| You've all heard it, that dreaded 60Hz hum through the | | | | dreaded ground loop. If you get a ground loop, current |
| speakers of a home theater or house audio system. | | | | flows between the two components. If the current |
| Hopefully you heard it at a friend's house and not your | | | | flows through the components internal audio signal |
| own. It can drive you completely nuts. You may have | | | | ground, you will get a hum.You can use an isolation |
| even tried, unsuccessfully, to fix the little noise problem. | | | | transformer, similar to the type used for cable TV |
| That can make you even more crazy. What causes | | | | ground problems, to eliminate the electrical connection |
| that horrendous noise through your speakers?More | | | | from one component to the other. These transformers |
| often than not humming through your speakers is | | | | are inserted in line with the audio signal connection |
| caused by a grounding problem. There are three main | | | | between the two components. If there is no audio |
| ground problems that cause problems in an audio / | | | | connection between the components, the problem |
| video system. These are ground loops, improper | | | | may be current flowing through the video portion. In this |
| grounding and lack of a ground altogether. The other | | | | case, a video isolation transformer should be used to |
| possible culprits that can cause noise are bad cables, a | | | | eliminate the ground loop.Sometimes power |
| faulty piece of equipment or electrical noise from a | | | | conditioners will stop noise problems by placing |
| lighting dimmer or electric motor. There are steps you | | | | equipment on different, electrically isolated outlets. This |
| can take to troubleshoot the noise and eliminate it from | | | | is done using isolation transformers. Sometimes this is |
| you theater.The first step is find out where it is coming | | | | ineffective however, due to the differences in internal |
| from. Disconnect your source and display equipment | | | | construction of different power conditioning equipment. |
| from your receiver or surround sound processor. If the | | | | Some safety regulations, such as UL 1950, specify that |
| noise stops, connect them back to the receiver or | | | | an isolation transformer is only allowed to isolate the |
| processor on at a time until the noise returns. When | | | | hot and neutral wires; the grounding wire must be |
| the hum comes back, you found where the noise is | | | | passed straight through. If this is the case, the ground |
| entering your system. Note that if you are connecting | | | | loop problem may still exist because many |
| remote equipment, such as running the signal from | | | | communication circuits are connected to the grounding |
| your theater room DVD player to the TV in the | | | | conductor and not the neutral. In this case, the isolation |
| bedroom, your chances to pick up noise increase | | | | transformer, or any power conditioner or UPS with an |
| dramatically. With such long runs, noise can be induced | | | | isolation transformer will have absolutely no affect on |
| into the long cable runs from adjacent electrical wiring. | | | | the grounding problem.The noise may be generated |
| It is also easy to create a ground loop, because the | | | | externally, from a dimmer or refrigerator compressor |
| equipment is plugged into two different, widely | | | | for example, and coming in through the main power |
| separated outlets, on different electrical circuits.If the | | | | input on the audio video equipment. In this case, a high |
| noise is caused by a cable box, the noise is likely | | | | quality power conditioner may be effective in reducing |
| caused by the cable TV ground. To test this theory, | | | | or eliminating the noise problem. You may also find that |
| disconnect the incoming cable TV feed to the rear of | | | | one of the signal interconnecting cables in your system |
| the cable box or TV while they are still connected to | | | | is faulty. This can also cause noise problems. Check |
| the rest of the system. If the noise is eliminated by | | | | for this by swapping the cables with one that you |
| disconnecting the TV cable, the problem is the cable | | | | know to be good.You can solve most noise problems |
| TV ground. You can electrically decouple the cable TV | | | | in your home theater or multi room audio/video system |
| feed from your system with a ground breaking | | | | by taking the systematic, step-by-step approach. Work |
| transformer. These are available from many sources. | | | | your way up the signal chain, eliminating each piece of |
| Be advised that many newer, digital cable TV systems | | | | equipment as you go. If you have nothing connected to |
| require any device in the signal chain to pass a full | | | | your speakers except the speaker wiring, and they still |
| 1,000 Mhz. Some of the older ground break | | | | hum, the problem is noise induced into the speaker |
| transformers will not do this. Be sure to check the | | | | wiring from adjacent power cables. Other than that |
| specifications of whatever device you are purchasing | | | | case, most problems are caused by ground problems, |
| to verify it will pass the digital cable TV signal.If the | | | | which you can find, and solve, if you take it one step at |
| noise is from your projector, TV, or monitor, it is most | | | | a time.Steve has 15 yrs in the consumer electronics |
| likely caused because the video display device is | | | | industry. He is a CEDIA certified designer with ISF and |
| plugged into a different outlet than the other a/v | | | | THX certificates. His experience includes: installer and |
| equipment. It could be on a different circuit as well. | | | | programmer; system designer; business unit director |
| These circuits may have two different ground | | | | for an a/v importer; sales rep for a CE distributor; and |
| potentials. That is, the resistance to ground is different | | | | principal of a $1.5M+ CEDIA firm. He's now senior sales |
| on each circuit. A difference in resistance to ground | | | | engineer for Digital Cinema Design in Redmond, WA. |
| from one ground point to another can cause the | | | | |