Mackie M1200/M1400 owner manual Input Wiring, Output Wiring, Feet, AC Power Distribution

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. With this in mind, we recommend using the following for a fully loaded 15A service:

Extension Cord Length	Wire Gauge
25 feet	14 AWG
50 feet	12 AWG
100 feet	10 AWG

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

The majority of AC outlets encountered in homes and clubs are served by a 240VAC cen- ter-tapped service entrance transformer. This provides two phases of AC power on either side of the center tap at 120V each.

In order to minimize ground loops, the safety grounds for all the outlets should be connected

HIGH VOLTAGE POWER LINE

	120V
PRIMARY	240V	SECONDARY
WINDING		WINDING
	120V
TRANSFORMER	EARTH
240V Center-Tapped Secondary	GROUND
	(NEUTRAL)

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 one leg of the service, and power the audio equipment from the other leg. This will help minimize noise from the lights coupling into the audio (particularly if SCRs are used).

When setting up for a show, oftentimes you are plugging into an AC power distribution sys- tem you know nothing about. You may even be faced with 2-wire outlets that are missing the third safety ground pin. It’s a good idea to have a three-wire AC outlet tester in your toolbox so you can check the outlets yourself to make sure they are wired correctly. These testers will tell you if the polarity of the hot and neutral wires is reversed and if the safety ground is dis- connected. Don’t use an outlet if it is wired improperly! This is to protect yourself as well as your equipment.

If you find that you must plug into a two- wire outlet, you will need to use a two-wire to three-wire adapter (cheater plug). These come with a metal tab that you put underneath the center screw that holds the AC outlet faceplate in place. This center screw should be grounded. You can check it by connecting the adapter to the outlet and then plugging in your AC outlet tester.

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.

If you want to build your own cables, refer to the “Connectors” section in Appendix C.

OUTPUT WIRING

Use heavy gauge, stranded wire for connect- ing speakers to the M•1200/M•1400 amplifier’s SPEAKER OUTPUT terminals. As the dis- tance between the amplifier and the speakers increases, the thickness of the wire should also increase. Speaker wire has resistance, and when electricity passes through a resistor, power is lost. The thicker the wire, the less re- sistance it offers, and the more power actually gets to the speakers.

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