Audio Developments AD256 - Manual (Page 25)

24
ADJUSTMENTS AND CALIBRATIONS
Meters - are to broadcast specification and either a VU or a PPM may be selected by
an internal DIL switch mounted on each meter driver printed circuit board.
Line-up-tone oscillator - the preset (VR6) that adjusts its level at the output of the
mixer is mounted on the output module printed circuit board.
Low-battery indicator - the preset (BATT) associated with this facility is also mounted
on the meter module printed circuit board. The low reading, when the first battery
indicator bar flashes, is set at the factory and corresponds to a set of batteries having
discharged to 9V.
Left
BATT
Right
IC1
PPM/VU Input
ON
ON
ILL
Meter Calibration
Each meter drive card has one preset potentiometer calibration control per indicator
bar; they control the adjustment of the indicator bar reading in relation to the signal
level being measured. All other aspects of the meter specification are taken care of
within the software and fixed values within the circuit components.
Access is gained to the meter drive card by removal of the output module; the drive
card being mounted on the rear of its LCD indicator. Extender cables are required to
enable the output module to be powered and operated outside of the chassis.
Meter adjustment - Set an input module for a line input and introduce a 1kHz tone
from an audio signal generator. Adjust levels to achieve a reading of 0dBu, if setting a
PPM scale, or +4dBu if setting a VU scale, at the appropriate main output, on an AC
millivoltmeter. Adjust the associated preset potentiometer to give the correct meter
reading for the signal level set.
Battery level adjustment - The low reading is set at the factory and corresponds to a
set of batteries having discharged to 9V. If a different calibration is required this can
be set by the preset potentiometer marked BATT on the above diagram.