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