Studio Technologies 42A Manual de usuario

www.studio-tech.com

50127-1213, Issue 2

User Guide

Issue 2, December 2013

This User Guide is applicable for serial numbers M42A-01051 and later

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Model 42A User Guide Issue 2, December 2013

Studio Technologies, Inc. Page 3

Table of Contents

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

Installation ..................................................................... 8

Post-Installation ............................................................. 12

Operation ...................................................................... 13

Troubleshooting ............................................................ 16

Technical Notes ............................................................. 18

Speciﬁcations ................................................................ 22

Appendix A .................................................................... 23

Block Diagram

Issue 2, December 2013 Model 42A User Guide

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Model 42A User Guide Issue 2, December 2013

Studio Technologies, Inc. Page 5

Introduction

The Model 42A is designed to create

broadcast-standard IFB outputs from line-

level audio sources. The unit’s primary

application is to interface analog outputs

associated with digital matrix intercom sys-

tems with broadcast IFB user devices. The

Model 42A creates four independent IFB

outputs. For convenience, the four outputs

can be connected by way of eight 3-pin

male XLR connectors; four of which are

located on the back panel and four on the

front. Each IFB output provides DC power

and two analog audio signals to support

the connected IFB user devices. The Model

42A’s audio quality is excellent; little hiss,

hum, or other artifacts are present. To

ensure optimal operation, the unit provides

resources for visually and audibly monitor-

ing the audio output signals. In addition,

the DC output voltage is monitored for fault

conditions.

Installation of the Model 42A is very simple.

Audio input connections are made using

a 25-pin D-subminiature connector. The

IFB output circuits interface using standard

3-pin XLR connectors. The compact, one-

rack-space package is constructed using

rugged steel and aluminum components.

Figure 1. Model 42A Interface front and back views

The unit’s AC mains power input can range

from 100 to 240 volts, 50/60 hertz. This

“universal input” ensures correct operation

virtually anywhere in the world.

There may be persons not familiar with the

term IFB. That’s not unreasonable as it’s a

somewhat obscure acronym for interrupt-

ible foldback. On its own, the term foldback

is an alternate way of describing a cue or

monitor function. Adding “interruptible”

before it means that the cue source can be

temporarily replaced with an audio signal

originating from a producer, director, or

other production personnel. IFB outputs

are often used in the broadcast industry

for talent cueing applications, both in

studio and ﬁeld settings.

Both “dry” and “wet” IFB outputs can

be deployed and their characteristics

are worth reviewing. The term “dry” IFB

typically refers to a transformer-balanced

line-level audio circuit with a nominal level

in the range of 0 to +8 dBu. This is essen-

tially a standard analog audio circuit that

is commonly used to interconnect audio

equipment. The term “wet” IFB refers to a

circuit that combines DC power and one

or two channels of analog audio. The DC

power source is typically in the range of

Issue 2, December 2013 Model 42A User Guide

Page 6 Studio Technologies, Inc.

30 to 32 volts. The audio is unbalanced

with a typical nominal level of –10 dBu. The

Model 42A implements “wet” IFB outputs.

As such, in this user guide the term IFB will

always indicate this type of circuit.

IFB outputs provide an effective means of

delivering power and two channels of audio

to user devices by means of standard au-

dio cables. These cables, ubiquitous to the

audio industry, interface using 3-pin male

and female XLR connectors. Using IFB

outputs and standard audio cables it’s a

simple matter to support user devices such

as listen-only beltpacks and announcer’s

consoles with no external power source

required. Whether the IFB source and user

devices are 100 or 1000 feet apart, reliable

operation can almost always be provided.

In many cases, the Model 42A Interface will

be used in on-air television applications.

Whether installed in a ﬁxed location or as

part of a mobile facility, the unit is capable

of providing excellent performance. In

addition, the Model 42A can be used for

non-broadcast applications. For example,

audio recording and post-production facili-

ties can also effectively use the Model 42A.

Combined with stereo or mono listen-only

beltpacks, also available from Studio Tech-

nologies, a variety of headphone cue sys-

tems can easily be deployed. And since the

Model 42A’s audio inputs are compatible

with standard line-level audio signals virtu-

ally any analog source can be connected.

Four Independent IFB Outputs

The Model 42A supplies four independent

IFB outputs. Each circuit consists of two

audio inputs and a 2-channel “wet” IFB

output. The audio inputs are transformer

coupled, have a nominal level of +4 dBu,

and are compatible with balanced or

unbalanced sources. In on-air television

broadcast applications the audio sources

will often be analog outputs from matrix

intercom systems. Two sources are typi-

cally designated to serve as a 2-channel

user cue signal. Generally one source is

conﬁgured in the matrix intercom system

as “interrupt” while the other is conﬁgured

as “program.” An alternate term often used

for the “interrupt” channel is “program-

with-interrupt.” This may be more descrip-

tive as the function is actually a program

source that gets interrupted with talkback

audio. The “program” channel is typically

a continuous source of program audio.

An alternate term is “program-only.”

For other applications, the Model 42A’s

audio inputs can be connected to a

2-channel or stereo audio source. This

conﬁguration may prove useful in radio

broadcasting, audio-with-picture, or re-

cording studio applications. The speciﬁc

application will dictate whether both cue

signals will be utilized by the end user.

In on-air sports broadcast situations a

“double-muff” (stereo) headset will provide

a user with both audio channels, one for

each ear. In interview or news-gathering

applications it’s common to use a single

“earpiece” to provide a user with only

program-with-interrupt audio.

Maintaining excellent audio performance

was a major Model 42A design goal—the

hiss, hum, and noise associated with typi-

cal IFB outputs was simply not acceptable.

The Model 42A meets those requirements

with audio that is “on-air” quality: low

distortion, high signal-to-noise ratio, and

ample headroom. On-air talent and guests,

production personnel, and technicians will

all appreciate the clean, quiet cue signals.

Model 42A User Guide Issue 2, December 2013

Studio Technologies, Inc. Page 7

The Model 42A’s IFB outputs provide

power and two channels of unbalanced

audio over a single 3-conductor output.

The output power is 30 volts DC with a

maximum current of 220 milliamperes. A

major strength of the Model 42A is the IFB

output’s ability to effectively deliver DC

power over a variety of conditions. Unlike

other interface devices that use a com-

mon but less-than-ideal circuit topology, a

unique IFB output circuit was developed

by Studio Technologies to achieve the

desired performance goals. The result is a

major improvement in effectively support-

ing IFB user devices over a wide range of

conditions. Connected devices can draw

up to the maximum 220 milliamperes of

current with little drop in DC voltage. This

output voltage stability is the key—wheth-

er drawing 50, 100, or 200 milliamperes,

the output will remain close to 30 volts.

In practical terms this means that reliable

IFB-based cue systems can now be de-

ployed in more stadiums, concert halls, or

motor racing facilities than was previously

possible—longer cable runs, more user

devices, excellent performance.

Audio Monitoring

To help conﬁrm proper installation and

ensure correct operation, the Model 42A

includes a full-featured audio monitor sec-

tion. Two 5-segment LED meters provide

an indication of the audio levels as they

appear directly on the IFB output connec-

tors. This capability makes it simple to

adjust and maintain correct audio levels

so that optimal IFB performance can be

achieved. A headphone output is also pro-

vided, allowing “real world” checking of

IFB audio quality. In addition to being able

to manually select the IFB output to be

monitored by the meters and headphone

output, an “auto scan” mode is also in-

cluded. This allows each of the four IFB

outputs to be monitored in a continuously

repeating sequence.

DC Monitoring and Fault

Shut Down

To prevent possible damage to the Model

42A’s output circuitry and connected user

devices, the DC output voltage present

on pin 2 of each IFB output is continually

monitored. If the voltage on an IFB output

falls below 24 volts its associated LED will

“ﬂash” as an error indication. If this under-

voltage condition continues for more than

four seconds a shut down mode will be

entered, turning off power to the IFB out-

put. After a 10-second interval the output

will again become active.

Compatibility

The Model 42A is compatible with virtu-

ally every digital matrix intercom system,

including those from Clear-Com®, RTS®,

and Riedel®. Interfacing requires only the

connection of analog output ports from

the intercom system to the Model 42A’s

audio inputs. Optimal performance will be

gained by conﬁguring the nominal audio

level of the intercom system’s “virtual” IFB

output ports to match the Model 42A’s

nominal +4 dBu input level. With the

Model 42A’s excellent audio and power

delivery performance it’s an ideal alterna-

tive to the interface devices offered by

the intercom system vendors. Using the

Model 42A the intercom system’s audio

quality can be maintained all the way to

the IFB users.

The Model 42A’s IFB outputs allow

virtually every type of IFB user device

to be supported. These include the

Issue 2, December 2013 Model 42A User Guide

Page 8 Studio Technologies, Inc.

Models 32A, 33A, and 34 listen-only belt-

packs and Model 200-Series announcer

console products from Studio Technolo-

gies. The 30-series units offer a range of

features while providing excellent audio

performance. The 200-series units com-

bine a variety of microphone control,

headphone monitoring, IFB and intercom

system interfacing, and related functions

into compact desktop units. Legacy

listen-only beltpacks from RTS, including

the 4020 and 4030, can also be directly

supported.

Alternate Applications

In addition to broadcast intercom applica-

tions, the Model 42A can be used to cre-

ate high-performance stereo headphone

cue systems. Line-level signals coming

from an audio console, a routing switcher,

or an off-air receiver can be connected

to the Model 42A’s audio inputs. The IFB

outputs can be connected to listen-only

beltpacks, several models of which are

available from Studio Technologies. For

example, the Model 35 Talent Ampliﬁer

will allow one or two pairs of stereo

headphones to be supported. Each of

the Model 42A’s four IFB output circuits

will support up to six Model 35 Talent

Ampliﬁers.

Installation

In this section you will be installing and

interconnecting the Model 42A. The one-

rack-space unit will be mounted in

an equipment rack. Audio input connec-

tions will be made by way of a 25-pin

D-subminiature connector. IFB outputs

will be interfaced using four 3-pin XLR

connectors. AC mains power will be

connected by means of a detachable

cord that is compatible with the Model

42A’s 3-pin IEC 320 C14 inlet connector.

System Components

The shipping carton contains the Model

42A Interface and associated user guide.

Units are also supplied with an AC mains

cord that has a North-American (NEMA

5-15P) standard plug on one end and an

IEC 320 C13 connector on the other end.

Units bound for other destinations may

require a different cord set; your dealer

or distributor should provide one.

Locating the Model 42A

The Model 42A’s IFB outputs provide DC

power and unbalanced audio to operate

external IFB user devices. These devices

are often IFB “beltpacks,” broadcast

announcer consoles, or other “talkback

boxes.” The Model 42A’s mounting loca-

tion will dictate the length of the cable

runs needed to link the unit with the con-

nected devices. In some cases the loca-

tion choice is already established. For

example, in mobile broadcast applica-

tions the Model 42A will almost always be

located in a production truck or trailer. But

in ﬁxed applications it may be possible to

select the Model 42A’s mounting location

so as to minimize cable length. In general,

shorter cables will lead to more reliable

and consistent system performance. It’s

also helpful if a technician can readily view

and access the monitor section that is lo-

cated on the right side of the Model 42A’s

front panel. The output status LEDs and

levels meters can serve important roles

in ensuring correct IFB output operation.

Access to the headphone output jack and

level control can also be useful.

Model 42A User Guide Issue 2, December 2013

Studio Technologies, Inc. Page 9

Mounting the Model 42A

Once the desired mounting location has

been selected, the Model 42A will require

one space (1U or 1.75 vertical inches) in

a standard 19-inch (48.3 cm) equipment

rack. Secure the unit into the equipment

rack using two mounting screws per side.

Audio Input Connections

The Model 42A has eight line-level audio

inputs, arranged as four 2-channel pairs.

Each pair serves one of the four IFB out-

puts. Each IFB output, along with its two

associated audio inputs, is completely

independent. Literally any analog audio

source with a nominal operating level

in the area of +4 dBu can be success-

fully connected. Transformer coupled,

the inputs are compatible with balanced

or unbalanced signals. In many applica-

tions the analog outputs from digital matrix

intercom systems will be connected to the

Model 42A’s audio inputs.

For on-air television applications the IFB

sources are generally conﬁgured to pro-

vide a single- or dual-channel cue “feed”

to talent personnel. In such cases chan-

nel 1 of a pair is generally designated as

the “interrupt” channel while channel 2 is

the “program” channel. For other broad-

cast applications, such as live radio, it’s

Figure 2. Detail of back panel showing 25-pin D-subminiature

connector used for audio inputs

possible that a stereo cue source will be

connected. In this situation the left source

would be connected to input channel 1

while the right source would be connected

to input channel 2. This might also be

the case with other professional audio

applications, such as recording and

post-production.

Audio input connections are made by way

of one female 25-pin D-subminiature con-

nector which is located on the Model 42A’s

back panel. A cable harness is required

with a 25-pin D-sub plug (male) on one

end and the desired mating connector(s)

on the other. This cable harness is not sup-

plied by Studio Technologies. (Note that in

some locations the term “cable loom” may

be used instead of “cable harness.”) The

wiring scheme used by the D-sub complies

with the now-ubiquitous one made familiar

by TASCAM® with their DA-88® product.

A wiring harness prepared for connection

to the Model 42A’s audio inputs is identical

to a DA-88-style input harness. Please refer

to Figures 3 and 4 for connection details.

Note that unlike a DA-88-style harness, the

Model 42A’s D-sub connector’s hold-down

screws use 4-40 threads. This complies

with the original design standard for D-

subminiature connectors which used

English rather than metric thread pitch.

Issue 2, December 2013 Model 42A User Guide

Page 10 Studio Technologies, Inc.

The Model 42A’s audio inputs have a

nominal signal level of +4 dBu. They are

transformer coupled, have an impedance

of 10 k ohms, and are compatible with

balanced or unbalanced sources. A bal-

anced source should be wired so that sig-

nal high is connected to the + pin, signal

low to the – pin, and shield to the shield

pin. With an unbalanced source, connect

signal high to the + pin, and shield to both

the – and the shield pins. If connecting an

unbalanced source in this manner results

in hum or noise, try connecting signal high

to the + pin, and shield to the – pin; leave

the shield pin unterminated.

As previously mentioned, the Model 42A is

compatible with matrix intercom systems

from Riedel. Appendix A, located near the

end of this user guide, provides detailed

connection information.

IFB Outputs

The Model 42A’s four independent IFB

outputs each supply DC power and two

channels of unbalanced audio. The IFB

outputs are designed to connect to a vari-

ety of devices that conform to the broad-

cast IFB standard. In this implementation

pin 1 is used for a combination of shield,

DC power return, and audio common;

pin 2 supplies a combination of DC power

and one channel of unbalanced audio;

pin 3 supplies a second channel of unbal-

anced audio. The DC power supplied on

pin 2 is 30 volts with a maximum current

of 220 milliamperes. The audio superim-

posed on the DC power has a nominal

signal level of –10 dBu. Its audio source

is the channel 1 audio input associated

with that speciﬁc IFB output. The audio

Signal Signal

Connections High (+) Low (–) Shield

IFB Output 1-Channel 1 24 12 25

IFB Output 1-Channel 2 10 23 11

IFB Output 2-Channel 1 21 9 22

IFB Output 2-Channel 2 7 20 8

IFB Output 3-Channel 1 18 6 19

IFB Output 3-Channel 2 4 17 5

IFB Output 4-Channel 1 15 3 16

IFB Output 4-Channel 2 1 14 2

Notes:

1) Connector type on Model 42A 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-style wiring harnesses are directly

compatible, with the exception of 4-40 screw threads being

required.

Figure 4. Connections for audio inputs using

dual-channel nomenclature

Signal Signal

Connections High (+) Low (–) Shield

IFB Output 1-Interrupt 24 12 25

IFB Output 1-Program 10 23 11

IFB Output 2-Interrupt 21 9 22

IFB Output 2-Program 7 20 8

IFB Output 3-Interrupt 18 6 19

IFB Output 3-Program 4 17 5

IFB Output 4-Interrupt 15 3 16

IFB Output 4-Program 1 14 2

Notes:

1) Connector type on Model 42A 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-style wiring harnesses are directly

compatible, with the exception of 4-40 screw threads being

required.

Figure 3. Connections for audio inputs using

IFB nomenclature

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