Mackie M800 Bedienungsanleitung PDF herunterladen (Seite 19)

19

AC Power Distribution

The majority of AC outlets

encountered in homes and

clubs are served by a 240VAC

center-tapped service en-

trance 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

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.

OUTPUT WIRING

Use heavy gauge, stranded wire for connect-

ing speakers to the M•800 amplifier’s

SPEAKER OUTPUT

terminals. As the distance

between the amplifier and the speakers in-

creases, 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

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. 2Ω 14 gauge

4Ω 16 gauge

8Ω 18 gauge

Up to 40 ft. 2Ω 12 gauge

4Ω 14 gauge

8Ω 18 gauge

Up to 60 ft. 2Ω 10 gauge

4Ω 12 gauge

8Ω 16 gauge

Up to 100 ft. 2Ω 8 gauge

4Ω 10 gauge

8Ω 14 gauge

Up to 150 ft. 2Ω 6 gauge

4Ω 8 gauge

8Ω 12 gauge

Up to 250 ft. 2Ω 4 gauge

4Ω 6 gauge

8Ω 10 gauge

TRANSFORMER

120V

120V

240V

HIGH VOLTAGE POWER LINE

EARTH

GROUND

(NEUTRAL)

PRIMARY

WINDING

SECONDARY

WINDING

240V Center-Tapped Secondary

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