CRL PMC-450 User manual

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I
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PMC-450
I PEAK MODULATION CONTROLLER
I
FOR AM
BROADCAST
I INSTALLATION AND OPERATION MANUAL
I
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PROFESSIONAL'S
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SYSTEMS
Circuit Research Labs, Inc.
2522 West Geneva Drive
Tempe.
Arizona 85282-3192
U.S.A.
1800)
535-7648 ,j602)
438-0888
FAX
438-8227

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...
,.,.....
PMC·450
PEAK
MODULATION
CONTROLLER
INSTALLATION
AND
OPERATION
MANUAL
Manufactured
under
one
or
more
o
f
t
he
f
o I I
ow
i n g U . S.
pa
t
en
t s :
3,582,964
4 ,
350,845
4 ,
383,229
4,393,346
4 ,
398
,
158
4 ,
679
,
239
PR
OP
RIB
TAR
Y
NOT/CB
4 ,
406,923
4 ,
609,878
Th
e
schematic
drawings
reproduced
in
this
manual
contain
p
r o
p
r
i
e
t
a r
y
d a t a t o C i r cu i t R
e·se a r c h Lab s , I nc . T he u se r o
f
t h i s
manual
agrees
to
make
no
disclosure,
reproductions
or
use
of
any
pa
r
t
o
f
t
hes
e
d
raw
i n
gs
except
by
pr
i
or
w r i t
ten
perm
i s
s
i
on
f
r om
Circuit
Research
Labs
,
Inc.
P
/N
PMC-450
10082
CIRCUIT
RESEARCH
LABS.
INC
.
2522
W.
Ceneva
Drive
Tempe,
AZ
85282
(602)
438-0888
11-2500·01
Rev
.
A-1
(C)
Copyright
Circuit
Research
Labs
,
Inc
.
1989
I ·,

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--
TABLE
OF
CONTENTS
1.
GENERAL
1. 1
SA
FE
TY
I
NF
ORMA
TI
ON
.
De f i n i t
i
on s o
f
Sa
f
et
y S
ymb
o Is .
Important
Safeguards
1.
13
I
NTROOUCT
ION
1
.27
WARRANTY
.
1. 32
NRSC
VOLUNTARY
STANDARD
Cav\PLIANCE
RECORD.
1.
35
PMC·450 SPECIFICATIONS.
2.
INSTALLATION
2 . 1
GENERAL.
2. 3
BEFORE
PONER·UP
.
2.4
PONER
LINE
AC
VOLTAGE
SELECTION
.
2. 6
INTERNAL
JUMPERS
2. 8
PCB
LED
INDICATORS
2.
11
INTERCONNECTIONS
General.
Balanced
Line
Connections
Unbalanced
Line
Connections
.
2.
18
INITIAL SET·UP
General
.
Set·Up
Procedure
Asymmetry
Set·Up
Tilt
Correct
Set·Up.
Auxi
I
iary
Output
(Day/Night
Operation)
2.31
GUIDELINES
FOR
SYSTEM
SOUND
SETTING
.
3.
OPE
RAT
ING
INSTRUCT
IONS
3. 1
GENERAL
....
3
.3
FRONT
PANEL
CONTROLS
,
SWITCHES
&
INDICATORS
.
Powe
r L
ED
I nd i
ca
to
r .
G/R
Input
AGC
Switch
.
Mid·Range
Presence
.
Hi·Freq
Equalization
.
Input
Level
Indicator
.
Ti
It
Correct
Control
.
PACE
1 • 1
1 • 1
1 • 1
1 • 2
1• 5
1 - 6
1 • 7
2 • 1
2 - 1
2 • 2
2 • 3
2-4
2 • 8
2 • 8
2 • 8
2 • 10
2 • 10
2 • 1 5
2 • 1 6
3 - 1
3 - 1
3 • 1
3 • 1
3 • 2
3 • 2
3 · 2
3 • 2
P
MC
· 4 5
O (C) Cop
y
r i ght Ci rcu i t Re s
e
a rc h La bs , Inc . 1989 Pa ge O• 1

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6 . 13 CATE CIRCUIT TEST. 6 - 3
6. 14 G/R TEST 6-3
6 . 15 BASS PRE-EMPHASIS CIRCUIT TEST 6-4
6.16 LIMITING TEST. 6-4
6. 17 NRSC PRE-EMPHASIS CALIBRATrON & TEST 6-4
6. 18 MID RANGE PRESENCE CALIBRATION 6-5
6.19 FILTER ADJUSTMENT & TEST 6-6
6.20 ASY~ETRY ADJUSTMENT & TEST. 6-6
6.21 TILT CORRECT TEST . 6-7
6.22 N'tONO OUTPUT TEST 6-7
6.23 PREPARATION FOR SPECIFICATION MEASUREMENT. 6-7
6. 24 TOTAL HARN'tONIC DISTORTION. 6-8
6 .25 FREQUENCY RESPO N SE 6-8
6 . 26 SIGNAL TO NOISE/NOISE RATIO . 6-8
6 . 27 INTERN'tODULATION DISTORTION 6-8
6.28 TROUBLESHOOTING. ~-9
General. 6-9
Suggested Component Checks 6-9
6.34 CUSTa...11ZATION. 6-11
6.43 FACTORY SERVICE. 6-14
7. APPENDIX
A.
B.
c .
D.
E.
F .
c .
SYSTEM INFORN\ATION
PARTS LISTS.
BLOCK DIAGRAM.
PC BOARD LAYOUT DIAGRAM .
SCHEN\ATIC DIAGRAMS
FRONT PANEL CONTROL BOARD SCHEN\ATIC.
FRONT PANEL PC BOARD LAYOUT DIAGRAfv1 .
7 - 1
7 - 2
7 - 10
7 - 1 1
7 - 12
7 - 17
7 - 18
PMC - 4 50 ( C ) Co py r i gh t C i r c u i t Re se a r c h La b s , I n c . 1 9 8 9 Pa ge O- 3

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LIST OF ILLUSTRATIONS
FIG. TITLE
PAGE
1·1 TYPICAL TRANSMITTED SPECTRU~ . . ...... .. 1· 4
2· 1
2 • 2
2 • 3
2 · 4
2 • 5
2 - 6
2 - 7
2 - 8
2-9
3 • 1
4 - 1
4 • 2
5 - 1
5 - 2
PMC -450 FRONT PANEL
PMC-450 BACK PANEL.
LINE VOLTAGE SELECTION .. ..
TYPICAL SYSTEM CONFIGURATIONS.
BALANCED LINE CONNECTIONS ..
UNBALANCED LINE CONNECTIONS .
NORMAL M:>DULATION ENVELOPE
UNDER-CORRECTED M:>DULATION ENVELOPE.
OYER-CORRECTED M:>DULATION EN V ELOPE .
TYPICAL TRANSMITTED SPECTRUM COv\PARISO N.
NRSC PRE-EMPHASIS . . . . . .
NRSC STOPBAND SPECIFICATION .
BASS PRE-EMPHASIS FILTER RESPONSE .
OUTPUT SPECTRUM OF PMC .
2 - ,
2 • 1
2· 2
2 • 5
2 • 7
2 • 7
2 - 1 3
2 • 13
2 -14
3 - 5
4·3
4·3
5·4
5 • 7
P MC · 45O ( C) Copy r i g ht Ci r cu i t Re sea r c h Labs , Inc . 1989 Page O• 4

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SECTION
1 ·
GENERAL
1.1
SAFETY
INFORMATION
1 . 2
DEFINITIONS
OF
SAFETY
SYMBOLS
..........
WARNING
••••••••••
CAUTION:
THE
WARNING
SIGN
DENOTES
A
HAZARD.
IT
CALLS
ATTENTION
TO
A
PROCEDURE,
PRACTICE,
CONDITION, OR
THE
LIKE,
WHICH,
IF
NOT
CORRECTLY
PERFORMED
OR
ADHERED
TO, COULD
RESULT
IN
DAMAGE
TO
THE
UNIT.
The
CAUTION
si1n
denotes a precaution.
It
calls
attention
to
an operating procedure,
practice, condition
or
the llke, which,
If
not correctly performed
or
adhered to, could
result
in
the unit not performing properly.
NOTE :
The
NOTE
sign
denotes
important
informatjon
.
I
t
calls
attention
to
procedure,
practice
,
condition
,
or
the
like
which
is
necessary
to
high
I
ight
.
1 . 3
IMPORTANT SAFEGUARDS
1 . 4
The
f
o I I
ow
i ng
genera
I sa
f
et
y
pre
ca
u t i
on
s
mus
t
be
observed
during
al
I
phases
of
ope
rat
ion,
service,
and
repair
o f t h i s e
q
u i pmen t . Fa i I u
re
to
comp
I y w i t h
these
pre
ca
u t i
on
s
or
with
speci
f
ic
warnings
in
this
manual
violates
safe
ty
s t a
ndards
of
design,
manufacture,
and
intended
use
of
thi
s
eq u i pme n t . C i r
cu
i t
Res
ea
r
ch
L
ab
s I n c . a s sume s
no
I i
ab
i I i t y
for
the
cu
s
tomer
' s f
ailure
to
comply
with
these
requiremen
t s .
1 . 5
RE
AD
i
ns
tructio
ns
ALL
INSTRUCTIONS
.
Al
I
safety
and
operating
should
be
read
be
f
ore
the
equipment
is
operated
.
1 . 6 GROUND AND
POJVER
CONNECTIONS .
To
minimize
shock
hazard,
this
equipment
must
be
connected
to
an
electrica
l
ground
.
Grounding
is
accomplished
by
proper
use
of
the
three
-
conductor
AC
power
cable
supplied
with
the
equipment
.
The
power
cable
must
either
be
plugged
into
an
approved
three-contact
electrical
outlet
or
used
with
a
three
-
contact
to
two-contact
adapter
with
the
grounding
wire
(green)
firmly
co
nn
ected
to
an
electrical
ground
at
the
power
outlet
.
This
equipment
must
only
be
operated
f
rom
the
type
of
AC I
ine
power
source
specified
.
See
Section
2 . 3
for
power
line
AC
voltage
selection
.
1 . 7
TRANSIENT
VOLTAGE
PROTECTION
.
In
areas
where
power
f
luctuations
and
voltage
spikes
a r e
present
on
the
AC
power
I
ine
additional
protection
may
be
necessary
.
1 . 8
DO
NOT OPERATE
IN
AN
EXPLOSIVE
ATMOSPHERE .
Do
not
operate
thi
s
equipment
in
the
presence
o f
f
larnnable
gases
or
f umes .
Ope
r a t i
on
o
f
any
e I ec t r i
ca
I i n s t r umen t i n su c h
an
en
v
i
r o nme n t
cons
t i
tut
es
a
de
f i n i t e sa f
et
y
hazard
.
PMC -4 5o ( C ) Cop y r i g h t C
i
r cu i t Re se a r c h Lab s , I n c . 19 89
Page
1-1

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1 .9 WATER AND NOISTURE. Do not operate this equipment near
water or in areas with wet floors . Do not operate this
equipment in high humidity atmosphere where condensation
forms on the equipment.
1. 10 ATTACHMENTS. Do not use attachments not recorrmended by
the manufacturer.
1. 11 VENTILATION. This equipment should never be placed
near or over a heat register or other source of heated air.
This equipment should not be placed in a built in
installation or rack unless proper ventilation is provided.
1.12 PARTS REPLACEMENT AND/OR ~IFICATION. The maintenance
instructions in this manual are for use by qua I i f ied
personnel only. To avoid electric shock do not perform any
servicing other than that contained in this manual . Do not
replace components with the power cable connected. Because
of the danger of introducing additional hazards, do not
ins ta I I substitute parts or perform any unauthorized
mod i f i ca t i on to t h i s equ i pme n t .
1. 13 INTRODUCTION
1.14 FEATURES:
1 . 15 ·NRSC Pre-Emphasis and Filtering Characteristic
·Gated Input Gain Reduction
·Patented Overshoot·Corrected Filtering Technique Removes
Out·of·band Components Without Loss of Peak Modulation
·Selectable Low-frequency Tilt Correction Circuit Improves
the Modulation Capabi I ity of Many Plate-modulated
Transmitters
·22 dB Range, 10 Segment Input Peak Indicator
·Programmable 1 dB step Peak Limiting Control
·Rugged 1 3/4. Rack-mount Chassis With Integral RFI
Protection
·Adjustable High Frequency EQ
·Adjustable Mid Range Presence
1 . 16 The CRL P MC • 4 50 i nco r po ra t e s de s i gns o r i g i na I Iy
developed for AM stereo. Gain reduction, pre-emphasis,
filtering , and limiting are combined to permit maximum
loudness with minimum distortion.
1 . 17 The PMC i s t he i de a I ch o i ce to up g r ad e a mo n au r a I au d io
processing chain to meet the NRSC (National Radio Systems
C orrm i t tee ) Vo Iun ta r y Nat i on a I St and a rd of January 10 , 1987 .
Th i s t r an s mi s s i on s t and a rd de f i n es spec i f i c p r e · emp has i s and
filtering requirements which are intended to help solve many
of the technical concerns in AM broadcasting. The pre·
emphasis curve was developed to allow receiver manufacturers
to employ a complementary de-emphasis characteristic in
wideband radios while improving the frequency response of
narrower and medium - bandwidth radios. The filter
specification, which limits transmitted audio bandwidth to 10
kHz, is intended to greatly reduce much of the interference
P MC · 4 50 (C) Copy r i g ht Ci r c u i t Re s e a r c h La b s , Inc . 19 89
Page 1-2

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between stations by reducing the conditions that cause
"splatter· effects (see Figure 1-1) . An 11 kHz cuto f f
frequency option can also be selected via a rear panel
sw i t ch . Th i s opt i on , i n many cases , can a I so y i e I d a
significant reduction in occupied bandwidth (this mode does
not con f orm to NRSC requirements) .
1.18 A gated input gain reduction circuit is included which
provides >20 dB of input gain control to prevent detrimental
I i mi t i ng e f f e ct s by ma i n ta i n i n g cons i st en t I eve I s i n to the
I i mi t er c i r cu i t s . Th i s e I i mi n ates •pump i n g • and other
processing artifacts caused by excessive peak limiting.
1.19 A resonant low pass clipping filter is used to prevent
excessive clipping harmonics which could result in higher
intermodulation artifacts. This patented filter eliminates
these excess i v e c I i pp i ng ha rmon i cs , a I I ow i ng the user to
i nc r ease I i mi t i ng to ob ta i n max i mum I o ud n es s cap ab i I i t y
without audible distortion .
1 . 2o I n
add i t i on , t he PMC - 4 50 i n c I u des a se I e c tab I e t i I t
correction circuit , which compensates for the low frequency
phase shift corrrnon in many plate-modulated transmitters .
This often results in an abi I ity to increase the overal I
modulation level by several percent.
1 . 21 Progranmable 1 dB per step peak limiting circuitry i s
provided with a range from Oto +s dB. This circuitr y
se I e
ct s t he amount o f i n s tantan e o us ga i n reduct i on ( I i mi t i ng )
applied to the audio signal .
1.22 To aid the user in properly setting the audio
into the unit , a 10 segment peak-reading LED input
meter with a range from ·20 to +2 dB is provided.
overload LED is also provided as one segment of
level
level
A red
indicator . Additional indicators are included to monitor
the
the
activity of filter overshoot - correction circuitry.
1.23 Audio interfacing
connector strip on the
active-balanced and fed
filters .
is done through the use of a barrier
back pane I . The Input and output is
through second-order Rf I suppression
1 .24 The PMC accepts either 115 or 230 volts AC (selectable
by prograrrrning the back panel power module), 48-440 Hz. The
un i t i s housed i n a s tee I enc I o su re for max i mum RF I irrmun i t y
and conforms to a standard 1 3/4" rack height measurement. A
r ac k s I i d e moun t i s av a i I ab I e a s an o p t i on .
1.25 The Mid Range Presence control al lows for the
adjustment of mid-band audio frequencies especially the voice
a r ea between lkHz and 4kHz . The control can add up to 6dB of
mid-range presence.
1 . 26 The EQ Control control Is the pre-emphasis curve and
includes a detent position that implements the NRSC Standard
Pre-emphasis curve.
P MC • 4 5o (C ) Cop y r i g ht C i r c u i t Re se a r c h L ab s , I n c . 19 89
Page 1-3

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FIGURE 1·1 TYPICAL TRANSMITTED SPECTRUM
(Laboratory transmitter, 15 minute peak-store display;
V:10 dB/div.,
H: 10 kHz/div., 300 Hz resolution
PMC-450 (C) Copyright Circuit Research Labs, Inc . 1989 Page 1·4

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1.27 WARRANTY
PRODUCT WARRANTY
1 .28 Circuit Research Labs, Incorporated warrants its
p r o du c t s to be f r e e o f de f e c t s i n ma t e r i a I s and / o r
workmanship . This warranty shall extend for a period o f (1)
year from the date the product was originally shipped to the
user .
1.29 Circuit Research Labs' warranty does not apply to
products that have been damaged due to and/or
subjected to
imp r ope r hand I i n g by s h i pp i n g comp an i es ,
negligence,
a cc i dent s , imp roper use, or a I t er at i on s not
authorized by
Circuit Research Labs, Incorporated.
1.30 THIS WARRANTY IS IN LIEU OF AND EXCLUDES ALL OTHER
WARRANTIES, EXPRESSED OR IMPLIED. CIRCUIT RESEARCH LABS,
INCORPORATED WILL NOT BE LIABLE FOR ANY INCIDENTAL OR
CONSEQUENTIAL LOSS OR DAMAGE WiATSOEVER, WiETHER BASED UPON
ALLEGATIONS OF NEGLIGENCE, BREACH OF WARRANTY, OR OTHERWISE .
THIS DISCLAIMER OF INCIDENTAL OR CONSEQUENTIAL DAMAGES
I t-·K L UDE S, BUT IS NOT L IM I TED TO , PROP E RT Y DAMAGE S , LOS S OF
PROFITS, LOSS OF TIME OR OTHER LOSSES OR INCONVENIENCE
RESULTING FR()\,1 ANY DEFECT IN THE MATERIAL OR V-.ORKMANSHIP OF
THIS PRODUCT OR ANY OTHER CONNECTION WITH THE PURCHASE,
OPERATION OR USE OF THIS PRODUCT. (S()\,1E STATES DO NOT ALLO.,V
THE EXCLUSION OR LIMITATION OF INCIDENTAL OR CONSEQUENTIAL
DAMAGES, SO THE ABOVE LIMITATION OR EXCLUSION MAY NOT APPLY
TO YOU) .
PRODUCT CHANGES
1.31 Circuit Research Labs Inc. reserves the right to change
the published specifications of equipment at any time, and to
furnish merchandise in accordance with current
specifications. While many previously sold products are later
upgraded by field bulletins , Circuit Research Labs Inc.
reserves the right to do so without incurring any liability
or obi igations to modify or update any equipment previously
sold .
P MC · 450 (C) Co p y r i g h t C i r c u i t Re se a r c h Lab s , I n c . 19 89
Page 1·5