Polarity (Phase)
You will probably be familiar with the concept of polarity in electrical signals and this is of particular importance to balanced audio signals. Just as a balanced signal is highly effective at cancelling out unwanted interference, so two microphones picking up the same signal can cancel out, or cause serious degradation of the signal if one of the cables has the +ve and
Grounding and Shielding
For optimum performance use balanced connections where possible and ensure that all signals are referenced to a solid,
If the use of unbalanced connections is unavoidable, you can minimise noise by following these wiring guidelines:
•On INPUTS, unbalance at the source and use a twin screened cable as though it were balanced.
•On OUTPUTS, connect the signal to the +ve output pin, and the ground of the output device to
•Avoid running audio cables or placing audio equipment close to thyristor dimmer units or power cables.
•Noise immunity is improved significantly by the use of low imped- ance sources, such as good quality professional microphones or the outputs from most modern audio equipment. Avoid cheaper
high impedance microphones, which may suffer from interference over long cable runs, even with
Grounding and shielding is still seen as a black art, and the suggestions above are only guidelines. If your system still hums, an earth/ground loop is the most likely cause. Two examples of how an earth loop can occur are shown below.
Warning!
Under NO circumstances must the AC power mains earth be disconnected
from the mains lead.
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