Studio Technologies 742A - Manual (Page 17)

Model 742A User Guide Issue 1, July 2012
Studio Technologies, Inc. Page 17
Audio Mixer
Post-Installation
Calibration
Reference Tone Direct Output
If the reference tone direct output is used,
it is important to confirm that its output
level is correct for the installation. In most
cases, the output level will need to be
adjusted to match the precise require-
ment of the system. This is because the
load applied to the output may very well
be different from the 100 k ohm load that
is applied during testing at the factory. As
previously noted, while the output circuitry
is capable of driving loads of 600 ohms or
greater, the output level will drop slightly
as the load impedance changes, espe-
cially as it approaches 600 ohms.
Depending on the Model 742A’s internal
configuration the tone frequency will
be either 400 Hz or 1 kHz. A trim poten-
tiometer allows adjustment of the output
level over a range of approximately +3 to
+7 dBu. The trim pot is accessible by way
of a small access hole in the back panel,
adjacent to the reference tone direct
output’s ¼-inch jack. (Refer to Figure 7 for
a detailed view.) At the factory this output
is loaded with 100 k ohms and then the
trim pot is adjusted to give an output level
of +4 dBu.
In practice, calibrating the output level is
quite simple:
1. Confirm that the reference tone direct
output is terminated with its installa-
tion-specific load impedance.
2. Ensure that the Model 742A is con-
nected to a source of AC mains or DC
power.
3. Using an appropriate adapter cable,
connect a high-input-impedance audio
level meter directly across the refer-
ence tone direct output. Ensure that this
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 volt-
meter is not adequate!
4. While carefully observing the level
meter, adjust the trim pot to give the
desired output level.
Labeling the Unit for Clarity
Once the Model 742A has been installed,
installation-specific labeling of the front
panel may want to be performed. (Refer
to Figure 11 for a detailed view.) This ad-
ditional clarity can greatly assist operators
in correctly using the unit. For example,
instead of the first line input channel having
the factory-standard text INPUT 5, it could
reflect its exact function, such as TAPE 1.
The unit’s front-panel graphics were specif-
ically created to simplify the task of adding
custom labels. Each front-panel section
heading text is underlined with a horizontal
green line, which, besides looking pretty
sharp, is intended to serve as a “guide” for
adding installation-specific labels. The dis-
tance from the guide line to the top of the
front panel was specifically designed
to allow ¼-inch-high label material to fit
correctly.
For a great look it’s recommended that
Brother® P-Touch ¼-inch (6 mm) labels be
created. Selecting tape material that prints
white text on a black background works out
perfectly for the Model 742A. The Brother
label cassette number TX-3151, white on
black, is appropriate for use with some of
their printers.