How to Get Rid of Hum When Using a Receiver
By John Papiewski
Humming and buzzing sounds in receivers can range from an occasional nuisance to a loud noise that can damage your speakers. In many cases, you can get rid of the hum by replacing a bad cable or correcting a minor wiring problem. Sometimes, however, the hum may be due to damaged or old audio components.
Torn Speaker Cone
In a speaker with two or more separate drivers, the “woofer” is the one that produces bass and low-frequency sounds. It is larger than the other drivers and comes in diameters ranging from about five to 12 inches and larger, depending on the speaker. The woofer material is typically made of flexible paper or plastic, and is subject to tearing from accidents and excessive sound levels. If the speaker is torn, it may emit a buzzing rattle during loud passages of low-frequency sound, such as from drums or bass instruments. You can usually inspect the woofers by removing the speaker grille or the back of the speaker cabinet; a tear will be easy to spot. If the speakers are expensive, a re-coning service can repair the broken driver with new material; otherwise, replace the speaker with a new unit.
Audio cables connect your receiver to other components such as turntables or compact disc players; these cables have both signal and ground wires, and hum can originate in poor cable connections. Make sure that RCA cables are fully seated into their sockets, as a misconnection can break the ground connection and produce a hum. Look also for physical damage to a cable or its end connectors and replace it as necessary. Long audio cables can pick up radio interference from fluorescent lights, dimmer switches and other electrical equipment. Other than speaker wires, use cables of six feet or less in length if possible. Note that fiber optic cables are not sources of hum.
Minor voltage differences between separate electrical outlets in a room can cause a phenomenon known as a ground loop, which is a classic cause of hum in audio systems. To reduce noise caused by this issue, connect all devices to a single outlet box if possible. If your audio equipment uses a few amps of current or less, plug a good-quality power strip into one outlet and plug each component into the strip.
Old Power Supply
Inside the receiver, a circuit called a power supply converts the standard 110-volt alternating current to a low-voltage direct current suitable for audio electronics. In the power supply, components called capacitors remove 60Hz hum from the DC; otherwise, the noise ends up in the receiver’s audio signal. If the receiver is more than 20 years old, chances are the electrolytic paste in the capacitors has dried out, reducing their efficiency. If you hear hum in all the receiver’s audio sources, the culprit could be bad capacitors. A qualified technician can usually replace these easily.
Chicago native John Papiewski has a physics degree and has been writing since 1991. He has contributed to "Foresight Update," a nanotechnology newsletter from the Foresight Institute. He also contributed to the book, "Nanotechnology: Molecular Speculations on Global Abundance."