Do not install other equipment (lighting, vending machines etc) to the technical earth - only use it for Audio Equipment.
If the star point is derived from mains earth, however, and not from a ground stake/plate, install separate clean and dirty mains outlets, wired individually to the mains distribution box. Use the clean supply for all audio equipment, and the dirty supply for all lighting, vending machines etc. Do not mix the two systems. It may be necessary to install an isolating transformer for the clean supply to ensure adequate isolation from
All audio connecting cables should be good quality twin screened cable. Do not use single screened cable.
It is very important that the screen is not used as the signal return. Therefore connect the screen at one end only. Connecting the screen at both ends will cause an earth loop into which external hum fields will be induced.
In areas where high levels of radio frequency interference are present the open end of the screen can be connected to earth through a 0.01 microfarad capacitor. This will appear as a short circuit at high frequencies, and lower the effective shield imped- ance to earth. However at audio frequencies the reactance of the capacitor will be sufficiently high to not cause an earth loop.
In general, the screen should be connected at the signal source, and not at the signal destination. The exception to this rule of thumb is when connecting to an unbalanced input or to an elec- tronically balanced input. In these cases the wires being screened are referenced to the destination earth.
Electronically balanced outputs which are to be operated in the unbalanced mode should be unbalanced at the output connector, not at the signal destination so that the signal current returns to earth via the shortest, least reactive route.
Q2 OPERATIONAND MAINTENANCE MANUAL 9601 | 13 |