null  User manual
Model 750
Audio
Mixer
Model 750 Front Panel
The unique requirements of electronic news-gathering (ENG)
trucks, satellite news-gathering (SNG) trucks, and specialized
remote broadcast applications demand more than just a generalpurpose audio mixer. That’s why Studio Technologies created the
Model 750, a special piece of equipment for special applications.
Only by taking the time to speak with industry professionals,
designers of ENG and SNG vehicles, along with numerous field
technical personnel, were the necessary specifications established.
Using that information as a “road map” to guide the process,
additional features, operating ergonomics, and the overall “lookand-feel” issues were addressed. The result is a high-performance,
easy-to-use audio mixer expressly designed to go “on-the-road.”
Model 750
Audio
Mixer
Product Highlights:
• Four mic/line inputs
• Two stereo line inputs
• Setup section, including voice record/playback
and tone generation
• Main and AUX stereo audio buses
• Studio-quality limiter/compressors
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Details, Details...
amplifier (VCA) integrated circuit for quiet, lowdistortion level control. For installation flexibility, three
sets of stereo output circuits provide access to the main
bus: two are electronically-balanced, line-level; the third
is transformer-balanced, with a selectable mic or line
output level.
Mic/Line Inputs
Four transformer-coupled input channels are provided
for connection to microphone or line-level signals. A
full set of features is provided for each input channel,
including selectable input sensitivity, +48V phantom
power, low-cut filter, phase reverse, level control, and
pan pot. For operator assistance, a bi-color LED provides
signal present and peak indication. Two illuminated
push-button switches control the routing of the input
signal to the main and auxiliary (AUX) audio buses. For
convenience, the four mic/line input sensitivity buttons,
like all the Model 750’s operator controls, are located on
the front panel.
Stereo Line Inputs
Two stereo line-level input channels are provided, and
are intended for connection with audio signals associated with video playback. The channels support “real
world” broadcast applications, where left and right
signals may, or may not, be an actual stereo pair. Routing
buttons allow each left and right input to be assigned
to the left output bus, to the right output bus, to both
output buses, or muted. A level control, along with a
bi-color signal present/peak LED, supports each left and
right input. Two illuminated buttons control the routing
of the input signals to the output buses.
Main Audio Bus
Signals from the mic/line input channels, stereo line
input channels, and the setup section combine to create
the main audio bus. The main bus is stereo, but can be
used to create two independent monaural audio mixes.
Studio-quality, stereo limiter/compressors are provided
to control the dynamic range of the main bus. Far from
a simple “clipper,” each limiter/compressor circuit
utilizes a sophisticated laser-trimmed voltage-controlled
Studio Technologies, Inc.
Three isolated main output connections
Extensive monitor section
Separate speaker and headphone outputs
VU meters with peak LEDs
All operator controls on front panel
Two rack-space mounting
AUX Audio Bus
The Model 750 provides a second stereo bus that can
be configured to operate in either of two modes: as an
auxiliary (AUX) output or as a monitor interrupt function. In the AUX output mode special applications are
easily supported, such as creating a “mix-minus” feed
or serving as a second stereo output bus for on-air use.
Signals from the mic/line input channels, stereo line
input channels, and the setup section can be assigned to
the AUX bus. Direct access to the AUX bus is provided
by means of an electronically-balanced, line-level output.
In most cases, however, the AUX interrupt mode will
be selected, allowing the normal monitor source to be
interrupted and the AUX signal monitored in its place.
Model 750 users will find this function extremely useful,
enabling one or more of the input channels to be monitored without interfering with signals assigned to the
main output bus. Two DIP switches, accessible from the
front panel, allow the interrupt function to be configured. One switch selects whether the monitor speaker
output will be interrupted by the AUX signal, the other
whether the headphone output will be interrupted.
Configurable Outputs
Four monaural, balanced, line-level outputs can serve in
a wide range of installation-specific applications. DIP
switches, located on the back panel, are used to select
from the five available signal sources: main audio bus
left and right, AUX audio bus left and right, and mic/
line input channel direct. The switches can be set
to create a number of resources, including: additional
Model 750 Audio Mixer
stereo outputs, monaural outputs from the main or AUX
audio buses, or direct outputs from the mic/line input
channels.
Monitor Section
Reminiscent of much larger audio consoles, the Model
750’s monitor section gives the operator an extensive set
of resources. Separate stereo outputs and level controls
are provided for connection to a monitor amplifier and
headphones. In addition to monitoring the main and
AUX audio buses, provision has been made for monitoring two external audio sources. These stereo inputs are
intended to be connected to off-air, microwave, or
satellite receivers. External Monitor Input 1 is compatible with “+4” signals, while External Monitor Input 2
can be set, using a front-panel DIP switch, for “–10” or
“+4” compatibility.
Multiple sources can be simultaneously selected for
monitoring. This can prove useful by allowing, for
example, an operator to simultaneously monitor a local
mix and an externally-provided mix-minus signal. A
mono function allows the monitored audio source to be
checked for phase cancellation problems and acceptable
“sum-to-monaural” performance.
The AUX interrupt mode allows monitoring of selected
input channels and the setup section without interfering
with normal operation of the main audio bus. For
operator assistance, the meters can be configured to
monitor the AUX bus whenever it is active.
The mechanical VU-type meters, along with peak level
LED indicators, provide a “user-friendly” indication of
audio-signal levels. Fanatics for addressing the details,
Studio Technologies has even eliminated the issue of
burned-out meter-scale illumination by implementing
a solid-state, LED-based lighting scheme.
Setup Section
Unique to the Model 750 are the features provided by
the setup section, the highlight being the ability of the
operator to record and play back three voice identification segments. The Left+Right segment allows a voice
message of up to 12 seconds in length to be recorded,
with playback going to the left and right output
channels. The Left Only and Right Only segments allow
recording of up to 4 seconds each, with playback going
only to their respective channels. The voice segments
can prove useful, allowing the facilities that receive the
vehicle’s signal (generally provided by microwave or
satellite links) to quickly “learn” more about the origin
of the transmission. Information such as vehicle identity,
physical location, the names of technical and on-air
personnel, mobile telephone numbers, and left and
right channel identifiers can easily be sent. The voice
audio source is selectable, being either an internal
microphone or an externally-connected signal.
The setup section also contains a digitally-controlled
sine-wave generator which, under software control,
produces a “0-level” single-tone reference or multi-tone
sequences. The single-tone output is selectable for either
400Hz or 1kHz—the two industry-standard frequencies.
The tone sequences allow frequency response testing of a
transmission chain, with the choice of either a basic or an
advanced sequence. In the basic setting a 1kHz “0-level”
reference is generated, followed by individual 10kHz,
1kHz, and 100Hz tones. In the advanced setting a 1kHz
reference is generated, followed by 14 individual tones,
ranging from 15kHz to 50Hz.
While the voice and tone setup signals can be assigned
to the main and AUX audio buses, a direct line-level
stereo output is also provided. This allows the generation of setup and test signals without interfering with
normal audio mixer operation.
Talk Back
The Model 750 includes a talk back function. Two pushbutton switches allow the selected voice source to be
routed to the setup direct output and/or the main and
AUX audio buses.
Installation
While the Model 750 is loaded with features, it only
requires two spaces in a standard 19-inch rack. Neutrik
XLR-type and ¼-inch, 3-conductor audio connectors are
used for audio interconnections. Mains power is factory
configured for 100, 120, or 220/240V, 50/60Hz.
Model 750 Back Panel
Model 750 Audio Mixer
Studio Technologies, Inc.
Model 750
Audio
Mixer
Specifications
General Audio Parameters:
Frequency Response: 20Hz-20kHz, ±0.5dB, stereo line in/main out 1
Distortion (THD+N): 0.04%, measured at 1kHz, mic in/main out 3
S/N Ratio: 80dB, referenced to +4dBu, mic in/main out 3
Headphone Output:
Compatibility: intended for connection to headphones with impedance
of 100 ohms or greater
Maximum Output Voltage: 8Vpp, 100 ohm load
Connectors:
Mic/Line, Stereo Line, Main Out 3: 3-pin XLR-type (pin 2 high)
All Other Audio: ¼-inch, 3-conductor phone jacks
AC Mains: 3-blade IEC-type
External Monitor Inputs:
Quantity: 2, stereo
Type: electronically balanced
Nominal Level, Input 1: +4dBu
Nominal Level, Input 2: –10 or +4dBu, selectable
Mic/Line Inputs: 4
Type: balanced, transformer-coupled
Level Range: selectable for mic or line level
Microphone Power: +48V phantom-type
Low-Cut Filter: –3dB at 85Hz, 18dB/octave slope
Status LED: bi-color, signal present/peak
Pan Type: constant energy
Pan Attenuation: 60dB, nominal
Stereo Line Inputs: 2
Type: electronically balanced
Nominal Level: +4dBu (–8 to +10dBu acceptable)
Status LED: 2, bi-color, signal present/peak
Main Audio Bus Limiter/Compressor: 2
Threshold: +10dBu (6dB above nominal output level)
Attack Time: 2mSec, nominal
Release Time: 100mSec, nominal
Slope: 5:1, nominal
Setup Section:
Record L+R Duration: 12 seconds, maximum
Record L Only, R Only Duration: 4 seconds, maximum
Record Audio Source: internal microphone or external line level,
selectable
Single Tone Frequency: 400Hz or 1kHz, selectable
Basic Multi-Tone Frequencies: 1kHz reference, followed by 10kHz,
1kHz, 100Hz
Advanced Multi-Tone Frequencies: 1kHz reference, followed by
14 tones (15kHz-50Hz)
Setup Direct Output Level: +4dBu, nominal, adjustable, range
–2 to +10dBu
Talk Back: connects voice audio source to setup direct and/or main
and AUX outputs
Record/Talk Back External Audio Input:
Type: electronically balanced
Level Range: –20 to +4dBu, adjustable
Outputs — Main 1, Main 2, AUX, Configurable, & Setup Direct:
Type: electronically balanced, compatible with balanced or unbalanced
loads
Nominal Level: +4dBu
Maximum Level: +27dBu into 10k ohms, +26dBu into 600 ohms
Metering: 2
Type: analog panel, VU scale, with signal peak LED
Calibration: 0 VU = +4dBu, nominal, adjustable, range –2 to +10dBu
Main Output 3:
Type: balanced, transformer-coupled
Nominal Level: mic –36, line +4dBu, selectable
Maximum Level: +22dBu into 10k ohms
Dimensions (Overall):
19.00 inches wide (48.3cm)
3.49 inches high (8.9cm)
9.50 inches deep (21.4cm)
Monitor Output:
Type: electronically balanced, compatible with balanced or unbalanced
loads
Nominal Level: –2dBu
Maximum Level: +21dBu into 10k ohms, +20dBu into 600 ohms
Mounting: 2 standard rack spaces
The Model 750 Audio Mixer is available directly from Studio
Technologies, Inc. in Skokie, Illinois, or selected dealers. Like all
Studio Technologies products, the Model 750 is backed by a
three-year limited warranty.
Studio Technologies has manufactured professional audio
products since 1978. Our equipment is used worldwide by
recording studios, television and radio stations, and film and
production companies.
The Model 750 complements the Studio Technologies’ IFB Plus
Series, a highly-integrated, two-channel IFB system for mobile
applications.
© by Studio Technologies, Inc., March 1998.
AC Mains Requirement: 100, 120, or 220/240V, ±10%, factory
configured, 50/60Hz, 40 watts maximum
Weight: 14.0 pounds (6.4kg)
Specifications subject to change without notice.
Studio Technologies, Inc.
5520 West Touhy Avenue, Skokie, Illinois 60077 U.S.A.
Telephone (847) 676-9177, Fax (847) 982-0747
www.studio-tech.com
50166-398, Issue 5
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