| You've all heard it, that dreaded 60Hz hum through the | | | | potentials. That is, the resistance to ground is different |
| speakers of a home theater or house audio system. | | | | on each circuit. A difference in resistance to ground |
| Hopefully you heard it at a friend's house and not your | | | | from one ground point to another can cause the |
| own. It can drive you completely nuts. You may have | | | | dreaded ground loop. If you get a ground loop, current |
| even tried, unsuccessfully, to fix the little noise problem. | | | | flows between the two components. If the current |
| That can make you even more crazy. What causes | | | | flows through the components internal audio signal |
| that horrendous noise through your home theater | | | | ground, you will get a hum. |
| speakers? | | | | You can use an isolation transformer, similar to the |
| More often than not humming and buzzing through | | | | type used for cable TV ground problems, to eliminate |
| your speakers is caused by a grounding problem. | | | | the electrical connection from one component to the |
| There are three main ground problems that cause | | | | other. These transformers are inserted in line with the |
| problems in an audio / video system. These are | | | | audio signal connection between the two components. |
| ground loops, improper grounding and lack of a ground | | | | If there is no audio connection between the |
| altogether. The other possible culprits that can cause | | | | components, the problem may be current flowing |
| noise are bad cables, a faulty piece of equipment or | | | | through the video portion. In this case, a video isolation |
| electrical noise from a lighting dimmer or electric motor. | | | | transformer should be used to eliminate the ground |
| There are steps you can take to troubleshoot the | | | | loop. |
| noise and eliminate it from your theater or | | | | Sometimes power conditioners will stop noise |
| entertainment system. | | | | problems by placing equipment on different, electrically |
| The first step to is to find out where it is coming from. | | | | isolated outlets. This is done using isolation |
| Disconnect your source and display equipment from | | | | transformers. This can be ineffective however, due to |
| your receiver or surround sound processor. If the noise | | | | the differences in internal construction of different |
| stops, connect them back to the receiver or processor | | | | power conditioning equipment. Some safety regulations, |
| on at a time until the noise returns. When the hum | | | | such as UL 1950, specify that an isolation transformer |
| comes back, you found where the noise is entering | | | | is only allowed to isolate the hot and neutral wires; the |
| your system. Note that if you are connecting remote | | | | grounding wire must be passed straight through. If this |
| equipment, such as running the signal from your theater | | | | is the case, the ground loop problem may still exist |
| room DVD player to the TV in the bedroom, your | | | | because many communication circuits are connected |
| chances to pick up noise increase dramatically. With | | | | to the grounding conductor and not the neutral. In this |
| such long runs, noise can be induced into the long cable | | | | case, the isolation transformer, or any power |
| runs from adjacent electrical wiring. It is also easy to | | | | conditioner or UPS with an isolation transformer will |
| create a ground loop, because the equipment is | | | | have absolutely no affect on the grounding problem. |
| plugged into two different, widely separated outlets, on | | | | The noise may be generated externally, from a |
| different electrical circuits. | | | | dimmer or refrigerator compressor for example, and |
| If the noise is caused by a cable box, the noise is likely | | | | coming in through the main power input on the audio |
| caused by the cable TV ground. To test this theory, | | | | video equipment. In this case, a high quality power |
| disconnect the incoming cable TV feed to the rear of | | | | conditioner may be effective in reducing or eliminating |
| the cable box or TV while they are still connected to | | | | the noise problem. You may also find that one of the |
| the rest of the system. If the noise is eliminated by | | | | signal interconnecting cables in your system is faulty. |
| disconnecting the TV cable, the problem is the cable | | | | This can also cause noise problems. Check for this by |
| TV ground. You can electrically decouple the cable TV | | | | swapping the cables with one that you know to be |
| feed from your system with a ground breaking | | | | good. |
| transformer. These are available from many sources. | | | | You can solve most noise problems in your home |
| Be advised that many newer, digital cable TV systems | | | | theater or multi room audio/video system by taking the |
| require any device in the signal chain to pass a full | | | | systematic, step-by-step approach. Work your way up |
| 1,000 Mhz. Some of the older ground break | | | | the signal chain, eliminating each piece of equipment as |
| transformers will not do this. Be sure to check the | | | | you go. If you have nothing connected to your |
| specifications of whatever device you are purchasing | | | | speakers except the speaker wiring, and they still hum, |
| to verify it will pass the digital cable TV signal. | | | | the problem is noise induced into the speaker wiring |
| If the noise is from your projector, TV, or monitor, it is | | | | from adjacent power cables. Other than that case, |
| most likely caused because the video display device is | | | | most problems are caused by ground problems, which |
| plugged into a different outlet than the other a/v | | | | you can find, and solve, if you take it one step at a |
| equipment. It could be on a different circuit as well. | | | | time. |
| These circuits may have two different ground | | | | |