DAPAudio D2250, Manual

Page: 30 / 43

To minimize the adverse affects of the unwanted coupling to the signal wires, it is important that the screen is
connected at one end only , i.e. the screen must not carry signal current . Any signal on the wires within the signal,
either directly , if the screen is connected at signal source end, or indirectly via the earthing system, if the signal is
connected at the signal destination end. The indirect connection will cause an increase in high frequency cross-talk
and should be avoided wherever possible.
Therefore, in general always connect the shield only at the signal source end .In high RF areas ,the screen can also be
connected to earth via a 0.01 μ F capacitor. This will present a short circuit at RF frequencies, thus lowering effective
shield impedance to ground .However, at low audio frequencies the reactance of the capacitor will be sufficiently high
not to cause an earth loop problem.
Points to Remember
-
In all cases, use good quality twin screened audio cable .Check for instability at the output.
-
Always connect both conductors at both ends, and ensure that the screen is only connected at once end.
-
Do not disconnect the mains earth from each piece of equipment. This is needed to provided both safety and screen
returns to the system star point.
-
Equipment which has balanced inputs and outputs may need to be electrically isolated from the equipment rack and/
or other equipment , to avoid earth loops.
It is important to remember that all equipment which is connected to the mains it a potential source of hum and inter-
ference and may radiate both electrostatic or electromagnetic radiation .In addition ,the mains will also act as a carrier
for many forms of RF interference generated by electric motors, air-conditioning units, thyristor light dimmers etc.
Unless the earth system is clean all attempts to improve hum noise levels will be futile. In extreme cases there will be
no alternative but to provide a completely separate and independent ‘ technical earth ’ to replace the incoming
‘ noisy earth ’ .
However, always consult your local electricity supply authority to ensure that safety regulations are not being infringed.
8 BUS MIXING CONSOLE
29