CRL PMC-450 User manual

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I
I
I
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PMC-450
I PEAK MODULATION CONTROLLER
I
FOR AM
BROADCAST
I INSTALLATION AND OPERATION MANUAL
I
I
I
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=:el
THE
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PROFESSIONAL'S
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CHOl,
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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

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,.
32
NRSC
VOLUNTARY
ST
AND
ARD
COMPLIANCE
RECORD
1. 33
Please
return
the
enclosed
post
paid
card
to
the
NRSC
,
so
that
broadcast
equipment
manufacturers,
receiver
manufacturers,
and
the
trade
press
can
be
informed
as
to
the
progress
of
conversion
to
the
voluntary
national
standard
.
1. 34
If
this
card
is
missing
notify
Circuit
Research
Labs
Inc
or
:
National
Radio
Systems
Corrmittee
c/o
NAB
Science
&
Technology
1771
N
Street
,
N.W
.
Washington,
D.C.
20077·6316
P
MC
- 4 5O ( C) Co p y r i g h t C i r cu i t R
e se a r c h Lab s , I n c . 1
9 89
Page
1-6

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1.35 PMC-450 SPECIFICATIONS
BLBCTR/CA.L
INPUT
Type:
Impedance:
Termination:
Level (adjustable):
OUTPUT
Type :
Impedance :
Level (adjustable) :
FREQUENCY RESPONSE
9.5 kHz filter
bandwidth selected:
11 kHz f ilter
bandwidth selected
Proo f Mode:
HARtv'lONIC DISTORTION
9.5 or 11 kHz BW :
Proo f mode :
S+N/N:
INPUT GAIN REDUCTION :
LIMIT I NG :
HI ·FRE Q EQUALIZATION :
(Ref. 0 dBm=0.775 YRMS)
Active balanced (differential)
>lOK ohms bridging
Selectable 600 ohms
<·10 to +20 dBm; ref. to 0 dB indication
on front panel level meter
Active balanced (differential)
100 ohms (to drive 600 ohm load)
<·20 to +20 dBm; ref. to 100% negative
mod u I a t i o n I e v e I , a s e s t ab I i shed
internally
(0 dB ref. at 400 Hz, +10 dBm input/output)
5o Hz t o 8 kHz ; +o / - 1 . 5 d B
·3 dB at 9.5 kHz
>30 dB atten. at 10 . 5 kHz
>4 0 d B a t t e n . a t 1 1 . 0 kHz
Conforms to NRSC standard using required
dynamic measurement method
50 Hz to 10 kHz; +0/· 1.5 dB
- 3 dB at 11 kHz
>30 dB atten. at 13.5 kHz
50 Hz to 15 kHz ; +/· 0.5 dB
(+10 dBm input/output, 20 kHz bandwidth)
<0.25% over selected operating bandwidth ,
at or below 100% negative modulation level
<o . 1%
>65 dB in operate mode
> 7 5 dB i n p r oo f mod e
Input leveling AGC ; selectable
in 2 dB increments to 8 dB,
>20 dB overal I range
Se I e c t ab I e i n 1 dB i nc r emen t s f r om
O to +s dB; dual band, crossover
frequency : 3 . 5 kHz
Follows NRSC standard pre-emphasis
characteristic, 20 Hz to 10 kHz, when
front panel HI-FREQ EQUALIZATION
control is i n NRSC position . The
cont r o I i s cont i nu o us I y var i ab I e f r om
the OFF position to the MAX
P MC · 4 5 O ( C ) Copy r i gh t C i r cu i t Re s ea r c. h L ab s , I n c . 19 89

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BASS PRE-EMPHASIS:
ASYiVtVIETRY:
TILT CORRECT :
INDICATORS:
GBNBRAL
OPERATING TEMP. RANGE :
PONER REQUIREMENTS:
OPERATING HUMIDITY:
OPERATING ALTITUDE:
SHIPPING WEIGHT:
DIMENSIONS :
MID RANGE PRESENCE :
position.
Internally selectable bass boost function
can be p I aced i n c i r cu i t to imp rove appa r en t
low frequency response of many AM receivers
Adjustable threshold al lows up to +150%
positive peak modulation
5e I e ct ab I e c i r cu i t a I I ow s co r rec t ion of I ow
f re qu ency phase sh i f t found i n some p I ate·
modulated transmitters
1. l0·Segment LED·type input level meter
with a 22 dB (28 dB with OVLD) dynamic
range
2 . +I · I imi t i nd i ca to r s mo n i t o r a c t i v i t y
of patented overshoot-corrected filter
circuitry
32 to 122 degrees F (0 to 50 degrees C)
100·130 or 200·250 VAC, 48·440 Hz ,
20 VA maximum , EMI suppressed,
IEC connector standard
0·95% RH, non condensing
0 · 15 , 00o feet AMS L
18 lbs . ( including standard accessories)
19" (48.3 cm) W, 1.75" (4.5 cm) H,
16 • (4 0 . 6 cm) D, i nc Iud i ng pro t r ud i ng
controls and connectors.
Allows the adjustment of mid·band audio
frequencies especially in voice area
between 1 and 4 kHz. Can add up to 6 dB
of mid-range presence .
Product specifications are subject to change without notice
because of technology updates and product improvements.
P MC · 4 50 (C) Copy r i ght Ci r cu i t Re sea rc h Labs , Inc . 19 89
Page 1·8

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SECTION
2 ·
INSTALLATION
2.
1
GENERAL
2.2
The
front
panel
of
the
PMC-450
is
pictured
in
Figure
2·
1
and
the
back
panel
is
pictured
in
Figure
2·2
.
••••••**•
DO
NOT
PLUC
IN
THIS
UNIT
UNTIL
THE
POWER
WARNING
LINE
SWITCH
HAS
BEEN
CHECKED
AND/OR
SET
FOR
0•0
•u•
THE
CORRECT
AC
POWER
LINE
VOLT
ACE
AS
PER
SECTION
2.4.
IT
IS
IMPORTANT
TO
CAREFULLY
FOLLOW
THE
PROCEDURES
LISTED
BELOW
IN
SECTION
2.3
BEFORE
POWER-UP
OF
THIS
UNIT
.
Pe
ak
Modu
latio
n
Co
ntroll
er
·~·
· .
·~
·
.,
.
'
~
.~ {:. ·······~~~·
..
:~:-
..
:s:..
.
..:~:-
..
" '
FIGURE
2-1
PMC-450
FRONT
PANEL
~. • •
~•
A
\1
1 0U1
~
UI
O,:-
• - ' • - , . a ,
♦
-
( HU
•t
J
uo
OH I I U I l• I
0
2
11ol3lel
el
e
leJeJeJeJeJeleJeJelel
o
:'.
·
.::.-:
:· ··;
1111
:::1.•
•
:-
o e
C::=J •
0
..
..
..
,·,
..
"
FIGURE
2·2 PMC-450
BACK
PANEL
2.3
BEFORE
POWER-UP
0
1.
Se t
th
e
power
I
ine
module
as
pe r
Section
2.4
C
0
CRL
SISHMS
• -
•H:
:r::
~
...
.
•
~
11,
::
• -
JH
:
2.
Set
the
internal
jumpers
as
required
for
the
intended
sy s
t em
a
pp
I i ca
t
i
on
a s
p e
r
Sec
t
i
on
2 . 6 .
3 .
Co
n
nect
the
unit
as
per
Section
2 .
11.
4 . Se t
th
e s
witches
and
controls
to
the
initial
settin
g s
li
s
ted
i n
Section
2.21.
PMC-450 (C)
Copyright
Circuit
Research Labs, Inc. 1989 Page
2-1

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2.4
POWER
LINE
AC
VOLT
AGE
SELECTION
2 . 5
The
PMC-450
is
equipped
with
a
power
I
ine
module
on
the
back
panel
with
an
integral
I
ine
voltage
PCB
selector
so
that
the
unit
can
be
operated
in
areas
having
various
line
voltage
av
ailabilities
.
The
unit
is
shipped
to
USA
destinations
set·
up
for
a
I
i ne vo
I
tag
e
of
1
1
5 /
1
20 V
AC,
us
i ng a 1/ 4
ampere,
s
I
ow·
b
I
ow
type
fuse
.
To
set
·up
the
un i t
for
a d i f
fer
en
t
I
i ne vo
I
tag
e
see
F
i gu r e
2 . 3
and
f o
I I
ow
t
he
p r o c e
du
r e
be
I
ow
.
1 .
2 .
~
100 D
12 0
■
220
D
240 D
FIGURE
2·3
LINE
VOLT
AGE
SELECTION
NOTE :
The
power
I
ine
module
used
may
vary
from
the
one
shown
above
.
Di
s
connect
the
power
cord
f r om
the
module
.
Open
the
~
compartment
containing
the
fuse
and
the
PCB
voltage
selector
by
pushing
in
on
the
raised
the
power
plug
receptacle
.
lever
adjacent
to
Remove
t
he
PCB
vo
I
tag
e se
I
e c
to
r
and
po
s i t i
on
i t
the
red
I
ine
on
the
edge
of
the
PCB
corresponds
opening
in
the
cover
opposite
the
legend
f
or
the
line
voltage
.
so
that
to
the
desired
3 . I
n
s
e r t t he
PCB
vo
I
t a g
e
se
I
e
c t o r f i rm
I
y i n t o t he
mod
u
I
e
slot
.
4 .
Remov e t
he
f u se f r om t
he
f u se
ho
I
de
r
comp
a r t
men
t
cover
.
Se
I e
ct
a
fuse
as
insert
the
fuse
i n
the
fuse
holder
.
on
the
back
of
I i
s t e
d
be
I
ow
100
to
130
VAC
operation
200
to
250
VAC
operation
1/4
ampere
,
slow-blow
type
1/8
ampere
,
slow-blow
type
the
and
NOTE :
Ope
r a
t i
on
o
f
t
he
u n i t
on
200·
250
VAC
will
require
r ep I ac emen
t
o f t
he
p I ug
u n i t
to
the
AC
I i ne .
that
is
used
to
connect
the
PMC•
4
50 (C )
Co
p y r i g h t C i r cu i
t
Re sea r c h L ab s , I n c . 19 89 Page 2• 2

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5 . CI o se the comp a r t men t cover and i n s er t the
into the receptacle on the module.
line cord
2.6 INTERNAL JUMPERS
2. 7 The PMC
the unit to
jumper s as
requirements.
at t h i s t ime .
i s eq u i
pp ed w i t h i n t e r na I j ump e r s to con f i gu r e
individual operational requirements. Set the
applicable for the individual station
(DO NOT adjust potentiometer R146 on the PCB
See Section 6 . 3 for making this adjustment) .
JUMPER FACTORY
FUNCTION OF JUMPER
POSITION
JS INSTALLED +1s V DISCONNECT JUMPER. The positive DC
power connection between the power supply
and t he c i r cu i t r y i s b r o ken when th i s jumper
i s removed.
J6 INSTALLED • 15 V DI SCONNECT JUMPER . The neg at i v e DC
power connection between the power supply
and the circuitry is broken when this jumper
i s removed.
J9 TERM TERMINATING OR BRIDGING INPUT JUMPER. In
the TBRM po s i t ion , the i n put has a 6 0 0 ohm
t e rm i na t i on . T he BR IDGB po s i t i on p r e s en t s
an impedance of >l0K ohms .
Jl0 OUT BASS CLIP JUMPER. This jumper selects the
low frequency response of the input leveling
AGC c i r cu i try . I n the OUT po s i t ion the I ow
frequency response is flat. In the IN posi·
tion the G/R circuits do not respond to
frequencies below 100 Hz . The OUT position
i s rec onme n de d for mos t a pp I i cat i on s .
Jll IN BASS PRE-EMPHASIS JUMPER. The IN position
produces a response peak at approximately
105 Hz o f approximately 3 dB above 400 Hz
reference. It also produces a rapid roll-
off below 100 Hz to prevent the transmission
of subsonic in f ormation. This position i s
used to improve the apparent f requency resp-
on se o f many r e c e i v e r s . I t may a I so
increase the performance of some plate modu·
lated transmitters that are unable to toler-
ate subsonic information . In the OUT posit-
ion , the frequency response is flat .
J17 OUT TILT CORRECT. This jumper is used in conju·
n ct i on w i t h the TI LT CORRBCT cont r o I ( back
panel) to provide tilt correction to the
s i gna I a t t he AUX OUT t e rm i na I s . When t he
P
MC - 4 50 ( C) Co py r i gh t C i r cu i t Re sea r c h Lab s , I n c . 19 89 Pa ge 2 - 3

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jumper
is
in
the
IN
position
the
TILT
CORRBCT
co n t r o I ad j u s t s t
he
co
r r ec t i o n c i r c -
uitry
used
to
compensate
for
low
frequency
phase
shift
(see
Section
2 .
25)
.
2.8
PCB
LED
INDICATORS
2.9
PONER SUPPLY PCB
INDICATORS
2 .
10
Apply
AC
Line
power
to
the
unit
and
verify
that
the
power
supply
voltages
are
present.
The
voltages
are
present
when
DS1
and
DS2,
the
red
LED's
on
the
main
PCB,
as
listed
be I
ow
, a r e i I I um i na t ed . I F DS
1
and / o r D52
AR
E NOT
i I
lum
i
nated
go
to
Section
6.4,
TROUBLESHOOTING.
LED VOLTAGE CCM'v\ENTS
DSl
+1
5 VDC
Fixed
;
measure
at
TP4
+!
-
50
mVDC
DS2
- 1 5 VDC
Fi
x
ed
;
measure
at
TPS
+!
-
50
mVDC
GATE LED
INDICATOR
This
LED
is
illuminated
when
the
gate
circuitry
is
activated
.
This
f
reezes
all
gain
control
action
when
the
level
drops
below
the
gate
threshold
(-20
dB)
.
LED DE
S
CR
I PTI
ON
DS
3
Gate
Indicator
2.
11
INTERCONNECTIONS
2 .
12
GENERAL
2 . 13
T
he P
MC
• 4 50 i s d es i gned t o i n t e r f a ce w i t h ma n y t yp e s o f
broadcast
equipment
.
See
Figure
2 . 4 f
or
some
typical
app I i ca t i o n s f o r t h i s u n i t w i t h i n t he o v e r a I I sy s t em. Th
i
s
unit
may
be
wired
for
either
balanced
or
unbalanced
operation
and
is
always
placed
inmediately
before
the
transmitter
in
the
audio
path.
P
MC
• 4 50 ( C ) C
o
p
y r i
g h t C
i
r c u
i
t R
e se a r c
h L
a
b
s ,
I
n c .
19 89 P
a
g
e
2 • 4

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r,
0
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STUlllO
AUDIO
CAL
AGC400
AGC
STUDIO
AUDIO
STL
TRANS.
CAL
f-----+
AGC400
STUDJO
AUDIO
AGC
CAL
STL
SEC400
4
BAND
R
EC
EIVER
COMPRESSOR
!
OPTIONAL)
(Al
USE
WITH
MONAURAL
STL
EQUALIZE
□
TELCO
LINE
\
CAL
CAL
-
SEC400
__..,
PMC450
-4
BAND
AM
COMPRESSOR
LIMITER
lll'TIONAL)
(Bl
USE
WITH
TELEPHONE
LINE
CAL
AGC400
AGC
CAL
SEC400
4
BAND
COMPRESSOR
!OPTIONAL)
CAL
PMC450
AM
LIMITER
(Cl
CO
-
LOCATED
STUDIO/TRANSMITTER
SITE
....
__.,
CA
L
PMC450
AM
LIMITER
MAIN
TRANS.
MAIN
TRANS.
MAIN
TRANS.
""
/

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2 .
14
BALANCED
LINE
CONNECTIONS
2.15
Most
broadcast
equipment
is
designed
for
balanced
line
operation
.
Connect
as
per
FICURE
2 .
5.
The
PMC-450
has
one
input
and
one
main
output
connection
. An
auxiliary
output
connection
is
also
provided
for
driving
a
second
transmitter
.
A
two
conductor
shielded
cable
should
be
used
(Belden
18451
or
equivalent)
with
a
red
and
black
twisted
pair
inside
a
shielded
covering.
Connect
the
red
lead
to+
terminal
on
the
barrier
strip,
the
black
lead
to
the
terminal
on
the
b a r r i e r s t r i p , and t he sh i e I d ( g r ound ) t o
GND
t e
rm
i na I o n t he
barrier
strip.
THE
CABLE
SHIELD
SHOULD
BE
CONNECTED TO
GROUND AT
THE
SOURCE
END
ONLY
TO PREVENT GROUND
LOOPS.
2 . 16
UNBALANCED
LINE
CONNECTIONS
2.17
Connect
the
equipment
EXACTLY
as
shown
in
Figure
2
.6
f
or
operation
with
unbalanced
line
equipment
.
The
PMC-450
has
one
i n
put
and
one
ma i n
output
connect
i
on
. An
aux
i I i a r y
output
connection
is
also
provided
for
driving
a
second
transmitter.
NOT E:
Wh
en u s i ng t he unba I an
c
ed I NPUT c onne c t i o n o n I y , t he
shield
is
connected
to
the
ground
terminal
and
the
negative(-)
terminal
is
connected
to
the
ground
by
a
jumper
w i
re
as
sh
own
i n F i gu
re
2- 6 .
CAUTION: When
using
an unbalanced output, the
shield must be connected
to
the
ground
terminal. The negative (-) output
terminal must be
left
unconnected.
This
equipment does not use transformers;
therefore, accidental
grounding
of
the
negative (-) output terminal will short
half
of
the output circuit. Also,
the
output level will be 6
dB
lower
than the
balanced output level. Unbalanced operation
is
not recommended
in
most applications since
RFI
suppression
is
most
effective
when a
balanced-line connection
is
used.
P
MC
- 4 5O (C ) Cop
y
r
i g h
t
C
i
r cu
i
t
R
e sea r ch L
ab s , I nc . 19 89 Page 2 - 6

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(
INPUT
OUTPUT
+ - GND + - GND
,,,--- ......
"
)--
INPUT
OUTPUT
AUX OUT
GND
\ J
/
OUTPUT
TO NIGHT OR
AUX TRANSMITTER
FIGURE 2·5 BALANCED LINE CONNECTIONS
INPUT OUTPUT
+ - GND + GND
-- '
: "'""41---....J
,_ - .,,,.
INPUT OUTPUT
AUX OUT
GND +
\
I
,.._ _ _ ,,,,
OUTPUT
TO NIGHT OR
AUX TRANSMITTER
* DO NOT CONNECT
FIGURE 2·6 UNBALANCED LINE CONNECTIONS
PMC • 4 50 ( C ) Co p y r i gh t C i r c u i t Re s e a r c h L a b s , I n c . 19 89 Pa ge 2 • 7