ABSTRACT
Large professional studios often have 'technical earth' systems, where a dedicated earth is sunk into the ground, and to which no equipment is connected other than the audio equipment. Sometimes this earth is isolated from other earths, and sometimes it is bonded to the earth which is used by electricity supply company. Nonetheless, the object of the exercise is to provide a ground reference plane with a low impedance to earth, which acts as a common reference plane for all electrical signals. Many pieces of equipment used in studios, such as most power amplifiers, are notorious for drawing current in surges. In some countries, anything other than a mono-phase connection would be prohibited by regulations which state that no pieces of single phase equipment connected to different phases can be installed within the distance of spread of a person's arms. It has long been known that supplying sensitive audio equipment from a balanced power source can resolve many noise problems.
