SoundCraft M-SERIES User Manual page 16

14
CHANNEL DIRECT OUTPUTS
The Direct outputs are on 3-pole 'A' gauge jack sockets, wired as shown on the left, and are impedance
balanced.
HEADPHONES
The PHONES output is a 3-pole 'A' gauge jack, wired as a stereo output as shown, suitable for headphones
of 200W or greater. 8W 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.
USER GUIDE