SoundCraft SPIRIT LIVE 4 2, User Manual

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Page 16
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The Aux and Channel Direct outputs are on 3-pole ‘A’ gauge jack sockets, wired as
shown on the left, and incorporate impedance balancing, allowing long cable runs to bal-
anced amplifiers and other equipment.
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The PHONES output is a 3-pole ‘A’ gauge jack, wired as a stereo output as shown,
suitable for headphones of 200 W or greater. 8 W headphones are not recommended.
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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 -ve wires reversed. This phase reversal can be a real problem when
microphones are close together and you should therefore take care always to connect
pins correctly when wiring audio cables. The mono inputs are provided with a Phase (
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switch to reverse the polarity of a selected input if a phasing problem is suspected.
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For optimum performance it is vital that all signals are referenced to a solid, noise-
free earthing point and that all signal cables have their screens connected to ground. To
avoid earth `loops’, use balanced connections where possible and ensure that all cable
screens and other signal earths are connected to ground only at their source and not at
both ends.
If the use of unbalanced connections is unavoidable, you can mimimise noise by fol-
lowing these wiring guidelines:
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On INPUTS, unbalance at the source and use a twin, screened cable as though it
were balanced.
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On OUTPUTS, connect the signal to the +ve output pin, and the ground of the out-
put device to -ve. If a twin screened cable is used, connect the screen only at the
mixer end.
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Avoid running audio cables or placing audio equipment, close to thyristor dimmer
units or power cables.
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Noise immunity is improved significantly by the use of low impedance 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 well-made cables.