Operation Manual

USER GUIDE
14
AUX OUTPUTS
The Aux outputs are on 3-pole ‘A’ gauge jack sockets, wired as shown on the left, and
are balanced, allowing long cable runs to balanced amplifiers and other equipment.
CHANNEL DIRECT OUTPUTS
The Direct outputs are on 3-pole ‘A’ gauge jack sockets, wired as shown on the left,
and are unbalanced.
HEADPHONES
The PHONES output is a 3-pole ‘A’ gauge jack, wired as a stereo output as shown,
suitable for headphones of 2009 or greater. 89 headphones are not recommended.
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 -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.
GROUNDING AND SHIELDING
For optimum performance use balanced connections where possible and ensure that all
signals are referenced to a solid, noise-free earthing point and that all signal cables
have their screens connected to ground. In some unusual circumstances, to avoid earth
`loops’ 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
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 -ve. If a twin screened cable is used, connect the screen only
at the mixer end.
•
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 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.
Grounding and shielding is still seen as a black art, and the suggestions above are only
guidelines. If your system still hums, an earth loop is the most likely cause. Two
examples of how an earth loop can occur are shown below.
WARNING! Under NO circumstances must the mains earth be
disconnected from the mains lead.