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Highlights
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Six mic/line inputs
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Setup oscillator with dedicated output
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Studio-quality compressor
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Internal power supply
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Flexible monitor section
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10-segment LED meter
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All operator controls on front panel
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Single rack-space mounting
Overview
The Model 740 Audio
Mixer is expressly designed for use in compact electronic-news-gathering
(ENG) vehicles. Many other specialized audio production applications can
also be supported. Model 740 features include six microphone/line-level
inputs, a monaural output bus, LED metering, and a flexible monitoring
section. It’s important to note that the feature set was carefully
selected to provide exactly what’s needed—and no more! Keeping it simple
was the design mantra. The Model 740 is targeted for use by operators
that have a multitude of tasks to perform, and too little time to do
them. Using its experience in mobile broadcast applications, Studio
Technologies was able to design the Model 740 to include all the crucial
features required to meet the needs of fast-paced news-gathering operations,
while still providing the operator with an extremely easy-to-use
product.
The hallmarks of the
Model 740 are application flexibility, simplicity in use, audio quality,
and long-term reliability. A number of internal configuration jumpers
allow the unit’s performance to be tailored to the needs of specific
installations. The carefully selected feature set ensures that the Model
740 will be a “team player” when it’s integrated into an audio system.
While there’s flexibility on the inside, the operator is presented with
an easy-to-use set of front-panel controls and indicators—the operator never has to access the back panel to operate the unit. In
this way the goal of delivering successful on-air and production audio,
day-after-day, can best be achieved. The Model 740’s audio quality is
“pro” throughout. The components were carefully selected to deliver
low-noise, low-distortion performance. 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.
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
Audio
Signals from the six
mic/line input channels combine to create a monaural signal called the
main output bus. A rotary control 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 audio bus. An LED indicator lights whenever the compressor circuit
is actively controlling the signal. Far from a
simple “clipper,” the compressor circuit utilizes a sophisticated
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 operating mode. From the factory the jumper is set so that the
compressor’s operating 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 nominal +4 dBu. This could prove useful when
using the Model 740 with level-sensitive RF transmission systems. For
other applications 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 loudspeakers. 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 independent output
circuit. A 3-position toggle switch is used to select the audio source
to be monitored. This allows monitoring of the main audio bus, along
with two external monaural audio sources. These external monitor inputs
are intended to be connected to devices such as off-air, microwave, or
satellite receivers. Alternately, other mobile broadcast support
equipment, such as a PC-based editing system, can be connected.
Unique to the Model 740 is the ability
to configure the monitor output to meet the needs of the “real world.”
This is accomplished by using an internal 3-position configuration
jumper to select the monitor output mode. From the factory the monitor
output is configured to “follow” the setting of the front-panel level
control. In addition, the monitor output mutes whenever a pair of
headphones is plugged into the front-panel jack. A technician can change
the jumper so that the monitor output still follows the setting of the
front-panel level control, but is not impacted by use of the front-panel
headphone jack.
A third jumper position allows a
technician to configure the monitor output such that it is electrically
before (“pre”) the level control. As with the previous mode, the output
isn’t impacted by use of the headphone output. This mode is very useful
when an amplified loudspeaker that contains a user-accessible level
control is connected. Examples of amplified speakers that contain user
level controls include the popular Fostex® 6301-series. With the jumper
in the pre-level-control position, only one level control—the one on the
amplified speaker—would be used to set the speaker level. This can greatly
minimize operator confusion while still utilizing the resources of the
Model 740’s monitor section.
Metering
A 10-segment LED meter
provides an indication of audio-signal level. An internal selection
jumper determines the audio source for the meter. From the factory the
meter is set to monitor the signal level of the main audio bus. A
technician can change the configuration so that the meter monitors the
source selected by the monitor section’s 3-position switch. In this way
the level of the main audio bus, as well as the two external monitor
sources, can be displayed by the meter.
Reference Tone
A sine-wave audio tone
is provided for alignment and reference use. From the factory the tone
is configured for 400 Hz. If required, a technician can revise the
frequency to be 1 kHz. A button on the Model 740’s front panel allows the
tone to be connected to the main audio bus. In addition, a dedicated
reference tone output is also provided. This continuous source of
sine-wave signal is accessed by means of a balanced line-level output on
the back panel. The dedicated reference tone output is intended to
provide a setup or test signal that is available at all times, and
without interfering with normal operation of the main audio bus.
Mounting, Connectors, and Mains Power
The
Model 740 requires one space in a standard 19-inch rack.
Industry-standard XLR-type and ¼-inch 3-conductor connectors are used
for all audio interconnections. To ensure maximum reliability, all
connectors were selected to be premium grade. For example, the XLR-type
connectors feature metal shells and are manufactured by Neutrik. AC
mains power is connected directly to the Model 740 by way of a standard
3-pin detachable IEC cord set; no external power supply is used. AC
mains power is factory configured for 100, 120, or 220/240 V, 50/60 Hz.
Model 740 Specifications
General
Audio Parameters:
Frequency Response: 20 Hz-20 kHz, ±0.5 dB, mic/line in to main out
Distortion (THD+N): 0.03%, measured at 1k Hz, +4 dBu, mic/line in to main
out
S/N Ratio: 74 dB, referenced to +4 dBu, mic/line in to main out, 22 Hz-22 kHz
Mic/Line
Inputs: 6
Input Sensitivity: switch selectable for microphone or live-level
signals; 43 dB line input “pad” implemented using sealed bifurcated
contact telecom relays
Operating Level Range: mic input position: –78 to –8 dBu; line position:
–35 to +35 dBu. Range specified to give +4 dBu on main output, master
level control set to unity gain position.
Type: electronically balanced
Impedance: mic position 2 k ohms, line position 15 k ohms
Common Mode Rejection Ratio: 70 dB @ 60 Hz, 69 dB @ 40 kHz (typical), mic
position, ref +4 dBu on main out
Status LED: bicolor, displays signal present and peak
Compressor:
Type: single-knee, VCA-controlled
Slope: 5:1
Threshold: configurable, choices are 1) 6 dB over nominal (+10 dBu on main
output, factory default), 2) 2 dB over nominal (+6 dBu on main out), 3)
disabled
Attack Time: 2 mSec
Release Time: 100 mSec
Status LED: compressor active
Main
Output:
Type: electronically balanced, capacitor-coupled, intended to drive
balanced or unbalanced loads of 600 ohms or greater
Source Impedance: 50 ohms, nominal
Nominal Level: +4 dBu
Maximum Level: +26 dBu into 10 k ohms, +25 dBu into 600 ohms
External Monitor Inputs: 2, monaural
Type: electronically balanced, direct-coupled, compatible with balanced
or unbalanced signals
Impedance: 24 k ohms, nominal
Common Mode Rejection Ratio: 90 dB @ 60 Hz, 70 dB @ 86 kHz, typical
Nominal Level: +4 dBu
Monitor
Output:
Type: electronically balanced, capacitor-coupled, intended to drive
balanced or unbalanced loads of 600 ohms or greater
Source Impedance: 50 ohms, nominal
Nominal Level: +6 dBu, with monitor level control @ 100%, mode selected
to be post level control (no headphone mute)
Maximum Level: +26 dBu into 10 k ohms, +25 dBu into 600 ohms
Signal Source: configurable, choices are 1) post monitor level control
with headphone muting (factory default), 2) post monitor level control, 3) pre monitor
level control
Headphone
Outputs:
Source: same as selected for monitor output
Configuration: separate output driver circuitry for front and back
headphone output connections
Type: monaural source configured to drive stereo headphones through of
100 ohm resistors
Compatibility: intended for connection to headphones with impedance of 100
ohms or greater
Maximum Output Voltage: 5.5 Vpp, 100 ohm load
Reference Tone:
Frequency and Wave Form: 400 Hz nominal, sine wave (technician can revise
to 1 kHz)
Direct Output Level: +4 dBu, nominal, adjustable over –1/+3 dB range
Direct Output Type: electronically balanced, capacitor-coupled, intended
to drive balanced or unbalanced loads of 600 ohms or greater
Direct Output Source Impedance: 100 ohms, nominal
Metering:
Type: 10-segment LED, modified VU ballistics
Source: configurable, choices are 1) display level of main output bus
(factory default), 2) source selected for monitor output
Connectors:
Mic/Line and External Monitor Inputs: 3-pin XLR-type, female
Main, Reference Tone Direct and Monitor Outputs: 3-pin XLR-type, male
Headphones: ¼-inch 3-conductor phone jacks
AC Mains: 3-blade, IEC 320 C14-compatible (mates with IEC 320 C13)
AC
Mains Requirement: 100, 120, or 220/240 V, ±10%, factory configured;
50/60 Hz; 0.2 A maximum
Mains Fusing: 1
Type: 5x20 mm, time-lag
Rating: 0.2 A for 100 V and 120 V AC mains, 0.1 A for 220/240 V AC mains
Dimensions
(Overall):
19.00 inches wide (48.3 cm)
1.72 inches high (8.9 cm)
7.2 inches deep (18.3 cm)
Mounting:
one space in a standard 19-inch rack
Weight:
7.0 pounds (3.2 kg)
Specifications
subject to change without notice.
Audio Mixers
Which Audio Mixer is right for your application? Review the
Audio Mixers Feature-by-Feature Comparison Chart.
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