Studio Technologies 742A - Manual (Page 7)

Model 742A User Guide Issue 1, July 2012
Studio Technologies, Inc. Page 7
Audio Mixer
output bus (or buses), minimizing the
chance of unwanted “leakage.” Pan pots
are fine in an audio mixer destined for use
in stereo music situations, but are inferior
when used for two-bus applications.
Line Inputs
Four input channels are provided for
connection to line-level signals. Features
provided for each line input channel in-
clude a rotary level control, level status
LED, and output bus assignment switch.
The rotary level control is used to set the
amount of input signal that is sent to the
selected main output bus (or buses).
The dual-color level status LED provides
signal present and peak level indication.
A 3-position switch allows the input signal
to be assigned to the desired output bus
(or buses).
Main Output Buses
Signals from the eight input channels
(four mic/line and four line) are routed
and combined to create the two main
output buses. A dual rotary control is used
to independently set the overall level of
the two buses. An electronically balanced
output circuit is associated with each
main output bus. They provide line-level
signals capable of driving balanced or
unbalanced loads of 600 ohms or greater.
Separate studio-quality audio compressor
circuits are provided to control the dynam-
ic range of each main output bus. An
LED indicator is associated with each
compressor, lighting whenever the circuit
is actively controlling signal level. Far from
simple “clippers,” the compressor circuits
utilize sophisticated laser-trimmed volt-
age-controlled amplifier (VCA) integrated
circuits for quiet, low-distortion opera-
tion. To help minimize operator error no
compressor on/off switches are provided
on the Model 742A’s front panel. Internal
configuration jumpers determine the com-
pressor circuits’ operating modes. From
the factory the jumpers are set so that the
compressors’ operating threshold is 6 dB
above the nominal +4 dBu output level.
This is an excellent general-purpose set-
ting for broadcast use where voice signals
are the primary audio content.
To meet the needs of other applications,
a technician can change the jumpers to
make the compressor threshold 2 dB
above the nominal +4 dBu. This could
prove useful when using the Model 742A
with level-sensitive RF transmission sys-
tems. For other applications a technician
can set the jumpers to a third position
which completely disables the compressor
functions.
Monitor Section
The Model 742A’s monitor section pro-
vides two line-level monitor outputs and
a “stereo” headphone output. Monitor
outputs 1 and 2 are electrically balanced
with their input sources associated with
output buses 1 and 2, respectively. The
headphone output has main output bus 1
as its left-channel source and main output
bus 2 as its right-channel source. Associ-
ated with the monitor section is a dual ro-
tary level control that allows independent
setting of the monitor output levels. The
level of the headphone output is always
adjusted using these controls. Internal
configuration jumpers are used to select
the exact signal sources for the line-level
monitor outputs. They can either be “post”
the controls, allowing an adjustable output
level, or set to a fixed –10 or +4 dBu nomi-
nal level. This allows the monitor outputs