Mackie HD1521 Owner's Manual - Page 6

HD1521 7. HIGH This knob allows up +3 to 3 dB of boost or cut +2 +1 at 12 kHz, with no 0 change in level at the -1 -2 unity (U) mark. This is -3 a shelving EQ. 20Hz 100Hz 1kHz 10kHz 20kHz 8. LEVEL This controls the overall signal level at the input to the built-in power amplifiers. It ranges from -6 dB to +6 dB of gain. The center detent is 0 dB (unity gain). 9. POWER LIGHT ON Press this switch in to turn on the front panel power LED if a visual indicator is preferred. The LED next to the switch will light as a reminder. If this switch is out, and the HD1521 is turned on, the LED on the front of the cabinet will not light, nor will the LED next to the switch. 10. THERMAL LED The HD1521 is equipped with a thermal protection circuit that monitors the internal temperature of the amplifiers and heatsink. If the temperature exceeds a safe operating level, this indicator lights and the input signal is muted to allow the amplifiers to cool. When the temperature cools to a safe level once again, the thermal protection circuit deactivates, the thermal LED turns off and the HD1521 returns to normal operation. When the HD1521 is in thermal protect mode, the power LED (12) will remain lit, indicating that the unit is still powered on despite the lack of output. If power light on (9) is engaged, the front panel power LED will go out when in thermal protect mode. Activation of the thermal protection circuit is an indication that you should take steps to avoid continued thermal problems. See "Thermal Considerations" on page 9. 11. SIG/LIMIT LED This bi-color LED illuminates green whenever there is a signal present at the main input connector. It senses the signal just after the level control, so adjustments to the level control will affect the sig/limit indicator. The HD1521 has a built-in limiter that helps to prevent the amplifier outputs from clipping or overdriving the transducers. The sig/limit indicator lights in yellow when the limiter is activated. It's okay for it to blink yellow occasionally, but if it blinks frequently or lights continuously, turn down the level control until it only blinks occasionally. Excessive limiting may lead to overheating, which in turn trips the thermal protect circuitry and interrupts the performance. See 'Thermal Considerations' on page 9 for more information. 12. POWER Use this switch to turn the HD1521 on and off. The LED next to the switch will illuminate when powered on. The front panel LED will also turn on, but only if the power light on switch (9) is engaged. Press the bottom of this switch to put the speaker into standby mode. The HD1521 will not function, but the circuits are still live. To remove AC power, either turn off the AC mains supply, or unplug the power cord from the speaker and the AC mains supply. As a general guide, the powered speakers should be turned on last, after the mixer and other sources. They should also be the first things turned off. This will reduce the possibility of any turn-on, or turn-off thumps in your speakers. 13. IEC AC Receptacle This jack accepts the supplied ­3-prong AC power cord. Before you plug the AC power cord into the powered loudspeaker, make sure that the voltage of your unit (listed above the IEC AC receptacle) is the same voltage as your local AC mains supply. Use only the power cord supplied. Also, disconnecting the plug's ground pin is dangerous. Don't do it. And no running with scissors either. Let's be safe out there!  HD1521