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Wire Sizing Chart
4 ft
7 ft
10 ft 13 ft 16 ft 19 ft 22 ft 28 ft
0-20 amps
14
12
12
10
10
8
8
8
20-35 amps
12
10
8
8
6
6
6
4
35-50 amps
10
8
8
6
6
4
4
4
50-60 amps
8
8
6
4
4
4
4
2
65-85 amps
6
6
4
4
2
2
2
0
85 -105amps
6
6
4
2
2
2
2
0
105-125 amps
4
4
4
2
2
0
0
0
125-150 amps
2
2
2
2
0
0
0
0
Let's look at a fairly small system. If you use a 50 watt/ch amp (25 amps) for the highs and
a 100 watt/ch amp (40 amps) for the woofers, you need at least a 4-gauge and maybe a
2-Guage wire to provide 65 amps at the trunk. Use the Wire Sizing Chart. Add up the fuse
values on the amplifier(s) then choose the proper size wire based on the distance from
the car battery to the amplifier location. Always use the same gauge wire for the main
ground as you do for the main power. Always make your ground as short as possible and
secure it to a clean solid surface, preferably the vehicle frame.
Mounting your ST-X III amplifier
Mounting your Zapco amplifier is easy. Just keep in mind a few guidelines:
• The amplifier can be mounted in any direction, on wood, metal, or carpet
• The metal chassis of the amp can be grounded or left isolated
• The amplifier requires adequate ventilation. Creating power creates heat, and
cooling requires air. Position the amplifier with sufficient surrounding area for air
supply and keep the end plates clear for future access
• Keep the amplifier out of the engine compartment or other locations that may
cause excessive heat or moisture
• Do not mount the amplifier to a subwoofer box or other place that may have
excessive vibration
Setting Gains
: Gain pots are not volume controls. Before you first turn on your system,
you should make sure all gain controls are set to minimum. Gain controls should be used
only if absolutely necessary. Turning up gain controls causes increased noise, makes
distortion more likely and reduces the dynamic range of your system. If you head unit
does not have sufficient output, you will get much better results by investing in a line
driver to provide more signal to the amplifier.
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Note: The ST-X III amplifiers have terminals that do not require connectors. You simply
insert a bare portion of wire and tighten the connection with the supplied Hex tool.
As the wire conforms to the connector the connection can loosen. You should re-tighten
the connection after about a week.
Some words about Power and Ground
The second most common cause of under performing amplifiers is insufficient power
current or a poor power connection. The most common cause of under performing
amplifiers is insufficient ground current or a bad ground connection.
12-volt current: Battery power works only if it travels in a complete circuit from the battery
positive terminal to the battery negative terminal. Main power input, of course, is attached
to the battery positive terminal. Ground current is returned to the battery through the
chassis to the point where the battery is grounded.
The current available for your amplifier to use to produce power will be restricted by the
smallest gauge of wire in the circuit and by the weakest physical connection in the circuit.
Wire Size
It's often surprising how many people will obsess about signal wire but routinely provide
the amplifier with only a fraction of the current it needs to do its job. The most common
wire gauge used in car audio is 10-gauge, and the most common location for amplifiers
is in the trunk.
Length of Run
Turn-on trigger wire
Ground to chassis +12 volt at Battery positive terminal
