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The Difference Between a Ground Loop Isolator and a Line Noise Filter

Music can excite, inspire, relax or instill a wealth of emotions in the listener. Thanks to modern technology, we can listen to high fidelity music in the comfort of our homes and when traveling in our cars. Noise -- unwanted sounds -- can take the enjoyment out of listening. Ground-loop isolators and line-noise filters are electronic devices that you install in certain situations to prevent noise and restore your listening pleasure.

Hum
- The electrical outlets in your home have a ground, or "neutral," wire that runs from every outlet to an earth ground. Its purpose is to provide a path for electric current to flow through it and blow a circuit breaker in the event of an electrical fault in an appliance. Wire, however, has resistance, and may not be at exactly the same voltage potential at all points in the home. In electronics, "hum" is the sound heard in amplifiers and other audio equipment characterized by a low frequency tone (60 Hertz or cycles in the U.S. and 50 Hertz in Europe). This tone corresponds to the frequency of the alternating current (AC) that is supplied to your home by the local utility company. The most common cause of hum is an electrical potential (voltage) difference between two pieces of equipment that are connected together. For example, the audio output from a computer may be plugged into a home stereo, or the audio output from a satellite receiver may be connected to your stereo. A hum in the sound can result if these two devices are plugged into two separate electrical outlets where the ground potential is not equal. This "ground loop" circuit causes unwanted electric current to flow through the ground path to each device. A ground-loop current flow may also show up as a series of black bars or stripes that slowly travel up the screen of a TV set if the TV is connected to a satellite receiver or a stereo.
Ground-Loop Isolators
- Hum caused by a ground loop current is resolved by connecting a device call a ground-loop isolator between the two pieces of equipment. The shield wire on the audio connecting cables between the two devices provides the path for the ground loop. A ground-loop isolator breaks this physical connection while allowing the audio signal to pass through untouched. Typically, a ground-loop isolator is a box about the size of a pack of cigarettes with two RCA jacks as inputs and two for outputs. Some models have short audio cables with male RCA plugs on the end for the isolator's output. These devices are "passive" and do not require any power to operate. Using standard stereo RCA audio cables, simply connect the isolator between the audio output of one device and the audio input of the other. No tools are required.
Noise
- While hum is a type of unwanted "noise," in the electronics industry the term "noise" generally refers to other types of spurious sounds, such as clicking, popping, crackling and hissing. Hum is a problem that occurs in the home, but interference noise is a problem arising in car audio systems and auto radios, including CB radios. These devices can pick up electrical noise from generators, alternators and ignition system components. The telltale symptom of ignition noise is the sound of the engine's whine in your car speakers.
Line-Noise Filters
- Line-noise filters are placed in the +12 volt battery line that supplies power to your car stereo or radio. The typical configuration is a small box with three wires extending from it. One wire connects to the +12 volt battery line, the other to the power input of the stereo or radio and the third to the vehicle's chassis ground.

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