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Dolby NR circuit
Condition:
Equipment:
¢ Record mode
¢ EVM (Electronic Voltmeter)
¢ AF oscillator
¢ Dolby NR switch...IN/(OUT
¢ ATT
¢ Oscilloscope
¢ Dolby NR select switch
¢ Resistor (600Q)
...BIC
¢ Input level controls...MAX
Record side
¢ Check of the Dolby-B type encoder characteristics
. Make connections as shown in fig. 17.
. Set the unit to the record mode. (NR select switch is OUT.)
. Apply a 1kHz signal to LINE IN.
. Adjust the ATT so that the output level at Pin 7 of 1C401 (L-CH) and 1C402 (R-CH) is 12.3mV.
. The output level at pin 21 should be OdB (375mV).
. Set the NR select switch to B, and make sure that the output signal level at pin 21 of 10401 (L-CH) and 1C402
(R-CH) is +6+1.5dB (753mV).
. Set the NR select switch to OUT, and adjust the frequency
to 5kHz.
The output signal level at pin 21 should be 0dB.
(375mvV).
. Set the NR select switch
to B and make
sure that the
Output signal level at pin 21 of 1C401 (L-CH) and IC402
(R-CH) is +8+1.5dB (948mV).
¢ Check to Dolby-C type encoder characteristics
9. Repeat steps 1-5 above.
10. Set the NR select switch to C and make sure that the
output signal level at pin 21 of 1C401
(L-CH) and IC402
:
(R-CH) is +11.5+2dB (1.4V).
AF oscillator
ATT.
6002
11. Set the NR select switch to OUT and adjust the frequency
rae eo
EVM Oscilloscope
to 5kHz.
The output signal at pin 21 should be OdB.
12. Set the NR select switch to C and make sure that the
output signal level at pin 21 of 1C401 (L-CH) and 1C402
Fig. 17
(R-CH) is +8.5+2dB (1V).
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