Pacific Recorders & Engineering SDA-8A User manual
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PACIFIC
RECORDERS
&
ENGINEERING
CORPORATION
EATURES:
■
BRIDGING STEREO INPUT TO EIGHT STEREO OUTPUTS
■
HIGil
OUTPUTLEVEL, HEADROOM CAPABILITY
■
ADJUSTABLE GAIN, UNITY TO 30 dB ,
BRIDGING/TERMINATING
INPUT
MODE SELECTION
■
VERY LOW NOISE AN
DISTORTION
■
EXCELLENT FREQUENCYAND TRANSIENTRESPONSE
■
TRUE VU
METERING, SWITCHABLE TO INPUTS/OUTPUTS
■
XLR -TYPE INPUT/OUTPUT
CONNECTORS
■
EFFECTIVE
RF
SUPPRESSION
The
SDA - 8
is
a
high
quality
stereo
distribution amplifier
designed
for
general
purpose
use
in professional
audio
systems. While
designed
as
a stere_o amplifier,
the
SDA - 8
features
excellent
crosstalk isolation
between
the
stereo
channels,
and,
therefore
is
also
an
ideal
distribution amplifier
for
two
monaural
sign~ls.
The i
nputs
are
balanced
bridging, 25K ohm,
which
are
switchable
to
600
ohm
terminating.
The
stereo
bridging
inputs
may
be
parallel
fed from a
common
signal
thus
providing
sixteen
outputs.
Careful
attention
to
the
inputtrans-
former
and
amplifier
designs
has
insured
excellent
frequency
and
transient
response
while minimizing noise
and
distortion.
T
he
gain
of
each
stereo
channel
may
be
adjusted
from unity
to
30
dB. This
wide
range
makes
SDA - 8
the
universal
amplifier
for
broadcast
signal
distribution.
The
gain
controls
are
feed-back
t
ype
which
maintain
optimum
noise
and
headroom
performance
for
a
ll
gain
settings.
T
he
distribution outputs
are
differential,
balanced
to
ground,
and
designed
to drive
600
ohm
or
higher
(bridging) loads.
E
ach
output
is
capab
le
of
simultaneous
levelin
excess
of +26
dBm into
600
ohm
loads,
and
+
27
dBm into lOK
ohm
or
greater
bridging
l
oads
.
The
VU
meters conform to ASA specifications
and
are
switch-
able
from
output
to
input
reading.
The
meters
are
driven
by
bridging buffer amplifiers which isolate t
he
distortion products
of
the
meter
movement
rectifie
rs.
T
he
buffer amplifiers allow a
"
O"
VU
calibration
trim
range
of +4 dBm to +8 dBm.
T
he
amplifier
and
power
supply
designs
are
a
combination
of
discrete
and
integrated
circuitry.
All
components
are
conser
-
vatively
ra
t
ed
for
high
performance,
long life
operation.
The
amplifier
is
cons
t
ructed
on
an
e
poxy
glass
,
double-sided
PC
board.
T
he
use
of
an
ex
tensive
ground
plane
shield
on
the
component
side
of
the
circuit
board,
in
addition
to
de-
coupling
and
bypass
techniques,
ensures
amplifier stability
in
high
RF
environments.
STEREO DISTRIBUTION AMPLIFIER
CONTROL
FUNCTIONS:
Input Termination switch
provides
a
600
ohm
termination
for
the
bridging
inputs.
Meter Input/Output switch
selects
the
meter
monitori.
source
.
INPUT
reads
the
level
at
the
amplifier input connectors;
OU
TPUT
reads
the
pre-split
leve
l of
the
output
amplifiers
Gain
Trim
controls
have
a
range
of unity to
30
dB
inpu
t to
output
gain.
.
SDA-8
unctional
Block
Diagram.
I
NPiJT
TEAMINATION
LEFlGAIN
ADJUST
Upper Trace
2KHz
Square
Wave
I
nput
Lower Trace
Amplifier
Ou
t
pu
t
Left Trace
0.2 ms/div
Right Trace
10 µs/div
Amplifier Output
Rise Time: 9µ s
Overshoot: 0%
Ringing: N
one
SDA -8 TECHNICAL SPECIFICATIONS
Source
Impedance
600 ohms
Input
Impedance
25K
ohms,
balanced
and
floating,
transformer
isolated.
Gain
Range
Unity to 30 dB.
Outputs
Eight
balanced,
differ~tial
outputs
per
channel.
Load
Impedance
600
ohms
or
greater
per
output
Source
Impedance
78
ohms,
resistive
Nominal
Output
Level
+8
dBm. VU
meter
may
be
recalibrated
for +4 dBm
reference
.
Maximum
Output
Level
+26
dBm into
eight
600
ohm
loads,
+27 dBm into
bridging
loads
.
Output
Isolation
Short circuit of
any
one
output
results in
no
amplitude
change
at
other outputs.
Crosstalk
Isolation
Greater
than
80
db
, 20Hz to 20KHz
Frequency
Response
20Hz to
20KHz,
+0,
-0.7
dB
Input
Noise
-112
dBm RMS
equivalent
input
noise,
600
ohm
source,
20KHz
bandwidth.
Output
Noise
-82 dB
below
output, (reference
+8
dBm), 600
ohm
source,
20KHz
bandwidth,
30 dB
gain
.
Distortion
, T.H.
D.
Less
than
0.005% @ lKHz,
+8
dBm.
Less
than
0.
07%
@ lKHz,
+26
dBm.
Less
than
0.
06%,
20Hz to 20KHz,
+8
dBm.
Distortion
I.M
.
Less
than
0.003% SMPTE,
+8
dBm.
Less
than
0.
03%
SMPTE,
+26
dBm.
Square
Wave
Response
Rise
time
less
than
10
µs.
No
overshoot or ringing. 2 KHz
square
wave
test
signal.
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SDA-8A
STEREO
DISTRI
BUTION
AMPLIF
I
ER
PR&E DOCUMENT#75-15
STATUS PAGE
(Revision
A-1
-JULY 1992)
This
listingprovidesareferenceofcurrentpagesofthisdocument,
and
theirrevisionnumbers(i.e.,
A.1,
A.
2,
etc.).
When
arevisiontothisdocumentisreceivedf
rom
PR&E
,simply
rep
l
ace
theoldpageswith the n
ew
on
es,
discard
theoldpages,andpostthe
new
status
page
inthefrontofthismanual
CHQIE.
:It
may
be
desirableto
retain
replac
ed
status pages in order to have a record of document changes). If
de
emed necessary by our
Eng
inee
ring
Department
,comment informationrelating to any change
may
also be included on this page.
eaa.~
ALL
PAGE26
Bev1s100
A
A·1
Comments
New Relea
se
.
Schematic revision.
R
EVISION
A• 1
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SDA-SA
STEREO DISTRIBUTION AMPLIFIER
TECHNICAL MANUAL
1.0 GENERAL INFORMATION
This chaptercontains
an
introduction to the SDA-8A StereoDistributionAmplifierTechnical
Manual
,
an
overview
of
the SDA-8A
's
features, its specifications and warranty information.
1.1 INTRODUCTION
PR&E
isin
the
business
of
supplying
the
finest audiosystems totheworld'sleading broadcastfacilitie
s.
Yourdecision to go with
PR&E
means that
you
expect morethan simpleworking hardware. Please be
assured that itis ourstrongdesire
to
provide each
of
ourcustomers with the kind
of
products,systems1
documentation and support that we would specify
if
we
were
in your position.
We
invite your comments and suggestions for improvement
of
thisdocument, and
of
all ourservices.
By
constantattentiontoourcustomer'sneeds,
we
willcontinuetoearnourreputation forexcellence,
and
to
refine ourunderstanding
of
the
requirements
of
the marketplace.
This
man
ualisdesignedtoprovidetheinformationrequiredtounderstand,install, operate,andmaintain
the
SDA-8A Stereo Distribution Amplifier. Itis assumed that
the
readerhas a working knowledge
of
audio devices, systems,and installation practices. Toobtain the maximum benefit
of
the
distribution
amplifier's capabilities, it
is
strongly recommended that the Installation, Setup and Operation,
and
Equipment Description chapters
of
this manual
be
read
c-0mpletely
prior
to
installing the unit.
Each SDA-8Aisthoroughlytestedand"burned-in"priortopackingforshipment. Should
you
encounter
any difficulty during installation or initial operation, we recommend that
you
contact
PR&E
for
assistance.
1.2 OVERVIEW
The SDA-8A is a high quality stereo distribution amplifier designed
for
general purpose use in
all
professional audio applications. Thesuccessor
to
the
very popularSDA-8, the SDA-8A incorporates
several
new
anduniquefeatureswhileusinghalftherackspace
of
theSD
A-8.
Among
the
improvements
areafrontpanelheadphonejack,atransformerlessinputwithanextremely
high
commonmoderejection
ratio (CMRR),
an
input mode switch allowing the
c})oice
of
stereooravariety
of
mono inputs, apatch
pointon the rearpanelfor the insertion
of
processingequipment, the use
of
Molex connectors,
and
the
placing
of
the output amplifiers on plug-in removable function modules, for ease
of
replacement.
Althoughprimarily astereoamplifier(withexcellentseparation between thestereochannels),the
SDA
-
1
REV
ISION
A
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SDA-SA
STEREODISTRIBUTION AMPLIFIER
8A
is
also
an
ideal distribution amplifierfor monaural signals. The unique input mode switch permits
the amplifier
to
distribute the STEREO inputto eight stereo outputs,
or
to distribute a choice
of
three
monaural modes (LEFr, RIGHT orSUM L+R) to sixteen monaural outputs.
Thefully-regulated powersupplyfeatures atoroidalpowertransformer.which
is
compact,efficient,and
has
very lowelectromagneticfield radiation. Theamplifierandpowersupplydesign areacombination
of
discrete and integrated circuitry.
All
components areconservatively rated for,highperformanceand
long-life operation.
All controls and adjusnnents are located behind a translucent plexiglass security panel to discourage
unauthorized tampering, while allowing viewing
of
thepowerindicatorand panel settings.
1.3 SPECIFICATIONS
Following is a list
of
specificationsfor the SDA-8A Stereo Distribution Amplifier:
INPUTS:
Source Impedance
Input Impedance
Input Level Range:
Main Input
Patch Return Input
Input Headroom
Input
CMRR:
Main Input
Patch Return Input
OUTPUTS:
Output SourceImpedance
Output Level:
Main Output
Patch Send Output
Headphone Output
Maximum Output Level (Main)
FREQUENCY RESPONSE
NOISE
DISTORTION, T.H.D.
600ohms or less.
40Kohms balanced, 600ohms switchable option.
Adjustable from -30dBu
to
+9
dBo
.
Nominal -10dBu.
Greater than 20
dB
above nominal input.
Greater than
80
dB
below lkHz; greater than 60
dB
from 20
Hz
to 20.kHz.
Greater than 40
dB
at lkHz.
80ohms balanced, 40ohms singleended.
Adjustable from +4 dBm to
+8
dBm.
Nominal -10dBu.
+4
dBm to
+8
dBm, depending on Main Output.
+26 dBm into 600ohm loads; +27 dBu into bridging loads.
+o
dB
, -0.6dB, from 20
Hz
to
20 kHz.
80
dB
below output, reference+8dBu, 600ohmsource, 20 kHz
bandwidth.
Lessthan0.008%,+26dBuinput, +26dBmoutputintoa600ohm
load, 80
kHz
meter bandwidth.
2
REVISION
A
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DISTORTION.
I.M
.D.
STEREOSEPARATION
POWER REQUJREMENTS
NOTES
:
SOA-8A
STEREO
DISTRIBUTION
AMPLIFIER
Lessthan0.008%,+26dBuinp
ut
.+26dBm outputintoa600
ohm
load, SMPTE test method.
Betterthan 80
dB
at 1
kHz..
10
wans at
117
V
AC,
+/- 10%, 60Hz.
A)
Thesespecificationsareforthebasicsignalpaths,
per
channel,with600ohmloadsconnected
to theprogramoutputs.
B) 0
d.Bu
corresponds
to
an amplitude
of
0.775 volts RMS regardless
of
the impedance
of
the
circuit. It is the same voltage value
as
0 dBm measured
in
a 600ohmcircuit. Thisenables
convenient level measurement with meters calibrated for 600ohm circuits.
C) Noise specifications arebased upon a 20kHzmeasurement bandwidth. The use
of
a meter
with a 30
kHz
bandwidth will result in a noise measurement increase
of
approximately
1.7
dB.
Pacific Reoordcn &
Engineering
Corporation
reserves
the
right
to
changespecifications withoutnotice orobligation.
1.4 WARRANTY INFORMATION
This product carries a manufacturer's warranty which is subject to the following guidelines
and
limitations:
A) Except as expressly excluded hereinafter, Pacific Recorders & Engineering Corporation
("Seller'')warrants equipment
of
its
own
manufactureagainstfaultyworkmanshipor
the
use
of
defectivematerialsforaperiod
of
one
(1)
yearfromdate
of
shipment
to
Buyer. Theliability
of
the Seller und
er
this Warranty is limited
to
replacing, repairing
or
issuing credit (at the
Seller's discretion) for any equipment, provided that Selleris promptly notified in writing
within five
(5)
days
upon
discovery
of
such defects by Buyer, and Seller's examination
of
suchequipmentshalldisclosetoitssatisfactionthatsuchdefectsexisted atthe timeshipment
wasoriginallymade
by
seller,andBuyerreturnsthedefectiveequipmenttoSeller'splace
of
businessinCarlsbad,California, packaging
and
transportageprepaid, withreturnpackaging
and ttansportage guaranteed.
B)
Equipment furnished by Sellerbut manufactured by another shall
be
warranted only
to
the
extentprovided by the other manufacturer.
C) Thermal filamentdevicessuchaslampsandfuses areexpresslyexcluded
from
thiswarranty.
D)
Thewarrantyperiod on equipment
or
partsrepaired
or
replaced underwarranty shall expire
3
REVISION
A
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SDA-8A
STEREO
DISTRIBUTION
AMPLIFIER
upon the expiration date
of
the original warranty.
E)
ThisWarrantyisvoid forequipmentwhich hasbeen subject
to
abuse, improperinstallation,
improper operation, improper
or
omitted maintenance, alteration, accident, negligence (in
use, storage, transponationorhandling),operation notin accordancewith Seller'soperation
and serviceinsttuctions, oroperation outside
of
theenvironmental conditions specified
by
Seller.
F)
This Warranty is the only warranty made by Seller, and is in lieu
of
all other warranties,
includingmerchantabilityand
fl.mess
foraparticularpurpose, whetherexpressedorimplied,
exceptas totitle andto theexpressedspecificationscontained
in
this manual. Seller's sole
liability for any equipment failure or any breach
of
this Warranty is as set forth in
subparagraph A) above; and Sellershall notbeliableorresponsible for anybusinesslossor
interruption, orotherconsequential damages
of
any nature whatsoever, resulting from any
equipment failure orbreach
of
this warranty.
4
REVISION
A
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SDA
-
8A
STEREO
DISTRIBUTION
AMPLIFIER
2.0 INSTALLATION
This chapter provides instruction in the proper installation
of
the SDA-8A. Included are sections
outlining general installation guidelines, cable preparation, rear panel configuration, audio input
connection, audio output connection, patch point connection, grounding and shielding, and power
connection.
2.1
GENERAL GUIDELINES
The SDA-8A should becarefully unpacked andinspected for any shipping damage. Ifthe inspection
reveals any damage, file a claim with the delivering carrier. The packing material should be kept
as
evidence
of
mishandling, as well as
to
allow return
of
the equipment to the factory
if
necessary.
ThepackeditemsshouldincludetheSDA-8Aitself, thepowercord, thelegendpanel(PR&E#80-1041)
and a connectorkit (PR&E #76-60). This connector kit is used to prepare the audio input and output
cables (as described in Section 2.2), and contains the following:
DESCRIPTION
ConnectorHousing,
12
Pin, Male
ConnectorHousing, 6 Pin, Male
Molex Crimp Pins, Male
Qll
1
9
70
PR&E#
15-605
15-603
15-3
When installing the SDA-8A,signal andACpowerconnectionsare madevia
th
e connectors locatedon
the rear
of
the unit (referenceFigure 2.2).
TheSDA-8Arequires onerackunit
of
height (1.75 inches) in a standard rack width
of
19
inches. The
depth
of
the SDA-8A from the rack rails is
10
inches, however, itisrecommended that the installation
allow an additional two inches
to
accommodaterear panel connections and cable bends.
Thelegendpanelismountedon thefarrightside
of
the SDA-8A,adjacenttotheVUmeteres,andis
held
inplace
by
thesame mounting screwswhich securethe SDA-8A in therackrails. Toinstall,simplyline
uptheholesinthelegendpanelwiththemountingholesintheSDA-8Afrontpanel,then securetheSDA-
8A into therackrails. Slide the legend into the legend panel from the right side.
NOTE:
Legenddimensions are 1-9/16" by
13/16".
Thepowertransformerusedin the SDA-8Ais a toroidal type, which exhibitsa lowradiated humfield.
NOTE
: Careshould
be
taken to avoidlocating the SDA-8A within six feet
of
any intenseelectromag-
netic hum fields such
as
those produced bylarge powertransformers and motors. Likewise, cables
to
andfrom theunitshould
be
routedtoachievemaximumpracticaldistancefrom ACmainspowerwiring.
Particularattention should
be
paidtosome
of
thelow-cost, supposedly"professional",poweramplifiers
which haveappearedinthemarketplace. In
many
casesthelowcosthas been partiallyachieved through
theuse
of
smallcorepowertransformersoperatingatorontheedge
of
saturation. Whiletheseunits
may
5
AE
V1
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,,
SDA
-
SA
STEREO
DI
S
TRIBUTION
AMPLIFIER
operate to their own specifications,theelectromagneticfields they radiate mayimpairtheperformance
of
the SDA-8A orneighboring equipment, such as tape recorders ormagnetic phonograph cartridges.
2.2 CABLE PREPARATION
Before beginning the installation, a plan should be drawn
up
showing how the system will be
interconnected.
All
cablesandconnectors should
be
tagged with numbersand/
o,
r legends,and logged.
Only unspliced, preferably new, cables should be used in connecting the
SDA
-8A. Audio input
and
output connections should be made
with
2-conductor stranded insulatedfoil shielded cable with drain
wire. Thecable used should beequivalent
to
Belden types
8451
, 9451.
or
8761.
Strip thecableinsulationjacketandfoil shieldback about 1-1/2inches. and sleeve the shielddrain wire
with heat-shrinktubing, leaving about 3/16 inch
of
the wire exposed. Then,strip theinsulation
of
each
signal wire back about 3/16 inch, and sleeve the shield (at cable ends) with heat-shrink tubing.
NOTE:
It isveryimportanttosleeve thecabledrain wire and the shield(atcableends) with heat-shrink
tubing. This isthe only means
of
assuring an installation in accordance with recommended grounding
procedures.
TheMolex pins are designedsothat the shorttab"ears"arecrimpedontothe stripped wire
to
make
the
electrical connection, while the long"cars" arc crimped overthe insulated section
of
the wire to help
support the connection. See Figure 2.1for
an
example
of
a properly crimped Molex pin.
WR:
WIRE
\I
ISIBI.E
N
WINOOW
HSULATION
CRIMP
(
STRAIN
RELE
F)
TERMINAL
-WHX1N"
FIGURE 2.1 MOLEX CRIMP PIN
or,
er
tocrunp, mse es o earso e o excnmppinintonote o ecnmpmgtoo
#70-3), withthe carspointingtoward the letter"B". Insert the wireintothe terminal so thatthe stripped
portionisbetweentheshortcrimpears,and
th
einsulationisbetweenthe longcrimpear
s.
Crimpthe short
ears.
Now
placethe longears
of
thepinintotool notch"A",withtheearspointingtowardtheletter"A".
Crimp
the long ears overthe insulated section
of
the wire.
: Whenusing Molex CrimpingTool#IITR-1719-C(PR&E#70-5),placeapinintoslot''B•.•with
n:~-
--~TICIN
6 R
EVI
SIONA
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SDA-SA
STEREO
DISTRIBUTION
AMPLIFIER
the long earson the
''B"
side
of
the tool and pointing toward the lener"B". Place the wire into
the
tool
from
the
"B"
side, and
then
crimp the pin.
Once the pins are crimped, they
may
be inserted and locked into
the
nylon
connector housing (a click
can
befelt indicatingthatthelockingearson thepin haveset).
If
apinisinserted
in
the
wrongconnector
position,
or
itis desired tomake a circuitchange, use theconnectorpin extractor tool (PR&E#70-4)
to
release the pin and press
it
out
of
the connector housing.
2.3 REAR PANEL CONFIGURATION
The rearpanel
of
the SDA-8A isconfigured to allow for ease
of
power, audioinput,audio output, and
patch pointconnection. Sec Figure 2.2 for
an
example
of
the SDA-8A
's
rear panel configuration.
,...,.
NO
.-
~It
IEAIA';f:10
·
--
~
,.,_
~·
EBB
BES
~AIITM
l , 2
ttlYM:M
HZ
112
A.I.
I.
P'ATCH
11-
1H
USA
...uc111caa."'
•-
.,_....,..
• I
OUTPUTS
•J
FIGURE2.2 REAR PANEL CONFIGURATION
SDA-8A audio inputconnection is accomplished bymeans
of
a 6-pin Molex connectorlocated
on
the
rearpanelassembly. Pinassignmentfor both stereoandmonaural applications isdefined
in
Figure2.3.
SHffiO
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0@"@
L
©©@
R
IN
STEREO
AUDIO
INPUT
WIRING
.,;-,
,;, .. .
,:
,·.
{.~=·
Pin
Number
Slanal Connector
Shleld
Low
High
&ereolnpufl.eft
IN
1 2 3
Stereo
fnpuVRight
IN
4 5 6
MONA.URAL
AUDIO
INPUT WIRING
Pin Number
Signal
ConnectOf'
Shleld Low High
Mono
lnDUI
IN
1 2 3
-No
Connection
•
IN
4 5 6
FIGURE2.3 AUDIO INPUT CONNECTION
connecnon
equipment
12
pin Molexconnectors foraudiowiring. Thissystem
of
pin
assignmentstakesadvantage
of
thethree
pinperrowdesign
of
theMolexconnectorsand, therefore,makesvisual inspection
of
thefinished
wiring
7
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SDA-BA
STEREO
DISTRIBUTION
AMPLIFIER
easier.
As
viewed from the rear
of
the product, the shields
(if
connected) are always connected to
the
leftpins,
the
low wires (black) to the centerpins and the high wires (red)
to
the right pins. While this
inspectionwillnotindicate
if
aconnectorisinthecorrectposition,itwillverifypropershieldandpolarity
connection.
2.5 AUDIO OUTPUT CONNECTION
SDA-8Aaudiooutputconnectionisaccomplished
by
means
of
the
eight6-pinMolexconnectorslocated
on
the
rearpanelassembly. Pin assignment is defined in Figure 2.4.
STEREO AUDIO OUTPUTWIRING
Pin
Numb«
Signal Connector Shield Low High
Stereo
Output/Left
Output#
1 2 3
(Output#)
Stereo
OUtput/Rloht
Output#
-4
5 6
FIGURE 2.4
AUDIO
OUTPUT
CONNECTION
NC
lTJt
~:
When using the SDA-8A for monauaral distribution,pins 1 through 3provideone output, and
pins 4 through 6 provide another. This increases the number
of
output connectors from 8 (for stereo
applications)
to
16 (for mono applications).
2.6 PATCH POINTCONNECTION
Thepatch connectorallowsfor
the
insertion
of
signalprocessingequipment atapointprior
to
theSDA-
8A'soutputamplifiers. This connectoris located on
the
rearpanel assembly, anditspin assignmentis
defined in Figure 2.5.
PATCH
POINT
AUDIOWIRING
Pin
Number
LSEND
RSEND
LRTN
RRTN
Signal Connector Shield Low High
Patdl Send/left
PATCH
1 2 3
Patdl SendlRighl
PATCH
..
5 6
PATCl-i
Patdl
Retum/1..eft
PATCH
7 8 9
Patdl Return/Righi
PATCH
10 11 12
FIGURE
2.5
PATCH
POINT
CONNECTION
en no processmg eqwpment 1s
ms
m e sign
assembly (PR&E #90-667) isinstalled at the patch point.
-~l!!_~
AND
SHIELDING
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SDA
·
8A
STEREO
DISTRIBUTION
AMPLIFIER
Groundinginmodembroadcastequipmentismorecriticalthan witholderdevices
of
morelimited
band
-
passcapabilities. Achievinglow impedancesys
tem
groundwithasmall piece
of
equipment
is
relatively
easy. However,theproblembecomesprogressivelymoredifficultasthe overallsystembecomeslarger.
When
designingourconsoles andaccessories,much thoughtis given
to
systemgroundingrequirements
and
theelimination
of
DCpath ground loop
s.
TheshieldpinsoneachSDA-8Aconnectoraretieddirectlytothechassis,asisthecentralaudioground.
The powercord assembly then provides SDA-8A to ground connection.
Apreferred method
of
connecting the lineshieldsina systemis toconnect both ends
of
every shield
to
all
affiliatedequipmenL However,thismethodisonlysatisfactory
if
everycomponentsharesa
common
earthground. Thiscanbeaccomplishedusingisolatedgroundreceptaclestiedtothestation,s"technical
ground".
If
isolated ground receptacles are not available when grounding the SDA-8A, observe the following
guidelines:
A) Shields
of
cablesconnecting the console to auxiliary equipmentshould be connected at the
consoleend only, and should not be terminated to the ground
of
the auxiliary equipment.
B) Ensure that the auxiliary equipment is connected to a "clean" ground by its power cord
assembly,
or
by the addition
of
a separateground wireconnected betweenthechassis
of
the
auxiliary equipmentand the station's "technical ground".
NOTE:
Buzz pickup is generally electrostatic, due to capacitive pickup between
an
audio line
and
a
powerline. When shieldedlinesareusedthis shouldbenoproblem, unless the audiolinesarerun in
the
samewire-way
or
areas
as
apowerline. Radio-frequency interferencecan alsomanifestitself
as
abuzz
in the program audio. RFinterference is minimized by the extensiveRF bypassing and ground-plane
techniques usedin the SDA-8A, and the shielded lines external
to
the unit.
2.8 POWER CONNECTION
TheSDA-8Aisdesigned
to
operatefrom
115
V
AC,
60
Hz,
andrequiresalinefuse witha1/2
ASB
rating.
Shouldthefuseeverneedtobereplaced.replacewiththeproper
type
only. Theappropriate3-wirepower
cord (supplied with the equipment) should
be
installed between SDA-8A and
th
e ACmains.
WARNING
:Donotdefeatthesafetygroundinanyway. Todosomay provideapotentiallydangerous
condition to the operator.
9 REVISION A
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S0A·SA
STEREO
DISTRIBUTION
AMPLIFIER
3.0 SETUPAND OPERATION
Thischapterprovidesinstructioninthepropersetupandoperation
of
theSDA·8A. Includedaresections
outliningcontrol panel configuration, input mode selection, level adjustment,
VU
meterselection, 600
ohmtennination,andlevelalignment
3.1
CONTROL PANEL
Thecontrolpanel
of
theSD
A-SA
isconfigured
to
allow forease
of
modeselection,
VU
meterselection,
and level adjustment. Thereisalso
an
LED to indicate thatpower issupplied to
the
unit, aheadphone
jack,anda600ohminputterminationselectorswitch. SecFigure
3.1
foran illustration
of
the
SDA-8A's
control panel.
• •
--
□
.ID'T
• IIIOKT
■
N'IIT
00UT1'UT
□
-
=---"'-
TEMI
-"'----
1.1!.FT
_
__,
__
Miff
__
,.__
____
YOOE
------IIETE
II
FIGURE
3.1
CONTROL
PANEL
CONFIGURATION
3.2 INPUT MODESELECTOR
The Mode selector, located on the SDA-8A's front panel assembly, is a four-position rotary switch
accompanied
by
fourLEDs, which indicatetheinputmodeselected (referenceFigure3.1). This
switch
allows the selection
of
one
of
four differentinputmodes: STEREO,LEFf, RIGHT, and SUML+R.
In
theSTEREOmode,indicated
by
theillumination
of
agreenLED,theamplifierdistributesastereosi
gnal
to the eight stereo output connectorslocated on the rearpanel.
In
each
of
the three monaural modes (LEFT, RIGHT
or
SUM L+R), indicated
by
the illumination
of
a
redLED, an identical signal issent to both leftandrightchanneloutputsoneach rearpanelconnector.
The
LEFf
mode sends the leftchannel input to both channeloutputs; the RIGHT mode sends theright
channel input to both channeloutputs; and the SUM L+R mode sums
the
left and right channel inputs
into one monaural signal, and then sends this monaural signal toboth channeloutputs. In this
way,
the
SDA-8A can
be
used to distribute a monaural signal to a total
of
16channeloutputs.
3.3 LEVEL ADJUSTMENT
There are twogaincontrolsforeach channel, locatedontheSDA-8A's front panelassembly (reference
Figure3.1). Thegain
of
eachinputamplifierisadjustable, toaccommodatenominalinputlevelsranging
from -30
d.Bu
to
+9
d.Bu.
The Step Gain control isafour-position rotary switch, which adjusts the
gain
in 10
dB
increments. TheGain control
is
arotary trim-potwith a continuous gain adjustment range
of
12
dB, to be used for "fine tuning". For a more detailed description
of
the
use
of
these controls, sec
•~-
•-CCWOM~
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SOA-8
.A
STEREO
DISTR
IBUTION
AMPLIFIER
Section 3.6.
Thegaincontrolsarein the fcedbackloop
of
theinputstages, tomaintain optimumnoiseandheadroom
performance for any gain setting. Theinput headroomremains ata constant 20 dB above the nominal
input signal level
3.4 VU METERS
The miniature VU meters fully confonn to ANSI specifications, and are switchable between the input
and
output
of
the amplifierby means
of
the winkeye Schadowinput/output selector button, located on
theSDA-8A'sfront panelassembly adjacent tothe
VU
meters(referenceFigure
3.1
). This button
will
be
orange when the VU meters are monitoring amplifier input, and black when the
VU
meters are
monitoring amplifieroutput
The meters are driven
by
bridging buff
er
amplifiers, to isolate the distortion by-products
of
the meter
movementrectifiers. Thesebufferamps allow a
"O"
VU
calibration trim with asignalrange
of
+4
dBm
to +8d.Bm.
3.5 600 OHM TERMINATION
TheSDA-8A
's
inputs arebalancedand bridging, with a 40kohmimpedance. Thismay
be
switched to
a600ohm termination,
if
necessary,bymeans
of
the600ohmTERMination buttonlocatedontheSDA-
8A's front panel assembly adjacentto the ONLED (referenceFigure 3.1). This button will beorange
when the600 ohm termination is implemented, and black when it is
not
3.6 LEVEL ALIGNMENT
TheSDA-8A isfactory calibrated at the time
of
shipmentforan output level
of
+8 dBm (unless a level
of
+4 dBm is specifically requested), with a -10
d.Bu
patch return level. Once aligned, the gain trim
controlsontheoutputamplifiersshouldnotrequiretrimmingunlesscomponentswhich affectamplifier
gain have beenreplaced.
If
this is the case, align the SDA-8A perthe following procedure:
NOTE
: The following proceduredescribes alignment foran output level
of
+8
dBm. The trim-pots
described in this procedure are all accessible through holes provided in the SDA-8A's
top
cover
(reference Figure 3.2).
1. Remove the patch connector shorting plug, orprocessingequipment (ifinstalled).
2. Connect a -10
d.Bu
1 kHz sinusoidal signal generator to the Left Patch Return (reference
Figure2.5),and an AC voltmeterwith a600ohminputtennination to theLeftOutput
of
one
of
the audio connectors.
3. Adjust the
LEFf
OUTPUT LEVEL ADJUST trim-pot until the outputmeasures
+8
dBm.
4. WiththefrontpanelMETERselectorintheOUTPUTposition,adjustthe
LEFf
VU
METER
11
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•
u,'l'Ol/fflUT
LIVll.__,.
•
IIIOlff
OUfflUT
LIVll.lllUllff
•
LDT
W/IONff
FIGURE
3.2
SD
A-8A T
OP
VIEW
ADJUST trim-pot until the leftmeterreads OVU.
5. Repeat steps 2 through 4 for theright channel.
SDA-SA
STEREO
DISTRIBUTION
AMPLIFIER
6. Replace the patch connector shorting plug
or
re-connect the processing equipment, and
connectthel kHzsignalgeneratortotheSDA-8A's
Left
InputConnector. Setthegenerator's
outputvoltage to
be
thesameastheoutputlevel
of
thesourceequipment to
be
connectedto
the SDA-8A's input.
7. Using the front panel STEPGAIN and GAIN control switches, adjust the amplifier's input
gain until theLeft VU meterreads OVU.
8. Repeat steps 6 and7 for the right channel.
12
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SDA-8A
STEREO
DISTRIBUTION
AMPLIFIER
4.0 EQUIPMENT DESCRIPTION
Thischapterdescribes thevariousequipmentand features incorporated intothe SDA-8A. Includedare
sectionsdescribing
the
inputcircuitry, mode selector, outputamplifier,
VU
meterbufferamplifier,
and
powersupply.
4.1
INPUTCIRCUITRY
NOTE:
The two stereo channels operate identically, so, for simplicity, only
the
left channel will be
discussed below.
Theinputamplifiersaredesigned toaccommodate thenominal inputlevelrange
of
-30
dBu
to+9
dBu
.
while maintaining
an
extremely highcommon moderejectionratio
of
60dB
or
greater (80
dB
below
1
kHz).
Th.is
canonlybeaccomplishedthrough theuse
of
carefulcircuitdesign, accurateadjustment,and
immaculate grounding and printed circuitlayout techniques.
NOTE:
The CMRR adjustments are factory aligned using an Automated Test Equipment
(A
.T.
E.)
system. and should not be adjusted by
the
user. To do so
may
severely degrade common mode
performance.
The input circuitryisdivided into three stages:
an
input attenuator.
an
adjustaple gain amplifier,
and
a
switchablegain amplifier.
Theinput attenuator. made
up
primarily
of
R5.
R6,
R7
and
R8,
serves to attenuateany common mode
signalcomponentto withinthe
<;":Ommon
mode
range
of
theadjustable gainamplifier. Trim-potR24
and
resistorsR
12
andR
14
providecommonmodebalancefortheattenuatorcircuit. Likewise,
C23
provides
high frequency common mode balance
for
input filtercapacitors
Cl
and
C8
.
The adjustable gain inverting amplifier is configured with three operational amplifiers on a plug-in
function module operating with cross-coupled input stage feedback with gain trim control
Rl
7. The
plug-infunctionmodulecontainsitsownlowandhighfrequencycommonmodebalancecontrols,
which
optimize the CMR
of
the module.
Cl6
serves
to
minimize DCoffset voltages
by
dropping
the
gain
of
A3
to unity at DC. The shield around this cap prevents capacitor signals from crosstalking into the
surrounding circuits, which would upset the common mode balance.
Theswitchable gain amplifierisconfigured asan inverting amplifier, whose gain
is
determined
by
the
4-positionfront panel GAIN switch. When theswitchis fully counterclockwise thefourresistors are
in
series,causing thegain to
be
minimum.
As
theswitch isrotated
in
theclockwisedirection, theresistors
aresequentiallyshonedout,causingthegain toincreasebyapproximately 10
dB
everystep. Theoutput
of
this amplifier drives the Patch Point ata nominal -10
dBu.
The input headroom
of
the entire circuitis 20
dB
above nominal input.
13
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SDA
-
SA
STEREO
DI
STR
IBUTION
AMPLIFIER
4.2 MODESELECTOR
The Patch Return inputs to
the
distribution amplifier are balanced, to prevent anycommon mode noise
from being introduced into the outboard wiring. The outputs
of
these unity gain differential amplifiers
drivechannel selectionrelaysK1
and
K101. Theoutputs
of
theserelaysdrivemono shortingrelay
K2
,
through resistors R36 and R136. The relays are energized when the
MODE
switch sends avoltage
to
the
appropriate coil.
When
theMODE switch isintheSTEREOposition.
OS
1isilluminated, and none
of
the threerelays is
energized, causingtheLeftand Right stereo signals tobe sent
to
theoutput amplifiers. When
the
mode
switch
is
in placed
in
either
the
LEFf
or RIGHT positions, either DS4 or
0S3
(respectively) is
illuminated,andeitherK1or
Kl
01
is
energized.causing theLeft
or
Rightsignal
to
be
sent
to
bothoutput
amplifiers.
When
the modeswitch
is
inthe
SUM
L+Rposition,
0S2
isilluminatedandK2isenergizedt
causing the Leftand Right signals toresistively
mix
through R36 and R136, andthecomposite
sum
to
be sent to both output amplifiers.
4.3 OUTPUT AMPLIFIER
NOTE:
The two stereo channels operate identically, so, for simplicity, only the left channel will be
discussed below.
Theoutput
of
MODE
selection relay
Kl
drives variable gain bufferamplifier
US
. The voltage
gain
of
U5
isadjusted
by
trim-pot R43 (accessible through theSDA-8A's top cover), and
has
again range of7
dB
to
14
.5
dB
. The output
of
U5
isconnected
to
line amplifiers
Al
and A2, which operate
as
apush-
pull pair to provide balanced drive to the distribution output lines.
Al
and
A2
are plug-in function
modules designed to deliver high currents while maintaining excellent distortion specifications. The
outputs
of
A1and
A2
areroutedtotherearpanelprintedcircuitboard, and totheeightoutputconnectors
through the 39ohm build-outresistors which servetoisolatethe loads.
NOTE:
Donot ground eitherthe high
or
low
lines
of
the balancedoutputs. Ifit is necessarytotake
an
unbalanced output, u
se
the high and shield connections only.
4.4 VU METER BUFFER AMPLIFIER
NOTE:
The two stereo channels operate identically, so, for simplicity, only the left channel will
be
discussed below.
The
VU
meterbufferamplifierconsists
of
dualintegratedcircuitamplifierU
6,
configuredforabalanced
symmetricalinputandoperating withcross-coupledfeedback. Thegain
of
theamplifiersisadjusted
by
trim-potR62 (accessiblethrough theSDA-8A's topcover),and
has
enoughgain range
to
accommodate
inputs from +3
dB
uto
+9
dBu. The output
of
the
two
amplifiersiscoupledtotheVU meterthrough
the
recommendedsourceresistance
of
3600ohms,atanominalsignallevel
of
+4
dBu(0VU). Lightemitting
diodes
OS
1and
0S2
provide overdrive protection to
the
meter movement
14
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SDA·SA STEREODISTRIBUTION AMPLIFIER
4.5 PO
WE
R SUPPLY
ThepowersupplyfortheSDA-8A usesatoroidalpowertransfonnertominimizetheradiated field. The
bipolar
16
voltsupplyispoweredfromtwoseparatewindings
of
powertransformer
Tl
.
wiredinacenter-
tapconfiguration. Thesecondariesarcrectified bydiode bridgeCR
12,
andfiltered bycapacitorsC1and
C4
. U1 is a positive and U2 a negative integrated circuit adjustable regulator. The various small
componentsaround theregulatorsare used tosettheoutputvoltage,andimprovethe noiseandtransient
response
of
the regulators.
15
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SOA-8A
STEREO
DISTRIBUTION
AMPLIFIER
5.0 MAINTENANCE
Thischaptercontainssectionsdescribingroutinemaintenance,installationandservicingtools,common
mode adjustment, and replacement parts for theSDA-8A.
5.1
ROUTINE MAINTENANCE
Routine maintenance is usually limited to checking button switches for proper operation and
kocping
panelsurfacesclean. Thepanelsurfacesarefinishedwithabakedpolyurethanepaintandmay becleaned
with a weak solution
of
dishwashing detergent. The security door is fabricated from plexiglass
and
should onlybecleaned using a clean, soft cloth.
Theknobs used for the SDA-8A's rotary controls are attachedtothepotand switch shafts with collets
instead
of
set screws. The machined brass collets provide the advantages
of
ttue alignment and
concentricity with the axis
of
rotation,
no
set screws toscore the shaft , the ability to clutch slip
when
excessiveforceisapplied,and
no
holesintheside
of
theknobforthe setscrew
s.
Toremoveacolletknob,
carefully pryoffthe topcap
of
the knobusing an Exacto knife
or
similartool. Use PR&E tool #70-44
(as shown in Figure 5.
1)
to
turn thenut on thecolletcounterclockwise. Once the nut is loosened, the
collct shouldrelease from the shaft. This nutshould notneed to
be
removed unless the colletrefuses
to
release.
COLLET
NUT(D=:
:
:=::
:
:::::
:
~..___PR&_E
#-70·44_
____.~
5.2 TOOLS
COLLET
KNOB
(WITH
CAP
REMOVED)
FIGURE5.1 COLLET
KNOB
REMOVAL
ThefollowingtoolsmaybedesiredforinstallingandservicingtheSDA-8A.
If
you
alreadyhaveaPR&E
console,
you
probablyown these tools.
If
not
, they can be pmchasedfor a nominal charge.
DESCRIPTION
MOLEX connectorpin crimp tool
MOLEXconnectorpin extractortool
MOLEX connectorpin crimp tool (#HTR-1719-C)
Wrench for collet knobs
5.3 CMRR ADJUSTMENT
PR&E#
70-3
70-4
70-5
70-44
The SDA-8A'scommon moderejection ratio (CMRR)
is
factory adjusted at the time
of
shipment,
and
shouldnotrequireadjustmentunlesscomponentswhichaffectamplifiergainhave
been
replaced. While
16 REVlS
IONA
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