THOMSON AUDIMAX 4440A Manual

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AUDIMAX
Models 4440A, 4450A
Automatic Level Control
OPERATING AND MAINTENANCE INSTRUCTIONS
THOMSON-CSF LABORATORIES,INC.
MAY 1 975
37 Brownhouse Road, Stamford. Conn 06902 • [phone]

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TABLE OF CONTENTS
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Page No.
SECTION I INTRODUCTION
1-1
General
1-1
1-2
Functional Description
1-1
1-3
Physical Description
1-2
1-4
Warranty
1-4
1-5
Factory Service and Repari
1-4
1-6
Specifications
1-4
SECTION II INSTALLATION PROCEDURES
2-1 Unpacking
2- 1
2-2
Physical Installation
2-1
2-3
Power Sot1 rce
2-3
2-4
Signal Connections
2-4
SECTION III
OPERATIONAL SET - UP PROCEDURE
3-1
Level Adjustments
3-1
• 3-2
Variations from Standard Operating Procedw-es
3-3
3-3
Gated Gain Stabilizer
3-3
3-4
Test Switch
3-5
3-5
De cay (Recovery) Time Switch 3-5
3-6
Modification of Monaw-al Unit to Stereo Unit
3-6
SECTION IV THEORY
OF OPERATION
4-1
General
4-1
4-2
Block Diagram Theory
4-1
4-3
Circuit Operation
4-4
4-4
Gated Gain Stabilizer ( GGS}
4-5
4-5
Functional Graphs
4-7
4-6
Power Supply 4-10
4-7
Test Switch and Meter
4-11
4-8 Stereophonic Operation
4-11
SECTION V MAINTENANCE
5-1
General
5-1
5-2
Quick Overall Check
5-1
• 5-3
Electrical Alignment Procedure 5-3

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SECT ION V (Cont)
5-4
5-5
SECTION VI
SECTIONVIl
Figure
1-1
2 -1
3-1
4 -1
5-1
5-2
7-1
7-2
7-3
TABLE OF CONTENTS (Cont)
Troubleshooting Suggestions
Transient Performance
PARTS LIST
DRAWINGS
LIST OF ILLUSTRATIONS
Audimax M0dels 4440A
and 4450A
Au
dimax Model 4440A or 4450A,
Outline
Drawin g
Audimax Unit, Front Panel Controls
Audimax Block Diagram
Audimax Ci rcui t Boards and Th ei r Locations
Idss Bench Test Circuit for TlS58 (Grn
Stripe) Replac ement of A2Q4
Audimax Unit,
Internal Int erconnec tions
Input/ Output Board Al or A3, Schematic
Dia gram and Parts Lo cations
Power Supply and Logic Board A2,
Schematic Diagram and Parts Locations
Page No.
5-5
5-14
6-1
7-1
1-0
2-2
3-0
4-0
5-0
5- 10
7-2
7-3
7-4
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INTRODUCTION •
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AUOIMAX 4440A
A. Model 4440A (Monaural)
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--- --
B. Model 4450A (Stereophonic)
Figure 1-1. Audimax Models 4440A and 4450A •
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1-1. GENERAL
SECTIONI
INTRODUCTION
The Audimax@ Models 4440A and 4450A, like their Thomson-CSF
Laboratories Volumax@ companion piece, are tools to help the broad -
caster achieve maximum audio program power within appropriate modulation
limits . Designed for use wherever high quality automatic-gain riding is
necessary, either model is a unique means of audio signal control for AM,
FM, and TV broadcastii1g, sound recordings, motion picture sound tracks,
and public address systems .
The Model 4440A is a single-channel unit for monaural service. The
Model 4450A is a dual-channel unit for stereophonic service. Model 4450A
units can be obtained either in factory assembled form or by field modifica -
dons of Model 4440A units. A field modification kit for this conversion is
available from Thomson -CSF Laboratories, Inc.
1-2. FUNCTIONAL DESCRIPTION
The Audimax
automatic level control is wholly different in concept
from ordinary compressors, limiters, or AGC devices. Two features which
are unique to the Audimax design 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 contjnuously being allowed
to rise and fall with consequent distortion, thumping and pumping, and audio
1- 1

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INTRODUCTION
"holes". The unique gated gain stabilizer bridges program lapses and thus
eliminates "s wish-up" of background noise. A special return - to-zero
function re turns gain to normal during standby co nditions.
Both the gain platform and the gated gain stabilizer us e logic c ircuits
to make processing decisions based on the incoming signal. Thus the Audi-
max is not just another AGC amplifier, but a sophisticated processing device
that eliminates the drawbacks of conventional units.
Th e Audimax princip les 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
Th e A udimax Mod els 4440A and 4450A ar e slim, neat packages de-
signed for standard rack mounting. Each has a front-panel gain reduction
meter and a few simple controls that seldom requir e resetting . Thr ee co n-
trols on th e left-hand side of the front pane l of either model are duplicated
on th e right-hand side of the stereo-model front pan el for the additional audio
channel. (The
right-hand side of the 4440A front panel is blank.) (See figure 1-1.)
Th e overall dimensions of eit her model are 19 inches wide x approxi-
mately 1-3/4 inch es high x approximately 15 inches deep . Th e Model 4440A
weighs 8. 5 pounds
and th e Model 4450A weighs 9. 5 pounds.
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INTRODUCTION
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Either model operates from a nominal 115v or 230v, !iO or 60 Hz sing l e-
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phase power source. The Model 4440A requires 10 watts and the Model 4450A
requires 15 watts. A 6-foot ac power cord with a thr ee - prong grounding plug
is supplied as a part of each unit.
Signal connections are made at a barrier strip on the rear panel.
The basic front-panel controls consist of an ac POWER ON-OFF switc h,
INPUT
and OUTPUT signal-level adjustments , a TEST switch for maintenance
checks, and a CONTROL ON-OFF switch that permits the Audimax channel to
be operated as a linear amplifier when automatic g ain control is not desired.
On the stereo model, the INPUT and OUTPUT signal level adjustments and the
CONTROL switch are repeated for the second channe 1.
The internal components of the Model 4440A co nsist of an ac power
transformer, an audio output transformer, and two eas il y accessible transistor
circuit boards. One board contains the input, amplification, and output c ir c uitr y
and much of the feedback and lo gic circuitry used for one audio channel. The
other board c ontains the Audi max de power supply and the remainder of the
audio
feedback and logic circuitry . The feedback and logic circuitry on the
second board is designed fo r either monaural or stereo operation. When a
Model 4440A
is converted into a Model 4450A, its original input/output ci rc uit
board is employed for the left channel.
The internal components of the Model 4450A are identical to those of the
Model 4440A with the
addition of an audio output transformer, front panel
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INTRODUCTION
• controls, and an input/output circuit board for the ri ght channel. The out-
put transformer, controls, and input/output board for the right channel are
identical to their counterparts for th e left channel.
1- 4. WARRANTY
A warranty, with a return post card, is included with your Audimax
unit.
Fill out the post card and return it to Thomson-CSF Laboratories, Inc.
as soon as possible to validate your warrant y.
1-5 . FACTORY SERVICE AND REPAIR
If you should experience difficulty in installin g, operating, or repair -
ing your Audimax unit, pl ease contact your distributor for assistance . If
• necessary, call Thomson -CSF Laboratories, In c ., Stamford, Connecticut
(Area Code 203, 327-7700).
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1-6. SPECIFICATIONS
A
UDIMAX Model 4440A (Monaural)
Control cha ra c teristic
Frequency response
Harmonic distortion
Signal-to - noise ratio
Gated gain stabilization
±10 dB of gain control
±1/ 2 dB from 50 to 15,000 Hz
L ess than 0. 5% from 50 Hz to 15,000 Hz
at +16 dBm output
Gr e at er than 70 dB with respect to
normal output lev el with normal ga in
(meter reading in green region)
Thr es hold adjustable from -20 dB to
normal input
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INTRODUCTION
Maximum gain
Input and output
impedances
Minimum input level
Normal output l evel
Maximum output
Maximum operating
temperature
Physical dimensions
Power requirements
40 dB (nominal)*
600
ohms or 150 ohms, balanced or
unbalanced
-25 dBm
14* VU program, 18* dBm sine wave
26 dBm*
+ 55°C
Standard 19" rack mounting, 1-3/ 4"
high, 15" deep except for cable and
connectors
10 watts at 115/230 volts ac, 50-60 Hz
AUDIMAX Model 4450A (Stereophonic)
Physical dimensions
Power requirements
Other cha r acteristics
Same as Mod el 4440A
15
watts at 115/230 volts ac, 50-60 Hz
Each channel same as Model 4440A
*These specifications do not include the 6-dB output pad
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2- 1.
SECTION
Il
IN STALLATION PROCEDURES
UNPACKING
Carefully unpack your Audimax unit and examine it for evidence of
physical damage that may have occurred during shipment. In the event of
damage, file a claim immediately with the transportation carrier. If future
transportation of the unit can be expected, save the shipping carton for re-use.
2-2. PHYSICAL INSTALLATION
The Audimax unit is designed to be mounted in a standard 19-inch
electronic equipment rack or 19- inch -wide conso le opening. The mounting
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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
beneath it. The ambient temperature should not exceed 130° F.
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For broadcast station applications, it is recommended that the Audimax
unit
be ins t alled in a studio and its output fed directly into the main audio line.
Satisfactory operation requires that the unit be presented with a c onstant 600-
or 150- ohm impedance throughout the audio band. A 6- dB 600- ohm pad is pro-
vided at the output for isolation purposes.
A fast-acting peak limiter is recommended for use at the transmitter (fol-
lowing
the Audimax unit). However, this peak limiter should be set to show only
occasional limiting of 5 to 6 dB. For best results, a Thomson-CSF Laboratories
2-1

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LINE coe D
6.5 FT. LG
~
~
~
INSTALLATION
PRODUCT NA ME PLAT£
,3 1 7__
TER'MINA/.. 80ARO
,-- .. -- - -- ----,
-- -~
. . - ~
~
- ----------- -- 1 9.00 --- ----- --i
o ~ 0 0
0MITTEO ON
MONO UN/ r
Figure 2-1. Audimax Model 4440A or 4450A,
Outline Drawin g
14.2
. 88
1 .00
:!. 015
/. 718
2-2

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INSTALLATION
• Volumax unit should be used instead of a conventional peak limiter.
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NOTE
The master volume indicator should
follow the Audimax unit. This will
discourage unnecessary gain riding
that might tend to defeat the automatic
ieatures of Audimax.
2-3. POWER SOURCE
The Audimax unit is equipped with a power transformer permitting the
se l ection of either 115-volt or 230-volt operation. If 230-volt operation is
required, the following procedure must be performed:
NOTE
For access to interna l parts, see
Section V of this manual.
A. Unsolder and remove the black/white lead from terminal 4 of TB-1
(figure 7-1). (This is the terminal strip adjacent to the power transformer.)
B. Unsolder and remove the brown lead from terminal 3 of TB-1.
C. Connect these two leads to TBl-1.
D. Unsolder and remove the white lead from TBl-4 and connect it
to TBl-1.
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INSTALLATION
• 2-4. SIGNAL CONNECT IO NS
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I nput and output leads should be conne cted to the barrier strip at the rear
of the c has sis as indicated in Figure 2-1. Terminals 1 and 2 are the input
terminals while terminals 4 and 5 are the output terminals. Terminal 3 is the
c
hassis grou nd. In the stereophon ic model, the left ch annel terminals are as
listed above while the right c hannel is connected as follows: input 6 and 7,
output 9 and 10, ground 8.
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3-0
POWER
SWITCH
OPERATIONAL
SET
-UP
TEST
SWITCH
INPUT
CO
NTR
OL
OUTPUT
,LEVEL SWITCH
LEVEL/
v
LEFT
CHAN
NEL
(OR MONA
URAL)
CO
NTROLS
GAIN
METER
I
NP
UT
CONTROL
OUTPUT
LEVEL SW
ITCH
LEVEL
RIGHT
CHA
NN
EL
CO
NTR
OLS
( ON
ST
EREO
MODEL ONLY)
Figure
3-1.
Audimax
Unit,
Front
Panel
Contro
ls
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SECTION III
OPERATIONAL
SET-UP PROCEDURE
3-1. LEVEL ADJUSTMENTS
A.
Monaural Model
With
proper input levels, average program material should cause the
front-panel GAIN meter to indicate approximately O dB gain . (This figure is
relative, and does not refer to actual gain of the amplifier.) In this way, the
advantages of ±10 dB of
le vel correction can be realized. See figure 3-1 for
the lo catio ns of controls. On the stereo model, the audio cont rols on the l eft
side of the front panel are provided for the le ft channel and those on the right
side of the front panel are provided for the right channel.
The INPUT level setting may be established by either of two methods:
(
1) Set the POWER and CONTROL switches at ON, and use a recording
or other pro gram source to adjust the INPUT level control as necessar y to
achieve the average 0-dB reading.
(2) An oscillator may be used in place of the usual program sources or
may be connected directly to the Audimax input. The oscillator output at 1 kHz
should be adjusted for a level 4dB above the normal VU level of the line in which
the Audimax unit is connected. The INPUT level control is then adjusted for the
0-dB
reading. When an oscillator is conn ected directl y to the Audimax unit, it
is important that proper impedan ce matching be observed and that no other loads
are present on the line.
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• OPERATIONAL
SET-UP
The OUTPUT l evel control is continuously variable over a 30-dB range
to provide for a maximum of 8 VU with normal program input when using
the 6 dB output pad or 14 VU without the pad.
B.
Stereo Model
Adjustment of INPUT levels for the Audimax stereo model is basic -
ally the same procedure as used for the monaura l unit exce pt that th e left
channel must be disconnected from the control line when adjusting the right
channel INPUT level and vice-versa. Accordingly, th e following procedure
should be performed when setting up the stereo model ;
(1)
Place the l eft CONTROL switch at ON and the right CONTROL
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switch at OFF and adjust the INPUT level for a O dB indication on the me ter
with normal program-level input connected to the left channel. As for th e
monaural unit, if an oscillator is used as a signal source, its output should be
adjusted to a l evel 4 dB above the normal VU l evel of the line in which the
Audimax unit is connected. Proper impedance matching is important and no
other loads shou ld be pr e sent on the line.
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(2) Place the l ef t CONTROL switch at OFF and the right CONTROL
switch at ON. Then adjust the right INPUT level for a O dB indication on the
meter with normal program-level input connected to the right channel.
(3)
Place both CONTROL switches at ON and adjust the OUTPUT
level controls as needed to produce the desired output l evels .
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OPERATIONAL SET-UP
• 3-2. VARIATIONS FROM STANDARD OPERATING PROCEDURES
Three variations from standard operating procedures should be made when
the Audimax unit is used:
A. If the master volume indicator is properly install ed at the Audimax
output,
there will be little tendency for manual gain control at this point. In
fact, the rule here should be "DON'T TOUCH !"
B. However, in individual studios pr ece ding the Audimax unit (through a
common console), it
may be occasionally desirable to readjust levels slightly.
This should be done slowly, whether the program level is too low or too high.
C.
The third variation from usual procedures concerns "fades". Since
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the Audimax wiit will defeat any slow, deliberate reduction of le vel, all fade
operations must be perform ed more rapidly than in the past. A little practice
will easily result in the required skill. The most convenient way to insure
proper procedures at all locations is to c onnect all cue lines to some point
beyond
the Audimax output.
3-3. GATED GAIN STABILIZER
The function of
the Audimax Gated Gain Stabilizer ( GGS) is to answer the
following question: Should
the gain be increased when a lapse occurs in the
audio
program? This is especially import ant for television and motion pictur es
where the lapses occur quite often. To pre ve nt level increases of system noise
• or audio signals which are clearly background effects, the GGS inhibits gain
3-3

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OPERATIONAL SET-UP
"recovery" during thos e intervals when the input level drops below a preset
thr es hold.
The GGS threshold has been factory set to inhibit gain increase when
the inc omi ng -signal lev el has dropped approximately 14 dB below the normal
line l evel. This figur e has been established after extensive field e xperience,
and represents a satisfactory value for t ypical broadcasting use . For special
applications, the GGS threshold may be moved upwards towards normal pro-
gram level by increasing the resistance va lu es of R63 and R64 on the input/ -
output board(s) Al (and A3). Or, the thr es hold may be lower ed by r educing
the values of these resistors. The following table gives suggested values:
GGS Threshold
-4 dB
-8 dB
-11 dB
-14 dB
-17 dB
R63, R64
1, 100 ohms
620 ohms
270 ohms
200 ohms
110 ohms*
Sine-wave verification of the GGS thr es hold level may be obtained by th e
following
pro ce dur e:
A. Apply a sine-wave input to cause the front-panel meter to read 0 dB
gain redu ction.
B. Remov e the signal and wait at least 15 seconds for full stabilization.
C. Re-apply th e input s ignal at a l eve l below the desired threshold and
slowly in c reas e the signal level until th e front panel meter just begins to defle ct
*May result in increased high frequency distortion .
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OPERATIONAL SET-UP
• toward the right. The input level at this time should be approximately .5 dB
less than that indicated in the foregoing table. This 5-dB difference is a
special factor that must be considered when sine-wave calibration of the GGS
threshold is performed.
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3-4. TEST SWITCH
The Audimax unit is, in operation, performing automatic level contr ol
when the TEST switch is in the OFF position. Turning the TEST switch to the
TEST position causes the gain to remain fixed at the mid point of it s con tro l
range. The function of the TEST position is to facilitate overall system per-
formance measurements .
3-5 . DECAY (RECOVERY) TIME SWITCH
The gain control action of the Audimax unit has been designed to provide
a precise degree of contro l with a minimum of noticeable change in the short term
dynamic range. As a tool for the broadcaster, it provides maximum modulation
co nsi stent with artistically acceptable performance for a wide variety of program
material. In some applications, however, it is practical and desirabl e to im-
pose more limitation on the dynamic range of the program material. This
is commonly done for the purpose of achieving higher average modulation, or
more uniform sound - - as in the case of a public address system. The
additional limiting may be achieved by decreasing the Audimax re covery time .
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OPERATIONAL SET-UP
Although the total gain-increasing action of the Audimax is a complex
function of many variables, one phase of the recovery characteristic may
be modified by changing th e ohmic va lue of the gated r ecovery resistance.
By decreasing this valu e, the speed of re cove ry is increased.
The ohmic value of the gated recovery r esistance can be varied through
the use of the internal DECAY TIME switch located on the power supply and
logic board A2. While selection of the most appropriat e r ecovery time is
left to the discretion of th e user, the following ta b le indicates general pref-
erences, based on programming format:
Format
Mixed
Talk
Top-40
Recovery Time
Slow (10 megohms)
Me
dium (4 megohms)
Fast (3 megohms)
3-6. MODIFICATION
OF MONAURAL UNIT TO STEREO UNIT
The expansion of the monaural Audimax Model 4440A to a stereo Audimax
Model 4450A
can be accomplished in the field with a Thoms on-CSF Labora-
tories conversion kit. This kit conta in s:
1) A3, the right channel input /o utput board, Thoms on-CSF Labora -
tories p/n 991627
2)
T3, output transformer, Thomson-CSF Laboratories p/n 961634
3)
Stereo nameplate strip
4) Right channel escutcheon pan el
5) R3, R4, INPUT and OUTPUT con trols, Thomson-CSF Laboratories
p/n 991303
3-6