© 2004 Wohler Technologies Inc. ALL rights reserved
21
AMP2-VSDA/AV
and
AMP2-VSDA/AM
User Manual P/N
821576
Rev-
B
AES Digital Gain Calibration Fine Adjustment (919050)
Section 3:
Technical Information
The digital gain calibration is set at the factory for +4 dB (Analog) = -20 dBFS (Digital). Three other values (+8 = -20, +6 = -9, and
0 = -18) may also be user selected via a DIP switch on the rear panel (
Item H
, page
14
). However, if a fine adjustment of the
calibration is desired, perform the following procedure:
1)
Remove the top cover. Save screws for later reassembly.
2)
You must remove the
919083 PCB
to access the trim pots (
P1-P4
) on the
919050 PCB
(see
Figure-3a
below for trim pot
locations).
3)
Connect a digital (
AES
) source of known digital amplitude and set the unit’s controls to monitor that source. For convenience
sake, it would be best to use your facility’s digital reference level, but any nearby level may be used with appropriate scaling of
output level required.
4)
Using an
accurate
DMM (preferably one having direct reading in dBv/dBu), measure the level on the Converted Analog Output
phoenix connectors (
Item I
, page
14
). Be sure to make measurement of the FULL balanced output, NOT just between one of
the outputs and ground!
5)
Locate trim pots
P1
,
P2
,
P3
, and
P4
(see
Figure-3a
below). Adjust
P4
(channel
1
) through
P1
(channel
4
) for the desired analog
level corresponding to the digital signal amplitude being supplied to the unit. For example, if your “house” Analog/Digital
correspondence is for a -18 dBfs digital level to correspond to an Analog level of +0dBu, it would be easiest to set the digital source
to -18 dBfs, set the gain calibration DIP switch for -18dBFS = 0dBu and then set
P1
through
P4
for 0dBu outputs on the phoenix
Analog Output connectors. But, if a digital source of -20dBfs is applied, even though the facility references are for -18dBfs, then
the analog output levels should be adjusted for a -2.0 dBu analog output level on the phoenix connectors.
Note:
If the meter being used to measure the analog outputs is not so accurate at those relatively low signal levels, you may wish to
increase the digital signal amplitude by some convenient factor like 10 or even 20 dB. (But of course you may not increase above
digital full scale.)
P1 - Adjusts Channel 4
P2 - Adjusts Channel 3
P3 - Adjusts Channel 2
P4 - Adjusts Channel 1
Figure-3a:
AES/EBU to Analog Module PCB (919050)
Digital Gain Calibration Trim Pot Locations
