Altec Lansing 6125A, 4200A manual Front Panel Features

Operating Manual 6125A and 4200A Multi-Channel Power Amplifier

6.FRONT PANEL FEATURES

6.1Power Switch

When the unit is switched on there is a five sec- ond delay, during which time the PROTECT circuit will activate, disconnecting the speakers from the amplifier output. When turning off the amplifier, the load is removed instantly, and the protect LED will briefly turn on as the power supply discharges.

6.2Signal Indicator

The signal present LEDs illuminate at an input level of about 13mVrms (-35.5dBu).

6.3Clip Indicator

The clipping LEDs illuminate at an input level of about 870mVrms (+1.0dBu), with all channels driven by 1KHz into 8Ω . This indicates that the signal processing circuitry has determined output levels to be approaching the available power supply rails and has begun to “soften” signal peaks. Actual onset of “hard” clipping depends on audio program and total load impedance and does not oc- cur until the signal processing circuitry can no longer com- pensate, which means that signal integrity can be maintained even if the clipping indicators illuminate for short periods of time.

6.4Thermal Status Indicator

The thermal LEDs illuminate when the tempera- ture of any one of the heat sink extrusions reaches 85 to 90°C. Both channels of the affected amplifier module will shut off until the measured temperature drops below about 70°C. The amplifier should be able to maintain proper

operation at an ambient room temperature of 50°C (122°F) or less with typical audio program and all channels driven into 4Ω .

6.5Protect Indicator

The protect LEDs illuminate when the fault moni- toring microprocessor has determined that one of the fol- lowing conditions exists:

-Power supply undervoltage

-Power supply overvoltage

-Output overcurrent

-Heat sink overtemperature

-Unacceptable DC output content

-Unacceptable high frequency output content

-AC power interruption

Because the signal processing module used in the 6125A and 4200A amplifiers processes two channels si- multaneously, a fault in one channel will result in a pro- tect condition for both channels processed by the same module, ex. channels 1-2, 3-4, and 5-6 (6125A only). Thus there will never be a case where only one of the amplifier channels is shown in protect mode. When a pair of protect LED's are illuminated, internal relays have removed the channel pair's speaker loads from the amplifier output and connected the speakers to ground. If the fault is isolated to one module (channel pair), the other channels will re- main unaffected.

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