CBS laboratories Audimax 4450 Installation and operating instructions

CBS Audimax 4450
Installation, Operation, and Maintenance
CBS Laboratories
Professional Products
Stamford, Connecticut 06905

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Installation, Operation, and Maintenance Manual
This manual is based on the CBS Laboratories manual, “CBS Audimax Models 4440A, 4450A Au-
tomatic Level Control—Operating and Maintenance Instructions,” produced by the Professional
Products Division, CBS Laboratories, Stamford, Connecticut 06905, August 1972. Copyright CBS
Laboratories, Inc.

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CBS Audimax 4450A Automatic Level Control
Table of Contents
1 General Description 7
1.1 Introduction 7
1.2 Functional Description 7
1.3 Physical Description 7
1.4 Specifications 8
2 Installation Procedures 9
2.1 Signal Connections 9
3 Operational Setup 11
3.1 Gated Gain Stabilizer 12
3.2 Test Switch 13
3.3 Decay (Recovery) Time Switch 13
4 Principles of Operation 15
4.1 Overall System Operation 15
4.2 Circuit Description 18
4.2.1 Gated Gain Stabilizer 23
4.2.2 Functional Graphs 23
4.2.3 Power Supply 26
4.2.4 Test Switch and Meter 26
4.2.5 Stereophonic Operation 26
4.3 Parts List 27
5 Maintenance and Adjustments 31
5.1 Quick Overall Check 31
5.2 Electrical Alignment Procedure 31
5.3 Troubleshooting Suggestions 32
5.3.1 Input/Output Circuits 33
5.3.2 GGS and Logic Circuits 33
5.4 Measured Performance 34

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Installation, Operation, and Maintenance Manual
Index of Tables
Table 1.1 Specifications for the Auximax 4450 8
Table 3.1 GGS Threshold Values for R63 and R64 12
Table 3.2 Decay Time Settings 13
Table 4.1a Parts List for the Audimax 4450 Input/Output Board 27
Table 4.1b Parts List for the Audimax 4450 Power Supply/Logic Board 28
Table 4.1c Parts List for the Audimax 4450 Chassis 29

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CBS Audimax 4450A Automatic Level Control
Index of Figures and Traces
Figure 2.1 Installation guidelines for the Audimax 4450. (Source: CBS Labs.) 10
Figure 3.1 Front panel layout of the Audimax 4450. (Source: CBS Labs.) 12
Figure 4.1 Audimax 4450 overall block diagram. (Source: CBS Labs.) 16
Figure 4.2 Audimax 4450 system interconnections. (Source: CBS Labs.) 17
Figure 4.3 Schematic diagram of the audio input/output board (A1, A3). (Source: CBS Labs.) 19
Figure 4.4 Circuit board layout of the audio input/output board (A1, A3). (Source: CBS Labs.) 20
Figure 4.5 Schematic diagram of the power supply/logic board (A2). (Source: CBS Labs.) 21
Figure 4.6 Circuit board layout of the power supply/logic board (A2). (Source: CBS Labs.) 22
Figure 4.7 Audimax 4450 gain characteristic curves. (Source: CBS Labs.) 24
Trace 5.1 Audimax 4450 frequency response. The left channel is shown in blue, the right channel
is shown in green. 35
Trace 5.2 Audimax 4450 THD+N. The left channel is shown in blue, the right channel is shown in
green. 35
Trace 5.3 Audimax 4450 input/output phase (left channel). 36
Trace 5.4 Audimax 4450 interchannel phase. 36
Trace 5.5 Audimax 4450 crosstalk. The left channel is shown in blue, the right channel is shown
in green. 36

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Installation, Operation, and Maintenance Manual

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CBS Audimax 4450 Automatic Level Control
1 General Description
1.1 Introduction
The Audimax 4450A, like the CBS Laboratories Volumax companion unit, is a tool to help the
broadcaster achieve maximum audio program power within appropriate modulation limits.
Designed for use wherever high-quality automatic-gain control is necessary, the 4450 provides a
unique means of audio-signal control for AM, FM, and TV broadcasting, sound recording,
motion-picture sound, and public address systems.
1.2 Functional Description
The Audimax is totally different in concept from ordinary compressors, limiters, or AGC
(automatic gain-control) devices. Two features unique to the Audimax are the gain platform and
the gated gain stabilizer.
The exclusive gain platform principle permits gain to remain on a stable plateau over a wide
range of input levels rather than continuously being allowed to rise and fall with consequent
distortion, thumping and pumping, and audio “holes.” The unique gated gain stabilizer bridges
program lapses and thus eliminates the “swish-up” of background noise. A special return-to-zero
function returns gain to normal during standby conditions.
Both the gain platform and the gated gain stabilizer use logic techniques to make processing
decisions based on the incoming signal. Thus, the Audimax is not just another AGC amplifier, but
a sophisticated processing device that eliminates the drawbacks of conventional units.
The Audimax principles apply not only to radio and television stations, but also are valuable
in recording, public address, background music, and two-way communication systems.
1.3 Physical Description
The Audimax Model 4450A is a slim, neat packages designed for standard rack mounting. The
unit has an illuminated front-panel dB meter and a few simple controls that seldom require
resetting. The overall dimensions are 19 inches wide, approximately 1-3/4 inches high, and
approximately 15-1/2 inches deep. The Model 4450 weighs 9.5 pounds. The unit operates from a
nominal 115 V ac 60 Hz single-phase power source. It requires 30 watts.
Input/output signal connections are made at a pair of connectors on the rear panel. The basic
front-panel controls consist of the following:
• An ac POWER ON–OFF switch.
• INPUT signal-level adjustment potentiometer.
• OUTPUT signal-level adjustment potentiometer.
(Source: CBS Labs.)

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Installation, Operation, and Maintenance Manual, General Description
• CONTROL ON–OFF switch that permits the Audimax channel (left or right) to be
operated as a linear amplifier when automatic gain control is not desired.
• TEST switch for maintenance checks.
The internal components of the Model 4450A consist of an ac power transformer, two audio
output transformers, and three easily accessible transistor circuit boards. Two of the boards
contain the input, amplification, and output circuitry, and much of the feedback and logic circuitry
used for the left and right audio channels. The third board contains the Audimax dc power supply
and the remainder of the audio feedback and logic circuitry.
1.4 Specifications
Typical specifications for the CBS Audimax 4450 are given in Table 1.1.
Table 1.1 Specifications for the Auximax 4450
Parameter Value
Control characteristic ± 10 dB of gain control
Frequency response ±0.5 dB from 50 Hz to 15 kHz
Harmonic distortion Less than 0.5% from 50 Hz to 15 kHz at + 16 dBm output
Signal-to-noise ratio Greater than 70 dB, with normal gain
Gated gain stabilization Threshold adjustable from –20 dB to normal input
Maximum gain 40 dB
Input and output impedances 600 ohms or 150 ohms, balanced or unbalanced
Minimum input level –25 dBm
Normal output level +16 dBm, sine wave
Maximum output level +26 dBm
Maximum operating temperature +55° C
Physical dimensions Standard 19" rack mounting, 1-3/4" high, 11" deep except for cable and connectors
Power requirements 30 watts at 115 V ac, 60 Hz

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CBS Audimax 4450 Automatic Level Control
2 Installation Procedures
The Audimax 4450 is designed to be mounted in a standard 19-inch electronic equipment rack or
19-inch-wide console opening. The mounting dimensions are shown in Figure 2.1. Install the unit
in a reasonably well-ventilated position, making sure there is no high-heat producing equipment
located beneath it. The ambient temperature should not exceed 130° F.
For broadcast station applications, it is recommended that the Audimax 4450 be installed in a
studio and its output fed directly into the main audio line. Satisfactory operation requires that the
unit be presented with a constant 600 or 150 Ω impedance throughout the audio band. A 6 dB 600
Ω pad is provided at the output for isolation purposes.
A fast-acting peak limiter is recommended for use at the transmitter (following the Audimax
4450). However, this peak limiter should be set to provide only occasional limiting of 5 to 6 dB.
The Audimax 4450 is equipped with a power transformer that permits the selection of either
115 V or 230 V ac operation. If 230 V operation is required, the following procedure must be
performed:
1) Unsolder and remove the black/white lead from terminal 4 of TB1 (see Figure 7.1). TB1 is the
terminal strip adjacent to the power transformer.
2) Unsolder and remove the brown lead from terminal 3 of TB1.
3) Connect these two leads to terminal 1 of TBl.
4) Unsolder and remove the white lead from terminal 4 of TB1 and connect it to terminal 1 of
TB1.
2.1 Signal Connections
Input and output leads should be soldered to the connector strips at the rear of the chassis. The
connector pin-out is as follows:
• Input (+) = 1
• Input (–) = 2
• Shield = 3
• Ground = 4
• Output (+) = 5
• Output (–) = 6
• Shield = 7
• Ground = 8
Connections are identical for the left and right channels.

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Installation, Operation, and Maintenance Manual, Installation Procedures
Figure 2.1 Installation guidelines for the Audimax 4450. (Source: CBS Labs.)