When two or more devices are connected to a common ground through different paths, ground path noise, or a ground loop can occur. A potential difference between these two grounds can cause unwanted noise voltage in the circuit paths. Currents flow through these multiple paths and develop voltages which can cause damage, noise or 50Hz/60Hz hum/buzz.
This can be eliminated in one of two ways:
- Remove one of the ground paths to convert the system to a single point ground.
- Isolate one of the ground paths with an isolation transformer, common mode choke, optical coupler, balanced circuitry, or frequency selective grounding.
Please Note: While this article addresses a very common ground loop problem, there are plenty of ways in which system buzz and hum can enter into a setup.
Common Problem 1: Check to see if you have a heavy power supply or an outlet in the wall that is worn out and will not grip. If the hot/neutral/ground prongs on the plug and the ground are making intermittent or light contact with the tang on the inside of the outlet, it can cause a hum through the system. The best solution for this is to replace the outlet with an industrial version. Industrial outlets have better gripping and will hold power cables more securely.
Common Problem 2: Check the polarity of the outlet - it may be wired backwards. This is one of the first things you may want to check if unplugging the cable box does not remove the hum (and in some cases, the reverse polarity may still be the culprit.)
Common Problem 3: Light dimmers, fluorescent lamps, and other appliances that share the same circuit or common ground with your equipment can cause hums.