Audio systems are especially susceptible to electrical noise.
Motor controls and light dimming systems generate considerable noise because they use SCR and Triac control.Those solid-state switching systems create fast-rise transients that reflect back on the same power company line that feeds the audio system.This high frequency trash causes hum and buzz problems.
The most widely used and cost effective method to isolate the sound system from high-frequency transients is an AC isolation transformer. The electrostatic (Faraday) shield of an isolation transformer greatly reduces the inter-winding capacitance. With lower capacitance the coupling from the primary (power company) to the secondary (audio system power) attenuates the noise.
Poor grounding causes hum problems. Long ground lines act as antennas for interference, both RFI (Radio Frequency Interference) and EMI (Electro Magnetic Interference).An isolation transformer, next to the power panel provides a short, low-impedance ground reference. The isolated secondary re-references the ground at the transformer output, typically a few feet from the power panel and audio equipment racks, not several hundred feet away where power enters the building.
