MACKIE SRM450
Owner's Manual

THERMAL CONSIDERATIONS
The SRM450 has two powerful amplifiers built-in. As amplifiers produce heat, it is important to dissipate the heat as quickly as possible. This results in increased reliability and longevity for the amplifier. That�s what the massive die-cast aluminum heatsink on the rear panel is for. The heatsink is cooled by convection, where cool air is drawn through it�s fins, carrying the heat away. In order for this convection cooling to work efficiently, it is important to provide adequate airspace behind the loudspeaker. When you position the SRM450, we recommend leaving at least six inches of air space behind it. In the unlikely event of the amplifiers overheating, a built-in thermal switch will activate, placing the amplifiers into standby. The THERMAL indicator on the rear panel lights, and the power LEDs on the front and rear panel turn off. When the amplifiers have cooled down to a safe operating temperature, the thermal switch resets itself, the power LEDs turn on, the THERMAL LED turns off, and the SRM450 resumes normal operation. Check to see if the PEAK LED on the rear panel is blinking frequently or lighting continuously. If so, you should turn down the LEVEL control a notch or two to avoid overheating the amplifiers. If the temperature in the room is too high, it could cause the amplifiers to overheat. In this case, you should try aiming a fan at the heatsink to move air through the fins faster.
THERMAL HEATSINK PEAK

AC POWER CONSIDERATIONS
Be sure the SRM450 is plugged into an outlet that is able to supply the correct voltage specified for your model. If the voltage should drop below 97% of the specified line voltage, the built-in amplifiers will no longer be able to supply rated power. (They will continue to operate down to 75% of the rated line voltage, but won�t reach full power, resulting in lower headroom.) Under maximum S.P.L. conditions, where musical peaks are clipping, the SRM450 120V model draws 2.5 amps on average (1.3 amps for the 240V model). Under normal conditions, the current draw is below 1 amp. We recommend that a stiff (robust) supply of AC power be used because the amplifiers place high current demands on the AC line. The more power that is available on the line, the louder the speakers will play and the more peak output power will be available for cleaner, punchier bass. A suspected problem of �poor bass performance� is often caused by a weak AC supply to the amplifiers.

AC Power Distribution
A 240VAC center-tapped service entrance transformer serves the majority of AC outlets encountered in homes and clubs (in the U.S.). This provides two phases of AC power on either side of the center tap, at 120V each. 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, or light-dimmer switches, are used).
HIGH VOLTAGE POWER LINE

120V PRIMARY WINDING 120V 240V SECONDARY WINDING

TRANSFORMER

EARTH GROUND (NEUTRAL)

240V CENTER-TAPPED SECONDARY

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