Mackie FR800/FR1400/FR2500 FR Series Owner's Manual - Page 8

FR SERIES AMPLIFIERS Front Panel Features 1. POWER 5. LEVEL CONTROLS Use this rocker switch to turn the unit on or off. This connects/disconnects the AC power to the AC power transformer. The amplifier is on when the top of the switch is pressed in. It is off when the bottom of the switch is pressed in. The Power On LED above the switch will light when the power switch is on. These two knobs control the levels of Channels 1 and 2. The knobs are detented to make it easy to set both controls to the same level. Usually, these controls are set all the way up. You might turn them down slightly if you have highefficiency speakers. Also, you could use them to control the level of line-level sources such as a CD player connected directly to the amplifier without a preamplifier or mixer. 2. VENTILATION Keep these ventilation slots free from any obstructions, so the air may flow freely and cool down the power transistors. 3. OL LEDs This is short for "overload." These red LEDs indicate when the output of the amplifier has reached the maximum, and is right on the edge of clipping. Clipping is bad for speakers and should be avoided. It is okay if the OL LED blinks occasionally. It means that the transient peaks of the music are just hitting the full output of the amplifier. However, if the OL (overload) LED is blinking frequently or continuously, turn down the source signal (i.e., the mixer's master faders) or the amplifier's Level controls. The amplifiers are designed so that a +3.4 dBu (1.15V rms) input signal drives the amplifier to full power into 4 ohms: FR•800 = 300 watts per channel into 4 ohms FR•1400 = 450 watts per channel into 4 ohms FR•2500 = 750 watts per channel into 4 ohms This equates to a gain of about 30 dB (30 dB, 32 dB, and 34 dB respectively). After you have set the levels for the mixer (or other signal source), adjust the Level controls on the amplifier as the final adjustment to set the overall volume for the system. In stereo and mono mode, use both level controls to control the levels going to each speaker. In bridged mono mode, turn the channel 1 level control down, and just use the channel 2 control. 4. SIG LEDs This is short for "signal present." These green LEDs indicate when a signal is present after the Level controls, at the output stage of the power amplifier. If the Level controls are turned all the way down (fully counterclockwise), these indicators will not light. 43 43 2 1 5 5  FR SERIES AMPLIFIERS