CBS VOLUMAX 4300 Manual
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~-,
.I
,\
..
l.
J.
TABLE
OF
CONTENTS
Page
No.
SECTION I INTRODUCTION
1-1
General
1-1
1-2
Functional
Description
1-1
1-3
Physical
Description
1-4
1-4
Principles
of
Operation
1-5
1-5
Warranty
1-6
1-6
1
Factory
Service
and
Repair
1-6
1-7
Specifications
1-6
SECTION
II
INSTALLATION
2-1 Unpacking 2-1
2-2
Physical
Installation
2-1
2-3
Power
Source
2-5
2-4
Electrical
Connections
2-6
SECTION
ill
OPERATIONAL
SET-UP
PROCEDURES
• 3-1
General
3-1
3-2 Input
and
Output
Phasing
3-2
3-3
Adjustment
for
Maximum
Modulation
3-6
3-4
Alternate
Method
of
Phasing
and
Setting
3-8
Modulation
Level
3-5
Headroom
Consideration
3-9
3-6
Proof-of-Performance
Measurements
3-11
3-7
Internal
Trimming
of
Output
Leve
1 3-12
SECTION
IV
THEORY
OF
OPERATION
4-1
Block
Diagram
and
Schematic
4-1
4-2 Input/Output
Circuitry
and
AGC
Action
4-1
4-3
AGC
Amplifier
4-3
4-4
Automatic
Peak
Phasing
(A
.
P.
P.)
Circuit
4-5
SECTION V MAINTENANCE
5-1
General
5-1
5-2
Alignment
Procedures
and
Tests
5-6
5-3
Troubleshooting
Audio Input
Section
5-20
• 5-4
Troubleshooting
Phase
Reversal
Section
5-21
5-5
Troubleshooting
Audio
Output
Section
5-21
i
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•
•
•
TABLE
OF
CONTENTS (Cont)
SE
CT
ION V (Cont)
5-6
5-7
5-8
5-9
SECTION
VI
6-1
6-2
6-3
6-4
6-5
6-6
SECTION VII
Figure
1-1
1-2
1-3
2-1
2-1
2-2
3-1
3-2
3-3
3-4
Troubleshooting
AGC
Section
Troubleshooting
Automatic
Peak
Phasing
Section
Troubleshooting
Phase
Indicator
Circuits
Troubleshooting
Gain
Meter
Circuit
PARTS LISTS
General
Resistors
Transistors
and
Diodes
Manufacturers'
Name
Abbreviations
Main
Assembly,
Volumax
4300 (
CBS
Laboratories
Part
No. 962400)
Printed
Circuit
Board
Assembly
(Al)
DRAWINGS
LIST
OF
ILLUSTRATIONS
Volumax
Model 4300
Phase
Switching,
Comparison
Waveforms
Volumax
4300
Rear
View
Volumax
Model 4300,
Installation
Drawings
(Sheet 1
of
2
Sheets)
Volumax
Model 4300,
Installation
Drawings
(Sheet 2 of 2
Sheets
)
Typical
Volumax
Installation
Block
Diagram
Volumax
Model 4300
Front
Panel
Controls
Correctly
Phased
Modulated
R-F
Envelope
Incorrectly
Phased
Modulated
R-F
Envelope
Squared
Tone Modulation (95
Percent)
Page
No.
5-22
5-23
5-26
5-27
6-1
6
-1
6-1
6-2
6-3
6-5
7-1
Page
No.
1-0
1-2
1-7
2-2
2-3
2-4
3-3
3-5
3-5
3-7
ii
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•
•
•
Figure
3-5
3-6
4-1
5-1
5-2
5-3
5-4
5-5
5-6
7-1
7-2
Table
5-1
5-2
LIST
OF
ILLUSTRATIONS (Cont)
Correctly
Phased
Modulated
R-
F Envelope
(as
Indicated
by
a
Trapezoidal
Pattern)
Incorrectly
Phased
Modulated
R-F
Envelope
(as
Indicated
by
a
Trapezoidal
Pattern)
Volumax
Model 4300
Block
Diagram
Volumax
Unit
with
Top
Cover
Removed
Factory
Test
Setup
Positive
Limit
Output
Levels
for
the
Three
Positions
of S3
Release
Time
Waveform
A.
P.
P.
Test
Circuit
Integrated
Circuit
Pin
Identification
Volumax
4300
Schematic
Diagram
Circuit
Board
Al
Parts
Locations
LIST
OF
TABLES
Power
Supply
Voltages
Voltage
Measurements
Page
No.
3-10
3-10
4-0
5-0
5-7
5-10
5-13
5-19
5-24
7-2
7-3
Page No.
5-3
5-4
iii
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•
1-1.
GENERAL
SECTION I
INTRODUCTION
This
manual contains
instructions
for
the
CBS
Laboratories
Model
4300 VolumaxR unit, a
specialized
professional
audio
peak
limiter
for
AM
broadcasters
that
prevents
overmodulation while providing maximum
pro-
gram
power
in
each
watt of
carrie
r power. When
used
in
conjunction with
an
automatic
l
evel
contro
l
such
as
the
CBS
Laboratories
AudimaxR,
it
also
guarantees
program-power
gains
several
times
greater
than
those
obtained
by conventional methods.
The
present
Volumax model combines
the
achieve-
ments of
earlier
Volumax models with higher
standards
of quality and fidelity.
Among the
improvements
is
an
excellent
signal-to-noise
ratio
of
at
least
70 db
• with
respect
to
maximum output.
1-2.
FUNCTIONAL DESCRIPTION
The Vo
lumax
unit combines a
superio
r
dual-action
peak
limiter
with
an
automatic
peak
phaser
to
ensure
that
the
higher
amplitude
peaks
of a
pro-
gram
wave always modulate
the
carrier
in
the
positive
direction
and
that
negative
peaks
are
precisely
limited
to
100
percent.
Th
e positive
direction
is
used
to
obtain modulation
levels
up
to
125
percent
as
allowed by
the
FCC.
Audio
is
passed
without modification when
there
are
no instantaneous
peaks
that
would
cause
overmodulation, but
each
such
peak
is
silently
limited
as
just
described.
No audible
clicks
occur
when a Volumax function
is
performed.
•
¾egistered
trade
mark
1-1
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•
•
•
INTRODUCTION
Designed
primarily
for
use
with
well
controlled
average
input
levels
such
as
provided by Audimax,
the
Model 4300 Volumax unit
supersedes
all
other peak
limiters
in
the
process
of
preventing
carrier
overmodulation.
A.
Conventional
Peak
Limiters
and Instantaneous
Phase
Switches
With conventional
peak
limiters,
the
broadcaster
must
either
reduce
the
program
level
so
much
that
the
limiting
of
peaks
is
not
severe
enough
to
cause
"pumping"
--
thus
lowering
average
modulating power
--
or
must
tolerate
the
"pumping" and consequent
distortion.
Although conventional
limiters
moderate
"pumping" by using long
recovery
times,
the
intervals
im-
mediately following high
program
peaks
waste
modulation capability; in
these
times,
the
limiter
is
insensitive
while
it
recovers
from
reduced
gain.
The
Volumax
unit
may be
regarded
as
an
instantaneous
phase-
switch
limiter.
Limiters
of
this
type may
waste
less
power, but
those
other
than
Volumax
introduce
audible
clicks
whenever
phase
switching occu..-s.
Volumax
is
silent
,
as
shown
in
figure
1-2.
SILENT SWITCHING The two photographs above show the word "content" displayed on an oscilloscope. The
photo on the left taken with the VOLUMAX
in
operation, shows clearly that phase switching took place during
the momentary pause between syllables-completely and silently.
The
photo on the right using an instantaneous
phase switch shows that the phase switching took place during the second syllable-and with an audible click.
Figure
1-2.
Phase
Switching,
Comparison
Waveforms
1-2
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INTRODUCTION
•
absolute
limits
have
a
ratio
of 1.
15
positive
to
1.00
negative.
If
the
125
percent
position
of
the
switch
is
chosen,
the
Volumax AGC
amplifier
increases
this
ratio
to
1.
25
to
1.00.
Because
of
the
FCC
ruling
which
places
the
limit
on
positive
modulation
at
125
percent,
the
125
percent
position
may
be
used
without
violation.
(See Section III. )
CAUTION
The
front-panel
LIMITER
switch
should
be
kept
in
NORMAL
position
during
regular
broadcast
opera-
tion.
1-3.
PHYSICAL DESCRIPTION
•
Packaged
in
CBS
Laboratories'
slimline
design,
the
Volumax
unit
re-
•
quires
only
1-3/4
inches
of
standard
19-inch
rack
height
and
only 15
inches
of
depth
behind
the
front
panel.
The
weight
is
6. 5 pounds.
Its
reliable
solid-
state
circuitry
is
packaged
on a
printed
circuit
board
with
appropriate
test
points
to
speed
maintenance
tests
and
troubleshooting.
Front
panel
controls
are
conveniently
arranged,
and
those
requiring
infrequent
use
(e. g. , INPUT
LEVEL, OUTPUT
LEVEL,
AND
O
UTPUT
MAX
dbm)
are
screwdriver
adjust-
ments.
A
front
panel
meter
indicates
the
relative
degree
of gain
reduction.
The
unit
can
be
operated
from
either
a 115-
volt
or
230-
volt
single-
phase
50
or
60
Hz
power
source.
On
delivery,
the
unit
is
connected
for
115-
volt
operation.
Wiring
changes
for
230-
vo
lt
operation
are
explained
in
para-
graph
2-3
.
1-4
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•
•
•
INTRODUCTION
The
unit
can
be
rack
mounted
simply
by
means
of
its
panel
mounting
flanges
(ears),
but
an
optional
chassis
slide
accessory
.
kit
is
available (CBS
Laboratories
p/n
962163-4).
1-4.
PRINCIPLES
OF
OPERATION
NOTE
For
a complete
circuit
description,
see
Section
IV
of
this
manual.
The
program
input
is
fed
to
a
differential
amplifier
allowing balanced
or
unbalanced inputs. An
AGC
amplifier
with
fast
attack
and
moderately
fast
recovery
times
is
then
used
to
reduce
the
gain of
the
program
signal
on
peaks
as
described
in
paragraph
1-2.
This
action
in
conjunction with
microsecond
-
fast
diode
limiting
ensures
absolute
control
of
the
limit
point.
Meanwhile,
the
input
program
signal
also
drives
a
polarity
detector
and a
pause
detector.
These
circuits
sample
the
signal
and
determine
from
its
asymmetry
and
level
whether
the
phase
of
the
signal
needs
to
be
reversed
to
allow
the
higher
peaks
to
produce
positive
modulation of
the
carrier.
They
also
determine
when
that
change should
occur.
The
actual
phase
reversal
is
accomplished
by a clocked flip-flop --
an
integrated
circuit
"borrowed"
from
the
computer
industry.
This
flip-flop
determines
whether
the
program
signal
will
pass
through
an
inverting
or
non-
inverting
path
in
the
Volumax unit.
The
operation
of
the
automatic
peak
phasing
circuit
is
predicated
on
the
fact
that
most
speech
waves
are
asymmetric;
in
other
words,
that
the
amplitude of one
side
may
be
as
much
as
10 dB above
the
other.
The Volumax
1-5
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•
•
•
INTRODUCTION
unit
can
sense
asymmetry
factors
as
low
as
3
dB
and
turn
them
into
useful
positive
supermodulation.
The OUTPUT LEVEL
control
on
the
front
panel
of
the
unit
provides
a wide
range
of
adjustment
of modulation
level.
This
control
is
a 600-ohm*
variable
H-pad
attenuator.
In
con
jun
ction
with
an
adjacent,
switchable, 16-db
attenuator
labelled
OUTPUT
MAX
dbm,
the
OUTPUT LEVEL
control
can
be
set
anywhere
in
a
0-to-20
dB
range
with
maximum
output
at
6
or
22
dBm.
1-5. WARRANTY
A
warranty
with a
return
postcard
is
included with yo
ur
Voluma.x
unit.
Fill
out
the
postcard
and
return
it
to
CBS
Laboratories
as
soon
as
pos-
sible
to
validate
your
warranty
.
1-6.
FACTORY SERVICE AND
REPAIR
If
you should
experience
difficulty
in
installing,
operating,
or
repair
-
ing
your
Voluma.x unit,
please
contact
your
distributor
for
assistance.
If
necessary,
call
CBS
Laboratories,
Professional
Products
Department,
Stam-
ford,
Connecticut (Area Code 203, 327-2000).
1-7.
SPECIFICATIONS
Input and output impedance
Input
level
Maximum output
600 ohms,
balanced
or
unbalanced;
150 ohms on
special
order
-24
to
+18 dBm
22 dBm
* 150 ohms
in
units
manufactured
for
the
150-ohm
output impedance option.
(See Voluma.x
specifications
in
paragraph
1-7.)
1-6
•
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•
•
•
INTRODUCTION
Positive
peak
limiting
100%, 115%
or
125%* of
negative
peaks
Maximum
gain
50 dB
Signal
to
noise
ratio
70
dB
with
respect
to
maximum
output
level
at
normal
gain
Frequency
response
±0. 5 dB,
50-15,
000 Hz
Harmonic
distortion
Less
than
1%,
50-15,
000 Hz
Attack
time
Less
than
1
microsecond
or
2
milliseconds,
depending on
pro-
gram
waveform
Recovery
time
250
milliseconds
Maximum
operating
55°c
(130°F)
temperature
Power
requirements
105-130
vac,
50-60
Hz, 20
watts
(210-250
vac,
50-60
Hz optional)
Physical
dimensions
Standard
19
inches
wide x
1-3/4
inches
high x
14-1/2
inches
deep
Weight 6. 5 lb.
Optional
equipment
Chassis
slide
accessory
kit
962163-4
Figure
1-3.
Volumax 4300
Rear
View
*
For
125
percent
operation,
it
may
be
necessary
to
trim
the
125
percent
peak
limiter.
See
Section
m.
..
1-7
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•
•
•
2-1.
UNPACKING
SECTION
Il
INSTALLATION
Carefully unpack
your
Volumax
unit
and
examine
it
for
evidence of
physical
damage
that
may have
occurred
in
transit.
If
the
unit
is
damaged,
file a
claim
immediately
with
the
shipping
carrier
and
notify CBS
Laboratories.
Should future
transportation
of
the
unit be anticipated,
save
the
shipping
carton
for
re-use.
2-2.
PHYSICAL INSTALLATION
The
Volumax unit
is
designed
to
be
mounted
in
a
standard
19-inch-
wide
electronic
eq
uipm
ent
rack.
It
requir
es
1-3/ 4
inches
of
space
for
the
panel
height and
is
15
inches
deep behind
the
front
panel. See figure
2-1.
Sheet 2 of
this
illustration
provides
instructions
for
mounting with
the
optional
chassis
slides.
As
for
all
transistorized
equipment,
the
unit
must
be
installed
in
a
reasonably
well-ventilated
position
with no high-heat producing equipment
beneath
it
.
CAUTION
Ambient
temperature
should not
exceed
130°F.
Figure
2-2
is
the
block
diagram
of a
recommended
installation. The
Volumax unit
is
normally
installed
at
the
transmitter
site
immediately
pre-
ceeding
the
transmitter
audio input
terminals.
However,
it
may be
installed
at
the
studio,
ahead
of
the
program
line
to
the
transmitter,
when the
phase-
amplitude
characteristic
between studio and
transmitter
are
known
to
be
uniform
under
all
climatic
conditions and
service
conditions
such
as
telephone-
2-1
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• INSTALLATION
company changes of equipment.
This
is
particularly
important
for
maximum
utilization
of
the
effects
of
the
Volumax automatic
peak
phasing
.
It
should
be
remembered
that
the
Volumax equipment
is
designed for
peak
protection
and
that
it
should not
be
used
for
"ga
in
riding"
on a
pro
g
ram
line.
Its
use
is
predicated
on
uniform
average
VU
input
levels.
Therefore,
the
use
of
an
automatic
level
control
such
as
the CBS
Laboratories
Audimax
unit
is
highly
recommended
. Since
phase-scrambling
devices
tend
to
defeat
the
purpose
of
automatic
peak
phasing,
such
devices
are
not
recommended.
The
Volumax unit has sufficient gain
to
correct
for
long-line and
equalizer
losses
incurred
when
the
transmitter
is
remotely
located.
Input
levels
as
low
as
-24
dBm
can
be accommodated.
If
the
input
•
level
exceeds
+
18
dBm,
the
range
of
the
input
level
control
will not be
suffi-
cient;
in
such
case,
a fixed pad should be
used
in
the line
to
the
Volumax unit.
•
2-3.
POWER SOURCE
The Volumax
unit
is
equipped with a
three
-
wire
power
cord
and
a
power
transformer
permitting
either
115
vac
or
230 vac operation. In
either
case,
be
sure
the
green
wire
in
the
power
cord
will connect
to
service
box
ground. As
delivered,
the
unit
is
wired
for
115
vac
operation.
If
230
vac
op-
eration
is
desired,
make
the
following modifications
at
the
terminal
strip
TBl
at
the
inside
rear
of
the
unit, next
to
the
power
transformer
T2.
A.
Remove
the
white
/b
rown
lead
of
the
transformer
T2
from
terminal
3 of
TBl
(figure 7-1). Leave
the
brown
lead
of
T2
connected
to
terminal
3.
2-5
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•
•
•
INSTALLATION
B. Remove
the
black
lead
of T2
from
terminal
4 of
TBl.
Leave
the
white/black
lead
of T2 connected
to
terminal
4.
C. Connect the white/brown and
black
leads
of T2
to
TBl-1.
This
connects
the
two
primary
windings of T2
in
series
as
required
for
a 230
vac
input.
D.
Replace
the
original
fuse
Fl
with a type 3AG-0.
15
amp
(SLO-BLO) fuse.
2-4.
ELECTRICAL CONNECTIONS
Connect
the
audio input and output
leads
to
the
barriered
terminal
strip
on the
rear
panel
of
the
Volumax unit. Use
terminals
1 and 2
for
the
input and
terminals
4 and 5
for
the
output.
Terminal
3
is
a
chassis
ground.
Terminals
6 through
10
are
not used.
The
phasing of
the
connections
is
such
that
if
the
side
of
the
input line with
the
higher
peaks
is
co
nne
cted
to
terminal
1,
the
automatic
peak
phaser
in
the
Volumax unit will
seek
its
"
normal"
phase
state.
Therefore,
be
sure
to
connect output
terminal
4
to
the
transmitter
in
the
phase
arrangement
that
will positively modulate
the
carrier.
If
unsure
of
the
phase
of
either
the
audio feed
or
the
transmitter
input,
see
the
setup
procedures
in
Section m of
this
manual.
Eith
er
balanced
or
unbalanced
lines
may
be
used
.
Temporarily
set
the
OUTPUT
MAX
dbm switch on
the
front
panel
in
the
6 position. Then connect
the
power
cord
to
the
power
source
(paragraph
2-3). The
unit
is
now
ready
for
operation.
(Place
OUTPUT
MAX
dbm
in
the
22 position only when
this
is
known
to
be
the
appropriate
setting. See Sectionm .)
2-6
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•
•
•
SECTION
ill
OPERATIONAL
SET-UP
PROCEDURES
3
-1.
GENERAL
The Volumax 4300 may be
used
with a wide
variety
of
a-m
transmit-
ters
differing
in
reactions
to
supermodulation
control.
Hence,
the
capabilities
and limitations of the
transmitter
of
concern
must
be
considered
when
adjust-
ing
the
Volumax unit
for
use,
particularly
in
the
selection
of
the
115
or
125
(positive modulation
percent)
position of
the
front-panel
POSITIVE LIMIT %
switch.
Within
the
transmitter,
the
power supply
for
the
final
amplifier
(and
modulator,
as
well, where
plate
modulation
is
used) should have a
reserve
capability
if
supermodulation
is
to
be
obtained without
excessive
carrier
shift
or
other
undesirable
effects.
Though
some
transmitters
are
marginally
de-
signed, with
little
or
no
reserve
current
capability,
most
modern a
-m
trans-
mitters
have enough power-supply
reserve
for
an
appreciable
amount
of
supermodulation. All
operating
a-m
broadcast
transmitters,
of
course,
have
enough power-supply capability
for
100
percent
positive and negative
modula-
tion.
If
125
percent
positive
modulation would
be
both
desirable
and
satisfactory,
the
modulation obtained
for
the
125
position
of
th
e POSITIVE
LIMIT % switch
sho
uld
be
measured
in
the
initial
tests
of
the
Volumax unit
(paragraphs
3-2
through
3-5).
If
the
positive modulation
measured
in
these
tests
is
more
or
less
than
125
percent,
see
paragraph
3
-7
at
the
end of
this
section
for
a
corrective
measure
.
3-1
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•
•
•
OPERATIONAL
SET-UP
In
the
operation
of
the
Volumax unit,
remember
that
musical
program-
ming
has
little
or
no
asymmetry
while
speech
can
have
an
asymmetric
peak
factor
as
great
as
10 dB
--
depending on
the
particular
voice and
the
nature
and
the
amount of
electrical
processing
which
its
analog
signal
undergoes.
Therefore,
the
most
dramatic
increases
in
positive
modulation should
be
ex-
pected
to
occur
during
live
speech
programming.
AS
delivered,
the Volumax
4300
can
sense
an
asymmetry
factor
as
low
as
3.
0 dB and make
the
decision
to
change
phase
when
desirable.
The
correct
moment
for
the
reversal,
as
de-
termined
by
an
internal
pause
detector
circuit,
is
the
next 120-millisecond
or
longer
program
amplitude
drop
of
more
than
16
dB.
3-2
. INPUT
AND
OUTPUT PHASING
Terminal
4 on
the
barriered
terminal
strip
{figure
2-1)
should be
connected
to
a point
in
the
system
where
the
Volumax output will
cause
posi-
tive
modulation of
the
transmitter
carrier.
This
can
be
tested
in
the
following
manner:
A)
Turn
power on and
select
the
6
or
22
position of the OUTPUT
MAX
dbm switch
as
appropriate
for
a maximum Volumax
output of 6
or
22
dBm,
respectively.
See
figure
3-1.
See
also
paragraph
3-3.
Then
turn
the
OUTPUT LEVEL
control
{figure
3-1)
fully counterclockwise.
B)
Set
the
POSITIVE LIMIT %switch
at
125 {percent)
C)
Use a 1 kHz
sine-wave
input
signal
to
deflect
the
reading
on the
front-panel
GAIN
REDUCTION
meter
to
the
red
-
green
(HEAVY
-
NORMAL) junction.
3-2
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•
• POWER
ON!
OFF
•
OPERATIONAL
SET-UP
POSITIVE
LIMIT
o/e
LIMITER
SW
TEST(
MOD
SET
PHASE
SW
AUTO-
MATIC
MAX
dbm
SW
(
22
dbm
6
dbm
SW
)
125o/.
I15o/.
100%
LEVEL
r
INCREASE
OUTPUT
CONTROLS
NORMAL
GAIN
INPUT
LEVEL
NORMAL REVERSE
REDUCTION CONTROL PHASE
INDICATORS
METER
INCREASE
(
Figure
3-1.
Volumax
Model 4300
Front
Panel
Controls
3-3
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