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,
low-distortion 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
non-professional 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-the-scenes
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 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-to-disable
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 single- or 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 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
side-tone 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.
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 general-purpose 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.
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.
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.
Option
cards include the direct microphone output card which provides
access to the dynamic or condenser microphone that is connected to
the Model 233’s mic input. 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.
Model 233 Specifications
General
Audio:
Frequency Response: 20 Hz-20 kHz, ±0.1 dB, mic in/main out
Distortion (THD+N): 0.008%, measured at 1 kHz, mic in/main out
S/N Ratio: 80 dB, referenced to –46 dBu mic in/–2 dBu main out
Connectors:
Mic In, Line In 1 & 2, Intercom Interface: 3-pin female XLR-type
Main Out, Talkback Out 1 & 2: 3-pin male XLR-type
Headphone Out: ¼-inch 3-conductor phone jack
24 Vdc Power In: 2.1 x 5.5 mm coaxial power jack with locking bushing,
compatible with Switchcraft S760K plug
Spare
Connector Locations: 3
Allows up to three Neutrik NC*D-L-1 connectors to be installed (*=3F, 3M,
5F, 5M, 6F, 6FS, etc.)
Microphone
Input/Preamplifier:
Type: electronically balanced
Input Impedance: 2 k ohms
Gain Range: 20 to 60 dB, adjustable in 10 dB steps
Compatibility: dynamic or phantom-powered mics
Phantom Power: 48 Vdc, nominal, meets IEC 61938
Compressor:
Threshold: 2 dB above nominal level
Attack/Release Time: 2 mSec/100 mSec
Slope: 5:1
Status LED: compressor active
Line
Inputs: 2
Type: balanced, transformer-coupled
Impedance: 10 k ohms
Nominal Level: –12 dBV to +6 dBu, adjustable
Intercom Interface:
Type: 2-channel, unbalanced (pin 1 common; pin 2 DC with channel 1
audio; pin 3 channel 2 audio)
Compatibility: single- and dual-channel intercom systems such as from
RTS™ and Clear-Com®
Impedance: 10 k ohms
Nominal Receive Level: –10 dBu
Nominal Talkback Level: –10 dBu
Sidetone (Null): 0 to –18 dB, adjustable
Main
Output:
Type: balanced, transformer-coupled
Nominal Level: –2 dBu
Maximum Level: +20 dBu into 2 k ohms
Impedance: 100 ohms
Line-Level Talkback
Output:
Type: transformer-coupled with series capacitors and isolation resistors
Impedance: 600 ohms
Nominal Level: +4 dBu
Maximum Level: +11 dBu (compressor restricts maximum)
Headphone
Output: 1, stereo
Compatibility: intended for connection to mono or stereo headphones or
headsets with nominal impedance of 100 ohms or greater
Type: voltage driver
Maximum Output Voltage: 8 Vpp, 150 ohm load
Auxiliary
Relay:
Function: software configurable
Contacts: 2, form C (Common, Normally Closed, Normally Open)
Rating: 1 A, 30 W (resistive)
Access: requires user-implemented connector scheme
Tally Output: 3.5 Vdc, 12 mA maximum,
nominal
Power Sources:
IFB Input: 24-32 Vdc, 125 mA
Intercom Interface: 24-32 Vdc, 125 mA
External: 24 Vdc, 90 mA @ 24 Vdc; acceptable range 20-30 Vdc. Units shipped
to North America and Japan include a 120 V input/24 Vdc output power
supply. Units shipped to all other locations include a universal
input/24 Vdc output power supply.
Dimensions
(Overall):
8.1 inches wide (20.6 cm)
3.3 inches high (8.4 cm)
8.5 inches deep (22.4 cm)
Weight:
4.5 pounds (2.1 kg)
Specifications
subject to change without notice.
