WIRING & CONNECTORS
Faulty connectors and cabling are some of the most
frequent sources of noise and poor sounding systems.
The following section should help you connect your system
correctly. It’s also worth spending a little time referring to
all of your user manuals, as wiring conventions can vary
between manufacturers - see diagrams.
BALANCED AND UNBALANCED MIC INPUTS
Soundcraft uses XLR sockets for its balanced mic inputs.
The wiring convention for XLRs is: Pin 1 - Shield, Pin 2 -
Hot (+ve) and Pin 3 - Cold (–ve).
Balancing is a method of audio connection which cancels
any interference in a signal, to give low noise operation.
This is achieved by using a 2-conductor mic cable, usually
surrounded by a shield, in which the ‘hot’ and ‘cold’ signals
are opposite polarity. Any interference picked up will be of
the same polarity on both hot and cold wires and will be
rejected by the mic input’s Difference Amplifier. You may
use unbalanced sources when wired as shown. However, do
not use unbalanced sources with Phantom Power switched
on. The voltage on Pins 2 & 3 of the XLR connector may
cause serious damage.
BALANCED AND UNBALANCED LINE INPUTS
Line inputs accept ‘A’ Gauge, 3-pole (Tip, Ring, Sleeve) 1/4
inch jack wired as shown in Fig. 7.3.
Note that for unbalanced operation the screen of the cable is wired
to both the Ring and the Sleeve of the jack.
INSERTS
A Mixer insert point is a single, ‘A’ Gauge, 3-pole (stereo),
switched jack socket (not unlike the headphone socket on a
hi-fi amplifier). When a 3-pole jack is inserted the signal
path is interrupted. The signal is taken out of the mixer via
the plug tip, through an external piece of equipment and
then back to the mixer on the ring of the plug. A special Y-
cord is required which has the stereo jack at one end and
two mono jacks, for the processor’s input and output, at
the other. See Fig. 7.4.
GROUND COMPENSATED OUTPUTS
Ground compensated outputs may, to all intents and
purposes, be treated as balanced outputs. Ground
compensation helps avoid hum loops when the console is
feeding into an unbalanced piece of equipment. Essentially,
the Ground Compensated output has three connections,
much like a conventional balanced output, except that the
pin normally designated ‘cold’ acts as a ‘ground sense’ line
enabling it to sense and cancel any ground hum present at
the output.
The convention for XLRs is: Pin 1 - Shield, Pin 2 - Hot,
Pin 3 - Ground Sense. For jacks, the wiring convention is:
Tip - Hot, Ring - Ground Sense, Sleeve - Shield.
For use with balanced destinations, the Ground Sense
output may be treated as ‘cold’ allowing the connection to
be made normally. Where the destination has an
unbalanced jack input, a two-core (balanced-type) lead
should be made up as shown. Unbalanced jacks may also be
plugged directly into Ground Compensated Output jack
sockets, but the benefit of hum rejection will be lost.
IMPEDANCE BALANCED OUTPUTS
Impedance Balanced Outputs are configured as normal
balanced outputs: Pin 1 - Shield, Pin 2 - Hot (+ve) and Pin
3 - Cold (–ve). See Fig. 7.2.
Impedance Balanced Outputs work on the principle that
hot and cold terminals have the same resistance. When
impedance balanced outputs are used with a balanced
input, good rejection is achieved for both common-mode
ground voltages and electrostatic interference.
Note: The cold terminal can be either shorted to ground locally or
left open-circuit for balanced and unbalanced operation.
SECTION
7: W
iring Up & Connectors
31
BALANCED
UNBALANCED INPUT
BALANCED INPUT
UNBALANCED
FIG. 7.3
FIG. 7.1
FIG. 7.2
FIG. 7.5
FIG. 7.6
FIG. 7.4
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