Studio Technologies 74 User Manual
for Surround
Model 74 Central Controller and
Model 75 Control Console
User Guide
Issue 2, January 2006
This User Guide is applicable for systems consisting of:
Model 74: serial number M74-00151 and later;
Model 75: M75-00151 and later
© 2006 by Studio Technologies, Inc., all rights reserved
www.studio-tech.com
50221-0106, Issue 2
Table of Contents
Introduction ................................................................... 5
Installation .................................................................... 9
Confi guration ................................................................16
Operation ...................................................................... 34
Technical Notes ............................................................39
Specifi cations ...............................................................44
Appendix A – MIDI Messages ......................................45
Block Diagrams
Model 74 Central Controller
Model 75 Control Console
for Surround
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Issue 2, January 2006 Model 74/75 User Guide
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Introduction
What This User Guide Covers
This User Guide is designed to assist you
when installing and using the Model 74
Central Controller and the Model 75
Control Console.
StudioComm for Surround
The StudioComm for Surround Model 74
Central Controller and Model 75 Control
Console work together to provide 5.1
surround and stereo source monitoring
capabilities, along with a full-featured
headphone “talkback” cue system. The
system is a perfect fi t for contemporary
facilities that need to perform a variety of
audio tasks. These can include surround
and stereo mixing and monitoring, live recording of voice, music, and sound effects,
and on-air broadcast applications. The
system’s features were carefully selected
to provide extensive capabilities while
remaining simple to operate. Of overriding
concern is maintaining the quality of the
connected audio sources. This is accomplished using a combination of excellent
circuit design and carefully selected components. The Model 74/Model 75 combination is ideal for adding surround monitoring
capability to disk-based recording systems.
It’s also well suited for upgrading a postproduction or broadcast facility to support
multi-channel monitoring.
A complete StudioComm for Surround
74/75 system begins with the Model 75
Control Console, a compact user control
surface that is intuitive and comfortable to
use. It is designed to reside at the operator’s location. The Model 75 connects
to the Model 74 Central Controller using
a single 9-pin cable. Occupying one rack
space, the Model 74 provides all audio
input and output circuitry, signal routing
and control, and power supply functions.
To complete the system up to four Model
35 Talent Amplifi er modules can be added.
These connect to the Model 74 using standard 3-pin XLR-type audio cables. Model
35 units are typically deployed in voiceover booths, studio areas, or other locations where voice or music talent needs
access to a headphone cue feed. Each
unit provides a stereo audio amplifi er, user
controls, and support for one or two pairs
of headphones.
Model 74 Central Controller
The Model 74 Central Controller is a
single rack-space unit that contains analog, digital, and power supply electronics.
Four analog sources can be connected:
two surround (5.1) and two stereo. In
many applications the fi rst surround input,
Surround A, will be connected to a multichannel output on an audio console or
digital audio workstation. The second surround input, Surround B, will be connected
to a playback device, such as a multitrack
tape recorder or disk storage system. For
fi lm or video post applications Surround
A would be considered the direct source,
while Surround B would be considered
the playback source.
The two stereo inputs, Stereo A and
Stereo B, are provided for general-purpose
use and can be connected to a variety
of 2-channel direct and playback sources.
For fl exibility, the surround and stereo
inputs are compatible with balanced or
unbalanced signals having a nominal level
range of –12 dBV to +6 dBu. Fifteen-turn
trim potentiometers are used to precisely
calibrate the input signals.
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The Model 74 provides two 6-channel
monitor outputs. A powerful system feature
is the ability to confi gure the monitor out-
puts to meet the exact needs of an installation. In a “straight-ahead” application
the monitor outputs might be confi gured
to support two independent surround (5.1)
loudspeaker systems. Alternately, one
surround and one stereo monitor system
could be connected. However, other more
unique confi gurations are also possible.
These include supporting alternate surround monitor speaker systems or adding
additional LFE or surround speakers. The
monitor outputs are electronically balanced
and designed for connection to audio power amplifi ers or amplifi ed loudspeakers.
Protection circuitry provides power-up and
power-down protection of the connected
loudspeaker systems.
Audio input and output connections are
made using four 25-pin D-subminiature
connectors. The Model 74’s audio path
features low-noise, low-distortion analog
switches for input source selection and
laser-trimmed voltage-controlled-amplifi er
(VCA) integrated circuits for monitor level
control. One 9-pin D-subminiature connector is used to connect the Model 74 to
the Model 75 Control Console. A second
9-pin “D-sub” connector is used to interface remote control signals with the Model
74. The Model 74’s talent amplifi er output
uses a 3-pin male XLR-type connector. An
infrared receiver module can connect to
the Model 74 using a 3.5 mm jack.
An advanced 8-bit microcontroller provides
the logic “horsepower” for the Model 74.
AC mains power is connected directly to
the Model 74, which is factory selected
for 100, 120, or 220/240 V operation.
The internal power supply utilizes two
toroidal mains transformers for quiet
audio operation.
Figure 1. Model 74 Central Controller Front Panel
Surround
Input A
trim pots
Surround
Input B
trim pots
Stereo
Input A
trim pots
Stereo
Input B
trim pots
Figure 2. Model 74 Central Controller Back Panel
AC mains
input connection
To/from
Model 75
Control
Console
Remote
control
inputs
Output to
Model 35
Talent
Amplifi ers
Monitor B output
and line-level
talkback input
Infrared
receiver
input
Monitor A output and
line-level cue audio
outputs
Surround Input B
and Stereo Input B
connections
Data
active LED
Surround Input A
and Stereo Input A
connections
Power
present LED
Issue 2, January 2006 Model 74/75 User Guide
Page 6 Studio Technologies, Inc.
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Figure 3. Model 75 Control Console Front Panel
Mute/solo
mode select
Monitor output
channel mute/solo
Stereo to mono
downmix
5.1 to stereo
downmix
Input
sources
Talkback
Model 75 Control Console
The Model 75 Control Console is a compact, self-contained unit designed to be
located at the operator’s position. It allows
fi ngertip control of all monitoring and talkback parameters. Numerous LED indicators provide complete status information. A
major strength of the Model 75 is its ability
to confi gure, under software control, many
of the operating parameters. All confi gura-
tion parameters are stored in nonvolatile
memory. The Model 75 Control Console
connects to, and is powered by, the Model
74 Central Controller. The Model 75 generates MIDI system-exclusive messages
to control the Model 74. Remote-control
signals connected to the Model 74 Central
Controller are routed to the Model 75 via
pins in the 9-pin interconnecting cable.
The Model 75 provides four buttons and
associated LEDs for selection of the surround and stereo sources to be monitored.
Talkback
microphone
Monitor Output
• Speaker system
select
• Reference level
• Mute all
• Dim
• Rotary level control
While in most cases only one input source
will be monitored at a time, multiple inputs
can be selected for simultaneous monitoring. This allows two, three, or all four of
the inputs to be combined (“summed”).
While there is no independent control of
the input levels, this feature can be useful
for creating rough mixes from the source
signals. It is also a fast, effective means of
making a “seat-of-the-pants” check on the
phase relationship between synchronized
signals.
The monitor output levels are controlled
using a large, easy-to-use rotary control.
The “curve” or “taper” of the level control
can be confi gured to match an operator’s
preference. The choices available are true
logarithmic and modifi ed logarithmic. The
level control auto mute all function allows
the monitor output channels to mute automatically whenever the rotary level control
is in its fully counterclockwise (minimum)
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position. This is useful in applications such
as on-air broadcast. By using the reference level function, the monitor output
level can be set to a pre-confi gured value.
This is provided for audio-with-picture applications that require a specifi c monitor
level. The reference level is easily confi g-
ured by taking an electronic “snapshot” of
the position of the rotary level control.
One button controls which monitor output, A or B, is active. For operator convenience, the dim function allows the monitor
output level to be reduced by a fi xed dB
amount. The dim level is confi gured from
four available levels. A mute all function
allows all of the monitor output channels
to be simultaneously muted. The mute/solo
section provides individual output channel
control. One pushbutton switch sets the
operating mode for either mute or solo. In
the mute mode, individual channels can
be muted as required. In the solo mode,
one channel can be monitored while the
others are automatically muted. Depending on the confi guration, multiple channels
can be simultaneously selected for “soloing.” The fl exibility of having both mute and
solo available allows an operator to quickly
select the most comfortable and productive
operating mode.
Two functions allow the format of the
monitored sources to be checked for
level or phase inconsistencies. The 5.1
to stereo downmix function is used to
create a stereo signal from a 5.1 (surround) source. The stereo to mono downmix function allows a stereo signal to be
added (summed) and monitored. The two
downmix functions can be simultaneously
enabled, allowing a surround signal to be
checked for mono compatibility. The operating mode of the stereo to mono downmix
function can be selected from two choices:
mono-to-left-and-right or mono-to-center.
This allows support for both music and
audio-with-picture applications. A bandpass
fi lter feature is associated with the stereo
to mono downmix function. It is included to
assist an operator in determining compatibility with “real world” playback environments. A bandpass fi lter can be inserted
into the path of the mono signal, allowing
the response of a monaural loudspeaker
associated with an inexpensive television
or portable radio to be simulated.
To support the headphone cue system
functions the Model 75 Control Console
includes three pushbutton switches and
an integral microphone. As expected, one
button is used to enable the talkback function. The other two buttons are used to set
the talkback level over an 8-step range.
These buttons are also used to select
which audio source is routed to the headphones. Two choices are provided: the left
and right channels of the source selected
for the monitor output, or the left and right
channels associated with Stereo B.
In many cases the talkback button contained in the Model 75 will be used to initiate the talkback function. However, some
applications may benefi t from being able
to remotely activate talkback. A hard-wired
signal can be connected to the remote
talkback input. In this way various types
of external wired and wireless equipment
can be interfaced. An infrared (IR) receiver
module can also be directly connected.
This allows the use of a wireless transmitter to enable talkback. The microphone
contained within the Model 75 Control
Console provides crisp, clear talkback
audio. But some installations may benefi t
from using an alternate source of talkback
audio. This capability is provided by the
Model 74’s line-level talkback audio input.
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For fl exibility, the system is designed to
easily integrate with recording consoles,
specialized playback systems, and audiofor-picture machine-control electronics.
Four hard-wired remote-control input functions are provided: mute all, dim, talkback,
and input select. By providing access to
the StudioComm’s mute all and dim functions, talkback or slate activity from an
audio console or other communications
system can control the monitor output
level. The remote talkback input allows
an externally provided contact closure or
logic signal to control the talkback function.
This allows easy integration with additional
wired or wireless talkback devices. The
remote input select function is provided
expressly for audio post applications, allowing automatic switching of the StudioComm’s input source whenever the mode
of a recording system changes between
playback and record. This function, referred historically as PEC/direct switching,
allows accurate monitoring during dialog
replacement, Foley, or other overdub
sessions.
Figure 4. Model 35 Talent Amplifi er Front Panel
Level control
Figure 5. Model 35 Talent Amplifi er Back Panel
Stereo/
mono
switch
To additional
Model 35
Talent Amplifi ers
Headphone
outputs
From Model 74
or another Model 35’s
loop thru connector
In most cases Model 35 Talent Amplifi er
modules will serve as the user’s headphone control center. Each Model 35
contains amplifi er circuitry, stereo level
control, mono switch, and two output jacks.
For convenience, a microphone mounting
stand adapter is included with each Model
35. In addition to the talent amplifi er out-
put, the Model 74 also provides a stereo
line-level cue output. This allows interfacing with other headphone cue systems or
could connect to a transmission system
associated with a remotely located studio
Installation
In this section you will be installing the
Model 74 Central Controller in an equipment rack. Audio input, monitor output,
and headphone cue system connections
will be made. One or more Model 35 Talent Amplifi ers will be connected. A location
will be selected for the Model 75 Control
Console and it will be connected to the
Model 74. If required, external equipment
will be interfaced to the remote control
inputs. AC mains power will be connected
to the Model 74.
or control room. The line-level cue output
can also serve as a source of “slate” audio
for workstations.
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System Components
The shipping carton contains one each of
the following: Model 74 Central Controller,
Model 75 Control Console, 9-pin D-sub
interconnecting cable, and user guide.
Units destined for North America also
include an AC mains cord. Your dealer or
distributor will provide an AC mains cord
for non-North American destination. Model
35 Talent Amplifi ers will be contained in
separate cartons.
Mounting the Model 74
The Model 74 Central Controller requires
one space in a standard 19-inch equipment rack. Select a location that is convenient to both the analog audio signals and
the Model 75 Control Console. A cable
is provided to connect the Model 75 with
the Model 74. Secure the Model 74 into
the equipment rack using two mounting
screws per side.
Audio Connections
the monitor output A and line-level cue
outputs is identical to that of a DA-88-style
output harness. A wiring harness prepared
for the fourth D-sub is slightly different. It is
used for connecting with the six channels
of monitor output B as well as the linelevel talkback input. As such, it will require
careful attention when selecting the right
terminations, e.g., six male plugs and one
female connector. Please refer to Figures
6 through 11 for the exact connection details. Be certain to note that the Model 74’s
D-sub connectors use 4-40 threads.
Unless there’s a special need, it may be
cost and time effective for you to purchase
commercially made cable harnesses. Let
the large market for DA-88-style cabling
help you painlessly install your system!
There is one caveat to using pre-made
harnesses. The sex of the connector
associated with the line-level talkback
input may need to be changed. Even so,
using pre-made cables harnesses may
still provide helpful.
Line-level audio signal connections are
made by way of four 25-pin D-sub connectors, located on the Model 74’s back panel.
To implement all the available features
four cable harnesses, each with a 25-pin
D-sub plug (male) on one end and the
desired connectors on the other end, are
necessary. These cable harnesses are not
supplied by Studio Technologies. Note that
our friends in some locations may use the
term “loom” instead of harness.
The wiring scheme used by the D-sub
connectors comply with that made familiar
by TASCAM® with their DA-88® product.
Wiring harnesses prepared for connecting to the Model 74’s surround and stereo
inputs are identical to DA-88-style input
harnesses. A wiring harness prepared for
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Surround and Stereo Inputs
The connector labeled Surround Input A
and Stereo Input A, as well as the
connector labeled Surround Input B and
Stereo Input B are used to interface with
the two 6-channel (5.1 surround) and two
2-channel (stereo) input circuits. Please
refer to Figures 6 and 7 for details on the
exact “pin out” of the D-sub connectors.
Each input circuit is electronically balanced
and intended for connection to balanced
or unbalanced sources with nominal signal levels of –12 dBV to +6 dBu. A 15-turn
trim potentiometer is associated with each
input channel, allowing the input sensitivity
to be adjusted to match the source’s level.
The confi guration section of this guide pro-
vides details on using the trim pots.
for Surround
Signal Signal
Connections High (+) Low (–) Shield
SURROUND A-L 24 12 25
SURROUND A-R 10 23 11
SURROUND A-C 21 9 22
SURROUND A-LFE 7 20 8
SURROUND A-LS 18 6 19
SURROUND A-RS 4 17 5
STEREO A-L 15 3 16
STEREO A-R 1 14 2
Notes: 1) Connector type on Model 74 is 25-pin D-subminiature
female. Installer must provide plug (male). Connector
uses 4-40 threaded inserts for locking with mating plug.
2) Wiring scheme follows TASCAM DA-88 convention.
Standard DA-88-type wiring harnesses are directly
compatible, with the exception of 4-40 screw threads
being required.
Figure 6. Connections for Inputs Surround A
and Stereo A
Balanced sources should be wired so that
signal high is connected to +, signal low to
–, and shield to the shield connection. With
an unbalanced source, connect signal high
to the + connection, and shield to both the
– and the shield connections. If connecting
to an unbalanced source in this manner results in hum or noise, try connecting signal
high to +, and shield to –; leave the shield
connection unterminated.
It is highly recommended that at least one of
the surround inputs be wired by way of an
audio patch bay. This will allow the channels associated with that input source to be
easily rerouted. While signals generated
within a facility will normally follow a specifi c
format, such as left, right, center, LFE, left
surround, and right surround, it is possible
that media provided by an outside facility
will follow a different scheme.
Signal Signal
Connections High (+) Low (–) Shield
SURROUND B-L 24 12 25
SURROUND B-R 10 23 11
SURROUND B-C 21 9 22
SURROUND B-LFE 7 20 8
SURROUND B-LS 18 6 19
SURROUND B-RS 4 17 5
STEREO B-L 15 3 16
STEREO B-R 1 14 2
Notes: 1) Connector type on Model 74 is 25-pin D-subminiature
female. Installer must provide plug (male). Connector
uses 4-40 threaded inserts for locking with mating plug.
2) Wiring scheme follows TASCAM DA-88 convention.
Standard DA-88-type wiring harnesses are directly
compatible, with the exception of 4-40 screw threads
being required.
Figure 7. Connections for Inputs Surround B
and Stereo B
Monitor Outputs
Two connectors are used to support the
two 6-channel (5.1 surround) monitor outputs. Please refer to Figures 8 and 9 for
details on the exact “pin outs” of the D-sub
connectors.
The monitor output channels are intended
for connection to audio amplifi ers associ-
ated with monitor loudspeakers, or to the
inputs of loudspeakers that contain integrated amplifi ers. The monitor outputs are
electronically balanced and capable of
driving balanced or unbalanced loads of 600
ohms or greater. While balanced operation
is preferred, unbalanced operation does
not pose a problem. To connect to an unbalanced load connect the + terminal as signal
high, and both the – and shield as the signal
low/shield. For optimal unbalanced operation, it is important to connect both – and
shield together directly on the D-sub plug,
not at the other end of the harness.
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Signal Signal
Connections High (+) Low (–) Shield
MONITOR OUT A-L 24 12 25
MONITOR OUT A-R 10 23 11
MONITOR OUT A-C 21 9 22
MONITOR OUT A-LFE 7 20 8
MONITOR OUT A-LS 18 6 19
MONITOR OUT A-RS 4 17 5
CUE OUT-L 15 3 16
CUE OUT-R 1 14 2
Notes: 1) Connector type on Model 74 is 25-pin D-subminiature
female. Installer must provide plug (male). Connector
uses 4-40 threaded inserts for locking with mating plug.
2) Wiring scheme follows TASCAM DA-88 convention.
Standard DA-88-type wiring harnesses are directly
compatible, with the exception of 4-40 screw threads
being required.
Figure 8. Connections for Monitor Output A and
Line-Level Cue Outputs
Signal Signal
Connections High (+) Low (–) Shield
MONITOR OUT B-L 24 12 25
MONITOR OUT B-R 10 23 11
MONITOR OUT B-C 21 9 22
MONITOR OUT B-LFE 7 20 8
MONITOR OUT B-LS 18 6 19
MONITOR OUT B-RS 4 17 5
UNUSED 15 3 16
TALKBACK INPUT 1 14 2
Notes: 1) Connector type on Model 74 is 25-pin D-subminiature
female. Installer must provide plug (male). Connector
uses 4-40 threaded inserts for locking with mating plug.
2) Wiring scheme follows TASCAM DA-88 convention.
Standard DA-88-type wiring harnesses are directly
compatible, with the exception of 4-40 screw threads
being required.
Note that while the Model 74’s electronically
balanced output circuits are capable of driving loads of 600 ohms or greater, the output
level will drop slightly as the load impedance
approaches 600 ohms. A 0.5 dB difference
in output level can be expected as the load
impedance changes from 10 k ohms to 600
ohms. This drop is not insignifi cant and leads
to the recommendation that input loads be
10 ohms or greater.
It’s important to note that the two 6-channel
monitor outputs can be used to create a
wide variety of monitor system implementations. Confi guration choices allow the two
outputs to perform tasks more nuanced
than just serving as a 6-channel A/B
switching matrix. Please carefully review
the confi guration section of this user guide
prior to connecting to the monitor outputs;
don’t let the system’s unique fl exibility go
underutilized!
Headphone Cue System
Two outputs and one input are associated
with the headphone cue system. The talent
amplifi er output supplies audio and DC
power for supporting Model 35 Talent
Amplifi er units. Using this method a great-
sounding, fl exible cue system can be easily
created. A stereo line-level output associated with the headphone cue system is also
available. A source of line-level audio can be
connected and can serve as the talkback audio source. This source can be used in place
of the microphone contained in the Model 75
Control Console.
Figure 9. Connections for Monitor Output B and
Line-Level Talkback Inputs
Talent Amplifi er Output
Up to four Model 35 Talent Amplifi ers can
be connected to the Model 74’s talent amplifi er output. The output connector is a 3-pin
male XLR-type. For best performance, use
low-capacitance shielded microphone-type
Issue 2, January 2006 Model 74/75 User Guide
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cable to distribute the talent amplifi er
signal. If there is a choice, select cables
with the heaviest wire gauge commonly
available. This will reduce voltage drop
when using long cable runs. Refer to the
Technical Notes section for additional
information.
The simplest installation would use a
microphone cable to connect the Model 74
to the fi rst talent amplifi er; the loop through
connector on that talent amp sending the
signal on to the next talent amp.
For convenience, you may want to wire
your facility to allow easy access to the
talent amplifi er signal at all locations where
talent amplifi ers might be used. The tal-
ent amplifi ers connect to the Model 74 in
parallel, so the connectors on the distribution panels or mult boxes should be wired
in parallel.
Warning: Do not connect the Model
74’s talent amplifi er output to any-
thing but Studio Technologies’ talent
amplifi ers. Some audio equipment
may be damaged by the DC voltage
contained on pin 2 of the talent amplifi er output connector.
be useful for connecting with a remotely
located studio or production facility. Using
ISDN or IP-based technology, being able
to send audio signals to literally any part of
the world has become a fairly simple task.
The headphone cue signals are accessible
on one of the 25-pin D-subminiature connectors, located on the Model 74’s back
panel. Please refer to Figure 8 for details
on the exact “pin out” of the D-sub.
The line-level cue outputs are electronically balanced, capacitor coupled, and
intended to drive balanced or unbalanced
loads of 600 ohms or greater. While balanced operation is preferred, unbalanced
operation does not pose a problem. To
connect to an unbalanced load connect
the + terminal as signal high, and both the
– and shield as the signal low/shield.
Note that while the line-level cue outputs
are electronically balanced, signal is only
driven on the + connection. The – connection serves only as a signal-balancing
return path. This simplifi ed output circuit
was deemed appropriate for headphone
cue system applications. It provides good
audio quality even though its circuitry is not
as sophisticated as that used by the monitor output channels.
Included with each Model 35 Talent
Amplifi er is a nifty mounting adapter that
allows the unit to be conveniently attached
to a microphone stand. Please refer to the
documentation provided in the Model 35’s
shipping carton for details.
Line-Level Talkback Input
An alternate source of talkback audio can
be connected to the Model 74. This audio
source can be used instead of the microphone contained in the Model 75. A confi guration parameter selects which source
Line-Level Cue Output
A 2-channel (stereo) line-level output
provides access to the headphone cue
system signals. The line-level cue output
channel is intended for connection to
an audio amplifi er associated with a
is active.
The audio source should have a nominal
level of +4 dBu and can be balanced or
unbalanced. Pins on one of the 25-pin
D-subminiature connectors are used to
connect the signal. Refer to Figure 9
headphone cue system. It could also
Model 74/75 User Guide Issue 2, January 2006
Studio Technologies, Inc. Page 13
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for details. Balanced sources should be
wired so that signal high is connected to
+, signal low to –, and shield to the shield
connection. With an unbalanced source,
connect signal high to the + connection,
and shield to both the – and the shield
connections. If connecting to an unbalanced source in this manner results in
hum or noise, try connecting signal high to
+, and shield to –; leave the shield connection unterminated.
Remote Control Inputs
Pin Signal
1 Shield
2 Spare A (to Model 74)
3 Spare B (to Model 74)
5 Remote Mute All (to Model 75)
6 Remote Dim (to Model 75)
7 Remote Talkback (to Model 75)
8 Remote Input Select (to Model 75)
9 Remote Control Common (to Model 75)
Notes: 1) Connector type on Model 74 is 9-pin D-subminiature
female. Installer must provide plug (male). Connector
uses 4-40 threaded inserts for locking with mating plug.
Support is provided for four hard-wired remote control input functions: mute all, dim,
talkback, and remote input select. The inputs are “pulled up” to +5 volts DC by way
of resistors and are active when brought to
the logic low state. Inputs of this type are
commonly referred to as GPI inputs. While
the input circuitry is protected from overcurrent and static (ESD) discharge, care
should be taken to prevent nasty signals
from reaching them. The inputs are active
only when held in the low state; they can’t
be confi gured to change state (“latch”) in
response to a logic pulse.
A female 9-pin D-subminiature connector,
labeled Remote Control Inputs, is located
on the back panel of the Model 74. It is
used to interface with the four remote
control inputs. Refer to Figure 10 for exact
connection details. Note that pin 1 (shield)
and pin 9 (remote control common) are
electrically identical. In addition to connecting to system common, they connect to the
Model 74’s chassis and mains earth connection. For convenience, the shield of the
interconnecting cable should be connected
to pin 1 (shield), while the return signals of
the remote control sources should connect
to pin 9 (remote control common).
Figure 10. Connector Pin Out for Remote
Control Inputs
Note that although the remote control
connections are physically made to the
D-sub on the Model 74’s back panel, the
remote control input circuitry is actually
located in the Model 75 Control Console.
Conductors in the cable linking the Model
74 to the Model 75 route the remote control signals to the actual input circuitry.
Connecting the Model 74 to
the Model 75
A cable with 9-pin D-sub plugs (males) on
each end is used to interconnect the Model
74 Central Controller with the Model 75
Control Console. A cable, approximately
20-feet (6.1-meters) long, is provided with
each system. The connector labeled To/
From Control Console on the back panel
of the Model 74 is used to connect to the
Model 75.
Should a cable of different length be required, it should be wired in a one-to-one
fashion for all nine pins. Pin 1 serves as
signal common and must be connected
at both ends. A shield connection for the
Issue 2, January 2006 Model 74/75 User Guide
Page 14 Studio Technologies, Inc.
for Surround
Pin Signal Direction
1 Power Supply Common 74 to/from 75
2 +15 Volts DC 74 to 75
3 Data (MIDI System-Exclusive) 75 to 74
4 Data Common 74 to/from 75
5 Remote Mute All 74 to 75 (Note 2)
6 Remote Dim 74 to 75 (Note 2)
7 Remote Talkback 74 to 75 (Note 2)
8 Remote Input Select 74 to 75 (Note 2)
9 Talkback Mic Audio 75 to 74
Notes: 1) Connector types on Model 74 and Model 75 are
9-pin D-subminiature female. Connectors use 4-40
threaded inserts for locking with mating plug.
2) Remote control sources connect to D-sub on
Model 74, then passively route to Model 75 via
74/75 interface D-sub.
Figure 11. Connections between Model 74 and
Model 75
cable should also be connected to pin 1 on
the Model 74’s end. For best performance
the cable generally should not exceed 50
feet (15.3 meters) in length.
The reality is that a cable longer in length
than 50 feet should work correctly, as long
as an excellent-quality cable is utilized.
We defi ne “excellent” as extensive shield-
ing along with very low capacitance. The
low cable capacitance is important as it
limits the amount of data-signal waveform
distortion. As far as determining an actual
maximum length, just test and see how
far away you can go—if it works, it works!
A termination resistor connected from pin
3 to pin 4 at the Model 75’s end of the
interconnecting cable may help to support a longer cable “run.” The value of the
termination resistor should be in the range
of 3.3 k (3300) to 10 k (10000) ohms. A
commonly available ¼-watt, 5% tolerance
resistor is perfectly acceptable.
Infrared Remote Control Input
An infrared (IR) receiver module can be
directly connected to the Model 74. This
allows, with an appropriate IR transmitter,
wireless activation of the talkback function. The IR receiver connects to the Model
74 using a 3.5 millimeter 3-conductor jack
which is located on the back panel. The jack
complies with the standard convention for
IR receiver modules: data on the tip lead,
ground on the ring lead, and 12 volts DC
on the sleeve lead. Compatible modules
are available from a number of companies.
As an example, the Xantech® 291-80 looks
nice and works adequately. For excellent
performance under compact fl orescent light-
ing conditions the Russound® SaphIR 860
Phantom has proven its worth.
For correct wireless talkback operation
selecting and programming a compatible transmitter is necessary. Refer to the
Confi guration section of this user guide for
details.
AC Mains Power
The Model 74 is internally confi gured to
operate from an AC mains power source of
nominal 100, 120, or 220/240 volts, 50/60
hertz. Units shipped to North America are
factory selected for 120 volt operation. Units
bound for Japan must be selected for 100
volts, while our friends “down under” and
in Europe receive units set for 220/240
volts. Before connecting the Model 74 to
AC mains power, check that it is confi gured
to match the local mains voltage. Look on
the back panel (adjacent to the power entry
connector) for the factory-confi gured volt-
age. Note that an incorrect confi guration
could prevent operation, or cause damage to the unit. Should it be necessary to
change the unit’s operating voltage it must
Model 74/75 User Guide Issue 2, January 2006
Studio Technologies, Inc. Page 15
for Surround
be performed only at the factory or by a
competent service technician.
The Model 74 uses an IEC-320 C14compatible connector to mate with the
AC mains cord. The wire colors in the AC
mains cord should conform to the internationally recognized CEE color code and
must be wired accordingly:
Connection Wire Color
Neutral (N) Light Blue
Line (L) Brown
Protective Earth (E) Green/Yellow
Safety Warning: The Model 74 does
not contain an AC mains disconnect
switch. As such, the AC mains cord
plug serves as the disconnection
device. Safety considerations require
that the plug and associated outlet
be easily accessible to allow rapid
disconnection of AC mains power
should it prove necessary.
operating parameters of the system should
be set using the Model 75 Control Console’s confi guration mode.
Level Calibration
Sixteen 15-turn trim potentiometers are
located on the front panel of the Model 74
Central Controller. Taking time to carefully adjust the trim pots will ensure that
accurate monitoring can take place. Each
trim pot allows input signals with a nominal
level of –12 dBV to +6 dBu to be utilized.
With care, it’s easy to calibrate the surround and stereo inputs to within onequarter of a dB of the desired value.
The monitor outputs are used as the
measuring point when adjusting the trim
pots. A laboratory-grade audio level meter or equivalent is required for accurate
calibration. In addition, the audio sources
connected to the inputs must be able to
generate continuous audio signals at their
nominal operating level.
As soon as AC mains power is applied, the
Model 74’s power present LED will fl ash
for a few seconds. After the completion of
a software startup interval the power present LED will light steadily. The data active
LED on the Model 74 will fl ash once upon
power up, then briefl y light upon comple-
tion of the Model 75’s power-up sequence.
The Model 75 will go through its own
power-up sequence, lighting each LED in
secession.
Confi guration
After the physical installation has been
completed, several confi guration issues
must be addressed. On the Model 74 the
surround and stereo inputs must be calibrated using the trim potentiometers. The
Issue 2, January 2006 Model 74/75 User Guide
Page 16 Studio Technologies, Inc.
Procedure
This procedure will calibrate the surround
and stereo input channels. The trim pots
will be adjusted in groups corresponding
to their associated input sources.
1. Begin by turning the audio amplifi ers
or amplifi ed speakers to their off state.
This will protect the loudspeakers and
the operator’s ears from possible
damage.
2. Rotate the level control on the Model
75 to the fully clockwise (maximum)
position.
3. Using the Model 75 Control console,
select Surround A as the input source
and Speaker System A as the selected
monitor output.
for Surround
4. On the Model 74, connect the audio
level meter to the left channel of monitor output A.
5. Confi rm that the audio source’s left
channel is generating a steady signal
at precisely its reference level.
6. Observing the level meter, adjust
Surround A, trim pot L, to give a precise +4 dBu level at the left channel
output of monitor output A.
7. Disconnect the level meter from the
left channel of the monitor output.
8. Repeat steps 4-7 for the right, center,
LFE, left surround, and right surround
channels of Surround A.
9. Repeat steps 3-8 for Surround B,
Stereo A, and Stereo B. Obviously, the
stereo inputs have only left and right
channels, requiring only that two trim
pots be adjusted for each.
10. After the calibration procedure has
been completed, rotate the level control on the Model 75 to the fully counterclockwise (minimum) position.
11. After ensuring that the Model 75’s level
control is set to minimum, return AC
mains power to the power amps or
amplifi ed speakers.
Model 75 Operating Parameters
Many StudioComm functions can be confi gured to meet the exact needs of your
installation. Here’s an overview of what
you can confi gure:
• Input channels active
• Speaker systems/monitor outputs
• Talkback
• Solo
• Power-up mute all
• Level control response
• Level control audio mute all
• Reference level
• Remote input select
• Dim level
• Remote mute all
• Remote dim
• Remote talkback
• Auto dim off
• Talkback dim
• Mono
The Model 75 confi guration diagrams,
located at the end of this section, give
details on how each parameter is set. An
overview of each confi gurable parameter
is provided in the following paragraphs.
Entering and Exiting the Confi guration
Mode
A small button is located on the back of
the Model 75 Control Console, adjacent
to the 9-pin D-sub connector. Pressing
and holding this button for two seconds
places the Model 75 into the confi guration
mode. In the confi guration mode the Model
75’s array of buttons and LEDs no longer
perform their normal functions, but instead
allow you to observe and change many of
the operating parameters. The mute/solo
mode LEDs light alternately to indicate that
the confi guration mode is active.
To leave the confi guration mode and
return the Model 75 to normal operation,
once again press and hold the confi gure
button for two seconds. Note that confi gu-
ration changes are stored only after the
confi guration mode has been exited.
Model 74/75 User Guide Issue 2, January 2006
Studio Technologies, Inc. Page 17
for Surround
Our apologies to those of you who fi nd the
confi gure button a pain to use, but it’s sup-
posed to be that way! Seriously, the top
of the button is slightly recessed from the
back panel, making it harder to accidentally activate. We didn’t want normal operation to cease because someone pushed
the Model 75 into a “rats nest” of music
scores or track sheets!
There is no problem frequently “tweaking” the Model 75’s operating parameters
to achieve the desired performance. The
confi guration data is stored in nonvolatile
memory, which is rated for thousands of
read and write cycles and a retention time
in tens of years.
Input Channels Active
This confi guration is a bit tricky to un-
derstand, but is really quite simple. The
confi guration parameter for the number of
channels active for each input is provided
for those special cases where a source
has less channels than its usual, e.g., less
than six for Surround A or B.
Let’s look at an example. Surround A
is connected to a 6-channel source, so
its default confi guration is fi ne. But the
source for Surround B is special, having
only three channels: left, center, and right.
This makes it not so “cool” for the operator to select Surround B for monitoring, as
the unconnected left surround, right surround, and LFE channels will get routed to
their respective monitor outputs. Will the
unused input channels pick up signifi cant
noise or hum? Unlikely, but why take a
chance at having a problem. Simply use
the input channels active confi guration
function to disable the three unused channels. Now when Surround B is selected,
only the appropriate channels are selected
for monitoring.
Note that when a channel associated with
an input is disabled the input routing circuitry, under software control, no longer
selects it, but the corresponding monitor
output channel does not mute. With our
example, when selecting Surround B, our
mythical L/C/R source, all selected monitor
output channels will remain active, but the
input routing circuitry won’t enable the LS,
RS, and LFE inputs. While to some people
this might seem confusing and possibly a
design fault, it was implemented this way
because the StudioComm system allows
multiple inputs to be simultaneously selected for monitoring; a surround source might
be selected at the same time as a stereo
source. Muting the outputs in response to
a single input channel being selected simply would not do!
A special mode has been included to
disable an input from being accessed by
the operator. This might be useful, for
example, when Stereo B is not connected
to a source, and has no valid reason to
be selected. This might also be useful
when connecting a special source, such
as a house “tie line” or router output, that
shouldn’t normally be accessible. Disabling
an input is simple to perform, just disable
all channels associated with it; six for Surround A and B, two for Stereo A and B. To
confi rm that an input has been disabled, all
LEDs associated with that input will fl ash
on and off. Once the Model 75 is returned
to the normal operating mode the disabled
input cannot be selected.
Speaker Systems/Monitor Outputs
The confi guration parameters associated
with the speaker system selection button
and monitor output channels offer an extremely powerful resource. With just a few
button presses a wide range of monitor
system implementations can be easily
Issue 2, January 2006 Model 74/75 User Guide
Page 18 Studio Technologies, Inc.
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