4-12
MAINTENANCE Orban Model 8400
F) Recall bypass preset: Navigate to the Bypass button and press Enter.
Bypass defeats all compression, limiting, and program equalization but re-
tains pre-emphasis.
G)
Verify a reading (noise) of <–80 dBu at the output of the unit.
H) Repeat steps (C) through (G) for the Right Analog Output.
4. Check frequency response of Analog I/O.
A) Verify 8400 software controls are set to their default settings. (Refer to page 4-9.)
B) Be sure you are still in BYPASS mode [see step (3.F)].
C) Connect the oscillator to the Left Analog Input XLR connector.
D) Inject the Analog Input XLR connector with a level of 0 dBu (20 dB below the
Analog Clip Level setting) with the oscillator set to 100 Hz.
This is 20 dB below the clip level, which allows headroom for pre-emphasis.
75μs pre-emphasis will cause 17 dB of boost at 15 kHz.
E)
Connect the audio analyzer to the 8400's Left Analog Output XLR connector.
F) Verify a level of 0 dBu ±1 dB. Use this level as the reference level.
G) Verify that frequency response at 50 Hz, 100 Hz, 400 Hz, 5 kHz and 15 kHz is
within ±0.1 dB of the reference level.
This procedure tests the analog input circuitry, the A/D converter, the DSP,
the DAC, and the analog output circuitry.
H)
Repeat steps (C) through (G) for the right channel.
5. Check distortion performance of Analog I/O.
A) Verify 8400 software controls are set to their default settings. (Refer to page 4-9.)
B) Be sure you are still in Bypass mode [see step (3.F)].
C) Press Escape until you see the Main Meter screen
D) Connect a THD analyzer to the Left Analog Output XLR connector. Set the THD
analyzer's bandwidth to 22 kHz.
E) Connect the oscillator to the Left Analog Input XLR connector.
F) For each frequency used to measure THD, adjust the output level of the oscillator
to make the
Comp meter on the 8400 read 100.
You will have to reduce the output level of the oscillator at higher frequencies
to compensate for the pre-emphasis boost in the 8400.
G) Measure the THD+N at the frequency levels listed below.
To Next Page
Loading...
