Studio Technologies 770 - Manual (Page 23)

Model 770 User Guide Issue 1, October 1997
Studio Technologies, Inc. Page 23
Model 770
The mic/line direct output may prove
especially helpful, providing a “mic/line
amplifier” for general purpose or emer-
gency use. In special situations, a signal
of virtually any audio level could be
“bumped” to nominal +4dBu.
VU Meter Calibration
A trim potentiometer allows calibration of
the monitor section’s VU meter. The range
of this trim pot allows “0” on the meter to
represent an output signal level of +1 to
+7dBu. From the factory, the VU meter
is calibrated so that 0 VU represents an
output level of +4dBu on main output 1,
when loaded with 100k ohms. In certain
cases it may be a good idea to check the
meter calibration, such as when main
output 1 is loaded with 600 ohms, or when
either main output 2, 3, or 4 is going to
serve as the “primary” output.
While not difficult, meter calibration is a
bit tedious:
1. Ensure that mains power is connected
to the Model 770.
2. Place the main output limiter/compres-
sor to the off state by placing the
button labeled LIMITER to the out
position.
3. Connect the 1kHz tone to the output
buses by placing the button labeled
1KHZ TO MAIN & AUX to the on (in)
position.
4. Select MAIN as the monitor source.
5. Designate main output 1, 2, 3, or, in
rare circumstances, 4 as the desired
“primary” output. This is the output that
the meter will be calibrated against.
6. Confirm that the designated main
output is terminated with its normal
load impedance.
7. Using an appropriate adapter cable,
connect an audio level meter directly
across the designated main output.
Ensure that the meter connection does
not remove the normal load. The level
meter must be a precision device that’s
intended for audio use—a general-
purpose voltmeter is not adequate!
8. Carefully observing the audio level
meter, set the main bus master output
control so that the output level is pre-
cisely +4dBu.
Figure 5. Detail of back panel showing meter
calibration trim pot