CBS laboratories VOLUMAX 4000 Manual

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I
·-
VOLUMAX
Model 4000
Automatic Peak Controller
OPERATING AND MAINTENANCE INSTRUCTIONS
THOMSON-CSF LABORATORIES, INC.
OCTOBER 1970
37 Bro w nhouse Road,Stamford, Conn . 06902 • [phone]

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SECTION I
1-1
1-2
1-3
1-4
1-5
1-6
1- 7
SECTION II
2- 1
2-2
2-3
2-4
SECTION ID
3-1
3 -2
3-3
3-4
3-5
SECTION IV
4-1
4-2
4-3
4-4
SECTION V
5-1
5-2
5-3
5-4
TABLE OF CONTENTS
lNTRODUCTION
General
Functional Description
Physical Description
Principles of Operation
Warranty
Factory Service and Repair
Specifications
INSTALLATION
Unpacking
Physical In sta llat ion
Power Source
Electrical Connections
OPERATIONAL SET - UP PROCEDURES
Ge
neral
Input and Output Phasing
Adjustm e nt for Maximum M odu lati on
Alternate Method for Phasing and Setting of
Modulation Level
Proof-of - P erfo rm ance Measurements
THEORY OF OPERATION
Block Dia gram
Input /Ou tput Circuitry and AGC Action
(Board Al)
AGC Amplifier (Board A2)
Automatic Peak Phasing (A. P. P.) (Board A3)
MAINTENANCE
General
Alignment Pro ced ur e
Troubleshooting Input Section -- Board Al
Troubl eshoo tin g Phase R eversal Section --
Board A3
Page No.
1-1
1-1
1-1
1-3
1-4
1-5
1-5
1-5
2-1
2-1
2-1
2-4
2-6
3-1
3-1
3-2
3-4
3-8
3- 11
4-1
4- 1
4-1
4-3
4 i
5-1
5-1
5-6
5-10
5-10

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TABLE OF CONTENTS (Cont)
Page No.
SECT I ON V (Cont)
5-5
Troubleshooting Output Section - -
5-11
Board Al
5-6
Troubleshooting AGC Section - - Board
5- 11
A2, Front Half
5-7
Troubleshooting Automati c Peak Phasing - •
5-12
Board A3
5-8
Troubleshooting Phase I ndicator Lamp
5-15
Circuits
5-9
Troubleshooting Gain Meter Circuit
5-16
SECTION VI
PARTS LIST
6-1
6-1
General
6-1
6-2
Resistors
6-1
6-3
Transistor s and Diod es
6-1
6-4
Manufacturers' Name Abbreviations 6-2
6-5
Main Assemb ly (Voluman 4000)
6-3
6-6
Sliding Deck and Printed Circuit Board
6-4
Assembly
6-7
Input /Output Circuit Board A ssembly Al
6-6
6-8
AGC/Power Supply Circuit Boa.rd 6-8
Assembly A2
6-9
A. P . P. Circuit Board A3
6-11
6- 10
Chassis A ssemb ly
6-16
SECT ION VII
DRAWINGS
7-1 / 7-2
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LIST OF ILLUSTRATIONS
Page No.
Figure
1-1 Volumax Model 4000 Automati c Peak 1-0
Contro ll er
2-1 Volumax Model 4000, Outline
Drawin g
2-2
2-2
Typical Vo lnm ax In stallation Block
2-3
Di agram
2-3
Typical Attenuator for Vo lumax Input Line
2-5
(Schematic Diagram)
2-4
Transformer T2 Re-Strappin g Connections
2-7
for 1 50 -Ohm Operation
3- 1 Volumax Model 4000 Front-Panel Controls 3-3
3~ 2
Correctly Phas ed Modulated R-F Envelop e 3-5
Obtained from Intentionally Overdriven
Volumax Unit
3 -3 In correctly Phased Modulated R-F Envelope 3-5
O btai n ed from Intentionally Overdriven
Vo lu max Unit
3-4 Squared Tone M od u la tion (95 Per ce nt) 3 -7
3-5 Correctly Ph ased Modulat ed R-F Envelope
3- 10
(
as Indi cated by a Trap ezoi dal Pattern)
3-6 In
co rr ec tl y Phas ed Modulated R-F Enve lo pe
3-10
(as Indicated by a Trapezoidal Pattern)
4-1 Volumax Model 4000, Blo
ck Diagram 4-0
4-2
A sym m etry Sensitivity as a Fun ction of
4-7
the Voltage at TP B, Board A3
5 -1 Location s of Volumax Circuit Boards
5-0
5-2
Spare Line Cord and Input /Outp ut Connector 5-2
for T est B enc h Operation
5-3
Int egrated Circuit Pin Ide ntifi cations 5- 14
7-1 Volumax Mod el 4000, Int ernal fnt ercon -
7-3 / 7-4
n ect ions
7-2
Input/Output Board Al, Schemati c Diagram
7-5 / 7 -6
and Parts Lo cat i ons
7-3 P ower Supply/ AGC Bo ard A2, Sc hem atic
7 -7/7-8
Diagram and Parts Location s
7-4
A. P . P. Board A3, Schematic Di agram and
?-9 /7 -10
Parts Lo cat i ons
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Table
5- 1
5
-2
LlST OF TABLES
Power Supply Voltages
AC Signal Voltages
Pag e No.
5-4
5-4
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•
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1- 0
Figure
1-1.
Volumax
Model 4000
Automatic
Peak
Controller

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1-1. GENERAL
SECTION I
INTRODUCTION
This manual provides instructions for the CBS laboratories Model
4000 Volumax*
unit , a high quality peak limiter for AM broadcasters that
positive ly preven ts overmodulation . When used in conjunction with an
automatic leve l co ntrol such as the CBS Laboratories Audimax*, it also
guarantees program-power gains severa l times greater than those
obta ined by conventional methods.
1-2. FUNCTI ONA L DESCRIPTION
The Model 4000 Vol umax combines a superior dual- action peak
limiter with an automatic peak phaser to ensure that the higher amp litude
peaks of a program wave always modulate the carrier in the positive
direction and that negative peaks are precisely limited to 100 percent.
Designed primarily for use with we ll contro ll ed average input levels
suc h as prov i ded by Audimax, the Volumax supersedes a ll previous peak
limiters in the prevention of carrier overmod u lation by instantaneous
program peaks.
*CBS Laboratories trademarks
1-1

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INTRODUCTION
With conventional
peak limit ers, the broadcaster must choose
between two "evils": either th e program l eve l must be reduced so
that the limitin g of peaks wi ll not be drasti c enough to cause "pumping"- -
thus lowering ave r age power - - or th e pumping (w hich amounts to an
audi bl e di sto rtio n) has to be tol era ted. Fu rth ermore, since conven-
tional limit ers moderate pumping by use of long re cove ry tim es, the
int er va ls immediately following high program peaks waste modulation
capability while the limiter recovers from r ed uced ga i n.
Th e Vol umax c ir c uitr y so lv es th ese prob l ems in a unique manner.
Control is effec t ed in two ways: time-varying AGC ac tion, and micro-
secon d- fas t diode limitin g. Th e r esu lt is an eve n, pl easant sound plus
the capability of tran sm ittin g program si gna ls with high p eak factor at
twice the ave r age program power l evel usually e>.'})ec t ed when conven-
tiona l limiters are used.
When the Vol umax POSITIVE LIMIT switch is set for 100 %, the
tim e -var ying AGC ac tio n r espon ds equa ll y to both positive and negative
wave
exc ur sions, and the limiting action is co mpletely symme tri c. If
the 120% position is chosen, th e Volum ax AGC amplifie r then requires
positive peaks 1. 2 times h ig her than th e negative peaks to cause equal
amo unt s of limiting and, in addit ion, th e "peak ce ilin g'' for positive pro -
gram excu rs i ons is moved up so that the abso lut e limits have a ratio of
1. 2 positive to 1. 0 negative. Finally, in th e 300% position, th e same
negative "peak ceili ng" is used as in th e other two switch posi ti ons, while
1 -2

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INTRODUCTION
the AGC ac tio n r esponds only to negative peaks. In this case , positiv e
peaks are a ll owed to pass throu gh the Vo lum ax unit without limitin g.
1-3 . PHYSICAL DESCRIPTION
P
ackaged in a new, s limlin e design, the Vo lum ax unit requ ir es only
1- 3/4 in ches of stan d ard 19-in ch rack height and only 13 -1 /2 inches of
depth behind
the f ro nt p anel. It s reliable solid - sta te circuitry is
packaged in functional gro ups on thr ee c ir c uit boards, and has approp r iate
test points to spee d mai n te nance t es ts and tr oubleshooting. The e ntir e
unit slides out of it s r ack mount ed enc l osu re to permit easy bench
se rv ic e while providing maximum accessibility to all components. Front
panel c ontrol s are convenien tl y arranged, and thos e requiring infrequent
use (e.g., th e INPUT LEVEL and OUTPUT SET co ntr ol s) are r ecessed
screw dri ver adjus tm ents. A front panel meter indicates the relativ e
d
egree of ga in reduc tion.
Th e unit can be operated fr om e ith er a 115-volt or 23 0-v o lt single-
phase 50 or 60 Hz power source. On de li very, the unit is connected for
115-vol t op erat ion. Wiring changes for 230-vo lt opera ti on are expla ined
in paragraph 2-3.
1-3

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INTRODUCTION
1-4. PRINCIP LES OF OPERATION
NO TE
For a com pl ete c ircuit description,
see Sectio.n IV of thi s manual.
Bri efly, th e prog r am input is fed to a differ e nti al amplifier a ll owing
balan ce d or unba lan ced inputs. An AGC amplifie r with a fast attack and
moderate ly fast recove ry times is th en used to reduce th e gain of the
prog r am signa l on peaks as described in paragraph 1-2 . Thi s ac ti on,
co upl ed with microsecond - fas t diode limitin g, en sur es absolu te co nt rol
of limit point. M ea nwhile, the input program signa l al so drives a
polarity detector and a pause det ector. Th ese circuits sample the signa l
and determine from its assymetry and l eve l whether the phase of the
si gna l needs to be r eve rs ed to allow high er peaks to produce posi tiv e
modulation of the car ri er and de te rmi ne when that change should occ ur.
The a ctual phase reversal is accomplished by a clocked flip-flop, an
int egrated circ u it " borrowed" from the computer industry. This
flip-flop determin es whether th e program signa l w ill pass throu gh an
inverting or non- invert ing path in the Vo lum ax unit. For a pr ec ise
adju stmen t of the modulation level, a ca librated output attenuator a ll ows
the
opera tor to vary th e output level upw ard or downward by 2. 5 db in
0. 5 db
steps with resp ect to a nominal OUTPUT SET l evel.
Th e oper ation of the a utomatic peak phasing ci rc uit is pr edica ted on
the fact th at most speech wav es are assyme tr ic; in oth er words, that th e
1-4