Audiolab 8000S Service Manual page 13

5.0 p e r fo r m a n c e t e s t s
5.2 Performance test procedure
For test point (TP) references, see section 6.0 Test Points.
No Action
5.2.10. Set up
amplifier for
1 W output
5.2.11. Measure signal
to noise ratio
(SNR)
5.2.12. Measure
distortion at
20 kHz
5.2.13. Measure
distortion at
100 Hz
5.2.14. Left channel
check
operation of
protection
circuit
Test Equipment
Audio Analyser
output: 1kHz,
500 mV
Audio Analyser
200Hz HP filter off
A-weighted filter on
Audio Analyser
output: 20kHz, 1 V,
200Hz HP filter on
A-weighted filter off
Audio Analyser
output: 100Hz, 1V
200Hz filter off
A-weighted filter off
Audio Analyser
output:
1 kHz, 100 mV
Oscilloscope
ch1: 0.5 V/div
0.2 Vms/div
ch2: 0.2 V/div
0.2 ms/div
trigger: ch1
Details
Adjust VOLUME knob until voltage on
output of amplifier is
2.83 V rms (or 1 W). If possible, set this
as 0 dB reference.
Remove input leads and replace with
shorted phono plugs.
Measure dB reading (if function is
available), which is equivalent to signal-
to-noise ratio.
Alternatively measure noise voltage and
calculate SNR.
SNR should be >80 dB.
SNR = 10 log signal power
10
noise power
SNR = 20 log signal voltage
10
noise voltage
Adjust the VOLUME knob to give
20 V rms at loudspeaker output.
Distortion should be <0.07% for left and
right channels.
Distortion should be <0.007% for left and
right channels.
Turn VOLUME knob to minimum.
Connect ground clip of oscilloscope
probe to 0 V (TP 0).
Connect probe for channel 2 to cathode
of D943 (TP 11).
Short circuit loudspeaker terminal.
Slowly increase VOLUME. Check
oscilloscope traces with Figure 5.2.
Trace will appear briefly and will
disappear when amplifier mutes.
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