14
USER GUIDE
USER GUIDE
USER GUIDE
USER GUIDE
USER GUIDE
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 equip-
ment.
Headphones
The PHONES output is a 3-pole ‘A’ gauge jack, wired as a stereo output as shown,
ideally for headphones of 200
Ω
or greater. 8
Ω
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 micro-
phones 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 always take care 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 or ground ‘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 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 -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 micro-
phones, 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/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.
