Studio Technologies 740 - Manual (Page 6)

Issue 3, May 2004 Model 740 User Guide
Page 6 Studio Technologies, Inc.
Model 740
Reliability over the long haul was a Model
740 design criteria. To that end the unit’s
enclosure is made of steel, combining
strength with effective RF rejection. On
the inside, all components are mounted
on an FR4 (fiberglass-based) circuit
board assembly.
System Features
Mic/Line Inputs
Six input channels are provided for
connection to microphone or line-level
signals. The electronically balanced
circuitry is “ruggedized” for reliability
under tough operating conditions. The
low-noise, low-distortion, high-headroom
audio performance is what’s expected
of sophisticated “pro audio” equipment.
Features provided for each input channel
include an input sensitivity button, rotary
level control, and level status LED. For
ease of use, the rotary level control sets
both the gain of the input circuit and the
level being sent to the main audio bus.
For convenience the six input sensitivity
buttons, like all the Model 740’s operator
controls, are located on the front panel.
For operator assistance, the bicolor level
status LED provides signal present and
peak level indication.
Main Output
Signals from the six mic/line input chan-
nels combine to create a monaural signal
called the main output bus. A rotary con-
trol sets the overall level of the main bus.
An electronically balanced output circuit
is associated with the main output bus.
It provides a line-level signal capable of
driving balanced or unbalanced loads
of 600 ohms and greater. A studio-quality
audio compressor circuit is provided to
control the dynamic range of the main au-
dio bus. An LED indicator lights whenever
the compressor circuit is actively control-
ling the signal. Far from a simple “clipper,”
the compressor circuit utilizes a sophis-
ticated laser-trimmed voltage-controlled
amplifier (VCA) integrated circuit for quiet,
low-distortion operation. To help minimize
operator error, no compressor on/off switch
is provided on the Model 740’s front panel.
An internal 3-position configuration jumper
determines the compressor circuit’s oper-
ating mode. From the factory the jumper
is set so that the compressor’s operat-
ing threshold is 6 dB above the nominal
+4 dBu output level. This is an excellent
general-purpose setting for broadcast use
where voice signals are the primary audio
content.
To meet the needs of other installations,
a technician can change the jumper to
make the threshold 2 dB above the nomi-
nal +4 dBu. This could prove useful when
using the Model 740 with level-sensitive RF
transmission systems. For other applica-
tions a technician can set the jumper to
a third position which completely disables
the compressor function.
Monitor Section
The Model 740’s monitor section provides
a line-level monitor output, along with two
headphone outputs. Associated with the
monitor section is a rotary level control
and a 3-position source select switch. The
monitor output is compatible with a variety
of monitor amplifiers and amplified loud-
speakers. For flexibility, two headphone
output jacks are provided, one on the
front panel and one on the back. Each
headphone jack is supported by an inde-
pendent output circuit. A 3-position toggle
switch is used to select the audio source