Studio Technologies Annoucer's Console 233 User Manual
User Guide
Issue 1, September 2007
This User Guide is applicable for serial numbers:
M233-00151 and later
Copyright © 2007 by Studio Technologies, Inc., all rights reserved
www.studio-tech.com
50336-0907, Issue 1
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Table of Contents
Introduction ................................................................... 5
System Features ........................................................... 6
Installation and Setup ................................................... 12
Configuration ................................................................ 17
Operation ...................................................................... 28
Advanced Operation ..................................................... 33
Technical Notes ............................................................. 34
Specifications ................................................................ 45
Appendix A .................................................................... 46
Block Diagram
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Issue 1, September 2007 Model 233 User Guide
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Introduction
What This User Guide Covers
This User Guide is designed to assist you
when installing, configuring, and using
the Model 233 Announcer’s Console. Additional background technical information
is also provided. A product block diagram
is included at the end of this guide.
System Overview
The Model 233 Announcer’s Console is
designed to serve as the audio control
“hub” for announcers, commentators, and
production personnel. The tabletop unit is
suited for numerous applications including on-air television and radio broadcasting. The Model 233 will also perform an
outstanding role in stadium announce
applications. The Model 233 is compatible
with essentially all broadcast and production audio system environments. Standard
connectors are used to interface microphone, headphone, on-air, talkback, line
input, and intercom signals.
Whether it’s the mic preamplifier, audio
switching, talkback signals, intercom interfacing, or headphone cue feed, superior
audio quality is maintained throughout. A
microprocessor provides the Model 233’s
logic power, allowing precise control of
the unit’s operation. With extensive flexibility built in, creating the desired operating
configuration is a simple matter. While the
operating features of the unit can be carefully tailored, the user is presented with an
easy-to-use set of controls and indicators.
A wide range of resources, great performance, and simplicity during use—these
are the hallmarks of the Model 233.
The Model 233 is a truly “next-generation
and then some” product. Exhaustive research into the needs and desires of field
production personnel was integral to its
creation. Providing a veritable “tool kit”
of features, the unit supports a wide variety
of applications that include on-air television
and radio broadcasting, stadium announcement, and simultaneous interpretation. In
addition, with the unit’s broad range
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Figure 1. Model 233 front panel
Figure 2. Model 233 back panel
of capabilities many other specialized
“behind-the-scenes” applications can
also be implemented.
System Features
Microphone Input
A high-performance microphone preamplifier circuit provides low-noise/low-distortion
amplification over a 20 to 60 dB gain range.
The gain is adjustable in 10 dB steps. The
input is compatible with balanced dynamic
and condenser microphones. The microphone power source is 48 volts nominal
and meets the worldwide P48 phantom
standard. An LED indicator serves as an
aid for optimizing the preamplifier’s gain
setting. The output of the microphone preamplifier is used by the main output as well
as being routed to the compressor circuit
that supports the talkback functions.
Main Output
The Model 233 provides a main output that
is designed to serve as the on-air, stadium
announcement, or other primary audio
feed. Nominally –2 dBu, it is designed as a
fully professional interface with high output
capability, low distortion, and low noise.
The output circuitry features a highperformance output transformer
expressly designed for professional
audio applications.
Talkback Functions
The talkback functions are intended
to provide personnel associated with
production trucks, control rooms, liveperformance, and sports venues with
talent-originated cue signals. The Model
233 contains two pushbutton switches
that control the talkback functions. Associated with each pushbutton switch is a
dedicated line-level talkback output. Each
pushbutton switch can also be configured
to send audio to one specific channel
associated with the Model 233’s dualchannel intercom interface.
The line-level talkback outputs are
transformer-coupled with a +4 dBu
nominal signal level. They contain resistors in series with the output connectors,
allowing line-level talkback outputs from
multiple units to be directly “summed.”
For non-on-air applications, a special
Model 233 feature set can be enabled by
placing the unit in its “production” mode.
This software-based mode allows the
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main output to be used as an additional
talkback output. This feature makes the
unit even more powerful when used in liveevent applications, such as serving as a
master console for an orchestra conductor
or production director.
With all the available talkback flexibility,
the exact needs of many specific applications can easily be met. And, of course,
whatever configuration is implemented,
the audio quality will be excellent.
Dynamic Range Control
To enhance the Model 233’s talkback
functions, a studio-quality compressor
circuit is provided to control the dynamic
range of the signal coming from the microphone preamplifier. Far from a simple
“clipper,” the circuit utilizes a sophisticated
laser-trimmed voltage-controlled-amplifier
(VCA) integrated circuit for quiet, lowdistortion level control.
The signal from the compressor is always
used by the talkback functions. For flexibility, the audio source for the main output
can be selected to be either the direct
output of the microphone preamplifier or
the output of the compressor. For on-air
applications the signal coming directly
from the microphone preamp would be
correct. But having dynamic range control
of the signal going to the main output can
offer increased performance for selected
applications. These could include stadium
announcement locations, award show
conductor positions, and use with nonprofessional announcers during sports
events.
User Controls and Status
Indicators
Three pushbutton switches, four LED
indicators, and three rotary controls
provide users with a clear, easy-to-use
interface. One pushbutton switch controls
the status of the main output. This is the
audio output intended for on-air, stadium
announcement, or other primary uses.
Two LEDs display the on/off status of the
main output. Two additional pushbutton
switches control the status of the talkback
functions. These are the audio cue signals
used to communicate with producers,
directors, “spotters,” or other behind-thescenes production personnel. A status
LED is associated with each talkback
button. Three rotary controls allow the
user to adjust the level of the headphone
output. Two of the controls are associated
with externally connected cue signals. The
third control is associated with the Model
233’s sidetone function, allowing the user
to monitor the signal associated with the
unit’s microphone input.
Flexibility
A large part of the Model 233’s unique
power is the ability to configure the operation of the main output and talkback
functions. To meet the needs of the many
specific broadcast and production applications, a variety of button operating
modes is available. The main output
button can be selected to operate from
among four modes. In the “push-to-mute”
mode the button performs a momentary mute of the main output. In this way
a “cough” button function is created,
something typically required for television
sports broadcasting. In the “push-to-talk”
mode the button provides a momentary
active function for the main output. This
mode would be appropriate for applications such as stadium announcement. An
alternate action “latching” configuration
allows the button to enable or disable the
main output as desired. This is useful in
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radio broadcasting, announce-booth, or
voice-over applications. The fourth mode
provides a hybrid function, supporting
both push-to-talk and tap-to-enable/tap-todisable operation. This operation is similar
to that found in many broadcast intercom
system user stations.
The two buttons associated with the talkback functions can be configured to operate from either of two modes. One of the
modes supports a “push-to-talk” function.
This is typically used for on-air broadcast
applications. The other mode provides a
hybrid function, the operation of which is
discussed in the previous paragraph. The
hybrid mode is especially useful when the
Model 233 is used in a production-support
application.
The main button mode configures how the
main output, when it is in the “latched” on
state, responds to talkback activity. One
choice momentarily turns off the main
output when talkback is active, returning
the main output to the on state when the
talkback function has ended. The other
choice “unlatches” the main output in
response to a talkback function.
Cue Sources
The Model 233 supports the connection
of up to four external audio sources, each
of which can be selected for routing to
the stereo headphone output. The sources
are line input 1, line input 2, intercom
channel 1, and intercom channel 2. Each
source can be individually assigned to
the left channel, the right channel, or both
the left and right channels. This allows a
wide variety of stereo and mono headphone mixes to be created.
For application flexibility, two line-level
audio sources can be connected to the
Model 233. Possible signal sources
include off-air receivers, wireless IFB systems, and audio consoles. The connected
signals can be from two independent
sources, or could be from a stereo audio
feed such as would be associated with a
broadcast music event. Two level trim potentiometers, located on the bottom of the
unit, allow signals with wide nominal audio
levels to be cleanly interfaced.
Audio signals associated with a singleor dual-channel intercom system can
be routed to the headphone output. The
Model 233’s intercom interface is compatible with standard party-line intercom
systems from manufacturers such as
RTS™ and Clear-Com®. A broadcast-type
IFB (interrupted foldback) circuit can also
be connected to the intercom input. This
“listen only” signal is often found in television broadcast applications.
Sidetone
The Model 233 includes an integrated
sidetone function that allows the output
of the compressor circuit associated with
the microphone preamplifier to be routed
to the stereo headphone output. This
provides a confidence signal to the user,
allowing them to hear exactly what is
being sent to the main and, if desired,
talkback outputs. This sidetone signal
can be a critical element when creating
an effective communications environment.
In on-air television and radio broadcast
settings the Model 233 user’s own microphone audio signal is typically returned
to the headphone output by way of a cue
audio source. But there are cases where
this signal is not available, such as when
“mix minus” cue feeds are utilized. This
type of cue feed includes everything but
the user audio, a requirement when significant time delays, typically associated
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with satellite transmission systems, are
present. In effect the Model 233’s sidetone
function adds the “minus” part to a “mix
minus” cue.
Several configurable parameters allow
the sidetone function to be tailored to the
needs of a specific Model 233 installation.
The sidetone function can be configured
to route audio to the left, right, or left and
right headphone outputs. It can also be
completely disabled. Sidetone can also
be configured to be active only when
the main output is active, or to be active
anytime the main output or either of the
talkback outputs is active.
Headphone Output
Three rotary controls are provided for
user adjustment of the headphone output.
Two of the controls adjust the levels of the
externally connected sources. The third
control is used to set the level of the sidetone function.
For flexibility the actual functioning of the
two controls associated with the external
sources is configurable. For traditional
on-air sports applications they can be
selected to the dual level control mode
which provides independent control of the
left and right channel volume. For use with
stereo cue signals, or to support user preference, the level/balance mode can be
selected. In this mode one control adjusts
the overall level of both the left and right
channels, while the other allows adjustment of the left/right level balance. To help
minimize the chance of broadcast cues
being missed, both level control modes
can be configured so that a minimum
headphone output level is maintained.
Alternately, the headphone output can be
set to fully mute when these controls are
at their minimum position.
A headphone control reverse mode is
provided specifically for on-air television
applications where a headset with boom
microphone is used. The reverse mode
ensures that no matter which headset
orientation is used by the talent, the two
“pots” controlling the external sources will
always work intuitively. This will result in a
comfortable work environment, allowing
the “left” control to impact the level to the
talent’s left ear while the “right” control
impacts the right.
The sidetone level control is dedicated to
adjusting the level of the mic audio signal
that’s routed to the headphone outputs.
Configuration switches allow which of the
headphone outputs—left, right, or both—
will receive the sidetone signal. When the
sidetone level control is set to its minimum
position the sidetone level is always set to
be fully muted.
Provision has been made to support applications where a monaural cue feed is
desired. A configuration switch allows the
summing (combining) of the selected left
and right headphone sources. In addition
to creating a dual-channel mono output it
also allows the level controls to be configured as a simple 3-channel mixer.
The headphone output is optimized to
meet the needs of contemporary headphones and headsets. Specifically, the
output circuits act as voltage, rather than
power, drivers. In this configuration they
can provide high output levels with very
low distortion and noise, along with minimal current consumption. The output circuits are configured to safely drive stereo
or mono loads. This ensures that all types
of headphones, headsets, and earpieces
can be directly connected.
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Intercom Interface
Of special note is the Model 233’s sophisticated intercom interface. It’s designed
to work correctly with industry-standard
single- and dual-channel party-line intercom systems, including those from RTS
and Clear-Com. An intercom line connected to the Model 233 can serve three functions: providing cue audio signals to the
headphone output, allowing talkback audio
to be sent to intercom users, and acting
as a Model 233 power source. Audio signals present on the single- or dual-channel
intercom line can be flexibly routed to the
stereo headphone output. Talkback audio,
controlled by the two talkback pushbutton
switches, can be sent to either or both of
the intercom channels. Trim potentiometers, located on the bottom of the unit, allow adjustment of the talkback-to-intercom
sidetone (null) level.
Other announcer console products can
exhibit talkback-to-intercom-related audio
oscillations (“squeals”) that end up in the
headphone output. A unique Model 233
feature ensures that this will never occur.
This is accomplished by means of a special
“auto-terminate” circuit that becomes active
whenever an intercom line is not connected
to the Model 233.
Audio Quality and Protection
The Model 233’s circuitry is carefully
tailored to provide excellent audio performance. Professional-quality components
are featured throughout. For reliability all
audio routing is performed using solid-state
devices under microcontroller direction. In
all critical audio paths, “clickless” electronic
switches provide noise-free control. All
audio inputs and outputs make extensive
use of protection components. This limits
the chance of damage from ESD and other
undesirable, yet real-world, hazards.
Power Sources
The Model 233 can derive its operating
power from an intercom line or an external
24 volt DC source. For redundancy, both
power sources can be connected simultaneously. An internal switch-mode power
supply ensures that all Model 233 features
are available, including phantom power,
when the unit is powered by either source.
Auxiliary Relay
Model 233 resources include a generalpurpose relay, allowing specialized configurations to be created. Under software control, the relay can be configured to follow
the state of the main output, talkback 1,
or talkback 2 buttons. Taking advantage
of the back-panel locations provided for
additional XLR-type connectors, a technician may easily create functions such as
an “on-air” indicator or implement a loudspeaker muting during talkback function.
Special configuration modes are even
included to allow direct control of the relay
using the talkback 1 or talkback 2 buttons
without impacting any of the Model 233’s
audio signals.
Tally Output
Another unique Model 233 feature is the
tally output. It provides an indication, in
the form of a current-limited DC signal,
of the status of the main output. Whenever
the main output is active the tally output
is active. This 3.5 volt nominal, 12 milliamperes maximum, signal is capable of directly lighting an LED indicator or triggering
an external control system. The tally output
is provided specifically for specialized applications such as television award show
broadcasts where remote monitoring and
control of the main output is required.
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Configuration
Model 233 configurations are made using
a number of DIP-type switches and four
trim potentiometers. One 8-position switch
array is used to set the gain of the microphone preamplifier, the on/off status of
phantom power, and control of the headphone output mode. A 12-position switch
array configures which of the four cue
audio sources, as well as the sidetone audio, are routed to the headphone outputs.
In addition, the last two sections of the
12-position switch array are used to select whether talkback audio will be routed
to the intercom interface. Two 8-position
switch arrays communicate the desired
operating modes to the microprocessor.
Two rotary “trim pots” are used to adjust
the sensitivity of the line inputs. Two additional rotary trim pots are provided to
adjust the sidetone (null) level for the intercom interface’s talkback functions.
All switches and trim pots are accessible
via the bottom of the Model 233’s enclosure; the unit does not have to be disassembled. Changes made to any of the
configuration parameters become active
immediately. To prevent access to the
configuration controls a security panel,
included with each unit, is attached to the
bottom of the enclosure.
Connectors
The Model 233 uses standard connectors
throughout. The microphone input, line
inputs, and intercom interface functions
use 3-pin female XLR-type connectors.
The main and line-level talkback output
functions use 3-pin male XLR connectors.
The headphone output utilizes a ¼-inch
3-conductor jack. The external source of
24 volt DC power is connected by way of a
2.1 x 5.5 mm “locking” coaxial power jack.
Additional Connector Locations
In the world of broadcast, production, and
public address audio it’s fair to say that
applications vary widely. To this end, up to
three additional XLR-type connectors can
be easily mounted into the Model 233’s
back panel. Multiple 3-position “headers”
located on the Model 233’s circuit board
provide technician-access to literally every
input and output connection. In addition,
some additional features, including the
remote control inputs and tally output, are
accessible using 3-position headers. Using
a factory-available interface cable kit, these
headers allow a Model 233 to be optimized
to meet the exact needs of specific applications. For example, some applications may
prefer to use a multi-pin XLR-type connector to interface with a headset. This could
be easily accomplished by adding the
appropriate 6- or 7-pin XLR-type connector and making a few simple connections.
Other applications may benefit from having “mult” or “loop-through” connections,
something easily incorporated into a
Model 233.
Multi-Pin Headset Connectors
As previously mentioned, some applications are best supported using headsets
that interface using a multi-pin connector.
In most of these cases the desired connectors are 6- or 7-pin male XLR-type wired to
an industry-standard pin-out scheme. Studio Technologies offers headset connector
assemblies that allow fast and painless installation into a spare connector location in
the Model 233’s back panel. Details about
these optional assemblies are available on
the Studio Technologies website.
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Studio Technologies, Inc. Page 11
Options
The Model 233’s standard resources are
more than sufficient to directly support a
large number of applications. But in the
“real world” of audio and intercommunications special needs always seem to arise.
To that end, Studio Technologies offers
a number of option cards. In addition to
passive or active components, each card
contains an integral connector, allowing
simple installation into a spare connector
location on the Model 233’s back panel.
For interest, the resources provided by
some of these option cards are worth
describing.
Installation and
Setup
In this section interconnections will be
made using the input and output connectors located on the Model 233’s back panel. Microphone, line-level audio sources,
intercom, main output, and line-level talkback output signals are interfaced by way
of 3-pin XLR-type connectors. A ¼-inch
3-conductor phone jack is provided for the
headphone output. A 2.1 x 5.5 mm coaxial
jack allows connection of an external 24
volt DC power source.
• The direct microphone output card
provides access to the dynamic or condenser microphone that is connected
to the Model 233’s mic input. Passive
components, along with the auxiliary
relay contact, create a “click-free”
microphone-level audio signal.
• The remote switch input card uses a
4-pin XLR connector to provide access
to the Model 233’s remote switch inputs.
Other general-purpose option cards
provide 3-pin XLR, 4-pin XLR, and 8-pin
EtherCon® connectors. With the range
of option cards available it’s hard to imagine an application that can’t be served.
But you’re welcome to try to “stump the
chumps” in the Studio Technologies
technical support department! But first
please check the complete list of the
available option cards listed on the Studio
Technologies website.
System Components
The following is included in the shipping
carton: Model 233 Announcer’s Console,
user guide, button label sheet, and 24 volt
DC power supply. For units shipped to destinations in Japan and North America the
power supply will have a nominal AC mains
input of 120 volts. For all other destinations
a power supply compatible with 220/240
volt AC mains will be included.
Microphone Input
The Model 233 is compatible with balanced
dynamic and condenser microphones.
Depending on the application, the microphone may be part of a headset, or be an
independent handheld or stand-mounted
model. The Model 233’s nominal 48 volt
power source will support essentially all
phantom-powered microphones. The quality of the Model 233’s microphone preamplifier and associated circuitry is such that
special applications may benefit from using
“high-end” microphones. If selected appropriately, models from manufacturers such
as AKG, Beyerdynamic, Crown, Neumann,
Sennheiser, and Shure will perform very
well in Model 233 applications.
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The selected microphone is interconnected by way of a 3-pin female XLR-type
connector which is located on the Model
233’s back panel. The mating connector
(male) should be wired so that pin 2 is
signal high (+ or hot), pin 3 is signal low
(– or cold), and pin 1 is shield. It’s possible
that an unbalanced microphone will also
work correctly but is not recommended.
However, if this is necessary the mating
connector (male) should be wired so that
pin 2 is signal high (+ or hot), and signal
common/shield is connected to both pins
1 and 3.
The Model 233 is not compatible with unbalanced “electret”-type microphones that
require a source of low-voltage DC for operation. These microphones, sometimes
found in low-cost headsets, are not generally suitable for on-air or other demanding
applications.
As of the writing date of this user guide,
the Sennheiser HMD25 headset remains
popular for on-air broadcast use. A fine
product, it works very well with the Model
233. Note that adding the suffix “-XQ” to
the headset’s part number (HMD25-XQ)
specifies a 3-pin male XLR-type connector
for the dynamic microphone and a ¼-inch
3-conductor plug for the stereo headphones. This configuration is very useful,
allowing the headset to work directly “out
of the box” with the Model 233.
If the writer may digress for a moment to
recount a story… an audio dealer once
shared a secret with me concerning headsets. He loved selling the “lower-end” (less
expensive) headset models, which he did
by the veritable “boatload.” Why? Because
these usually broke soon after going into
service! He knew that on a regular basis
he’d receive orders for more of them.
Had these users, from the beginning,
purchased only premium-quality headsets,
their total cost of ownership would have
been much less. Enough said…
Headphone Output
The Model 233’s headphone output is
compatible with stereo or mono headphones, headsets, or earpieces. Connecting devices with a nominal impedance
of 100 ohms or greater is preferred. This
shouldn’t be an issue as essentially all
contemporary devices already meet this
condition.
Devices are connected to the headphone
output by way of a ¼-inch 3-conductor
phone jack located on the Model 233’s
back panel. As is standard for stereo
headphones, the left channel is connected
to the “tip” lead of the ¼-inch headphone
jack. The right channel is connected to
the “ring” lead of the jack. Common
for both channels is connected to the
“sleeve” lead.
Devices with ¼-inch 2-conductor “mono”
plugs can also be used with the Model
233’s headphone output. In this arrangement only the tip lead (left channel) will
be active. The 2-conductor plug will
physically connect (“short”) the ring lead
(right channel) to the sleeve lead (common). Technically this won’t damage the
circuitry associated with the right-channel
headphone output. (51 ohm protection
resistors are electrically in series with the
headphone output circuits.) However,
energy will be wasted if an audio signal
coming out of the right channel goes into
a “dead” short. There is a simple means
of eliminating this issue; when configuring
the headphone sources simply do not
assign any to the right channel headphone output. Refer to the Configuration
section of this user guide for details.
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Studio Technologies, Inc. Page 13
Main Output
The Model 233’s main output is intended to
be the “on-air” or primary signal that typically connects to the input of an audio console. The output is transformer balanced
with a nominal signal level of –2 dBu. The
actual level will depend upon the gain setting of the microphone preamplifier, sensitivity of the microphone, and how loudly
the user speaks into the microphone. The
transformer used in the main output is intended for professional audio applications.
Its source impedance is very low and can
drive lengthy cable runs without difficulty.
It is capable of driving loads as low as 600
ohms but performs best with loads of 2 k
ohms or greater. (This should not prove to
be an issue as virtually all contemporary
audio equipment has a relatively high input
impedance.) As the secondary winding of
the output transformer connects directly to
the main output connector, care should be
taken so that a DC voltage is never present
on the interconnecting cable.
The main output is interfaced by means of
a 3-pin male XLR-type connector located
on the Model 233’s back panel. The interconnecting cable’s mating connector
(female) should be wired so that signal
high (+ or hot) is on pin 2 and signal low
(– or cold) is on pin 3. The cable’s shield
can be connected to pin 1, but it will have
no function. Also, the cable’s shield must
not be terminated on the metal “shell” connection of the mating connector. To limit
the chance of grounding interaction between the Model 233 and connected equipment, pin 1 on the main output’s connector
is isolated from any point in the Model 233.
The fact that pin 1 “floats” will minimize the
chance of hums, noises, or buzzes being
present on the equipment connected to
the main output.
Line-Level Talkback Outputs
The two line-level talkback outputs are
intended to be connected to control
rooms, production trailers, or other locations where talent-originated voice cues
are required. The outputs are transformer
balanced with a nominal level of +4 dBu.
To enhance talkback audio quality, a compressor circuit controls the dynamic range
of the signal coming from the microphone
preamplifier.
For protection against accidental connection to cables that have DC power present,
the line-level talkback outputs are capacitor coupled. In series with the talkback
output leads are 300 ohm resistors, making the effective output impedance approximately 600 ohms. These resistors
create a passive summing network, allowing talkback outputs on multiple Model
233 units to be connected (“bridged”)
together.
The line-level talkback outputs are connected by way of two 3-pin male XLRtype connectors which are located on
the Model 233’s back panel. The mating
connectors (female) should be prepared
so that signal high (+ or hot) is provided
on pin 2. Signal low (– or cold) should
be provided on pin 3. The cables’ shields
can be connected to pin 1. But, like the
main output, in order to minimize the
chance that ground-interaction problems
will arise, pin 1 on the line-level talkback
output connectors are isolated from the
Model 233’s chassis and circuitry. By
making pin 1 “float,” often-feared “ground
loop” problems shouldn’t arise. Note that
the metal shell of the mating connector
must also be “floating.”
The line-level talkback outputs are intended to drive the lengthy cable runs that
Issue 1, September 2007 Model 233 User Guide
Page 14 Studio Technologies, Inc.
are often part of broadcast and production
audio applications. While the output circuitry is not intended to be “on-air” quality,
overall audio performance should be very
good. Devices connected to the line-level
talkback outputs can range from amplified
loudspeakers, analog inputs on intercom
systems, and input channels associated
with audio consoles. Connecting the outputs to devices that allow easy control of
the signal level can be helpful. For example, connecting to spare input modules on
an audio console provides the flexibility to
add gain or attenuate as required. Dedicated talkback-associated outputs on the
audio console can then be routed to the
final destination(s).
As previously mentioned, the line-level
talkback outputs on multiple Model 233
units can be directly connected together.
Using a simple “Y” or “W” cable, this passive summing (adding together or “bridging”) of talkback signals allows one audio
cable to serve as a master talkback path.
A side effect from using this passive summing technique is that signal attenuation
will occur. The audio quality won’t suffer,
but an audio “pad” is created. If two linelevel talkback outputs are connected together, a signal attenuation of 6 dB can be
expected. Connecting three talkback outputs together will result in 9.5 dB of attenuation. And four talkback outputs “multed”
together will lead to 12 dB of attenuation.
In most cases this attenuation won’t pose
a problem. Typically a device that receives
the talkback signal, such as an amplified
loudspeaker, will have an adjustable input
sensitivity so this attenuation won’t prove
to be a problem.
Line Inputs
The Model 233 allows two line-level audio
sources to be connected. These sources
can be individually routed to the left channel, right channel, or both the left and right
channel of the headphone outputs. The
inputs are balanced, transformer-coupled
with a nominal impedance of 10 k ohms.
Capacitors, in series with the transformer’s
input leads, prevent a DC voltage present
on a connected source from impacting
performance. The line inputs are compatible with signals that have a nominal level
of –12 dBV to +6 dBu. Two trim potentiometers, located on the bottom of the
Model 233’s enclosure, allow signals over
this wide nominal level range to be effectively utilized.
Audio sources are connected to the line
inputs by way of 3-pin female XLR-type
connectors which are located on the unit’s
back panel. Prepare the mating connectors (males) so that pin 2 is signal high
(+ or hot), pin 3 is low (– or cold), and pin
1 is shield. If connecting a source in this
manner results in hum or noise, it’s possible that removing the shield connection
from pin 1 can eliminate the issue. With
an unbalanced source connect pin 2 to
signal high (+ or hot) and both pins 1 and
3 to shield. If connecting an unbalanced
source in this manner results in hum or
noise, connect pin 2 to high (+ or hot) and
pin 3 to shield; leave pin 1 unterminated.
Intercom Interface
The Model 233’s intercom interface is
designed to directly connect with standard
single- and dual-channel party-line intercom lines. The one or two audio signals
provided by the intercom line can serve as
audio sources for the headphone outputs.
Each signal can be individually assigned
to the left channel, the right channel,
or both the left and right channels. The
Model 233 can also be configured to send
talkback audio to either or both of the
Model 233 User Guide Issue 1, September 2007
Studio Technologies, Inc. Page 15
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