crown Amcron D-75A, Amcron D-75, Crown D75 crown-d45a-d75a-service-manual

D-45 / D-75A Amplifier Service Manual

Exported to select countries as Amcron.

®

POWER AMPLIFIER

SERVICE MANUAL

D-45 / D-75A

©1995 by CROWN INTERNATIONAL, INC.

P.O. Box 1000, Elkhart, IN 46515-1000

Telephone: [phone]

Shipping Address:

57620 C.R. 105

Elkhart, IN U.S.A. 46517

Amcron®, Crown®, and IOC® are registered trademarks of Cr own International, Inc.

K-SD4575A

11-95

1

D-45 / D-75A Amplifier Service Manual

The information furnished in this manual does not include all of the details of design, production, or variations
of the equipment. Nor does it cover every possible situation which may arise during installation, operation or
maintenance. If you need special assistance beyond the scope of this manual, please contact the Crown
T echnical Support Group.

Mail: P.O. Box 1000 Elkhart IN 46515-1000

Shipping: 57620 C.R. 105 Elkhart IN 46517

Phone: [phone]

Facsimile: [phone]

WARNING

TO REDUCE THE RISK OF ELECTRIC

SHOCK, DO NOT EXPOSE THIS

EQUIPMENT TO RAIN OR MOISTURE!

CAUTION

TO PREVENT SHOCK DO NOT USE THE POLARIZED AC

PLUG OF THIS UNIT WITH AN UNPOLARIZED EXTENTION

CORD, RECEPTACLE OR OTHER OUTLET WHERE THE

BLADES CANNOT BE FULLY INSERTED.

ATTENTION

POUR PREVENIR LES CHOCS ELECTRIQUES NE PAS

UTILISER CETTE FICHE POLARISEE AVEC UN

PROLONGATEUR. UNE PRISE DE COURANT OU UNE

AUTRIE SORTIE DE COURANT, SAUF SI LES LAMES

PEUVENT ETRE INSEREES A FOND SANS EN LAISSER

AUCUNE PARTIE A DECOUVERT.

2

D-45 / D-75A Amplifier Service Manual

Table of Contents

Introduction ............................................................ 4

General Parts Information.......................................5

Specifications ......................................................... 6

Circuit Theory ......................................................... 7

Voltage Conversion ..............................................10

Internal Settings.................................................... 11

Electrical Checkout Procedures ........................... 12

Exploded View Parts List, Front............................14

Exploded View Parts List, Rear ............................ 16

Q43308-8 Main Module Component Layout.........18

Q43308-8 Main Module Parts List ........................ 19

Q43156-1 Output Module Component Layout...... 21

Q43156-1 and Q43309-6 Module Parts List ......... 22

3

D-45 / D-75A Amplifier Service Manual

Introduction

This manual contains service information on Crown
power amplifiers. It is designed to be used in con­junction with the applicable Owner's Manual. However ,
some important information is duplicated in this Ser­vice Manual in case the Owner's Manual is not readily
available.

NOTE: THE INFORMATION IN THIS MANUAL IS INTENDED
FOR USE BY AN EXPERIENCED TECHNICIAN ONLY.

Scope

This Service Manual comes in several sections. The
contents of each section apply to all models listed on
the front cover except the Electrical Checkout Proce­dure sections which are model specific. The informa­tion in this manual will cover each version of the mod­els covered with an emphasis on the U.S. (120V AC 60
Hz) version. The sections covered include General
Parts Information, Circuit Theory, Specifications, V olt­age Conversion, Electrical Checkout Procedures, Ex­ploded Views (mechanical art with parts list), Printed
Circuit Board Art (tracework drawings), Module Parts
Lists, and Schematics. Note that component parts with
circuit board comprise a complete module. Module
part numbers are always associated with a specific
circuit board, although an unpopulated circuit board

may be built up with different parts to create differ ent
modules. Note that Crown does not sell blank
(unpopulated) circuit boards.

Each of the compact audio power amplifiers are de­signed for professional or commercial use. Providing
power amplification from 20Hz-20KHz with minimum
distortion, they feature balanced inputs with bridged
monophonic capability . Specific features vary depend­ing on model family .

Warranty

Each Owner's Manual contains basic policies as re­lated to the customer. In addition it should be stated
that this service documentation is meant to be used
only by properly trained service personnel. Because
most Crown products carry a 3 Y ear Full W arranty (in­cluding round trip shipping within the United States),
all warranty service should be referred to the Crown
Factory or Authorized Warranty Service Center. See
the applicable Owner's Manual for warranty details.
To find the location of the nearest Authorized Service
Center or obtain instructions for receiving Crown Fac­tory Service please contact the Crown T echnical Sup­port Group (within North America) or your Crown/
Amcron Importer (outside North America).

Crown

Technical Support Group

Factory Service

Parts Department

Mailing Address:

P.O. Box 1000

Elkhart, IN USA 46515-1000

Shipping Address:

57620 C.R. 105

Elkhart, IN USA 46517

Phone: [phone]

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Facsimile: [phone]

4

D-45 / D-75A Amplifier Service Manual

General Parts Information

General Information

Later sections include both mechanical and electrical
parts lists for this product. The parts listed are current
as of the date printed. Crown reserves the right to
modify and improve its products for the benefit of its
customers.

Part Numbering Systems

As of the printing of this manual, Crown is using two
numbering systems. The elder system always uses
eight characters. The first character is a letter. Com­mon letters used are C, D, H, M, P, and Q. The second
through sixth characters are numbers. The numbers
build sequentially (for each prefix letter) as new parts
are added to our parts inventory system. (In some
cases there will be a space then a four character
number after the prefix letter; the space is considered
a character.) The seventh character is usually a hy­phen, though it may be a letter to indicate a revision or
special note. The last character is called a check-digit,
and is useful to Crown for internal tracking.

Crown is in the process of converting to a new part
number system. Length may vary from eight to twelve
characters. There is still a letter prefix, then five num­bers. These five numbers identify a type of part. The
seventh character is a hyphen. Remaining characters
identify the details of the type of part identified by the
first part of the number.

Standard and Special Parts

Many smaller electrical and electronic parts used by
Crown are stocked by and available from electronic
supply houses. However, some electronic parts that
appear to be standard are actually special. A part
ordered from Crown will assure an acceptable re­placement. Structural items such as modules and
panels are available from Crown only.

prepaid and will be billed. All others will receive ship­ment on a C.O.D. or pre-payment (check or credit
card) basis.

Terms

Normal terms are pre-paid. Net-30 Days applies to
only those firms having pre-established accounts with
Crown. If pre-paying, the order must be packed and
weighed before a total bill can be established, after
which an amount due will be issued and shipment
made upon receipt of pre-payment. New parts re­turned for credit are subject to a 10% re-stocking fee,
and authorization from the Crown Parts Department
must be obtained before returning parts for credit.

Crown is not a general parts warehouse. Parts sold by
the Crown Parts Department are solely for servicing
Crown/Amcron products. Part prices and availability

are subject to change without notice.

Crown

Parts Department

Mailing Address:

P.O. Box 1000

Elkhart, IN USA 46515-1000

Shipping Address:

57620 C.R. 105

Elkhart, IN USA 46517

Ordering Parts

When ordering parts, be sure to give the product
model, and include a description and part number
(CPN/DPN) from the parts listing. Price quotes are
available on request.

Shipment

Shipment will be normally made by UPS or best other
method unless you specify otherwise. Shipments are
made to and from Elkhart, Indiana USA, only. Estab­lished accounts with Crown will receive shipment freight

Phone: [phone]

TT

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Facsimile: [phone]

5

D-45 / D-75A Amplifier Service Manual

Specifications

Unless noted otherwise, all specifications are based
on driving an 8 ohm load per channel, both channels
driven. The AC supply is 120V AC 60Hz. Crown speci­fications are guaranteed through the warranty period
(normally 3 years). Because our testing methods are
more stringent than our published specifications, ev­ery Crown amplifier will exceed its published specifi­cations.

Power

Output Power

Note: Maximum average power at 1 KHz with less than

0.1% THD.

D-75A

16 Ohm Stereo—25W/Ch
8 Ohm Stereo—40W/Ch
4 Ohm Stereo—55W/Ch
16 Ohm Bridge Mono—80W
8 Ohm Bridge Mono—110W

D-45

16 Ohm Stereo—20W/Ch
8 Ohm Stereo—25W/Ch
4 Ohm Stereo—35W/Ch
16 Ohm Bridge Mono—50W
8 Ohm Bridge Mono—70W

Load Impedance: Safe with all types of loads. Rated for
4 to 16 ohms in Dual, and 8 to 16 ohms in Bridged
Mono mode.

AC Mains: 100, 120, 200, 220, and 240 VAC units are
available (all voltage requirements are ±10%). 50 to
400 Hz AC mains can be used with international units
depending on the transformer configuration. North
American 120 VAC, 60 Hz units are not convertible
and can only be used at the specified voltage and
frequency . Both units draw 15 watts or less when idle.
Maximum AC power consumption is 150 watts.

second. (Slew rates are limited to useful levels for ul­trasonic/RF protection.)

Damping Factor: Greater than 400 from DC to 400 Hz.
Input Impedance: Nominally 20 K ohms balanced, and

10 K ohms unbalanced.
Output Impedance: Less than 15 milliohms in series with

less than 3 microhenries.
Input Sensitivity: 26 dB voltage gain. Configurable for

0.775 volt sensitivity .

Mechanical/Features

Power Switch: A two-position front panel rotary switch.
Level Controls: A detented front panel rotary potenti-

ometer for each channel used to control the output
level.

Dual-Mono: A dual-mono jumper located inside the
amplifier.

AC Line Connector: Standard three-wir e grounded con­nector.

Power Indicator: This orange indicator shows that the
unit has been turned on.

IOC Indicators: A red indicator for each channel flashes
if the amplifier causes any distortion of 0.05% or more.

Signal Presence Indicators (SPI): A green indicator for
each channel flashes to show that there is amplifier
output.

Input Connectors: A balanced three-pin female Neutrik
combination XLR and 1/4 inch phone connector for
each channel.

®

Performance

Frequency Response: ±0.1dB from 20 Hz to 20 KHz at 1

watt.
Phase Response: +10° to -15° from 20 Hz to 20 KHz at

1 watt.
Signal-to-Noise Ratio: 106dB below full rated output

from 20 Hz to 20 KHz at 1 watt.
Total Harmonic Distortion (THD): Less than 0.001% at

full rated output from 20 Hz to 400 Hz increasing lin­early to 0.05% at 20 KHz.

Intermodulation Distortion (IMD): Less than 0.05% from

0.01 to 0.25 watts; less than 0.01% from 0.25 watts to
full rated output.

Controlled Slew Rate: Greater than 6 volts per micro­6

Output Connectors: A four-terminal barrier block (two ter ­minals per channel) and stereo headphone jack. Head­phone output is unpadded and in parallel with the main
outputs.

Chassis Construction: Durable black finish on the steel
chassis, and an aluminum front panel with Lexan over ­lay specially designed to provide maximum heat con­duction and minimal weight.

Cooling: Convection.
Dimensions: 19 inches (48.3 cm) wide, 1.75 inches

(4.45 cm) tall and 8.38 inches (21.27 cm) deep be­hind the front mounting surface.

Approximate Weight: Net 10 lbs (4.53 Kg). Shipping 12
lbs (5.45 Kg).

Mounting: Standard EIA 310 19-inch rack mounting.

D-45 / D-75A Amplifier Service Manual

Circuit Theory

Overview

It should be noted from the start that the D-45 and the
D-75A have identical circuitry except for the size of
the power supply . The same schematic is used for both
models. It is also important to realize that over time
Crown can introduce improvements to its amplifiers.
Though often changes are minor, and are made for a
variety of reasons it is a good idea to see if any Tech­nical Notes have been issued on these models. This
manual is up to date as of the time of writing, Novem­ber 1995.

This section of the manual explains the general op­eration of the D-45 and D-75A amplifiers. Topics cov­ered include Power Supply , Balanced input stage, Er ­ror amp, Signal T ranslator , Last V oltage Amplification
stage, Bias, Output stage, Protection circuitry, IOC,
and Signal Presence Indicators (SPI).

Block Diagram

The following discussion refers to the block diagram
in figure 1.

The balanced input signal is converted to an unbal­anced signal at the input stage. This unbalanced sig­nal is then routed through the volume control into the
Error Amp which provides voltage amplification with
extremely low distortion by means of several feedback
paths, one of which is from the output stage providing
distortion control from input to output. Any difference
in the comparison between the input signal and out­put signal of .05% or greater will result in an Error sig­nal, and the IOC indicator will light. Next, the signal is
feed into the Signal T ranslator . This transistor converts
the signal reference from gr ound to the negative sup­ply, allowing greater voltage swing capabilities. The
Last Voltage Amp (LVA) then recieves the signal and
gives it more voltage amplification. This is the main
voltage amplification stage. The output of the L V A pro­vides the signal drive to the output stage which pro­vides the current necessary for the final output power .

Ch 1 In

IOC

+

-

Bal. Input

AC Line

Error Amp

±10V

Sig. Translator Output Stage

Power Supply

Feed Back Loop

Last
Voltage
Amp

Ch 1 Out

Mono
Switch

SPI

To Ch 2
Input Op-Amp

Figure 1: D-45, D-75A amplifier circuit block diagram (channel one only)

7

D-45 / D-75A Amplifier Service Manual

Circuit Theory

Power Supply

The power supply consists of a single power trans­former with two sets of secondary windings which are
paralled together . The AC power is then full wave rec­tified and filtered with capacitors C8 and C9. The re­sult is VCC voltages of ±31VDC for the D-45, and
±35VDC for the D-75A.

The power supply is protected by the fuse F1 which is
in series with the primary of the transformer. The power
indicator lamp is in series with a 27K ohm resistor and
is across the primary of the transformer .

The ±10 volt supplies, which supply voltage to the in­tegrated circuits, are regulated by the 10 volt zener
diodes D1 and D2. VCC supplies voltage to these
zeners through R1 and R2.

Balanced Input Stage

In order to eliminate annoying noise and RF interfer­ence, a balanced input stage is incorporated into the
design of the D-45 and D-75A. U100 is the balanced
input op-amp which provides the correct phase inver ­sion used in balanced input design. As per the defini­tion of a balanced input signal, an input from a bal­anced line is fed into the inverting (-) and non-invert­ing (+) inputs of U100B,C (pins 5 and 6 for Ch 1 and
pins 9 and 10 for Ch 2). The balanced line consists of
two signals 180 degrees out of phase. The output sig­nal of the op-amp (pins 7 and 8) in unbalanced and in
phase with the non-inverting (+) input. Any "noise" that
is common to both the non-inverting and inverting in­puts is canceled and is not present at the output.

Error Amp

U100, which is used in the balanced input stage, is
also used in the Error Amp stage. This op-amp is a
low noise, large gain, large bandwidth integrated cir­cuit. It acts as an input voltage amplifier producing
extremely low distortion by means of the feedback path
from the output of the amplifier. The ratio of the feed­back resistor (R108/208) to the input resistor (R103/

203) fixes the overall gain at 26dB. Diodes R109/209
and R110/210 prevent overdriving the Error Amp. Be­cause the Error Amp amplifies the difference between
the input and output signals, any difference in the two
waveforms will produce a near open loop gain condi­tion which in turn results in a high peak output volt­age. This high peak is the Error Signal which results in
IOC indication.

Signal Translator

The Signal T ranslator transistor Q100/200 provides no
voltage amplification, but rather converts the ground
referenced input signal to a signal with a refer ence to
the negative supply . The result is higher voltage swing
capabilities from Q102/202, the Last V oltage Amp. The
output of the T ranslator produces a voltage across the
resistor R114/214, which then drives the LV A.

Last Voltage Amplifier (LVA)

The Last Voltage Amplifier transistor, Q102/202, is the
main voltage amplification stage. All signal voltage that
appears at the output is developed here. R114/214
connected at the base of Q102/202 serves several
purposes. It provides collector current for Q100/200.
It provides bias voltage for Q102/202. And it provides
signal voltage to drive Q102/202. The transistors Q101/
201 prevent Q102/202 from being overdriven.

Bias

The output of the Last Voltage Amplifier provides the
signal drive to the predriver , driver , and output transis­tors in order to amplify the current for the final output
power. The bias transistor Q103/203 provides a bias
voltage of 2.1V DC. This bias voltage is distributed
throughout the current amplification stages in the fol­lowing manner:

1) Base to Emitter junction of Q107/207, positive
predriver , is 0.6V.

2) Base to Emitter junction of Q108/208, positive driver ,
is 0.6V . The negative driver and output transistors have
fixed base-emitter bias.

3) Base to Emitter junction of Q109/209, positive out­put transistor is 0.314V (biased to sub turn-on state).

As the amplifier under loaded operating conditions
increases in temperature, the bias sensing transistor,
Q103/203, temperature increases proportionally. This
condition reduces the bias supply which results in pre­vention of thermal runaway .

Output Stage

There are several categories or classes in which am­plifiers are placed, the most common being class A, B
or C. Each class or combination thereof, has a spe­cific bias current applied to the transistor which deter­mines its operating conditions. Class A amplifiers will
be biased in such a way that its transistors operate
always in the active region (360 degrees) between
saturation and cutoff. Class B amplifiers are biased at

8

D-45 / D-75A Amplifier Service Manual

Circuit Theory

cutoff (180 degrees), and class C below cutoff. The
D-45 and D-75A output stages are designed with Class
AB+B mode of operation where the driver transistors
carry the bias current while the output transistors serve
only as boosters. The output transistors sense when
the driver transistors are developing significant cur­rent draw from the load and thus take over and deliver
the needed current. The output stage is of a quasi­complementary format using no bias current into the
output transistors themselves. The result is maximum
efficency with minimum crossover notch distortion and
idling amplifier heat.

Protection Circuitry

The D-45 and D-75A utilizes Voltage-Current limiting
for protecting the output stages. V-I limiting is supe­rior to most other forms of protection because it di­rectly senses the overload condition and instantly re­acts to relieve the overload, and acts only as long as
the overload exists.

Should the output voltage or current become danger ­ously high, the voltage induced across the current lim­iting sense resistors (R128/228, R129/229) is fed to
the limiting transistors (Q104/204, Q105/205). These
transistors will then "clamp" a limit on the signal as it
threatens to push the output stage beyond its capa­bilities. The limit point is determined by a combination
of the predriver plus limiter current equaling the avail­able current source on the main board. In other wor ds,
the signal drive that is fed to the predrivers is limited
or clamped.

IOC (Input Output Comparator)

The front panel IOC display (E102 and E202) is driven
by a window comparator circuit that uses an opera­tional amplifier IC (U3). Any small nonlinearity in the
amplifier causes an error signal to appear at the out­put of the main IC op-amp (U100) (see the section on
Error Amp). This error signal is then responsible for
raising the bias voltage on U3 and inturn activating
Q114/214 which illuminates the LED.

SPI (Signal Presence Indicator)

E101 and E201 are the green front panel indicators
which illuminate any time the output of their channel
reaches 1 volt peak-peak or above. Q115/215 senses
the output voltage through the resistor R131/132 and
turns on the LED which is powered by +VCC.

9

D-45 / D-75A Amplifier Service Manual

Voltage Conversion

The 120 volt 60 Hz models, sold in the United States,
are not voltage convertable. They do not use a multi­tap transformer. These domestic models ar e to be used
only with 120 volts, 60 Hz.

All other models, sold outside the US, use a multi-tap
transformer which can be configured for different volt­ages. Use the following diagram (figure 2) to deter­mine the jumper configuration for the different voltages.
The units terminal strip is located near the front of the

amplifier on the right side (front panel toward you).
These export models can be operated with an AC
mains frequency of 50 to 400 Hz. The back panel
sticker indicates the unit's factory configuration.

10

Figure 2: Voltage jumper configurations for export models

D-45 / D-75A Amplifier Service Manual

Internal Settings

Internal Settings

From the factory, the amplifier is configured for dual
(stereo) operation and an input sensitivity of 26 dB
gain. The amplifier may be configured for higher power,
single channel, bridge-mono operation. The amplifier
may also be configured for an input sensitivity of 0.775
volt.

26 dB Gain vs. 0.775 Volt Sensitivity

For most applications, the amplifier's default setting of
26 dB gain will be ideal. With this default setting, full
output power is achieved with an input signal of 0.837
volts for the D-75A, and 0.632 volts for the D-45. Some
applications may require the gain structure to be
calculated based on a sensitivity of 0.775 volts. And
although the 26 dB gain setting provides a sensitivity
for each amplifier that is very near 0.775 volts, the

0.775 volt sensitivity setting is provided for applica­tions that demand this sensitivity with a high level of
precision.

To activate the 0.775 volt sensitivity, both the top and
the bottom covers must be removed. After the covers
are removed use the following instructions.

D-75A
Solder #22 jumper wires at the locations marked
R152 and R252 on the main circuit board.

D-45
Desolder and remove the resistors in locations
R103 and R203. In place of the old resistors,
solder ¼ watt, 665 ohm (1%) resistors.

Dual vs. Bridge-Mono Mode

The D-75A and D-45 amplifiers are configured at the
factory for dual operation because it is commonly used
in two channel or stereo applications. The amplifiers
have excellent crosstalk characteristics, so each chan­nel can be used as an independent, single channel
amplifier. For more conventional stereo applications,
left and right source signals can be connected to
inputs 1 and 2 to drive a pair of stereo loudspeakers.

For some applications, it is desirable to have higher
power output from a single (mono) channel. The bridge­mono mode makes this convenient. Bridge-mono mode
can be used in single channel applications such as
paging. It also lets you get the absolute maximum
power out of the amplifier, like with the D-75A which
delivers 80 watts (2 x 40) in dual mode and 110 watts
(1 x 110) bridge-mono into 8 ohms. The bridge-mono
mode also provides an easy power and performance
upgrade path for stereo applications. A single ampli­fier might provide adequate power until a second
amplifier can be added for use in a "dual mono"
configuration.

To activate the bridge-mono mode, both the top and
bottom covers must be removed. After the covers are
removed use the following instructions.

1. Remove the jumper from the pins marked with
the words "DUAL" and "MONO"

2. Reinstall the jumper so the two pins closest to
the word "MONO" on the circuit board are shorted.

Reassemble the unit.

3. Reassemble the unit.

To convert back to the Dual mode, simply move the
jumper back to the "DUAL" position.

11

D-45 / D-75A Amplifier Service Manual

Electrical Checkout Procedures

General Information

The following test procedures are to be used to verify
the operation of both the D-45 and D-75A amplifiers.
DO NOT connect a load or inject a signal unless di­rected to do so by the procedure. These tests, though
meant for verification and alignment of the amplifier,
may also be very helpful in troubleshooting. For best
results, tests should be performed in order .

All tests assume that AC power is from a regulated
120VAC source. Test equipment includes an oscillo­scope, a DMM, a signal generator, loads, and I.M.D.
and T.H.D. noise test equipment.

Standard Initial Conditions

•Level controls fully clockwise.

•Stereo/Mono jumper in the Stereo position.

•26 dB gain (factory setting).
It is assumed, in each step, that conditions of the am­plifier are per these initial conditions unless otherwise
specified.

Test 1: DC Offset

Spec: ≤ ±.01 VDC for both channels throughout the

range of the input level control travel.

Initial Conditions: Controls per standard, inputs shorted.
Procedure: Measure DC voltage at the output connec-

tors, while rotating the input level controls. There is no
adjustment for the output offset. If spec is not met,
there is an electrical malfunction.

Test 2: Output Bias Adjustment

Spec: .350 VDC, ±.01 VDC.
Initial Conditions: Controls per standard, heatsink at

room temperature.
Procedure: Measure the DC voltage across the base
and emitter of an output transistor in each channel.
Adjust R112 for channel 1 and R212 for channel 2.

Test 4: Common Mode Rejection

Spec: ≥ 60 dB at 1 KHz.
Initial Conditions: Controls per standard.
Procedure: No load. Inject a 0 dBu (.775 V) 1 KHz com-

mon mode sine wave (inverting and non-inverting in­puts shorted together) into each channel, one chan­nel at a time. At the output measure less than 15.9 mV.
Adjust R157 for channel 1 and R257 for channel 2.

Test 5: Input Sensitivity

Spec: Gain of 20 (26 dB)
Initial Conditions: Controls per standard.
Procedure: No load connected. Front panel level con-

trols turned full CW . Inject a 0.775 V, 1 KHz sine wave
into the input of each channel. Measure between 15.46
V and 16.42 V at the output of each channel. There is
no calibration adjustment for voltage gain. If gain is
not in spec then there is an electrical malfunction.

Test 6: Level Controls

Spec: Level controlled by level controls.
Initial Conditions: Controls per standard.
Procedure: No load. Inject a 1 KHz sine wave. With

level controls fully clockwise you should see full gain.
As controls are rotated counter clockwise, observe simi­lar gain reduction in each channel. When complete,
return level controls to fully clockwise position.

Test 7: Current Limit

Spec: D-45—Current limit between 6.12 &12.0 amps.

D-75A—Current limit between 7.75 & 12.0 amps.

Initial Conditions: Controls per standard.
Procedure: Load each channel to 1 ohm. Inject a 1 KHz

differentiated square wave (or 10% duty cycle). See
figure 3 for differentiator cir cuit. Incr ease output level
until current limit occurs. Current limit should occur
around 10 amps (10 Vpk). See above specifications.

Test 3: Quiesent AC Power Draw

Spec: ≤ 20 Watts
Initial Conditions: Controls per standard. This measure-

ment must be made after bias adjustment.
Procedure: With no input signal and no load, measure
AC line wattage draw. If current draw is excessive,
check for high AC line voltage or high bias voltage.

12

In

.047 uF

1K Ohm

Figure 3: Differentiator Circuit

Out

D-45 / D-75A Amplifier Service Manual

Electrical Checkout Procedures

Test 8: Slew Rate

Spec: >6 V/µS.
Initial Conditions: Controls per standard.
Procedure: Load each channel to 8 ohms. Inject a 10

KHz square wave. For the D-45 adjust the output mag­nitude for 10 Vp-p. For D-75A adjust the output mag­nitude for 12 Vp-p. Observe the output. It shall be
square with no ringing.

Test 9: Harmonic Distortion

Spec: ≤.1% THD.
Initial Conditions: Controls per standard.
Procedure: Load each channel to 8 ohms. Inject a 20

KHz sine wave into each channel. For the D-45 adjust
the output for 12.7 V AC. For the D-75A adjust the out­put for 16.7 VAC. No filters shall be used at this time.
Measure ≤.1% THD.

Test 10: Output Power

Spec:

D-45 8 Ohm Stereo—25W/Ch

4 Ohm Stereo—35W/Ch

D-75A 8 Ohm Stereo—40W/Ch

4 Ohm Stereo—55W/Ch

Initial Conditions: Controls per standard.
Procedure: Load each channel to 8 ohms. Inject a 1

KHz sine wave into each channel. For the D-45 mea­sure at least 14.2 VAC at the output of each channel.
For the D-75A measure at least 17.9 V AC at the output
of each channel. Load each channel to 4 ohms. For
the D-45 measure at least 11.9 VAC at the output of
each channel. For the D-75A measure at least 14.8
VAC at the output of each channel. All power mea­surements must be at less than 0.1% THD.

Test 11: Short Test

Spec: Must not damage components, fuse shall not

blow.

Initial Conditions: Controls per standard.
Procedure: Inject a 60 Hz sine wave into both chan-

nels. If testing a D-45 adjust the output to 14.2 V AC, if
testing a D-75A adjust the output to 17.9 VAC. Short
only one channel at a time. Amplifier must not dam­age any components to pass the test.

KHz) filter. For the D-45 measure ≤ 71µV of noise at the
output of each channel. For the D-75A measure ≤ 89µV
of noise at the output of each channel.

Test 13: Intermodulation Distortion

Spec: ≤ .01% at 0dB, ≤ .05% at -30dB.
Initial Conditions: Controls per standard.
Procedure: Load each channel to 8 ohms. Inject a SMPT

standard IM signal (60 Hz and 7 KHz sine wave mixed
at 4:1 ratio). For 0 dB reference on the D-45, set the 60
Hz portion of the sine wave to 12.7 VAC. For 0 dB
reference on the D-75A set the 60 Hz portion of the sine
wave to 16.7 VAC. Set the 7 KHz portion at 25%. With
the IM analyzer, measure less than .01% at 0 dB and
less than .05% at -30 dB.

Test 14: Headphone Jack

Spec: Output signal same as output jacks.
Initial Conditions: Controls per standard.
Procedure: Inject a 1 KHz sine wave into each channel.

By rotating the level controls, verify that the outer ring
is ground, the inter ring is channel 2 and the tip is
channel 1.

Test 15: Display Check

Spec: SPI at 1 V output, IOC at output clip, power on.
Initial Conditions: Controls per standard.
Procedure: Inject a 1 KHz sine wave into each channel.

Verify that the green LED's start to light around 1 volt
output. Verify that the red LED's light when the amplifier
is in voltage clip. Verify that the power indicator is lit.

Post Testing

After completion of testing, if all tests are satisfactory,
the amplifier controls should be returned to the position
required by the customer. If conditions are unknown or
unspecified, factory settings are as follows:
Level Controls: Between 9 and 11 O'Clock.
Power Switch: Off.
Rear Panel Barrier Block: All screws tight.
Internal Settings: Dual (stereo) mode. 26 dB gain.

Test 12: Signal to Noise

Spec: 106 dB below full rated output from 20 Hz to 20

KHz.

Initial Conditions: Controls per standard.
Procedure: Load each channel to 8 ohms. Meter to read

the output shall have an audio band pass (20 Hz-20

13

D-45 / D-75A Amplifier Service Manual

Exploded View Parts List

1

2

10

11

12

3

4

5
6

7
8

9

11

22

23

24

14

13

14
15

16

17

18

19

20
21

17

25

26

27
28

29

30

31
32

33
34

35

Not Shown: Power Cord -A11793-0306L, 2A Fuse -A10285-13

Figure 4: Exploded View, Front

D-45 / D-75A Amplifier Service Manual

Exploded View Parts List

Item Description Part # Quantity

1 Knob, Level D 6265-9 2
2 LED Mount C 9369-7 4
3 Set Screw, 6-32 x .18 C 6005-0 2
4 Overlay, D-45 F12545J3 1

Overlay, D-45 Amcron F12549J5 1
Overlay, D-75A F12546J1 1

Overlay, D-75A Amcron F12548J7 1
5 Knob, On/Off D 8559-3 1
6 Set Screw, 6-32 x .25 C 9460-4 1
7 Lockwasher, #4 Internal Star A10094-2 12
8 Screw, 4-40 x .375 Taptite A10110-10406 8
9 Front Panel Extrusion D 8553-6 1

10 Speed Nut A10178-1 2
11 Rack Ears D 8583-3 2
12 Screw, 6-32 x .75 Socket Head A10092-70612 4
13 Screw, 6-32 x .25 Flat Head A10091-10604 5
14 Bottom Cover M20073K5 1
15 Terminator Module Q43309-6 1
16 Board Support, .5 Inch Screw Mount C 9947-0 2
17 Fuse Holder C 5597A5 1
18 Hex Nut, 6-32 A10102-5 1
19 Screw, 8-32 x .25 Flat Head C 2136-7 4
20 Back Panel M21399J6 1
21 Strain Relief C 9949-6 1
22 Bracket F10104-2 2
23 Top Cover F12454J8 1
24 Screw, 6-32 x .37 Pozi-Drive C 4329-6 2
25 Screw, #8 x .375 C 6457-3 4
26 Nylon Transformer Pin D 3557-2 2
27 Power Transformer, D-45 (Domestic) D 8555-1 1

Power Transformer, D-45 (Export) D 8554-4 1

Power Transformer, D-75A (Domestic) D 8556-9 1

Power Transformer, D-75A (Export) D 4668-6 1

28 Screw, 8-32 x .87 A10086-10814 2
29 Nylon Transformer Shoulder Washer A10099-4 2
30 Transformer Mount, .5 x 9/16 C 3556-5 2
31 Screw, M3X.5X7MM PNHD W/NYLOC D 7261-7 4
32 Lockwasher, #8 Internal Star A10094-6 2
33 Screw, 8-32 x .375 Taptite A10110-10806 2
34 Barrier Block, 4 Position, Chassis Mount C 9950-4 1
35 Screw, 6-32 x .5 A10110-10608 2

15

36

37

38
39

40
41

42

D-45 / D-75A Amplifier Service Manual

Exploded View Parts List

57

58

53
50

59

37

43
44

45
46

47

48
46

49
50

51
52

53
50

54

Not Shown: Neon Lamp -C 2500-4, 27 KOhm Res -A10266-2732

75

74

48

62

60

61

48
62
63

64
65

66

60

67
68

69

70
71

72
73

55
56

Figure 5: Exploded View, Rear

16

D-45 / D-75A Amplifier Service Manual

Exploded View Parts List

Item Description Part # Quantity

36 Terminator Module Q43309-6 1
37 Bracket F10104-2 2
38 Fiber Shoulder Washer, .25 A10099-8 4
39 Solder Lug D 2934-4 4
40 Washer, 7/17OD x .203ID A10100-16 4
41 Lockwasher, #10 Internal Tooth A10094-8 4
42 Screw, 10-32 x .5 A10087-11008 4
43 Green LED (SPI) C 7863-1 2
44 Red LED (IOC) C 8903-4 2
45 Level Control Pot. 20 KOhm Audio 31DNT C10000-5 2
46 Screw, 6-32 x .62 A10086-10610 9
47 Screw, 6-32 x .375 A10086-10606 2
48 Lockwasher, #6 Internal Star A10094-4 19
49 Power Transistor, NPN C 4751-1 4
50 Lockwasher, #4 Internal Star A10094-2 12
51 Hex Nut, 4-40 A10102-3 4
52 Insulator, TO-3 Anodized C 3570-6 4
53 Screw, 4-40 x .375 Taptite A10110-10406 8
54 Phone Jack, 3 Conductor C 3507-8 1
55 Lockwasher, .375 Internal Star A10094-10 1
56 Nut, .376-32 Knurled C 3495B2 1
57 Filter Capacitor (D-45, 5000µF) D 8557-7 2

Filter Capacitor (D-75A, 10,000µF) C 4250-4 2
58 Fiber Washer, .500OD x .195ID A10101-19 4
59 Main Module Q43308-8 1
60 Power Switch, SPST Rotary, 12A (Incl. Nut) C 9463-8 1
61 Bracket, Neon Lamp M20069-7 1
62 Hex Nut, 6-32 A10102-5 11
63 Insulator, 1 x 3 Fishpaper D 2600-0 1
64 Terminal Strip D 4985-4 1
65 Front Panel Extrusion D 8553-6 1
66 Bridge Rectifier, 6A C 3062-4 1
67 Output Module Q43156-1 1
68 Insulator, TO-3 Nylon D 4071-3 4
69 Power Transistor, TIP 47, NPN C 4647-1 4
70 Screw, 4-40 x .62 A10086-10410 4
71 Nylon Shoulder Washer A10099-1 4
72 Torque Spreader, TO-220 C 6541-4 4
73 Mica Insulator, TO-220 C 6052-2 4
74 Solder Lug D 1220-9 1
75 Fiber Washer, .375 x .141 x .031 A10101-9 2

17

D-45 / D-75A Amplifier Service Manual

Q43308-8 Main Module (D 8268-1 Board)

18

Figure 6: Main Module Component Layout (Q43308-8)

D-45 / D-75A Amplifier Service Manual

Q43308-8 Main Module Parts List

Capacitors

C2 C 6806-1 .01µF, 100V
C4 C 6806-1 .01µF, 100V
C6 C 6806-1 .01µF, 100V
C11 C 6806-1 .01µF, 100V
C12 C 6806-1 .01µF, 100V
C100 C200 C 6813-7 27pF, 200V
C101 C201 C 5311-3 22µF, 50V NP
C102 C202 C 6809-5 220pF, 100V
C103 C203 C 8576-8 100µF, 35V
C104 C204 C 6813-7 27pF, 200V
C105 C205 C 6813-7 27pF, 200V
C106 C206 C 6813-7 27pF, 200V
C107 C207 C 6806-1 .01µF, 100V
C108 C208 C 9447-1 120pF, 200V
C109 C209 C 9447-1 120pF, 200V
C110 C210 C 6811-1 100pF, 200V
C111 C211 C 9240-0 5pF, 200V
C112 C212 C 6806-1 .01µF, 100V
C113 C213 C 9447-1 120pF, 200V
C114 C214 C 6806-1 .01µF, 100V
C115 C215 C 6806-1 .01µF, 100V
C116 C216 C 6806-1 .01µF, 100V
C117 C217 C 6806-1 .01µF, 100V
C118 C218 C 6806-1 .01µF, 100V
C120 C220 C 6804-6 .1µF, 50V
C121 C221 C 9465-3 10µF, 50V
C122 C222 C 6804-6 .1µF, 50V
C123 C223 C 6804-6 .1µF, 50V
C124 C224 C 6950-7 82pF, 100V
C125 C225 C 6950-7 82pF, 100V
C126 C226 C 6804-6 .1µF, 50V
C127 C227 C 6804-6 .1µF, 50V
C130 C230 C 6806-1 .01µF, 100V

Diodes

D1 C 9011-5 1N4740A, 10V
D2 C 9011-5 1N4740A, 10V
D102 D202 C 3181-2 1N4148
D103 D203 C 6212-1 1N270, SEL
D104 D204 C 3181-2 1N4148
D105 D205 C 2851-1 1N4004
D106 D206 C 2851-1 1N4004
D109 D209 C 3181-2 1N4148
D110 D210 C 3181-2 1N4148

Inductors

L101 L201 C 3510-2 470µH
L102 L202 C 3510-2 470µH

Transistors

Q100 Q200 C 3954-2 MPSA56
Q101 Q201 D 2961-7 2961
Q102 Q202 D 2961-7 2961
Q103 Q203 D 2961-7 2961
Q104 Q204 C 3625-8 2N4125
Q105 Q205 D 2961-7 2961
Q106 Q206 C 3625-8 2N4125
Q107 Q207 C 3528-4 MPSA06
Q110 Q210 C 3954-2 MPSA56
Q113 Q213 D 2961-7 2961
Q114 Q214 D 2961-7 2961

Resistors

R1 C 9952-0 560 2W
R2 C 9952-0 560 2W
R3 A10265-10022 10K .5W 1%
R6 A10266-2R72 2.7 .5W
R7 A10266-1R02 1 .5W
R100 R200 A10265-10021 10K 1%
R102 R202 A10266-1021 1K
R103 R203 A10265-51102 511 .5W 1%
R104 R204 A10265-10021 10K 1%
R105 R205 A10266-2R72 2.7 .5W
R106 R206 A10266-8221 8.2K
R108 R208 A10265-10022 10K .5W 1%
R109 R209 A10266-5631 56K
R110 R210 A10266-3921 3.9K
R111 R211 A10266-2221 2.2K
R112 R212 C 6048-0 500 Trim
R113 R213 A10266-7511 750
R114 R214 A10266-8211 820
R115 R215 A10266-5601 56
R116 R216 C 7778-1 5.6 .5W FP
R117 R217 A10266-1811 180
R118 R218 A10266-1011 100
R119 R219 A10265-10022 10K .5W 1%
R120 R220 A10266-1211 120
R121 R221 A10265-10022 10K .5W 1%
R122 R222 A10266-1212 120 .5W
R123 R223 C 7778-1 5.6 .5W FP
R124 R224 A10266-1811 180
R125 R225 A10266-2011 200
R126 R226 A10266-4722 4.7K .5W
R127 R227 A10266-4722 4.7K .5W
R138 R238 A10266-3331 33K
R139 R239 A10266-1541 150K
R140 R240 A10266-3331 33K
R141 R241 A10266-1541 150K
R142 R242 A10266-1531 15K
R143 R243 A10266-4721 4.7K
R145 R245 A10266-1522 1.5K .5W

19

D-45 / D-75A Amplifier Service Manual

Q43308-8 Main Module Parts List

Resistors (Cont.)

R146 R246 A10266-1021 1K
R147 R247 A10266-4711 470
R149 R249 A10266-1331 13K
R150 R250 A10266-1331 13K
R151 R251 A10265-95311 9.53K 1%
R152 R252 OPEN
R153 R253 A10265-10021 10K 1%
R154 R254 A10265-10021 10K 1%
R155 R255 A10265-10021 10K 1%
R156 R256 A10265-10021 10K 1%
R157 R257 C 9079-2 200 Trim

Integrated Circuits

U3 C 4345-2 LM339
U100 C 7558-7 MC33079

Miscellaneous

J1 C 9455-4 Socket, 10 Pin
J2 C 9455-4 Socket, 10 Pin
J3 C 7526-4 Header, 3 Pos.
J4 C 9454-7 XLR/Phone Jack
J5 C 7526-4 Header, 3 Pos.
J6 C 9454-7 XLR/Phone Jack
S1 C 9941-3 Header, 3 Pos. R/A
S1X C 6419-3 2 Pos Shunt (jmp)
U100X C 3450-1 14 Pin IC Socket
Z1 A10124-24 #24 Buss Wire
Z2 A10124-24 #24 Buss Wire
1 D 8268-1 Bd, D75 Main #3

20

D-45 / D-75A Amplifier Service Manual

Q43156-1 Output Module (P 9730A4 Board)

Figure 7: Output Module Component Layout (Q43156-1)

21

D-45 / D-75A Amplifier Service Manual

Q43156-1 Output Module and Q43309-6 Terminator Module

Q43156-1 Output Module
Capacitors

C131 C231 C 1751-4 .01µF 500V

Diodes

D107 D207 C 3181-2 1N4148

Headers

P1 C 4730-5 9 Pin
P2 C 4730-5 9 Pin

Transistors

Q115 Q215 D 2961-7 2961

Resistors

R128 R228 C 3291-9 .1 5W
R129 R229 C 3291-9 .1 5W
R131 R231 A10266-3322 3.3K .5W
R132 R232 A10266-5614 560 2W

Board

1 P 9730A4 Bd, D75 Output

Q43309-6 Terminator Module
Capacitors

C119 C219 C 7706-2 .1µF 100V

Inductors

L103 L203 H43294-0 2.75µH

Resistors

R148 R248 A10266-2R73 2.7 2W

Board

1 P10422-7 Bd, D45/75A Term

Note: Driver Transistors, Output Transistors, and LED's
are not included with the Output Module. See Ex­ploded View for part numbers. Also not included with
the module parts list, but soldered to output module
are:

C1 C 5050-7 4.7µF, 100V

Soldered between -VCC & Ground

C5 C 5050-7 4.7µF, 100V

Soldered between +VCC & Ground

1 D 7168-4 Ground Buss Bar

22