Mackie HR824 Service Manual page 18

HIGH FREQUENCY AMPLIFIER TESTS.
NORMAL RESPONSE TEST
Disable the compressor circuit by shorting together pins 1 and 2 of J12.
Set your audio signal generator for an output of 300mVrms (-10.46dBV)
Set the ACOUSTIC SPACE, LOW FREQ and HIGH FREQ switches to NORMAL.
Do these measurements fairly quickly because the amplifier will be warming up.
The level of the output may be different from that shown, due to the factory settings of
the calibration pots. Just make sure that the speaker under test follows the overall shape
and that the switch works as follows:
HIGH FREQUENCY SWITCH TEST
Switch the HIGH FREQ switch to +2dB and verify a 2dB increase at 20 kHz.
Switch the HIGH FREQ switch to -2db and verify a 2dB decrease at 20 kHz.
THD
Measure the THD at 3 kHz and verify it is less than 0.1%
30
20
25
15
10
20
15
5
10
5
0.0 1
1k
18
HIGH FREQUENCY AMPLIFIER OUTPUT
HIGH FREQ
NORMAL
2k 3k 5k
FREQ(Hz)
20
15
+2dB
10
-2dB
5
Base
Camp
1
10k
20k 30k
30
25
20
15
10
5
0.0