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2.) Monitor the output signal via oscilloscope. After 3 to 4 signal periods, the limiter has controlled the high
distortion level down to a minor residual distortion (THD = 1% .... 1.5%).
Attack time: 3-4 ms
Release time: 30-40 ms
5.3 POWER-ON DELAY
Make sure that the signal is present at the power amplifier input. Switch the power amplifier via the Power-ON
switch on. Approximately 2 seconds after switching the power on, the signal will be present at the output.
5.4 FAN CONTROL
Upon switching the power amplifier’s power on, the fans will run for approximately 2 seconds and stop when the
power amplifier has regained "normal" temperature. In idling condition (Power-ON, no signal present) the fans
are switched between SLOW and OFF mode, depending on the heat sink's temperature.
Removing the connector CN5 lets the fans run in FAST mode.
The fan voltage is measured between pin CNS2X.4 and pin CNS1X.4:
SLOW ca. 17.5 V
FAST
ca. 29.0 V
5.5. SOAR-PROTECTION TEST
Drive the power amplifier up to 69 V in 4
Ω
. Parallel-connect a 1 resistor. The protection circuit reacts and
continuously tries to re-start! The protect-LED lights. Repeat the test with a 2 resistor. The power amplifier should
not switch off.
Caution:
If the SOAR-protection does not react in case of mains undervoltage, repeat the test with parallel-
connecting a 0.5
Ω
resistor instead of a 1
Ω
.
5.6. SHORT-CIRCUIT CURRENT-LIMITING TEST
- drive each channel with a burst signal (f = 1kHz, 1-3 cycles, rate
≈
1 sec.), with U(E) = 0dB
- connect a 1
Ω
load resistor
- the short-circuit current-limiter limits the output voltage at the load resistor symmetrically
(monitor via oscilloscope) to a peak voltage value of 40 V
(approximately 40 A maximum Peak Output Current).
5.7. DC-VOLTAGE PROTECTION TEST
- feed a test signal ( f = 5 - 7 Hz ) to the power amplifier without load resistor connected.
- starting at an input voltage of approximately 5 Veff, the protection circuit reacts and continuously tries to re-
start!
The protect-LED blinks in the same frequency.
- repeat the test with f = 14Hz. The power amplifier should not switch off.
5.8. HF-PROTECTION TEST
Caution:
Perform tests without load resistor connected to the power amplifier only.
Feed a +20dBu sine burst signal
f = 100kHz
(40ms ON, 960ms OFF) to the power amplifier input.
The protection circuit has to react. The power amplifier continuously tries to re-start.
The PROTECT-LED blinks in the same frequency.
Repeat the test with
f = 50kHz
. The power amplifier should not switch off.
5.9. INDICATOR TEST
Feed a 1kHz sine signal while slowly increasing it.
At approximately -26dBu the SIGNAL-LED starts lighting and at approxi8dBu the LIMIT-LED lights.
