Studio Technologies 750 - Manual (Page 18)

Issue 3, May 1997 Model 750 User Guide
Page 18 Studio Technologies, Inc.
Model 750
Setup Direct Output
The setup direct output is a stereo line-
level output that provides direct access
to the voice and tone signals. Trim potenti-
ometers allow adjustment of the output
level from approximately –2 to +10dBu.
The trim pots are located on the back
panel, directly above the setup direct
output’s ¼-inch phone jacks. At the fac-
tory these outputs are loaded with 100k
ohms, and then the trim pots are adjusted
to give an output level of +4dBu.
If the setup direct output is to be used in
an installation, it’s important that the left
and right channel output levels be ad-
justed to precisely match the requirements
of the system. Even if you simply want to
use the standard output level of +4dBu,
it’s still important to confirm the factory
calibration. Also note that while the output
circuitry is capable of driving loads of 600
ohms or greater, the output level will drop
slightly as the load impedance ap-
proaches 600 ohms. A 0.5dB difference in
output level can be expected as the load
impedance changes from 20k ohms to
600 ohms.
In practice, calibrating the output level
is quite simple:
1. Confirm that both the left and right
channels of the setup direct output
are terminated with their normal load
impedance.
2. Ensure that the Model 750 is con-
nected to mains power.
3. Activate the setup section’s single tone
output by placing the single tone
button to the on (in) position. The voice
and multi-tone buttons should be in
their off (out) position.
4. Using an appropriate adapter cable,
connect an audio level meter directly
across the left channel setup direct
output. Ensure that your 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!
5. Carefully observing the level meter,
adjust the trim pot associated with the
left channel to give the desired output
level.
6. Repeat steps 4 and 5, this time for the
right channel.
External Record/TB Audio
Source
During installation, an external source of
audio may have been connected to serve
in lieu of the Model 750’s internal micro-
phone. This audio source will be used for
voice recording by the setup section, as
well as by the talk back functions. The
external audio source needs to have a
nominal audio level of –20 to +4dBu. A
trim potentiometer, located on the back
panel directly above the record/TB exter-
nal audio input jack, adjusts the input
sensitivity of the circuitry. For correct
operation it is crucial that this trim pot be
adjusted so that the source audio level is
“matched” with the requirements of the
Model 750.
The procedure is a bit convoluted, but not
difficult:
1. Ensure that mains power is connected
to the Model 750.