking at has a clean power surge protector. Seems like problems arise when two different amplified pieces are in two seperate areas of a house, and then are connected together via line level (like a sub or two a/v receivers). I know shielding and running by power lines can be problem. Anyway, I'm rambling, any general input is greatly appreciated.

I've only ever encountered 4 different hums in my career. Froms amps with grounded power cords, which a cheater plug usually fixes; from cable, which a ground loop isolator cures; from foil-backed insulation lying on an in-ceiling speaker, and from improperly grounded turntables.

I'm ashamed to say I only vaguely understand the science of ground loops. I'm sure someone will take the time to type it out, and I thank them in advance.

Doug @ HomeWorks

These are the best I've found.

http://www.comtran.com/


Dave

If the sub, or another amplifier from a different room is connected via line level, the easiest way to end the ground loop issue, should it arise, is to check which circuit breakers the two electrical cicuits are on. If the breakers are both are in even numbered slots, move one of them to an odd numbered slot, if one is odd and one even, move either one by one slot.

Basically shifting from in phase to out of phase. One way will eliminate the loop, the other won't. And right at the moment I can't think of which way works, and which doesn't, but one or the other will do it....lol

OK, grounding is probably the most unpredictable problem, and probably the one with the most potential causes.
In pro audio, many of these problems are mitigated or eliminated by virtue of the balanced configuration of most equipment, although balncing can sometimes be the source of a problem if the shield is tied to the chasis ground. Balanncing eliminates induced signal over a cable run, and incidental static elctriciy events. it doesn't fix electically introduced hums.

The biggest source of electrically induced noise (60Hz, or some of the higher Hz noises) is difference in potential of AC electrical sources (as you pointed out, tying two line level sytems together in remote locations). This means that the distance to the AC electrical source for each system is different, thus there is a difference of potential in the circuit which can be mainfest as noise (current travelling). There are no easy asnwers, just some do's and don't's. Even then sometimes you won't know why you fixed it, just that you did. Other problems might be cuased by electrical dimmers, or even a bad neon transformer nearby. But like a bear attack, first you have to decide whether the bear is attacking, or you just defending itself. With hum, you have to find out whether it is being induced in your signal runs, or originating from the electrical sourve (sometimes by way of a difference in potential).

If possible, always have all of your audio / visual equipment on the same phase of the panel, and if psooible, keep any lighting dimmers on the other phase. If you have multiple line level locations, keep them also on the same phase. Sometimes a dedicated ground ( in the earth outside) for the audio stuff is required. Sometimes an isolated transformer is required. Rest assured, a clewan power surge protector won't fix some of these problems. It can't. The only AC power devices I think are worthwhile are the ones that provide AC voltage regulation, not line conditioning,, but actually rock solid voltage regulation.

Another thing that can cause hum in a system is cablevision. sometimes the cable network is poorly grounded at the pole, or even farther up the chain. sometimes a couple of VHF transformers wired back to back will nuke it, sometimes not.

To troubleshoot these problems, first check all of your wiring and cables / connectors. Then start unplugging devices. If you can't solve it, get the electrician involved and see if you can rearrange the electrical panel configuration in order to optimize your needs

Actually, that's a bit wrong. In most panels, the odds are on the left side and the evens on the right. However, that's not how the 'busses' are configured.

The adjacent left and right slots are on the same phase. For example, 1 (left) and 2 (right) are on 'A' phase, 3 (l) and 4 (r) are on 'B', 5 and 6 on 'A', etc.

To identify phases vs. spaces, go down the panel and count A,B,A,B,etc. Again, the left and right slots on the same horizontal level are the same phase.

That's why a double-pole breaker can be placed anywhere in the panel and pick up power from both phases.Of course, 3-phase panels go A,B,C,A,B,C,etc.

True that moving a breaker up or down one space will swap which phase it's on.

Same phase should help, but if a swap either way makes a difference, then there's an underlying reason, and it may be something that should be remedied.

There's an old saying among old electricians and technicians: "a ground is a ground is a ground . . . or is it?" Theory and reality don't always agree.

Under normal circumstances, no current flows in an equipment grounding conductor (EGC), so all equipment chassis should be at the same (0v-to-ground) potential.

Most modern electronics have bypass capacitors in them to effectlively-ground induced high-frequency noises. Plus, 60Hz fields are induced everywhere.

Therefore, some current does flow, which means that there are potential voltages, no matter how small, on modern equipment chassis, and each one has its own level.

Normally, shielded cables are used as interconnects, so the chassis are electrically connected. With each power cord that has an ECG comes a parallel path.

Any voltage difference between the chassis results in a current flow in the shield, and this signal is added to the desired signal in the cable, and amplified.

The most sensitive inputs are the most susceptible, and these are the ones in the micro-volt (antenna/cable) and milli-volt (phono and microphone) ranges.

The better electronics have circuitry where the signal ground and chassis ground are not tied together. This and "ground-lift" switches can do a lot to reduce hum.

Some people have success with cutting through the shield at one end of a cable, and cable-TV 'ground-breakers' are usually 1:1 isolation transformers.

This is one application where "balanced" interconnects shine. While the shielding assures induced-noise protection, ground is not used as a signal reference.

"Thus endeth the lesson." . . . for now.

Larry
www.fineelectricco.com

balanced circuits nuke induced transients and other signals by usingthe primary side of the transformer to allow "defferance signals flowing down the conductors at equal intensity to cancel themselvels out allowing the AC signal to pass un affected. The shild ensures that the defferance signal or induced signal is of equal intensity by the time it reaches both signal conductors. The drain wire whcich is attached by virtue of it's contact to the shield will alow static electricity to be grounded.

Anything that is tied to the chassis ground is susceptible to anything else tied to that same reference. sometimes lifting the screen (pin 1) in a balanced system at one end will solve a problem. It's always an adventure, and always frustrating until you get rid of the problem. I have recently experienced the joys of plasma hum bars. New stuff for me

Listen up people. At least 1/2 of what is written here is dead wrong. Actually I think it's closer to 80% but I'm heading out to a client meeting and don't have time to read it all word for word. Bill Whitlock & Jensen Transformers. www.jensen-transformers.com get to his training at NSCA if at all possible. Cheater plugs should only be used as a TEST device and SHOULD NEVER UNDER ANY CIRCUMSTANCE BE LEFT IN PLACE. IT IS COMPLETELY ILLEGAL & CAN KILL SOMEONE. Induced 60 cycle hum is completely different from a ground loop. If you used the proper cable and connections you will rarely run into this problem. Ground loops happen all the time and are a fact of life. proper design and installation keeps them to a minimum but only an isolation transformer will break the loop if it is large enough to cause a problem. Just remember that you are now listening to the transformer. cheap ones can be fine for distributed audio but only Jensen should be used for mid-fi & hi-fi Home Theater.

P.S. the proper connection for balanced line is to have pin 1 tied to the chassis, not lifted. The imfamous PIN 1 problem arrises from the manufacture running PIN 1 (the shield) directly to the input board, inducing the noise directly into the electronics.

Also, I would recommend going to Jense Transformers web site and looking through their FAQ or white paper section (can't remember which). There are some excellent and fairly definitive articles explaining ground loops, and how to troubleshoot them.

check this out for balanced interconnects

[Link: audiocontrol.com]

that is correct, and you would be surprised at how many do this

which is why the solution can often be lifting pin #1 at one end

Induced 60 cycle hum is completely different

All the shielded cable in the world won't get rid of an induced source of noise in an unbalnced circuit, by virtue of the fact that the shield is actually on of the signal carrying conductors

We are never affected by 60 hz hum, induced or otherwise.




Power here is 110v, 50hz

The drinks are on me.

I took the CEDIA course on grounding/ground loops, and even still everything is mostly mystery.

My system had exactly one grounded device: the amp. With all my components hooked up and with properly grounded cable TV leading to 4 devices, everything was fine. Then I added satellite. Installed dish on a grounded metal tower, but then had the bright idea of installing a second ground in the middle of the line. This introduced a mild hum on my analog DSS input, which I lived with for 6 months until finally trying to limit the line to one ground. Eliminated the problem.

Then I added a fancy new DVD player, which very oddly came with a grounded cord. This introduced a HORRIBLE ground loop through the amp's DVD input - even with just a digital coaxial line connecting the DVD to the amp, I had a hum - on the digital input! The only solution I could devise was putting a cheater on the DVD.

I still feel this particular solution is safe because 1) Why in the world does a DVD player need to be grounded, and 2) The system and DVD player are still grounded through the amp.