Crown D-75 User manual

0-75
DUAL-CHANNEL
POWER AMPLIFIER
SERVICE MANUAL
CROWN INTERNATIONA L, INC. 17 18 W. MISHAWAKA RD. ELKHART, IN 46517·4095
C 1989 Crown International. Inc.
K80 1 86A6
3' 89

FULL THREE-YEAR WARRANTY
S UMMARY OF WARRANTY
We, CROWN INTERNATIONAL. INC ., 1718 West Mishawalca Road. Elkhart, Indiana46517-4095 ('Narrantor) warrant to you. the
ORIGINAL PURCHASER AND ANY SUBSEQUENTOWNER of each NEW Crown product, for aperiod of three (3) yeaTS from th e
date of purchase by the original purchaser(warranty period) lhal1hc product is free ofdefects in materials or workman s hip :md will mcet
or exceed all advcn iscd specifications for such a product.
ITEMS EXCLUDED FROM WARRANTY
Weare not responsible forproducl failure !;8uscd by misu$(l, accidcntornegieci. This warran\ydoc $not extend [0 any produl:lon which
the serial number has beendefaced, altered. or removed. Itdoes nol cover damage \0 loudspeakers or any other products resulting from
Crown product failure. Itdoes nOI cover defcclS ordamagccauscd by your use OfWl8Uthoril.oo modifications, parts, or service. Italso
e)( clude$ batteries and damage caused by leaky or defective batteries.
WHAT WE WILL DO
We will remedy any defect in materials or workmanship by repair, replacement. or refund. We may not elect refund unless you agree,
or ooless we are unable to provide replacement, and repair is not practical or cannot be t im ely made . If arcfood iselccted, men you must
make me derective or malfunctioning component available10 Crown free and clear of all liens or other encumbrances. The refund will
be equal to me actual purchase price, not including interest, insurance, closing costs, and other finance charges le ss a reasonable
depreciation on the productfrom the dateof original purchase. Warranty work can only be performed at our authorized servi ce centers
or at the Crown factory. We will remedy the defect and ship the product from the sCJvice center or Crown factory within areasonable
time aftef receipt of the defective product at the aumoriz.cd service center or Crown factory. All e)(pcnses in remedying the def ec t.
including sUrfaceshippingcoslSin the United States. will
be bome by Crown. (Purchaser must bear thee)(pensc of shipping(he product
between any foreign country and the port
of entry in the United States and all tues, duties. and other custom's fee for such foreign
shipments.)
HOW TO OBTAIN WARRANTY S ERVI CE
YOli must notify us of your need for warranty service not later than ninety (90) days after expiration of the warranty period . We will
give you written ootice
ofthcdcaler scrvicecenter.> 10 whom you may dclivcrthe product. or we will give you an authorization 10 return
it for factory service. All components must be shipped in a factory pack, which, if needed, may beobtained from Crown frec of charge.
Corrcctiveaction will be taken within a reasonable time
of the date of roceiptofthe defective product by us or our scrvicecentcr. If the
repairs made by Crown or the authori7.cd serviceecnter arc not satisfactory, notify Crown or the authorized service center immediately.
DI SCLAIMER OF CONSEQUENTIAL AND IN CIDENTAL DAMAGE S
YOU ARE NOT EmTT'LED TO RECOVER FROM US ANY CONSEQUENTIAL OR INCIDENTAL DAMAGES RESULTING
FROM ANY DEFECT IN OUR PRODUCT. THIS INCLUDES ANY DAMAGE TO ANOTHER PRODUCT OR PRODUcrS
RESULTING FR OM SUC H A DEFECT. SOME ST ATES 00 NOT ALLOW T HE EXCLUS I ON O R LI MI TAT I ONS OF
INC ro ENTA L OR CONSEQUENT I AL OA MAGES,SOT HE ABOVE LI MI TATION OR EXC LUSI ON MAY NO T AP P LY
TO YOU ,
WARRANTY ALTERATIONS
NO PER SON HAS T HE AUT HOR ITY TO ENLARGE, AMEND, OR MODIFY THIS WARRANTY . TH E WARRANTY IS NO T
EXTENDED BY THE LENGTH OF TIME W HI CH YOU ARE DEPRIVED OF THE USE OF TH E PRODUCT. REPAIRS AND
REPLACEMENT PARTS PROVlDEDUNDE R THE TERMS OFT HIS WAR RANTY SH ALL CARRY ONLY THE UNEXPIRED
PORTION OFTH IS WARRANTY.
DESIGN CHANGES
We reserve the right to change the design of any prodUCI from time to time without notice and with no obligation \0 make corrcsponding
changes in products previously manufactured.
LEGAL REMEDIES OF PURCHASER
T HIS WARRRANTY GIVES YOUSPECJFIC LEGAL RIGHTS, AND YOU MAY HA VEOTHER R1 G HT S WHIC H VARY FROM
STATE TO STATE . No action to enforce this Warrantyshal1 be commenced latcrthan ninety{9O)days after e)(piration of the warranty
period.
CR OW N INT E RNAT IONA L, INC.
1 718 West M isha w aka R oad, Elkhart, Indiana 46517·4095.
TH IS STATEMENT OF WARRANTY S UPERSEDES ALL OTHERS CONTAINED IN THI S MANUAL 3/
88

The i nf onnation furni s hed in thi s manual does nO( inc lu de all of thedetailsofdesign. produ c tion,
or variationsoftheequipmenl. N or does it co ve r every po ssi ble situation whi ch may arise during
ins ta llation, operation or maintenan ce . If you need special assistance., beyond t he scope of (his
manual, please contaCt the Cro .... 'Tl Interr.ational Customer Services Dcpanment.
Crown International, Inc.
1716 West Mishawaka Road
Elkhart, Indiana 46517-4095
Phone: [phone]
Fax: [phone]F AX
Twx; [phone]
WARNING
TO PREVENT SHOCK OR FIRE HAZARD,
DO NOT EXPOSE TO RAIN OR MOISTURE!
CAUTION
TO PREVENT SHOCK DO NOT USE THE POLARIZED AC
PLUG OF THIS UNIT WITH AN llliPOLARIZED EXTENSION
CORD, RECEPTACLE
OR OTHER OUTLET WHERE THE
BLADES CANNOT BE FULLY INSERTED.
ATTENTION
POUR PREVENIR LES CHOCS ELECTRIQUES NE PAS UTILISER
cenE FICHE POLARISEE AVEC UN PROLONGATEUR. UNE
PRISE DE COURANT OU UNE AUTRIE SORTIE DE COURANT,
SAUF 51 LES LAMES PEUVENT ETRE INSEREES A FOND SANS
EN LAIS SER AUCUNE PARTIE A DECOUVERT .

9 ~(j'@llilllOll _____ -"o -,-- z"-, '-'PO:::WE=Rc:.A"M "- PL"'IFc:IE"'R-'---- _________ ---"'RE"'V'-". 0
Table of Contents
1 Introduction ___ . ___ . ______ . ___ ._._. __ .. _._..._. .. __ . ____ I-I 7 Specifications
___ ... .... _. __ ._._._._._._. _____ ._. _____ 7- 1
1.1TheD-75..................................................... 1-1 7.1 Ge n era l....................................................... 7-1
1. 2 Warramy ................................ .. ................ ",1- ,1 7.2 Monaural,................................................... 7-1
7.3 Stecoo ......................................................... 7-2
2 Facilities. ___ . _____ .... _._._ ... _ .................. _._ ... _._ 2- 1
7.4 PcrfonnanceGraphs...................................... 7-4
3 Required Test EquipmenL ... _ ..... _ ...... 3-1
8 Schematics ._ .. _._ ... _ .. _ .... __ ... .. ___ .. ______ ._ ..._ ... 8-1
4 Maintenance........................................... 4·1
4.1 Safety First .... ............................................. 4-1
4.2 Inspec ti on ................................................... 4-1
4.3 Disassembly .. . .............. .......................... .... 4-\
4.4 Reassembly ................................................. 4-2
4.5 Troubleshooting........................................... 4-2
9 Parts._ .... .... .._ .... __ ........ _ ._._._ ... ___ ._._._ ... _ ... _ ... 9-1
9. 1General Infonnat.ion ...................................... 9-1
9.2 Standard and Special Parts .............................. 9-\
9.3 Ordering P aIlS .............................................. 9-1
9.4 S hipm ent .................................................... 9-\
9.5 Te nn s......................................................... 9- \
9.6 lIlu SU'atcd Parts Li sts .................................... 9-2
5 Voltage Conversion ___ ._._ . _._._._ ... _. ___ . ______ 5-1 Appendics A: Installallon.
___ ._ .............. _. A-I
A. I Mo untin g ........ .......................................... A·I
6 Circuit Theory_ .. _._._._. _________ .......... _._ . _._._._ 6- 1 A.2
Wiring ....................................................... A·I
6. 1 Block Diagram Circuil Th eory....................... 6·'
6.2 Balanced/Unbalanced Input Stage.... ............. .. 6-2
6.3 Inpu t Operational Amplifier........................... 6-2
6.4 Signal Translator............_............................ 6-2
6.5 Fi nal Voltage Amplifier................................ 6-3
A.2.1 SLC r co ..................................................... A-I
A.2.2 Monaural ................................................ A-I
A.3 Input ......................................................... A·I
A.4 Ou t pU I. ...................................................... A-2
A.S Load Potcction ........................................... A·3
6.6 Bias.......................................................... 6-3
6.7 Ou tput Stage............................................... 6·3 Appendics B: Operation
.......... _ ... ___ ._._ ... 8-1
6.8 Pro tection Circu itry ............. .. .. .................... 6-3
B.I Precautions................................................. B-1
6.9 I {)Cn.I (InputlOutpu(Comparator).................. 6-4 B.2 Controls..................................................... B-1
6 .1 0 Sig nal Prcscnce Ind ica tor............................. 6-4
B.3 PrOLCction .................................................. B· I
B.4 Fuse Rcplacemcnl .. ..................................... B-2

illustration
1 .1 0·75 ........................................................
2. 1 Front Facilities (0.75).................................
2.2 Rear Facilities (0·75)............ ......................
4 .1 2 Ohm Load Wavefonn...............................
4.2 10KHz Square
Wave ...................................
4
.3 20KHz Sine Wave ......................................
4.4
1M Distortion Test Se(·up............................
4.5 Signal to Noise Test Set·up..........................
5.1 AC Mains Voltage Conversion ..._.................
6.1 0- 75 Block Diagr$l...................................
6.2 Balanc ed Input Sta~e ..................................
6.3 In put Operati onal Amplifier..........................
6.4 Signal Translato r............................. ... ...... ..
6.5 Final Voltage.Amplifier .. .................. .. ....... ..
, .,
2·'
2·2
4·)
4-3
4·)
44
44
5 ·1
6-1
6-2
6·2
6·2
6-3
6.6 Bias, Output and Protection Stages................. 6·3
6.7 IOC........................................................ 64
6.8 Signal Presence Indicator.............................
7.1 Power Matrix .......................................... ..
7.2 Nominal Frequency Responce..................... ..
7.3 Nominal Output Impzdance..........................
7.4 Nominal Phase Respon ce.............................
7.5 Nominal Power Efficien cy ...........................
7.6 Nominal Damping Factor ..........................
..
7.7 Nomi nal Output Phase Angle........................
7.8 Nominal Crosstalk......................................
7.9 Nominal Noise Spectrum.................... .. .......
8.1
0- 75 Schematic Diagrams.............. .. ............
9. 1 0- 75 Main Modules....................................
9.2 Output
Modu l e< ..........................................
9.3 D-75 Front Pan el Assernbly..........................
9.4 0-75
Neon Bracket Assembly ......................
9.5
0·75 Back Panel Assembly..........................
9.6
D-7 5 Ca pa ci tor Bracket Asse mbl y.................
9.7 D -75 Final Assembly ..................................
A.1 0- 75 Mounting OimentiooS".......................
A.2 Input High Pass Filter..... .. .. ........................
A.3 InpUi Low Pass Filter.................................
A.4 Wire Ga u ge Nomograph .............................
A.5 Connection to an Inductive Load. ..................
A.6 Fuse Nomog r aph .......................................
64
7·)
74
74
7·5
7·5
7·6
7·6
7·7
7·7
g·l
9·2 .3
9·9
9·11,
12 , I3
9·16
9·17
9-19
9·20
A·I
A·2
A·2
A·3
A·3
A4

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~RE~Vcc. O'--- _________ -' O "'. 7"', "- P"O". W E"R" A "' M "'P"'U" F I"'ER "- ____ (SU'©JMDIfil9
Fig. 1.1 0-75
1 Introduction
Thi s manual contains co mplete service infonnation on Ih e
Crown D-
75 power am plifier. It is designed 10 be u se d in
conjunction wi th th e 0-75 In s ttu c tion Manual. However,
so me imponam informaLion is duplicated in thi s Service
Manual in case th e In s tru c tion Manual is not readily
availabl
e.
NOTE: THE INFORMAn ON IN THIS MANUAL IS
INTINDED FOR USE BY AN EXPERIENCED
TECl-II\ 'lClAN ONLY !
1.1 The 0- 75
The 0 -75 amplifier is a co mpact. aud io JX)wer amplifier
d
es igned for professio nal us e. Providing medium power
amplification
from 20 Hz-20KHz with minimum
distortion, th e un it features balanced inputs, signal
presence
and i()C1'loi indicators, monophoni c capabi lity
and a means fo r iSOlating elec lri c al ground from chass is
gro und .
1.2 Warranty
ProdUC t !.ha l is covered by warranty mus t be Se rvic ed by
an Au th orized Crown Service Ce nt er or at the Cr ow n
Factory Service Depanmenl. Any questions
co nce rn i ng
warranly policy should be directed to th e attention or
Tech ni cal Service Depanment at:
Crown Internat i onal , Inc.
1718 W. Mishawaka Road
Elkha rt, Indiana 46517·4095
Phone; [phone]
FAX, (2191294-8329
Twx: [phone]
Introduction 1-1

I · • .. • crown D75· • I
F C DE E D C B A
FIG. 2. J FRONTFAC/LlTfED (0-75)
2 Facilities
A. Power
The AC powe r swilth, mounted at th e ri ght-hand comer
of th e0-75 is as imple 2 position "on/orr' co ntrol. If th e
AC powe r switch is po sitioned at "on", the powe r
irw:licato r should be on(8).
B. Power Indicator
Amber indi cator thai th e unit is on.
C. Level
Th e level of eachch annel is independen tl ycontrolled by
thesecontrols. The control for ch an nel 2 should be turned
do wnand not u sed when opera tingin MONO mod e.
D. IOC '"
An InputlOutpul Comparator LED is pr ovided for each
channel. Ill umination may occur at such Lim es as wh en
there is too high an input level, im proper load impedance,
output s
tag e clipping or even an amplifier based probl em.
2·1 Faci lities
E. Signal Presence Indication
Asig nal pre se n ce indi cat ion LED is pr ov id ed for each
channel to i
ndi cate whe nsignal is presenl Unl ike the "onJ
orr' state o rlh e I OC indicators the SP) LED's will vary
with signal Jcvcl
F. Output Monitor
As ta ndard 1/4 inch stereojack is provided on th e fron t
panel. It is in parallel with the main outputs (0) and can
be used to dri ve headphones. -
G. Output Binding Posts
Dual binding postco nn ectors arc provided at lh e output of
eac hcha nnel . Use dual banana plugs on lh e spe aker
cables for connection to thcjacks. In brid ged·MONO,
only the t wO top jacks (red) are used.
H. Dual-Mono
S li de this sw i tc h to the left (c h. I) for MONO mode and
10 lh e ri ght (e h. 2) for Stereo mode operation. In MONO
mod e the input and l ev el con trol for c ham 'IC l tw o should
not
be used and o nl y balanced (ungrounded) loads sho uld
be connected 10 th e outp ut jacks.

REV. 0
0·75 POWER AMPLIFIER
N L M H
G K J J K
FIG. 2.2 RearFacilities (D-75)
I. Ground Barrier Strip
Isolation of chassis ground from signal ground is easily
accomplish ed by re m ov in g th e shoning strap from thi s
tenninal strip.This may help rem ove any hum problem s
c aused by "gro und loops." (Circ uit ground is i so la ted
from c has s is ground by 2.7 ohm s.)
J. Input Phone Jack
An unbalanced 1/4 in ch phone jack is provided at the
inpul o( eachchannel. ~ use thc input jack for
c hannel 2 in MONO mode.
K. Balanced-Input Receptacle
A balanced XLR con nector is provided at th e input of
each cha nn e l.
L. Fuse
The AC line is safelY fused. If the unit is configured for
lOOVAC or 1 20YAC o pera ti on. a 2 amp fuse is used and
if SC I up for 200V AC . 220V AC or 240Y AC , a 1 amp fuse
is used. Th e use of an y ot h er fuse v alu e will invalidatc th e
warranty
M. Power Cord
As tandard thr ee- wire (gro unded ) AC cord with a 15 amp
plu g ar e pr ov ided
N. Se rial Number Sticker
Facilities 2-2

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3 Required Test Equipment
Many of the service and repair problems with the D· 75
can be performed with a limited amount of test
Equipment Requirements
Oscilloscope
Capable of displaying a
IOMHz signal
Volt-Ohmmeter Low-voltage resistance probe
lOOmv (range). High-voltage
resistance probe (I.5V range)
Fr cq . Counter
Signal Generator Sine!Square
wave available;
flat frequency responce.
TIlD .1%
maximum
Circuit Breaker 15 ampere rating
AC Line Vo l tag e Peak: reading meter (displays
Mo nitor rms equivalem to a
sinusoidal peak for any
waveform)
equipment. However,
in order 10 return the unit to its
"factory new" specifications. the fol lowing list ofrequircd
test equipment is recommended. The "Requirements"
co
lumn provides information to allow intelligent selcctin
of substituleS ifthe "Suggcsted Supplier and Mode'" is
not available or is considered impractical
to obtain.
Application Su ggested Model
Monitoring output during Telequipmcnt
D54A or
service and testing equivalent
Check resistance values Auke 8024 or equivalent
(low voltage probe). Check.
se mi co ndu ctor junctions for
opens or shorts (high
voltage probe) Check DC
voltages
For accurate general Heath
SM I 18A
monitoring
Prov ide teSt signals for
Wavctek 130 -Series or
service and checkout equivalent
In AC line to unit.; proteCtS
circ uitr y from ove rload if
power supply has shorted
Monitor Line voltage Circ
uit available from
Crown
R9qired Test Equipmefll 3·1

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REV. 0
D-75 POWER AMPLfFIER
7 rem
4. Maintenance
Effective repair involves three basic steps: 10 Determine
the symptom(s) of the problem; 2) Identify the cause(s) of
me symptom(s); 3) Repair the unit 10 eliminalC the
caus.e(s), Before proceding through these steps it is highly
recommended that you first observe the safelY precautions
in the next section and conduct a visual inspection ofthe
unit.
4.1 Safety First!
To avoid risking electric shock, turn offand unplug the
D-75
from the AC power outlet before attempting to
disassemble or reassemble it
If the unit has been in recent usc, the large power supply
capacitors will probably have enough power stored within
th
em to present a shock hazard to you ana theampliiler
circuitry. To safely discharge them, place a 10 ohm, 5
watt resistor across the +
and -terminals of each capacitor
for several seconds. Usc caution wh en handling the
discharge resistor-particularly avoiding skin contact
with
the leads while dischargi ng me capacitors.
A void risk of fire hazard from shoned power supplies by
plugging the defective amplifier imo an AC oullet which
has a 15 amp circuit breakcr.
4.2 Inspection
Acareful visual inspection is valuable for most problems
which you
may encounter.To inspect the amplifier,
remove t
he cover panels as described in section 4.3.1
Begin the in spection by looking for anything which
appears abnormal. l ik e broken wires and burnt or visibly
damaged components. Check wire an d component solder
joints. Inspect the prinlCd ci rcuit board(s) for broken
traces and loose connections. Be thorough-the l ime you
spend vi suaUy inspecting the amp is time well spent.
4.3 Disassembly
The eXlCnt of disassembly required will depend upon me
extent of in spection. service, testing, adjustment an d
repair to be performed. Hlustrutions referred to in
parenthesis are located in the parts list (Section 9) of this
manual.
4.3.1. Cover Removal
A fairly complete visual inspection can be performed by
removing the top (91) and bottom (90) covers. To
remove Lhcsc pans, proceed as follows:
I. Re move lhe eight rfour per side) phillips hcad
mounting screws that secure tOp cover (91). Gently lift
covcr
up and removc.
2. Remove the nine phillips hcad mounting screws that
secure bottom COver (90). COvcr will easily be removable
upon !;Crew eXlJ"action.
3. Remove each rack car (93) for easier a::cess to front
pa. "lcl componen ts .
4.3. 2. MaIn Board Removal
The D-75 has been specially designed fo r ease of service.
Probably the best ex.ample of this is the modular layout of
the Main Board. Note that all connections are made
through eimer push-on terminals or through
two 9 pin
arrays (with the exception ofone ground wire which is
soldered).
To rem ove the Main Board proceed as follows:
I. Refer to the component s id e board layout, Fig. 6.7.
2. Unsolder and remove the black wire marked "ground".
3. Disconncct me 15 color-cooed push-on wires localed
throughout the underside of the main board. Their
locations arc marked by wire color.
4. Remove the four mounting screws and nylon spacers
(33) located on the top side of the board. Gently rock the
board up and down until it becomes free.
5. All work needed on this board may now be performed
effortlcssl y.
4_3.3. Output Modul e Replac emen t/Re pa ir
The D-75 Output Module should not have to be removed
unles~ the t>oard il~lf is faulty and needs replacing. If this
is the case, refer to the disa'is.embly instructions listed
below. A ll other components on or around the Output
Module
may be replaced without actual removal of the
boa:"d. This procedure is also listedbclow, after the
disassembly instru::tions.
I. Replacement
a. Remove the Main Board (See Main Board
Removal).
b. Unsolder and remove the fou r Ourput
transistors (25) by unscrewing the 8 mounting screws
(two on each). Note: In order to case replacement of
spacers located beneath each sc rew!nut combinati on,
leave the 0-75 in its normal/ying position-flat!!
c. Removc the four driver transistors (24) screws.
d. Gently lift ooard upward, being careful not 10
jar the position of spacers located beTICath.
c. Rem ove all external wiring to Output Module
and note location for future ie-connection.
f. Replace board.
Maintenance 4-1

2. Repair
3 . All component parts localcd on the Output
Module
may be removed by applying standard soldering!
desoldering methods (See Section 7) from the lOp of th e
board.
Use extra care when working with a pan localed
near the front panel so as not to mar the finish.
b. Front panel controls
and LED's may be
replaced without removing the OutpUt Module Board (Sec
the following section).
3. Output transistor replacement-Output transistor (25)
c
an be rep laced by removing two mounting screws (per
outp
ut) and unso l de ri ng the twO main connecting pin s.
Note as per e}{ ploded view drawing ins ulating wafer (TO-
3,2 1), and its position in assembly.
4.3.4. Front Panel Pans Replaceme nt
As previously stated, all front panel componcm pans can
be replaced wi thout Output Modu le removal.
Generally.
th is operation is performed by unsoldering all
or pan ofobsuucting components. Adetailed in slruC ti on
format is listed below.
I. Input leve l control removal is accomplished by
rem ov ing the al umi n um knobs (28) and re lated hardware
(20). Channel one pot can
be pulled back and s li d out the
left-hand side when the headphone jack ( 15 ) and
assoc iaLed hardware is remo ved (10, 14) (rack ear (93)
sh
ou ld be removed). Channel tWO input level
pOlentiometer
can be rem ove after the " ri g ht " l ead of
R232 is disconnected and the grounding bus strip is
moved away from th e working area. The potentiomeler
may need considerable, but ge ntle pressure in order for it
to come fr ee.
2. 10C. Sig nal L ED Replacemen t. Wh en hand ling any
one
of the fou r panel LED's (22, 23), e}{trcme care is
necessary
in order 10 achieve a success ful repair.
Unsolder leads
of LED 10 be replaced. With a pair of
needle-nose pliers, remove the black suppon ring located
behind th e LED. Nex t carefu ll yextract the faulty LED by
pulling straight back and removing from th e reat.
Replace the LED and reverse of above.
Note: When
installing an LED always observe correct polariI Y! It may
be helpful when inserting the rear bla ck support ring to
apply pressure with a 1/4 ft nut driver a ll ow ing the leads
to
move up the middle of the d ri ver (See Fig. 7.17).
3. On/ Off Switch Replacement To replace the front
panel OfI/off switch (35) remove aluminum knob and
related hardware (27. 2,10, II ). With a small Oat-head
screwdriver, slowly pry orr fuse bkx:k holder from
adhesive. Pu sh sw itch back until solder lugs are exposed.
Remove wire. and slide the switch to th e right and out the
end. Rep lacement is th e reverse ofabove. Note: It ma y be
necessary to replace th e adhesive s trip located beneath th e
4-2 Maintenanc9
fuse block .
4. Neon "Orr-On" Indicator Replacement. Because of
the special mounting procedure u sed with the front panel
power indicator (42), Crown recommends factory
rep lacement only.
4.3. 5. Back Panel Parts Replacement
All co mpon e nt parts located on th e back pane lof th e 0-
75 c an be rep laced with re latively l ittJe effort (see
exploded view drawing, rear pane l assembly). Should
quc. .. tion s arise eo ntact th e Crown Technical Service
Department.
4.4 Re assembly
Reassembly is essentia ll y th e reverse of disassembly. If in
doubt about t ypes and sizes of attaching pans, refer 10 the
appropriate illusuation in Sec ti on 9
4.5.Troubleshooting
Th e three steps to effective troubles hOOl.ing and repair
were mentioned earlier. They ean be su mmarized in the
three fo ll owing questions: What is the problem (e ffec!) ?
What is causing th e probl em (cause)? What can be done
10 eliminate the cause (repair )? The purpose of this
section is to help you answer these qu es tion s in an orderly
manner.
Finding
and fixi ng the problem(s) is not the end of
maintenancc. The final step is to thoroughly test the
amp lifier to be certain that it meets th e faclOry
specifications after it ha .. been repai red . The test
procedures
in section 4.5.3 will he lp you do this as we ll as
aid you in locating th e cause of problem(s).
4.5.1 Identifying Symptoms
Why was th e amplifier brought in for repair? Can you get
it 10 malfunction again? (Some problems can be
intcnniu.ant and diffic uilLQ fmd.) If yo udon't observe
anything
wrong with the amplifier, tactfully inquire how
the owner used itand try 10 detennine if it was mi sused or
some other co mponent in th e ir syStem co uld have been at
faull. (Appendices A and B co ntain the in stallation and
opcmtion in structions for the 0-75.)
If
yo u l ac ks uffi c ient infonnation about the problemand
there isn'l anything obvious wrong sk ip to the next
sec t io nand procede dircctJy to th e test procedures in
section 4.5.2.
Using it can determine if the amplifier
meets f ac tory specs.1f yo u have any qu estions regarding
warranty coverage, please callCrown's Technical Service
Departmcot.

"RE",V,,-" O"--- _______ _ _ --'D'- ":.;: '5"-P-"O"WE"'R.:.:A"'M:::.P.=
Ll
c.:
F
'=ER"-- ____ (£(j'@Qd1!)(flJ (3
4.5.2 Test Procedures
Test or Adjustment
I. Quiescent OC offset
2. Bias adjustment
3. Power (s ingle channel)
4. Prot.ection Circuit
5. High Frequency
%
-
Rg. 4.1 2 Ohm Load Waveform
Input Signal
Characteristics
None
None
1 voit;IKHz
sine wave
1 voit;lKHz
sine wave
I vo l t; 10KHz
sq. wave
I voit;lKHz
sq.
wave
!
-
I.
Il'
•
Instructions/Comments
± lOmV
Positive output, base-emiuerjunction should be between
.3V and .35V. Adjustable by RIl2, R212.
Into 8 ohms, 20 vrms ( SO watts) should be obtainable
before signalclip.
InlO 4 ohms, 11.5 vrms (75 walts) should be obtainable
before signal cJLp.
Int o 2 ohms, signal will appear as in Figure 4.1.
Into ar\ 8 ohm load, a 25 volt peak to peak: square wave
sig nal should exhibit no ringing (see figure 4.2)
Into an 8 ohm load, a 19vrms sine wave signal sh ould
exhibit no ringing (see Figure 4.3).
, ,
Fig . 4.2 10KHz Sq. Wave
Fig. 4.3 20KHz Sine Wave
Maintenance 4·3

9 (£(f'@(hMUll ____ _ --'O;:.."'75"PD="''''E"R."AM=PL" IF" 'E,,R '- ____ _____ ---'R'''E,.,V'-'' .0
Test or Adjustment
6. Inlcnnodulation Distortion
7. IOC
8. Signal to Noise
9. Quiesent AC Power
'IO " ~ T
~
I<. VOl NE rt ~ .-
."
Input Signal
Ch aracteristics
. SV + /· 2%:60Hz·
7KHz signal
s ummed in4:1
ratio
2.5V peak.peak
5Hz sq. wave
I J:.~ I ~ ~,
r.::EL~TI\Ol I , "","IOU"1 ~.-:;:.
INPUTS D4$CQNN«:I( O)
~
,- ,
(l< AHHR
Instructi on s/ COmm e nts
( See Fig. 4.4) When using th e Crown IMA, typical
reading s will be as follow s:
OdB ·. OO4 %
-SdB lhrough -25dB= . 03 %
·30dB·. 03 %
·3SdB·.
03%
I OC s hou ld illuminate once for every rise time and once
for every fal l time (twice every full cycle) , Test
gene rator rise lime mu st be l ess man 1.0 microsecond.
( See Fig .4.5) SignallO noise s hould be 1 000B below
rated OUtput with meter bandwidth of 20Hz to 20KHz.
IS walts at idle as monitored by wattmeter on AC li ne;
1 20 watlS at fu ll rated outpu t.
I
~
I
~
~
~'.
IIE!\IIM I,NlIICIUN()£() WlW'PE D
AAO.INO QUl'NT CA&(
/'
OM
••
I~ I
...........
h
{ ~ l TH(A
C IWI'<IE L
~ w m
Fig . 4.4 1M Distort io n Test Set - up
Fig. 4 .5 Signalto Noise res l Sel-up
4-4 MaintBnanc9

A ~E",V"-."-O __________ --,,D-,.75=PO::."':.:;E",R.:.; A o:M:::P-,L::..'F,,IE.:.;R _____ (£[J@(1ill)1fil9
5 Voltage Conversion
Often Crown produCIS are purchased in one country and
later moved to another requiring an AC mains conversio n.
For this reason the following chan/explanation as well as
a wor l d-wide voltage map is provided.
The 0-75 power supply may be c onnected for any of five
vo ltages. Convening from one 1.0 anothercan be
accomplished with a soldering iron and a pair of wire
cutlers. Follow th e fable sh ow n with the sc hematic, and
the drawi ng below.
CA UTION:Because there is a ri sk of el ectric sh ock,
only a competent techn ic ian should attempt to alter
tbe line voltage
co nfigura ti on.
1. Remove the tOp cover of the D- 75 (held on by 8
sc rews).
2. With
the unit ri ght si de up, and the front panel toward
you, locate lhe terminal strip on the
front in the near right-
hand comer.
3. Make the appropriate change in jumpers for the
desired operat in g voHage. See Fi g. 7.30.
4. RepIace the 2 amp line fuse with a I amp type 3AG
fu
se. for all connections 200V and above.
5. Change the line cord tage 10 read !he correct voltage.
Note: Use only a 2 am p fu se for lOOVAC or 12 0VAC
operation. Use only a 1 amp fuse for 200VAC, 220VAC
or 240V AC operation.
100 VAC
r~ ~ ¥ ~ ~ ~
200 VAC
II &~~~~
220 VAC
~l~~~
z w
tf I-
o 240VAC ~
Rg. 5. 1 AC Ma ins Voltage Conversion
Maintenance 5· t

This Page LeN Blank Intentionally

REV. 0 0-75
POWER AMPLIFIER
6 Circuit Theory
6.1 Block Diagram Circuit Theory
The following cliscussioo re f ers lO the block diagram in
Fig. 6.1.
When using th e XLR Balanced Input.lwo signals, I SO°
out of phase, will be introduced 10 th e Balanced Input
circuioy. Here, th e two s ignals arcadded together to
become the Unbalanced o utput of the Balanced input
circuitry,
Thi sc ombincd sign al is th en fed to a s tage of powe r
amp l ifi c ation where it is boos t ed to a l eve lof s uffi c ient
amplitude to drive an Ou t put Load.
A ponion of the output signal is routed to the Signal
Presence cin:uilry. Pr ovided th e ou tput sig nal has J!l
amplitude of at least one vo ll peal.: to peak, the green
s ignal prese nce indicators willlighl and vary in imensily
with Lilc O UlPU Lsi gna l.
The o utput signai is f ed back to a.'l d com pared with Lile
i npu t signal. An y n onl ineariti es ex i sti ng between th ese
two signals will generate acorrection signal to th e
amplifier
and the JOC indi cators on the fronL panel.
~ In pbue . ,..;,t, 1M • i9UI 00QUII1O
The P owe r Suppl)' supp li es th e proper voltages to the
various circuit componeOis within the amplifie r.
P:trz;
UNBAl
POWER
INPUT
A MP
CH,
CH 1
3AlINPUT I
r8
s~
,-d'
POWER
MONO", I
AC LINE
SUPPLY
SWITCH
MONO
Lf\-
BAlINPUT I
~
s~
UNBAl POWEM
INP UT
AMP
CH2 CH2
F ig. 6.1 D ·7 5 Block D ia gram
Circuit Theory 5 -1

~ If:::(f(g)(Id!!)(fj) _ ____ --'D'C-'-'75'-'PO~W!"E":'R~A""M":P,o,L1F':"=cER~ ___ _ ______ ~A!OEV~. 0
The following ex planation refers 10 schematic diagram
MI-270b located in th e In struction Manual as well as al
theend of Section 9. How ever, each circuil under
discussion is reprinted below in order to aid in circu it
familiarization. Only channell is shown for sim pli city.
6.2. Balanced/Unbalanced Input Stage
In order to eliminate annoying RF interference, balanced
inp ut (as well as unbalanced) s ta ges ate iocorporalCd in
the 0-75. U2A and U2B are the balanced input op amps
which provide
the correct phase inv ersion used in
balanced input design. As per definition ofa balanced
input s ignaJ , an input from a balanced lin e is fed 10 the
inverting (-) and non-inverting (+) inputs of U2A (pins 2
and 3). This has the effect ofdriving the inputs J 80
degrees out of phase. 1be output signal will now be
unbalanced and in phase with the signal applied 10 pin 3,
but without any annoying noise lIlal may ha ve been
present at the input. Th e reason for this is because
unlik e the aud io input signal, the noise signal produced
(by so me c:\temal source) will appear on both s id es oflhe
balanced line and will cancel each other at the op amp
output Note the fo ll ow ing diagram.
IDa
''''''''
Balanced
"',,"'
el2S
82PF I 9.9K
9.9K
Fig. 6.2 Balanced Input Stage
6.3. Input Operational Amplilier
The input op amp, UlOO is a low noise. large ga in
bandwidlh integrated circuit. Unde r its formal name, LF
6-2 Circuit Theory
357, itacts as an input voltage amplifier producing
emcme1y low distortion by means of several feedback
paths. The
gai ndctcrmining components for this stage arc
two voltagc dividing resistors, RI03 and RIOS. Note that
lhcy act as a feedback palh from lh c outp ut ofUlOO (pin
6) to lhc in verting input of U 100 (p in 2). Both s ig nals
cntering U
100 al p in 3 will be in phase w ith each othcr
because of
lhis feedback path and will thus produce an
output (pi n I) ofalmost zero. Thc sma ll amount of
output signal
that is prescnt is thcre because of the slight
diffcrence
in ohmic value (with respect to gai n) of
voltagc divider, RIDS and R103.
cIa,
25
N
:; R102
'K
-l
. ~1O~ ± Rl04
200PFT 10K
7
R'03
'"
. 5W
'"
0110 0109
:'f
*
~,
•
C~f
- 1~V
"
~
_ RIS1
.~
- 9. 53K RI52 ;
i'
'"
OPEN
Fig. 6.3 Input Operational Amplifier
C'06
27PF
R'08
toK
.5W
The IC op amp will always try to keep a zero potential
difference between bolh
inputs. Any type of non-linearity
will cause the OJ> amp to produce a large output, and
lhcrfore a substant ial size correc tion signal in order to
retain the small output level.
6.4. Signal Translator
The opcmtion of the D-75 front-end circuitry (IC op amp
through QI02) is to basically provide voltage
amplification. However, lh e signailfan slatOf transistor
(Q I OO) provides no vo lta ge amplification itself, but
rather converts the ground referenced input signal to a
s ignal with a reference to the negative supply. The result
is hi ghcr vo lta ge swing capabilities from QI02 (Final
Voltage Amplifier).
"'"
3 Ul(l(l
>-, -- -ka,co,,£!
Fig. 6.4 Signal Translator
C"r
"r