Highlights Overview Mic/Line Inputs

Highlights Overview Mic/Line Inputs
The Model 742 Audio Mixer is expressly designed for use in electronic-newsgathering (ENG) vehicles, small production trucks, and other specialized mobile
broadcast applications. Many other audio production applications can also be
supported. Model 742 features include four mic/line inputs, four line inputs,
two output buses, LED level metering, and flexible monitoring. The Model
742 was specifically designed as a dual-channel audio mixer, rather than as a
typical stereo device. This approach makes it excellent for use in “dual-path”
on-air applications.
Highlights
• Four mic/line and four line-only inputs
• Setup oscillator with dedicated output
• Studio-quality compressors
• 10-segment LED meters
• Flexible monitor section
• All operator controls on front panel
The Model 742 is targeted for use by operators with numerous audio sources
• Internal power supply
that need to be quickly and reliably adjusted and routed to create one or two
independent audio mixes. In these days of operators having too many tasks to
• Single rack-space (1U) mounting
handle, and too little time to do them, the Model 742 is a refreshing combination
of performance and simplicity. Using their experience in mobile broadcast applications, the engineers at Studio Technologies
were able to design the Model 742 to include all the crucial features required to meet the needs of fast-paced news-gathering
operations, while still providing the operator with an easy-to-use product.
Overview
The hallmarks of the Model 742 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 meet the needs of specific installations. The carefully selected
feature set ensures that the Model 742 will be a “team player” when it is 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 742’s audio quality is “pro” throughout. The components were carefully selected to deliver low-noise, lowdistortion performance.
Long-term reliability was also part of the Model 742’s 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
Four input channels are provided for connection to microphone or line-level signals. The electronically balanced circuitry is “ruggedized”
for reliable operation 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, level status LED, and output bus assignment switch. To support condenser microphones, the four mic/line inputs can be
internally configured to provide 12-volt phantom power.
For ease of use, the rotary level control sets the gain of the input circuit as well as the level being sent to the selected main output
bus (or buses). For convenience the input sensitivity button, like all of the Model 742’s operator controls, is located on the front panel.
For operator assistance, a dual-color level status LED provides signal present and peak level indication. Associated with each mic/line
input channel is a 3-position output bus assignment switch. This allows each input to be assigned to bus 1, bus 2, or both, quickly
creating two fully independent audio “feeds.”
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Bus assignment switches, rather than the more-typical “pan pots,”
were specifically selected for the Model 742’s design. This allows a
more positive assignment of an input source to the desired 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 include 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 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 dynamic 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
voltage-controlled amplifier (VCA) integrated circuits for quiet,
low-distortion operation. To help minimize operator error no compressor on/off switches are provided on the Model 742’s front
panel. Internal configuration jumpers determine the compressor
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
setting 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 742 with level-sensitive RF transmission systems. For other
applications a technician can set the jumpers to a third position
which completely disables the compressor functions.
Monitor Section
The Model 742’s monitor section provides two line-level monitor
outputs and a “stereo” headphone output. Monitor outputs 1 and 2
Studio Technologies, Inc.
are electrically balanced with output buses 1 and 2, respectively,
assigned as their audio sources. The headphone output has main
output bus 1 as its left-channel source and main output bus 2 as
its right-channel source. Associated with the monitor section is
a dual rotary level control that allows independent setting of the
levels. The level of the headphone output is always adjusted using
these controls. Internal configuration jumpers are used to select
the operation of the line-level monitor outputs. They can either
be “post” the controls, allowing an adjustable output level, or be
set to fixed –10 or +4 dBu nominal levels. This allows the monitor outputs to be compatible with a variety of monitor amplifiers,
amplified loudspeakers, or to even serve as an additional set of
main bus line-level outputs.
From the factory the monitor outputs are configured to the “post”
setting, enabling them to “follow” the setting of the front-panel
level controls. This is appropriate where monitor loudspeakers
and associated power amplifier channels are used. A technician
can change the jumper positions so that the monitor outputs are
electrically before (“pre”) the level controls. Two jumper positions
are available, corresponding to –10 and +4 dBu nominal output
levels. The “pre –10” position 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
jumpers set to the “pre –10” 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 and enhance
performance.
When configured for “pre +4” operation, the monitor outputs are
again “pre” the level controls, but this time with a nominal level
of +4 dBu. This can be used for various applications, including
providing an additional set of main bus outputs. In certain cases
this may eliminate the need for an external distribution amplifier
to be included as part of the installed system.
Metering
As previously discussed, dual-color signal present/peak LEDs
are associated with each of the eight input channels. In addition,
two 10-segment LED meters provide an indication of audio signal levels on the main output buses. The meters use three LED
colors: green, yellow, and red. The LEDs are calibrated such that
the actual output level, in dBu, is indicated.
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
Model 742 Audio Mixer, Issue 1, Page 2
the Model 742’s front panel allows the tone to be connected to
the main output buses. 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, without interfering
with normal operation of the main output buses.
Mounting, Connectors, and Mains Power
Industry-standard XLR-type and ¼-inch 3-conductor connectors
are used for all audio interconnections. To maximize reliability, all
connectors were carefully selected from among premium-grade
models. For example, the XLR-type connectors feature metal shells
and are manufactured by Neutrik®. AC mains power is connected
directly to the Model 742 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 volts, 50/60 Hz.
The Model 742 requires one space in a standard 19-inch rack.
Model 742 Specifications
General Audio Parameters:
Frequency Response: 20 Hz to 20 kHz, ±0.5 dB, mic/line in to
main outs
Distortion (THD+N): 0.03 %, measured at 1 kHz, +4 dBu, mic/line
in to main outs
S/N Ratio: 74 dB, referenced to +4 dBu, mic/line in to main outs,
22 Hz to 22 kHz
Mic/Line Inputs: 4
Input Sensitivity: switch selectable for microphone or live-level signals; 43 dB line input “pad” implemented using sealed bifurcated
contact telecom relays
Phantom Power: 12 Vdc, nominal, meets IEC 61938 P12 standard
Operating Level Range: mic input position: –76 to –8 dBu; line
position: –32 to +28 dBu. Range specified to give +4 dBu on main
outs, master level controls set to unity gain.
Type: electronically balanced
Impedance: mic position 1.3 k ohms, line position 15 k ohms
Common Mode Rejection Ratio: 74 dB @ 60 Hz, 73 dB @ 40 kHz
(typical), mic position, ref +4 dBu on main outs
Status LED: dual-color, displays signal present and peak
Line Inputs: 4
Operating Level Range: –14 to +28 dBu. Range specified to give
+4 dBu on main outs, master level controls set to unity gain.
Type: electronically balanced
Impedance: 24 k ohms, nominal
Common Mode Rejection Ratio: 85 dB @ 60 Hz, 85 dB @ 40 kHz
(typical), ref +4 dBu on main outs
Status LED: dual-color, displays signal present and peak
Compressors: 2
Function: controls dynamic range of output buses 1 and 2
Type: single-knee, VCA-controlled
Slope: 5:1
Threshold: configurable, choices are: 6 dB over nominal (+10 dBu
on main outs, factory default); 2 dB over nominal (+6 dBu on main
outs); disabled
Attack Time: 2 ms
Release Time: 100 ms
Status LEDs: 2, compressor active
Main Outputs: 2
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
Monitor Outputs: 2
Signal Sources: output buses 1 and 2
Type: electronically balanced, capacitor-coupled, intended to drive
balanced or unbalanced loads of 600 ohms or greater
Source Impedance: 50 ohms, nominal
Nominal Level: configurable, choice are: +6 dBu, with monitor level
control @ 100%, mode configured for POST level control; –10 dBu
when configured for PRE –10; +4 dBu when configured for PRE +4
Maximum Level: +26 dBu into 10 k ohms, +25 dBu into 600 ohms
Headphone Output:
Signal Sources: output buses 1 and 2 (“post” monitor level
controls)
Type: stereo, configured to drive stereo headphones through
100 ohm series resistors
Compatibility: intended for connection to headphones with
impedance of 100 ohms or greater
Maximum Voltage: 8 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
Meters: 2
Function: displays level of output buses 1 and 2
Type: 10-segment LED, modified VU ballistics
Connectors:
Mic/Line and Line Inputs: 3-pin female XLR-type
Main Outputs: 3-pin male XLR-type
Reference Tone Direct Output, Monitor Outputs, Headphone
Output: 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 volts, ±10%,
factory configured; 50/60 Hz; 0.2 A maximum @ 100 and 120
volts, 0.1 A maximum @ 220/240 volts
Mains Fusing:
Type: 5 x 20 mm, time-lag
Rating: 0.2 A for 100 and 120 volt AC mains, 0.1 A for 220/240
volt AC mains
Dimensions (Overall):
19.00 inches wide (48.3 cm)
1.72 inches high (8.9 cm)
9.5 inches deep (24.1 cm)
Mounting: one space (1U) in a standard 19-inch rack
Weight: 8.5 pounds (3.9 kg)
Specifications subject to change without notice.
© by Studio Technologies, Inc., October 2004
Studio Technologies, Inc.
Skokie, Illinois USA +1 847-676-9177
www.studio-tech.com
50266-1004, Issue 1
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