HD1521

7. HIGH

This knob allows up to 3 dB of boost or cut at 12 kHz, with no change in level at the unity (U) mark. This is a shelving EQ.

+3

+2

+1

0

–1

–2

 

 

 

–3

 

 

 

20Hz

100Hz

1kHz

10kHz 20kHz

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

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 “Ther- mal Considerations” on page 9.

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 overheat-

ing, which in turn trips the thermal protect circuitry and interrupts the performance. See

‘Thermal Considerations’ on page 9 for more informa- tion.

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 possi-

bility of any turn-on, or turn-off thumps in your speak- ers.

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