Studio Technologies 240 User Manual

User Guide

Issue 1, August 2013

This User Guide is applicable for serial numbers:

M240-00151 and later

Copyright © 2013 by Studio Technologies, Inc., all rights reserved

www.studio-tech.com

50353-0813, Issue 1

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Table of Contents

Introduction ................................................................... 5

System Features ..........................................................

Installation and Setup ................................................... 8

Configuration ................................................................

Operation ......................................................................

Advanced Operation .....................................................

Technical Notes ............................................................

Specifications ...............................................................

Appendix A ................................................................... 33

Appendix B ................................................................... 34

Block Diagram

6

13

20

23

24

32

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Issue 1, August 2013 Model 240 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
Model 240 Producer’s Consoles with
serial numbers of 00151 and later. Addi­tional background technical information is
also provided. A product block diagram is
included at the end of this guide.

demands of this important and highly
specialized field. Compatible with broad
cast and production audio and intercom
system environments, the tabletop unit is
well suited for applications including sports
and entertainment television programming,
radio and TV news, and corporate events.
While the Model 240 is sophisticated on
the inside, users are presented with a
simple-to-use, great sounding “tool” to
help them do their job better.

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System Overview

The Model 240 Producer’s Console is
designed for producers, directors, or those
who need to efficiently communicate with
on-air broadcast personnel and related
production crew. The unit provides the
resources of a 4-channel talent cueing
(“IFB”) central controller combined with
a 2-channel party-line (PL) intercom user
station. Incorporating numerous configu­rable features and extensive upgrade flex­ibility, the Model 240 can meet the exacting

Four pushbutton switches control the rout
ing of microphone audio to the four main
outputs and, if selected, the 2-channel PL
intercom interface. Each button can be
configured for push-to-talk or alternate­action operation. A status LED is located
above each button and provides a clear
indication of talk status. Two line inputs
allow a variety of audio sources to be
connected. They can be used as program
audio for the four main outputs or routed
to the 2-channel headphone output.

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Figure 1. Model 240 front panel

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Figure 2. Model 240 back panel

System Features

Headset for Microphone
and Phones

A 5-pin XLR connector is provided for con­nection of a broadcast-style headset. The
selected headset should contain a dynamic
microphone and a single or dual earpiece.
While not directly intended for on-air
applications, the microphone preamplifier
is excellent, providing low-noise, low­distortion, and high headroom performance.
For optimal sound quality the gain of the
mic preamp can be configured from among
five choices. A sophisticated audio com­pressor circuit follows the microphone
preamplifier to minimize the chance of
signal overload. The headphone output
features low-noise circuitry with plenty of
all-important headroom. Many parameters
associated with the headphone output can
be configured to meet user requirements.

Main Outputs

Four main outputs are provided which can
be independently configured to meet the
specific needs of broadcast and production
applications. They can be, at their most
basic, considered talkback channels that,
under pushbutton control, contain the signal

from the connected headset’s microphone.
When an additional audio source is se­lected for use by a main output a compos­ite program/interrupt talent cueing signal is
created. Each main output provides a line­level signal that’s transformer and capaci­tor coupled for superior compatibility and
reliability. Resistors in series with the
output signals allow passive mixing of
multiple main output channels. And not
to be ignored is the audio quality: clean,
quiet, and “click free.”

Intercom Interface

The intercom interface is compatible
with single- and dual-channel party-line
(PL) intercom circuits commonly found
in broadcast, production, and industrial
applications. Direct connections with PL
circuits associated with RTS™ TW and
Clear-Com® intercom systems is assured.
The Model 240 can be configured to serve
in a listen-only mode where PL intercom
receive audio is routed to the headphone
output. Main outputs 3 and 4 can also be
independently selected to send talk audio
to the intercom circuit. The latter makes
the Model 240 function as a full 2-channel
intercom user station. The intercom circuit
can also provide the power required by the
Model 240.

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Line-Level Audio Inputs

Two line-level audio inputs allow the con­nection of a variety of cue signals. The
inputs are capacitor and transformer
coupled, ensuring consistent and reliable
interfacing with almost any audio source
found in the field. Two trim potentiometers
allow adjustment of the input signal level.
The two line inputs can be configured for
use with the four main outputs as well as
with the headphone output. The four main
outputs can be independently configured
to use this “program” audio to create talent
cue signals. While line input 1 is always
assigned to main outputs 1 and 3, the
choice of line input 1 or line input 2 is
independently assignable to main outputs
2 and 4. Each main output can then be
configured for how it uses its associated
program audio source. They can be set to
have no program audio, continuous pro­gram audio that combines with talk audio,
program audio that’s fully muted when talk
is active, or program audio that’s “dimmed”
(attenuated by 15 dB) when talk is active.
In this way four independent “dry” (non­powered) talent cue (IFB) channels can
be easily created.

Headphone Output

A 2-channel (stereo) headphone output
is provided for monitoring program or in­tercom audio signals. Physically the head­phone output connections are part of the
5-pin XLR headset connector located
on the Model 240’s back panel. Each
headphone output channel can be inde­pendently configured to monitor the two
line-level inputs or the two intercom inter­face channels. Two rotary controls allow
the user to independently adjust the level
of the left and right headphones output
channels. A configuration setting allows
the headphone output to be placed in

monaural mode, mixing the signals select
ed for the left and right channels. This can
be useful when single earpiece (“single­muff”) headsets or in-ear transducers are
used. A sidetone function is also available,
allowing audio from the microphone input
to be routed to the left and/or right head­phone channels. A separate rotary control
is provided for the user to adjust the side­tone level.

Provision has also been made to allow
two additional line-level audio sources
to be connected and routed to the head­phone output channels. Using optional
line input cards mounted in the back panel
openings of the Model 240, functions such
as announcer/commentator pre-fader
listen can be implemented.

There may be applications where con
necting monitor loudspeakers, rather than
a headset or headphones, would be ben
eficial. This can be easily implemented by
installing one or two optional line output
cards. A configuration feature allows the
headphone output level to be reduced
(“dimmed”) whenever a talk function is
active. This will minimize the chance that
acoustical interference and possible feed­back will take place between the loud­speakers and the connected microphone.

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Relay Contacts

Five normally open (not shorted) solid­state relay contacts are provided as “tally”
signals for application-specific use. Four of
the contacts are associated with the four
talk functions, closing (shorting) whenever
a pushbutton switch and associated main
output function is active. They can prove
useful in applications such as enabling a
call light or activating a wireless transmit­ter. The fifth contact offers a special func­tion, closing (shorting) whenever any of the

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talk functions are active. This is specifically
provided as a “trigger” to mute loudspeaker
systems that are located in the same
physical area as the Model 240.

Signal Flow

This document can only highlight some of
the Model 240’s capabilities. For a detailed
view of the unit’s signal flow it’s recom­mended that the block diagram, located
at the end of this guide, be reviewed.

communicated via the data link; combining
of the main output audio signals is done
passively. The Model 240 can be powered
by an external source of 24 volts DC.
Alternately, a connected party-line inter­com circuit can provide the required power.

Installation and Setup

Rugged, Flexible, Reliable

The Model 240 uses a rugged desktop
enclosure with a removable security plate
on the bottom that provides access to the
many configuration switches and trim pots.
(The unit does not have to be disassem­bled to be configured!) Laser-engraved on
the plate is a complete set of configuration
information so that field setup can be fast
and accurate. Four openings in back of the
Model 240’s enclosure allow installation of
a variety of option modules. These allow a
range of additional features and resources
to be easily added for a myriad of poten
tial applications. Numerous 3-pin header
connectors are provided on the Model
240’s printed circuit board assembly. These
provide access to all audio inputs and
outputs, along with many special input and
output signals. These include four contact
inputs associated with the four pushbutton
switches. A competent technician can use
them to create a highly-customized feature
set for meeting the exact needs of specific
applications.

The four pushbutton switches associated
with the talk functions use gold-plated con­tacts for reliable long-term operation and
include backlighting using white LEDs. A
data link allows two Model 240 units to be
interconnected as an integrated 2-location
system. The status of the talk channels is

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In this section interconnections will be
made using the input and output con­nectors located on the Model 240’s back
panel. The main outputs, line inputs, and
party-line (PL) intercom signals are inter­faced by way of 3-pin XLR connectors.
A headset is connected using a 5-pin XLR
connector. A 2.1 x 5.5 mm coaxial jack
allows connection of an external 24 volt
DC power source.

System Components

The following is included in the shipping
carton: Model 240 Producer’s Console,
Model 240 User Guide, button label sheet,
and 24 volt DC power supply.

Headset Connection

The Model 240 is compatible with head­sets that have a dynamic microphone
and single- or dual-earpieces. These are
commonly referred to as single- or dual­muff headsets. The microphone portion
of compatible broadcast-quality headsets
will typically have a source impedance of
200-300 ohms. The impedance of the ear­pieces can range more widely. Connecting
devices with earpiece impedance of 100
ohms or greater is preferred. Some com­mon devices have an earpiece impedance
of 50 ohms and while not optimal they
should also function correctly.

Issue 1, August 2013 Model 240 User Guide
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The quality of the Model 240’s microphone
preamplifier and associated circuitry is
such that special applications may benefit
from using “high-end” headsets. If selected
appropriately, models from manufactur­ers such as AKG, beyerdynamic, or Audio
Technica will perform very well.

Headset interconnection is made by way
of a 5-pin female XLR connector which is
located on the Model 240’s back panel. The
mating connector (male) should be wired
following the details provided in Figure 3.

Pin Number Function

1 Mic low (–)

2 Mic high (+)

3 Mic Shield/Headphone Output
Common

4 Headphone Output Left Channel

5 Headphone Output Right Channel

Figure 3. Headset connections (5-pin male XLR)

It’s recommended that a headset with a
balanced microphone be used. But it’s also
possible that a headset that incorporates an
unbalanced microphone could work correct­ly. In the latter case wire the mating connec­tor (male) with pin 2 as signal high (+) and
pin 1 as signal common/shield.

A potential crosstalk issue comes from the
fact that pin 3 of the 5-pin XLR serves as
both the microphone connection’s shield and
the common lead for the left and right head­phone output. This allows headphone audio
current that’s flowing through the common
lead to induce signal into the microphone
input. While the microphone input circuity’s
common-mode rejection capability will limit
the impact, the current can reach a “critical”
amount causing induced noise. Typically
this won’t happen during normal operation
but it’s possible. But whit a common path

nothing can be done to guarantee that
this condition will never occur. Installing
separate microphone input and headphone
output connectors in the spare connector
openings in the Model 240’s back panel can
go a long way toward minimizing this issue.
The Technical Notes section of the guide
offers additional details on this subject.

When an appropriate interface cable is fab

­ricated the microphone input portion of the
headset connector is also compatible with
line-level audio sources. This allows the
output of an intercom user station, wireless
microphone receiver, or audio console to be
directly connected. When the microphone
preamplifier gain configuration DIP switches
are set for 0 dB (no gain) the nominal level
of a connected line-level source should be
approximately –2 dBu.

Wiring options would also allow connection
of a separate microphone and pair of head

­phones. This can be accomplished by creat­ing an external “break out” cable that wires
a 5-pin male XLR to separate 3-pin female
XLR and 3-conductor ¼-inch phone jacks.

The Model 240 does not provide micro

­phone “phantom” power. This is not due to
a technical limitation or oversight but rather
reflects a design decision; the intended
applications won’t typically require phan­tom. The Model 240 is also not compatible
with headsets that include an unbalanced
“electret”-type microphone that requires
a source of low-voltage DC for operation.
These microphones, sometimes found in
low-cost headset models, are not generally
suitable for professional applications.

Main Outputs

The four main outputs are intended to
be connected to listen-only beltpacks,
inputs on wireless monitor transmitters,
audio-to-powered-IFB interfaces, or other

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locations where cue signals are required.
The outputs are transformer balanced
with a nominal level of 0 dBu. To enhance
talk audio quality, a compressor circuit
controls the dynamic range of the signal
coming from the Model 240’s microphone
preamplifier.

For protection against accidental connec

­tion to cables that have DC power present,
the main outputs are, in addition to being
transformer-isolated, capacitor coupled.
Also in series with the main output leads
are 300 ohm resistors, making the effec­tive output impedance approximately 600
ohms. These resistors create a passive
summing network, allowing main outputs
on multiple Model 240 units to be connect­ed (“bridged”) together.

The main outputs are connected by way
of four 3-pin male XLR connectors which
are located on the Model 240’s back panel.
Prepare the mating connectors (females)
so that pin 2 is signal high (+) and pin 3 is
signal low (–). Each cable’s shield can be
connected to pin 1. But in order to mini­mize the chance that ground-interaction
problems will arise, pin 1 on each of the
main output connectors is isolated from
the Model 240’s chassis and circuitry. By
making pin 1 “float,” the chance of often­feared “ground loop” problems should be
minimized. Note that the metal shell of the
mating connector must also be “floating.”

The main outputs are intended to drive
the lengthy cable runs that 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 main outputs can
range from amplified loudspeakers, analog
inputs on intercom systems, inputs on

in-ear monitor system transmitters, and
input channels associated with audio
consoles.

As previously mentioned, the main outputs
on multiple Model 240 units can be directly
connected together. Using a simple “Y” or
“W” cable, this passive summing (adding
together or “bridging”) of signals allows one
audio cable to serve as a composite output
path. A side effect from using this passive
summing technique is that signal attenu

­ation will occur. The audio quality won’t
suffer, but an audio “pad” is created. If two
main outputs are connected together, a
signal attenuation of 6 dB can be expected.
Connecting three main outputs together
will result in 9.5 dB of attenuation. And four
main outputs “multed” together will lead to
12 dB of attenuation. In most cases this at

­tenuation won’t pose a problem. Typically a
device that receives the 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 240 allows two line-level audio
sources to be connected. These sources
can be individually routed to the four main
outputs as well as the headphone output
channels. 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 the source from impacting
performance. The line inputs are compat­ible with signals that have a nominal level
of –10 to +6 dBu. Two trim potentiometers,
located on the bottom of the Model 240’s
enclosure, allow signals over this wide
nominal level range to be effectively utilized.

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Audio sources are connected to the line
inputs by way of 3-pin female XLR con­nectors which are located on the unit’s
back panel. Prepare the mating connectors
(males) so that pin 2 is signal high (+),
pin 3 is low (–), 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 (+) and both
pins 1 and 3 to shield. If connecting an
unbalanced source in this manner results
in hum or noise, try connecting pin 2 to
high (+) and pin 3 to shield; leave pin 1
unterminated.

Intercom Interface

The Model 240’s intercom interface is
designed to directly connect with standard
single- and dual-channel party-line (PL)
intercom circuits. The one or two audio sig­nals provided by the intercom circuit 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 240 can also be config­ured to send main output channel 3 and
channel 4 audio to the intercom channels.
In addition, the intercom circuit can pro­vide the DC power required to operate the
Model 240’s circuitry.

An intercom circuit is connected to the
Model 240 by way of a 3-pin female XLR
connector which is located on the back
panel. The mating connector (male) should
be wired so that common is on pin 1, DC
with channel 1 audio is on pin 2, and chan­nel 2 audio is on pin 3. With single-channel
intercom circuits common is on pin 1, DC
power is on pin 2, and audio is connected
to pin 3.

The Model 240’s intercom interface is
directly compatible with broadcast and
production party-line intercom circuits as
sociated with systems from manufacturers
such as RTS and Clear-Com. Intercom cir­cuits associated with other similar systems
should be equally compatible. RTS TW­series systems are normally interfaced
using 3-pin XLR connectors. These con­nectors are wired with common on pin 1,
DC power and channel 1 audio on pin 2,
and channel 2 audio on pin 3. Most Clear­Com party-line systems are single-channel
with common on pin 1, DC power on pin 2,
and audio on pin 3.

The DC power supplied by the connected
intercom circuit is generally sufficient to
operate the Model 240’s circuitry. The ac
ceptable input range is 24 to 32 volts, with
a required current of 150 milliamperes.
Note that the specified input voltage is
given when measured directly at the Model
240’s intercom input connector (with the
connector terminated on the Model 240)
and not at the source of the intercom
circuit’s power.

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Multi-Unit Interconnection

Two Model 240 units can be interconnect­ed so as to function together. Audio sig­nals on multiple main output channels are
combined passively; there is no internal
digital or analog busing created. (This is
“old school” but works well!) Interconnect­ing cables would be prepared so that the
pins on two 3-pin female XLR connectors
would be connected 1-to-1, 2-to-2, and
3-to-3 and the combination routed to the
input on the destination device. The Model
240’s main output circuitry is designed to
be passively combined so there is no risk
of damage by doing this. The audio level
on both units will drop approximately 6 dB
due to the passive combining.

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Studio Technologies, Inc. Page 11

Line inputs that are going to be assigned as
main output sources should be connected
only on the Model 240 being designated
as the primary unit. Otherwise signals will
“clash” on the combined main audio out­puts. An intercom circuit would have to be
connected to both Model 240 units, and
configured identically, for correct operation
to take place.

An RS-485 data bus links the microcon
troller integrated circuits on the two units
and conveys button status information.
Only one pair of wires for the data bus is
required. An installer-provided connector
is necessary. Please refer to the Technical
Notes section of this guide for connection
details.

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External Power Input

An external source of 24 volt DC power can
be connected to the Model 240 by way of
a 2.1 x 5.5 mm coaxial power jack which
is located on the back panel of the unit.
The center pin of the jack is the positive
(+) connection. While the requirement for
the external source is nominally 24 volts,
correct operation will take place over a 20
to 30 volt range. The Model 240 requires
125 milliamperes at 24 volts DC for correct
operation. Included with each Model 240
is a 24 volt DC external power supply. The
power supply’s DC output cable has been
terminated with a Switchcraft® S760K co­axial power plug. This “locking” type of plug
correctly mates with the Model 240’s 24 Vdc
input jack. The locking feature is important,
allowing the external power source to be
securely attached to the Model 240.

As previously discussed in this guide, an
intercom circuit connected to the Model 240
can serve as the unit’s power source. For
redundancy, the intercom circuit and the ex­ternal 24 volt DC source can be connected

at the same time. If one of them becomes
inoperative the remaining source will pro­vide power for the Model 240.

The Model 240’s circuitry establishes the
priority in which the unit draws its operat
ing power. If an external source of 24 volt
DC power is connected, it will always serve
as the primary source. This minimizes the
impact that the unit’s power draw could
have on a connected intercom circuit. If no
external source of 24 volt DC is connected
then power will be drawn from the intercom
circuit.

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Pushbutton Labeling

The four pushbutton switches used in the
Model 240 were selected for several rea­sons. Foremost was the fact that they are
highly reliable, using gold-plated contacts
for long life in less-than-ideal environ­ments. A second reason was that apply­ing customized labels to the button caps
would be very simple. Labels, text printed
on clear material, can be placed under the
clear lens that is part of the button cap.
And with the integrated white LED back­lighting the label text will be highly legible.

From the factory the four lenses in the
button caps are not directly labeled. This
is because there are simply too many
possible uses for the Model 240 to allow
“default” labels to be meaningful. Text on
the graphics label on the Model 240’s front
panel does provide a simple indication of
the button positions, showing 1, 2, 3, and

4. But it’s expected that some applications
may benefit from more-specific labels
being added to the button caps.

As a “head start” for some applications, a
clear sheet with a number of commonly
used button designations printed on it is in
cluded in the shipping carton. These were
created at the factory using a standard

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Issue 1, August 2013 Model 240 User Guide
Page 12 Studio Technologies, Inc.