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