MACKIE M1400/M1400i - Manual (Page 24)

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The extension cord used to supply power to
the “amp rack” should have a third wire safety
ground to avoid presenting a safety hazard. We
also recommend using a cord that has conduc-
tors large enough to avoid severely limiting the
amplifier’s ability to supply high currents on
transients.
Power amplifiers can have
momentary peak current re-
quirements many times
above the nominal average
current draw. According to
Ohm’s Law, the greater the resistance of the
linecord, the more input power is lost between
the AC outlet and the power amplifier (across
the linecord). And to further aggravate the
matter, this relationship is nonlinear. The
amount of power lost across the linecord in-
creases exponentially as the current demand
increases. So if the current demand doubles
momentarily because of an exceptionally loud
bass note, the amount of AC input power lost
across the linecord increases four times. You
can see that it is very important to keep the
resistance of the linecord to a minimum. That’s
why we recommend using a heavy gauge exten-
sion cord (like 14 gauge or bigger). Remember,
wire gets thicker as the gauge number gets
smaller (10 gauge is thicker than 14 gauge).
AC Power Distribution
In order to minimize ground loops, the safety
grounds for all the outlets should be connected
to a common (“star”) grounding point, and the
distance between the outlets and the common
grounding point should be as short as possible.
If lighting is used in a show, it is preferable
to power the lights from a different AC circuit
than the one powering the audio equipment.
This will help minimize noise from the lights
coupling into the audio (particularly if SCRs
are used).
INPUT WIRING
Use a high-quality 3-conductor shielded
cable to connect the signal between the signal
source (mixing console, equalizer, etc.) and
the balanced inputs to the amplifier. If you’re
using the unbalanced inputs, use a high-quality
2-conductor shielded cable. Your Mackie
Dealer can recommend a suitable cable for
your application.
OUTPUT WIRING
Use heavy gauge, stranded wire for connect-
ing speakers to the M•1400/M•1400i
amplifier’s
SPEAKER OUTPUT terminals.
As the distance between the amplifier and the
speakers increases, the thickness of the wire
should also increase. Speaker wire has resis-
tance, and when electricity passes through a
resistor, power is lost. The thicker the wire, the
less resistance it offers, and the more power
actually gets to the speakers.
The thickness of wire is rated in gauges.
Use the chart below to determine the correct
gauge of wire to use according to the distance
between the speakers and the amplifier, and
the impedance of the load the amplifier is driv-
ing. This ensures that the power lost across the
speaker wire is less than 0.5 dB.
Load Gauge of
Wire Length Impedance Wire
Up to 25 ft. 2
Ω
14 gauge
4
Ω
16 gauge
8
Ω
18 gauge
Up to 40 ft. 2
Ω
12 gauge
4
Ω
14 gauge
8
Ω
18 gauge
Up to 60 ft. 2
Ω
10 gauge
4
Ω
12 gauge
8
Ω
16 gauge
Up to 100 ft. 2
Ω
8 gauge
4
Ω
10 gauge
8
Ω
14 gauge
Up to 150 ft. 2
Ω
6 gauge
4
Ω
8 gauge
8
Ω
12 gauge
Up to 250 ft. 2
Ω
4 gauge
4
Ω
6 gauge
8
Ω
10 gauge