Speaker Buzz Due to Outlet Ground

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An annoying low-frequency hum in your speakers usually means your audio system has a ground loop, a condition in which poor grounding produces electrical noise. The severity of the noise ranges from a soft buzz to a booming hum that's loud enough to damage your speakers. Fixing the buzz means tracing signals through your audio system and ensuring that equipment shares a common power ground connection.

Ground Loop

  • A standard audio cable connects two pieces of audio equipment, such as a turntable and amplifier. The cable's outer shield joins the signal grounds of the equipment together, but the power supplies must also share an electrical ground; if they do not, the cable carries a slight AC voltage difference between the two devices, producing the tell-tale 60-Hz ground loop buzz in the speaker. Even a good AC electrical system has differences of a few millivolts between nearby outlet ground terminals; this difference grows larger as the distance between outlets increases, or when outlets do not share a common breaker circuit.

Correct Audio Grounding

  • The more complex an audio system's connections, the more opportunities for ground loops to creep into it. Ideally, all audio cables run to a single, central device, such as an amplifier or mixing console, and the power to all equipment comes from a single breaker circuit. This minimizes the voltage differences between device power-grounding connections.

Troubleshooting

  • A ground loop forms between two pieces of equipment when they do not share a common power ground. In many cases, you can isolate a grounding problem by unplugging all audio sources connected to an amplifier and reconnecting them one at a time; when the hum returns, that device has a grounding issue. Some types of professional audio equipment, such as power amplifiers, have a "ground lift" switch that disconnects audio signal grounds, leaving the power safety ground intact; using this can solve some ground loop problems. If this issue continues to plague you after you've examined your equipment, consider hiring an electrician to check your outlets.

Safety Grounding

  • The rounded third terminal on the power outlet provides an electrical ground; this is an essential safety feature that reduces shock hazards. Do not attempt to fix a ground loop by clipping off the electrical ground on the plug or by using a "ground-lift" accessory plug between the outlet and your equipment. The only exception to this rule is equipment that runs on batteries or low-voltage DC battery chargers -- these do not pose a shock hazard and do not need an outlet ground.

References

  • Photo Credit Jupiterimages/Comstock/Getty Images
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