Operating instructions

4-6
MAINTENANCE ORBAN MODEL 9400
Field Audit of Performance
Required Equipment:
 Ultra-low distortion sine-wave oscillator / THD analyzer / audio voltmeter
(With verified residual distortion below 0.01%. Audio Precision System
One, or similar high-performance system.)
(The NAB Broadcast and Audio System Test CD is an excellent source of
test signals when used with a high-quality CD player.)
 Spectrum analyzer with tracking generator
(Stanford Research Systems SR760 or equivalent. Alternatively, a sweep
generator with 50-9,500 Hz logarithmic sweep can be used with an oscil-
loscope in X / Y mode, or you can use a computer-controlled test set like
the Audio Precision System One. )
 Digital voltmeter
Accurate to ±0.1%.
 Oscilloscope
DC-coupled, triggered sweep, with 5M Hz or greater vertical bandwidth.
 Two 620 ±5% resistors.
 Optional: Audio Precision System 1 (without digital option) or System 2 (for digi-
tal tests).
It is assumed that the technician is thoroughly familiar with the operation of this
equipment.
This procedure is useful for detecting and diagnosing problems with the 9400's per-
formance. It includes checks of frequency response, noise and distortion perform-
ance, and output level capability.
This performance audit assesses the performance of the analog-to-digital and digi-
tal-to-analog converters and verifies that the digital signal processing section (DSP)
is passing signal correctly. Ordinarily, there is a high probability that the DSP is per-
forming the dynamic signal processing correctly. There is therefore no need to
measure such things as attack and release times — these are defined by software
and will automatically be correct if the DSP is otherwise operating normally.
It is often more convenient to make measurements on the bench away from high RF
fields which could affect results. For example, in a high RF field it is very difficult to
accurately measure the very low THD produced by a properly operating 9400 at
most frequencies. However, in an emergency it is usually possible to detect many of
the more severe faults that could develop in the 9400 circuitry even in high-RF envi-
ronments.