Crown Audio DC-300A User Manual

DC-300A

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crolun

INSTRUCTION MANUAL

IM-9

S3P2-15-6

SERIAL NO

ISSUED

DC-300A

DUAL CHANNEL

LABORATORY AMPLIFIER

CROWN INTERNATIONAL, INC., BOX 1000, ELKHART, INDIANA 46514

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crown

0

In-runaTlonac

BATCH ID

DCA-11

Proof of Performance Report

DC-300A laboratory power amplifier

Serial Number

1. Quies. offset of less than

2.

1 KHz 180 watts
8 ohms, per channel, both channels
operating, 0.1% total harmonic
distortion

RMS

minimuminto

1OmV

Line Voltage

Amcron Label

CH.l

Requirement\ao,VAC

J

SERIAL NO

020163

CH.2

J

3.

4 ohm test

4. Protection tests

5.

Reliability test

6. 20KHz 155 watts per channel
minimum RMS (both channels

operating) into 8 ohm. 0.05% total
harmonic distortion

7.

10 KHz. sq. wave

8. Mono operation

9.

IM Dist. into 8 ohms (%)
(60-7KHz

10.

Hum and noise-db below

8 ohm (20Hz

4:1)

S.M.P.T.E.

-

20KHz)

155W

into

-002

-002
*

c?oJ.

_ cl03

_ @O’j

.00cc

..

c

ci/ Y’

‘2 1

z

49mW

db

155W

49.0W

15.5w

4.9w

1.55w

490mW

155mW

15.5mW

‘TOTAL

PERFORMANCE

IS WHAT COUNTS"

CROWN test and check-out procedures reflect our basic design
philosophy; we believe that reliability can be engineered into a
product. As such, our check-out is designed to expose and
correct a problem, before it happens. This testing begins when
the unit is still a pile of parts; grading and selection of
components is standard. The final test-inspection is the culmina­tion of this vigorous program, but our concern doesn’t stop here.
Our products are backed by an extensive field service program,
and protected by a comprehensive warranty.

A word about our testing procedure is in order. All
cations are referenced to an AC input of 120 VAC. The high
current demand with high power tends to cause the line voltage
to sag, or the sinusoidal waveform to distort. With a distorted
waveform (or lower line voltage) the peak voltage is lowered.
Since it is the peaks that charge the filter capacitors in the
amplifier power supply, and thus determine the maximum power
output, a line voltage problem reduces the maximum power
output. CROWN uses a peak equivalent AC voltmeter which
measures the peaks of any waveform and converts this to an
equivalent rms reading for a sinusoidal waveform. This way we
can vary or regulate the line voltage, no matter how distorted
the waveform, to an equivalent of a 120 VAC sinewave. We are
then measuring a true maximum output power.

With regard to the precision load which we use for our testing,
we realize that a resistive load is quite different than a reactive
speaker. However, using readily available parts, a precision

resistive load is the easiest to duplicate, with respect to

obtaining consistent results. We specify that the load must be

resistive, having less than 10% reactive component at any

frequency up to five times the highest test frequency. The

resistance value should be maintained within
levels.

The following discussion examines each of the test procedures
listed on the facing page. This is an attempt to help you under­stand, in layman’s terms, what the tests mean.

Quiescent Offset
amplifier’s output is balanced with reference to its input.
Thus the amplifier will not “bias” the program with a
dc component. To meet specifications, offset must be less
than 10 mv.

1KHz -

This test measures the power across an 8 ohm

load at

a frequency of 1 KHz with both channels operating.

This is a determination of how much power an amplifier
can produce before a specified total harmonic distortion
is reached. For the
at less than

4 Ohm Test
performance at impedances below that for which it is
rated. We check the wave form for level (it must reach a
specified voltage before clipping) purity, and stability.

-

This simply

DC-300A,

.1%

THD.

-

This is a critical examination of the DC-300’s

assures

the power is 180 watts

our specifi-

1%,

at all power

that your

Protection Test

4.
determines the threshold at which the protection circuitry
will be activated. Sharp clipping should occur with no
evidence of instability. The positive and negative limiters
operated independently and therefore may not be activated
simultaneously.

5.

Reliability Test
an extremely vigorous
low frequency input signal driving the output to full
power across a short circuit for a predetermined period of
time.

6.

20KHz

-

We specify that at any frequency between 1Hz and
2OKHz the DC-300A will produce 155 watts minimum
rms (both channels operating) into an 8 ohm load, at a
sum total harmonic distortion of .05% or less. We choose
20KHz

as the test frequency because high frequencies
produce more heat than lower frequencies. Thus, if the
amplifier can safely pass the
safely at lower frequencies.

10 KHz Square Wave

7.
amplifier’s frequency response and rise time. (How fast
the amplifier can follow rapid signal changes.) The output
square wave (with an 8 ohm load) should be clean and

sharp, with no ringing or overshoot.
Mono Operation

8.

the stereo mono switch. A signal is applied to channel 1
input only and the mono output is observed between the
two red output terminals of the amplifier.

IM

Distortion Test - At CROWN we feel that IM

9.
distortion testing yields a truer picture of amplifier

performance than harmonic distortion testing. While a
large amount of documentation supports this opinion,

some of the reasons are apparent, even in layman’s terms.

For example, a sinusoidal waveform (used in HD testing)
bears little resemblance to the complex waveforms

associated with actual program materials. IMD testing

uses such a complex waveform. Also, harmonic distortion
is not always aurally offensive. The human ear may

interpret such distortion as pleasing, but usually finds IM
distortion rather obnoxious. In order to support this
design philosophy, we designed and built our own IM
analyzer with residual noise and distortion low enough to
test our amplifiers.

Hum and Noise

10.
small a signal can be amplified without it becoming “lost
in the mud”. The test is limited to the audio band width
of

20Hz-20KHz,

for the DC-300A is: hum and noise from
will be at least
watts. This means that with a 155 watt output the noise
will be only
of a watt

11.

Quiescent AC power Input at 120 VAC - This test

confirms that your amplifier is not drawing excessive

power while “idling”. If an amplifier exhibits a tendency
toward instability, or oscillation, it may draw power with
no signal input. The DC-300A will draw 40 watts or less
at idle.

-

This is a test with a 2 ohm load which

-

This test puts the output stages through

thermal

cycling. The test is a very

This tests the amplifier at its rated power level.

20KHz

test, it will operate

-

This test critically examines the

-

This is a check for proper operation of

-

This test, in plain English, tells you how

with a bandpass filter. Our specification

110db

below the full power output of 155

.00155

micro watts. (That’s 1.55 billionths

)

20Hz

-

20KHz

Section 1 DESCRIPTION

1

.1

General
Specifications

1.2
Warranty

1

.3

Section 2 INSTALLATION

Unpacking

2.1

2.2 Mounting
Normal

2.3

2.4 Connecting Output Lines ................................................................................................,

2.4.1

Section 3 OPERATING INSTRUCTIONS

MonoOperation
Connecting

2.5

Connecting

2.6

Controls

3.1

The

3.2
OperatingPrecautions

3.3

Load

3.4
Cleaning

3.5

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Installation

Hi-Fi

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Lines

Input
Power

and Adjustments

Protection

Protection

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Mechanisms

Methods

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TABLE OF

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CONTENTS

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2,

PAGE

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3, 4, 5

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1

Section 4 CIRCUITRY

Principles

4.1
Test

4.2

Service. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ......

4.3

Section 5 APPLICATION NOTES

Application
Application
Application Note No. 3

TITLE

DC-300A

l-l
l-2 DC-300A Performance Graphs

I.M. Distortion

Harmonic
Frequency
Power
Phase
Noise
Crossta Ik

Nominal

Damping
Power
Input

of Operation

Procedures

Pictorial

Distortion

Response

Response

Spectrum

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .._..............

Limits

Factor

Efficiency

Impedance

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Note No.

Note

Response

1 - V-l

No.2 -

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of V-lOutput

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vs.

Gain

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Limits of a

VFX-2

-

Speaker Protection . . . . . . . . ....................................................... 29

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Load

23
24
24

25

27

LIST OF ILLUSTRATIONS

PAGE

1

5
5
6
6
7
8
8

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9
10
10
11

2-l
2-2
2-3
2-4
2-5
2-6
2-7
2-8
2-9

2-10

3-l
3-2
3-3
3-4
3-5

Maximum Output vs. Load Impedance
output
output IL I..
Mounting Dimensions
Normal Hi-Fi Hook-up
Rear View of Chassis

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(Z)

.

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......

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Source Resistance and Damping Factor vs. Length and Size of Output Leads
Schematic For Full Range Electrostatic Speaker Connections
Schematic of Earphone Pad
DC-3ODA Mono Hook-up

..............................................................................................

...................................................................................................

Table For Selection of Input DC Blocking Capacitor
Low-Pass

Filter

For

Severe

RFAtInputs

Table of Line Voltage Connections

.....................................................................................................

Operating

Controls

........

Graph of VI Operating Range of DC-300A Output

For

Fuse

Selector

RelayControlled

Nomograph

Protector with

Turn-On-Transient

Muter

Loudspeaker

Overload

ForLoad

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Protection

Indicator

Protection

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11
1 2
12
13
14
14

15
15
16
16
17

17
18

19
20
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22

1 .1 GENERAL

Section 1

DESCRIPTION

DC-300A PICTORIAL

The DC-300A is a dual-channel high-power amplifier for
precision amplification of frequencies from DC to
The unit features extremely low harmonic and

ulation distortion, very low noise, highest “damping
factor,”
the large output power, It is possible to obtain a monaural

70-volt balanced line without using an output transformer.
The DC-300A contains a new CROWN developed Signal

Programmed Automatic Current Executor (SPACE

control) electronic amplifier protection circuit which

manifests no

audio frequencies any impedance load including totally

reactive loads may be driven with no adverse effects.
Only maximum output power will be affected by varia­tions in load impedance. At sub-sonic to DC frequencies
the limiter acts as a VI limiter to provide optimum pro­tection for the extremely rugged silicon hometaxial
output devices (total of 16 for a total of 2400W dissipation).

A pair of thermal switches remove power from the unit

if overheating occurs due to insufficient ventilation, The
AC line is fused to protect the power supply.

See Section 3.2 for a description of the protective systems.

and quality parts and workmanship. Because of

flyback

pulses, thumps, or shut-down. At

20KHz.

intermod-

26 diodes, 1 bridge rectifier, and 3 zener diodes are used in
the

DC-3OOA
effective number of semiconductors is 60 transistors, 30
diodes, and 3 zener diodes.

The output devices, 8/channel, are conservatively em­ployed, having a total peak current rating/channel of 120
amps in a circuit that is limited to a maximum of 28
amps. Among its unique features, the circuitry includes
the CROWN-pioneered and patented
figuration.

The input operational amplifiers are powered by two
voltage-regulated supplies. This results in complete
channel-to-channel isolation and independence from line
voltage variations.

Total direct coupling results in perfect, instantaneous,

thump-free overload recovery even on non-symmetrical

waveforms. This cannot be said for any AC-coupled
amplifier presently in existence. Turn-on is instantaneous
with no program delays.

circuitry. With the integrated circuit, the

AB+B

output con-

The power supply features a 1 KW transformer and large

computer-grade filter capacitors giving over 48 joules

of energy storage.
A total of 44 discrete transistors, 1 linear IC (dual op amp),

Front-panel controls include two independent heavy-duty

level controls and a power switch with an associated pilot
light. DC balance controls, which never need adjustment
in normal operation, are located behind the front-panel.

1.2 SPECIFICATIONS

1.2.1 STEREO SPECIFICATIONS

Output Power

Frequency Response
1 KHz Power
Harmonic Distortion

I.M. Distortion

(60Hz-7KHz 4:1)

Slewing Rate

Damping Factor
Output Impedance
Load Impedance

Voltage Gain

Input Sensitivity

Output Signal

155 watts per channel minimum RMS (both channels oper­ating) into an 8 ohm load over a bandwidth of 1

Hz-20KHz

at
a rated RMS sum total harmonic distortion of 0.05% of the
fundamental output voltage.

±0.1dB DC-20KHz
180 watts RMS into 8 ohms, per channel, both channels operating, 0.1% total harmonic distortion.
Less than 0.001% from

per channel into 8 ohms.
Less than 0.05% from 0.01 watts to 0.25 watts and less than 0.01% from 0.25 watts to

into 8 ohms, per channel.
8 volts per microsecond (slewing rate is the maximum value of the first derivative of the output

signal, or the maximum slope of the output
Greater than 750,
Less than 7 milliohms in series with less than 3 microhenries.
Rated for 8 ohm usage; safely drives any load Including completely reactive loads.

20.6±2%

1.75
Unbalanced, dual channel.

or

volts±2%

at 1 watt into 8 ohms;

20Hz-400Hz.

DC-400Hz

26.3±0.2dB
for 155 watts into 8 ohms.

into 8 ohms.

at maximum

±ldB DC-100KHz.

and increasing linearly to 0.05% at 20KHzat 155watts RMS

155watts

signal).

gain.

1

.2.2

MONAURAL SPECIFICATIONS

Output Power

Frequency Response
1 KHz Power

Harmonic Distortion

I.M. Distortion

Slewing Rate
Damping Factor
Output impedance
Load Impedance

Voltage Gain

Input Sensitivity

Output Signal

310 watts minimum RMS into a 16 ohm load over a

bandwidth of 1

Hz-20KHz

at a rated RMS sum total har­monic distortion of 0.05% of the fundamental output
voltage.

±0.15dB,

360 watts RMS into 16 ohms.
Less than 0.001% from

16 ohms.
Less than 0.05% from 0.01 watts

into 16 ohms.
16 volts per microsecond.
Greater than 700, DC-400Hz into 16 ohms.
Less than 15 milliohms in series with less than 6 microhenries.
Rated for 16 ohm usage; safely, drives any load including completely reactive loads.

41.2±2% or 32.3±0.2dB at maximum gain.

1.75 volts for 310 watts into 16 ohms.
Balanced, single channel.

DC-20KHz

at 1 watt into 16 ohms; ±1

20Hz-400Hz

and increasing linearly to 0.05% at 20KHz at 310 watts into

to 0.25

watts and less than 0.01% from 0.25 watts to

dB, DC-6OKHz

at 1 watt into 16 ohms.

310 watts

4

1.2.3 GENERAL SPECIFICATIONS

below rated output

Hum and Noise

(20Hz-20KHz)
Phase Response
Input Impedance

110dB

-15°

+0,

100K

Zero to

ohms at minimum gain,

20KHz

at 1 watt

10K

ohms at maximum gain.

Amplifier Output

Protection
Overall Protection

Turn-on
Circuit

Power Supply

Power Requirements

Heat Sinking

Chassis

Controls

Connectors

Short, mismatch, and open circuit proof. Limiting is instantaneouswith noflyback pulses, thumps,
cutout, etc. No premature limiting on transients.

AC line fused. Thermal switch in AC line protects against overheating caused by insufficient
ventilation. Controlled slewing rate voltage amplifiers protect overall amplifier against RF burn­outs. Input overload protection is furnished by internal resistance at inputs of amp.

instantaneous, with minimum thumps and no program delay.
Wideband

60 transistors, 30 signal diodes, 3 zeners and 6 rectifier diodes.

1 kilowatt transformer with massive computer-grade filter capacitors storing over 48 joules of

energy. Two regulated supplies for complete isolation and stability.
Requires

Draws 40 watts or less on idle, 500 watts at 300 watts total output.

Massive black-anodized heat sinks are thermally joined with the chassis, thereby utilizing the en-

tire amplifier as a heat sink.
All aluminum construction for maximum heat conduction and minimum weight.

front panel is a single extrusion.

Independent input level controls are on front panel. Power switch, with integral pilot light is on
front panel. Non-interacting DC balance controls are mounted behind front panel. A mono-stereo
switch is located above the input jacks on the rear panel.

Input - ¼ inch phone jack
Output - Color coded binding posts
AC Line

multiple feedback loop design utilizing one linear IC (dual op-amp). Total equivalent of

50-4OOHz

-

Three-wire (grounded) male connector on 5 ft. min. cable

AC with selectable taps for 100, 120, 200, 220 and 240V

±10%

Heavy

operation.

aluminum

Dimensions

Weight

Finish

19 inch standard rack mount (W.E. hole spacing), 7 inches high,
surface).

45 pounds
Satinized aluminum front panel, with gray suede Lexan insert.

9¾

inches deep (from mounting

10

TO DC

60

10

100

FREQUENCY (Hz)

1K

10K

1OOK

10

100

1KHz 1OKHz

FREQUENCY (Hz)

1OOKHz

2.1 UNPACKING

Section 2

INSTALLATION

As soon as the amplifier shipment is received, please
inspect for any damage incurred in transit. Since the unit
was carefully inspected and tested at the factory, it left
the factory unmarred. If damage is found, notify the
transportation company immediately. Only the consignee
may institute a claim with the carrier for damage during
shipment. However, CROWN will cooperate fully in such
an event. Se sure to save the carton as evidence of dam­age for the shipper’s inspection.

Even if the unit arrived in perfect condition -as most do
it is advantageous to save the packing materials. They
will prove valuable in preventing damage should there
ever be occasion to transport or ship the unit. Note
the carton and internal pack - each is designed for pro­tection during transit, particularly of the power trans­former weighing over 25 Ibs. Do

this factory pack!

nof

ship the unit without

-

2.2 MOUNTING

The DC-3DDA is designed on a standard 19 inch rack

mounting format. However, it may be custom mounted
if sufficient support is provided. For dimensions see
Fig.

2-1.

In any circumstance, sufficient ventilation must
be provided for the unit. Good ventilation practice allows
air to flow completely under, around, and through the
amplifier. If the unit is placed above a horizontal surface,

7

-I-

r

an air space should be allowed above and below the unit.
If sufficient ventilation is not provided, the unit will
intermittently turn off due to the built-in thermal pro-

tection. Such a condition (if observed) will also be ac-

companied by a warm front-panel due to the integral
heat-sinking employed in the amplifier.

Applications requiring long sustained signals at high

power levels may require the use of a cooling fan.

2.3 NORMAL HI-FI INSTALLATION

1. Remove output covers, exposing dual binding-posts.

Two-conductor speaker cables must connect to the OUT-

PUTS using terminal lugs, tinned ends, or the special
“banana” plugs supplied with the
in-line fuses as recommended in the Accessory Bag and
Fig. 2-2. (Not needed with CROWN speakers.)

2. Since the DC-300A is a “basic amplifier,” the main
outputs of the control-center or “preamplifier” must be
connected via shielded audio-cables to the two jacks
marked INPUT. Use RCA-pin at preamp and standard
¼

inch phone-plug at the

The two cables should be tied parallel along their entire
length, using the accessory cable ties.

DC-300A.

DC-300A.

Connect the

FIG. 2

- 1

MOUNTING DIMENSIONS

3. U/L requirements specify a 3-wire AC power con­nector; however, proper connections to a switched outlet
on the control center require the use of a 3-to-2 wire
adapter. NOW, plug the AC into a switched outlet on the
control center.

4, Your Control Center may now be turned on. Then

advance the

(1

50°

clockwise).

When using the CROWN IC-150A Control-Center, the
VOLUME should attain almost full rotation (2 to 4 o’clock)
for loudest “concert-hall”volume. If at 3 o’clockthevolume
is low, increase the DC-300A input gain controls; if too
high, decrease the

To assure maximum enjoyment and full speaker protec­tion, read the following detailed sections on OUTPUTS,

INPUTS and Chapter 3-OPERATION.

13

DC-300A

DC-300A

Input-Gain Controls about %-open

gains.

CONTROL

CENTER

RIGHT

SPEAKER

3 to 2 WIRE ADAPTER

SWITCHED OUTLET

POWER CABLE _

/

/

lb---

JJ

MDP PLUGS

DUAL BANANA

IN-LINE FUSES

FIG. 2-2

NORMAL HI-N HOOK-UP

CABLE TIE(S)

NOTE! /

SHIELDED AUDIO CABLES MONO-STEREO SWITCH

Or A o’hl

TO ¼" PHONE

7)

LEFT

SPEAKER

2.4 CONNECTING OUTPUT LINES

Input and output connectors are located on the back of
the chassis as shown in Fig. 2-3.

It is always wise to remove power from the unit and turn

the input level controls off while making connections,

REAR OF CHASSIS

WITH OUTPUT COVERS REMOVED

especially
eliminate
liable for
its being overpowered! (CROWN speakers excepted.)

Before making connections, it is recommended that the
operator familiarize himself with the amplifier’s
tective system. See Section 3.2. Section 3.3 entitled
“Operating Precautions” should also be read.

Because of the location of the output connectors
coded binding posts), it will be easiest to make these
connections first. High-quality, dual “banana” plugs are
the preferred connections for permanent installations,
critical applications, and when testing the amplifier.

Because the output wire gauge and length raises the
resultant source impedance or lowers the Damping Factor
by adding its series resistance, the nomograph (Fig. 2-4)

if the load is a loudspeaker system. This will

any chance of loud blasts. CROWN is not

damage incurred to any transducer due to

pro-

(color-

15

40

RL

LOAD

30

RESISTANCE

(ohms)

20

15

10

9

8

7

6

Rl

R,

DAMPING

7.

.04

s-.06

R,

-

--

SOURCE

.l

~MOOO ft.1

RESISTANCE

2-COND.

CABLE --

8000
5000

--ANNEALED

1000

T

COPPER

500.-

WIRE

IAWGI

50.---t24

5

4

FIG. 2-4

SOURCE RESISTANCE AND DAMPING FACTOR VS. LENGTH AND SIZE OF OUTPUT LEADS

is provided for wire selection. For dynamic moving-coil
loudspeakers the value of

RL

should preferably be that
measured by an ohmmeter across the voice coil, rather
than the manufacturer’s rating. For electrostatic speak­ers and such, the manufacturer’s rated impedance should
be used for R.

If the load (matching transformer, inductance, or
range electrostatic speaker system) appears as a

full-

short-

circuit at low frequencies, a large non-polarized
capacitor (paralleled with a resistor) should be placed

in series with the load.

For electrostatic speakers (if the manufacturer has not
provided a capacitor) an external non-polar capacitor of
590-708 mfd and 4 ohm power resistor should be placed

in series with the plus (+) speaker lead. This will pre­vent large low-frequency currents from damaging the
electrostatic transformer
activating the

DC-3OOA’s

or from

unnecessarily

protective systems. An ef-

fective test to determine if such parts are needed is to

F/G. 2-5

-

SCHEMA TIC FOR FULL RANGE

ELECTROSTATIC SPEAKER CONNECTIONS

measure the DC resistance between the output terminals
with an ohmmeter. If the resistance is less than 3 ohms,
the parts should be added as shown schematically

in Fig. 2-5.
When selecting connectors for the output lines, the follow-

ing general precautions apply (with all power connectors):

1. A male plug, carrying signal, must not be on the
far end of the line where it can be exposed, giving
rise to both shock and short-circuit hazards.

16

Connectors which might accidentally cause the two

2.

channels to be tied together during making and
breaking of connection should not be used. A common
example is the standard 3-circuit

l/4

inch phone jack

and plug when wired for stereo sound.
Connectors which can be plugged into AC power

3.

receptacles should
Connectors having low-current-carrying capacity

4.

never

be used.

are “verboten.”
Connectors having any tendency to short, or having

5.

shorted leads, are unadvisable.

Most commercially-available headphones employ a 3-
circuit

l/4

inch phone plug which violates condition number

2. This is no handicap if a pad is inserted between the

amp and jack, which is the only sensible thing to do,
when such a large amplifier is coupled to such a small
transducer. If this precaution is ignored, not only may
the transducer be burned out but permanent hearing loss

could result. The recommended pad is shown in Fig. 2-6.

2.

Connect output lines as per the following drawing, Fig­ure 2-7. The output from the

DC-3OOA

in Mono is BAL-

ANCED and is isolated from the chassis, and from the

input grounds to the DC-300A.

CAUTION: Be certain that all equipment (meters,
switches, etc.) connected to the Mono output lines is
balanced. Both sides of the line must be totally isolated

from the input grounds, to the DC-300A. If this is not ob-

served, severe oscillation may result.

lo

st.r.0

Earphenor

FIG. 2 - 6

SCHEMATIC OF EARPHONE PAD

2.4.1 MONO OPERATION

A mono-stereo switch on the rear panel adjacent to the in-

put jacks, allows the DC-300A to be operated normally
(stereo) or in mono, with no internal modification. (See
figure 2-2.) When in the mono position, the input circuitry of
the

DC-3OOA

is changed so that the two amplifiers are

“added” for mono output. (See mono specifications, page

3).
Care must be taken in the external hook-up to assure proper

operation. Proceed as follows:

The input line should be plugged into

1

the

channel 1 input
jack. The level is adjusted with the channel 1 input level
control.

NOTE: The Channel 2 input jack and level control are
not defeated in the Mono mode. However, the Channel 2
input should not be used in this mode. If a Channel 2
input is added to the Channel 1 input, distortion may
result. If Channel 2 input is used alone, very low power
output will result. For best results unplug the input to
Channel 2 when operating Mono.

FIG. 2-7

DC-300A MONO HOOK-UP

2.5 CONNECTING INPUT LINES

Connecting the inputs will require avoiding three basic
dangers: Undesirable signals to the inputs, “ground loops,”
and feedback from output(s) to input(s).

For loudspeaker-driving applications, the input should be
free of any DC, as this could cause overheating of the
loudspeaker voice coil. A simple visual test for DC on the
inputs (providing the woofer is visible) is to slowly turn up
the input level control with the amp on and watch for any
displacement of the cone. If very much displacement is
observed, the DC content of the input may be excessive and
require a blocking capacitor. The graph of Fig. 2-8 indicates

the effect of the size of the blocking capacitor on the

frequency response. Only a low-leakage type paper, mylar,
or tantalum capacitor should be used for this purpose.

TABLE FOR SELECTION OF

INPUT DC BLOCKING CAPACITOR

If large amounts of ultrasonic or RF frequencies are found
on the input, such as bias from tape recorders, etc., a
pass filter should be placed on the input. While
obtainable RF input levels will not damage the amplifier,
they may cause burn-out of tweeters or other sensitive
loads, activate the amplifier’s protective systems, or cause
general overload in the controlled-slewing-rate stage of the
amp (which is employed to provide RF overload protection).
The following filters are recommended for such applica­tions.

low-

practically-

power line may provide this feedback path. Proper
grounding, and isolation of inputs of common AC line
devices is good practice. Refer to Section 4.2, par. 5 for

testing precautions.
An extremely common form of this problem is encountered

when using electrostatic loudspeakers or any other kind of
load that is joined to the AC power mains. Capacitive
coupling through the load’s supplies may allow the
amplifier’s output to be fed through the AC mains and into
the grounds of input equipment resulting in a system
oscillation.

To combat the problem, first try reversing the speaker leads
on all channels if possible. If this does not solve the
problem, try grounding the power amplifier to the AC
ground with its 3 wire plug. (A ground loop may result

through an FM tuner with an earth-grounded antenna

system when deploying the 3 wire plug. The use of ,005
disc capacitors in series with the FM antenna leads will
eliminate
should of course be as short as reasonably possible, and a

turntable baseplate ground should always be broughtto the

phono preamp with a separate ground wire, never via the
input cable ground. If the oscillation still persists, start

thisproblem.)All hookup(interconnecting)cables

UF

removing input devices, working towards the amplifier until
the oscillation disappears. This will identify the point of
feedback. If an offending piece of equipment is found it
should be inspected for unnecessary AC line-to-ground
capacitances such as

line

filters,

etc. If possible such should

be removed. Such devices should never be found in the

load, although it is true that some RF loudspeakers have

used such filters to reduce

RFI.

FIG. 2-9

LOW-PASS FILTER FOR SEVERE RF AT INPUTS

A second problem area is “ground loops”

jargon for undesirable circulating currents flowing in a
grounding system. A common form of loop (possibly result­ing in hum in theoutput)isapairof inputcableswhosearea

is subjected to a magnetic hum field. In practice, both
cables should lie
the power transformer. Tying the input and output grounds
together may also form a ground loop.

A third problem (with input and output grounds together, as

in testing or metering) is feedback oscillation, from load
current flowing in the loop. In industrial use, even the AC

together

along their length, and away from

-

electronic

2.6 CONNECTING POWER

The amplifier is furnished with a three-wire AC plug as
standard equipment. Adapters are readily available com-

mercially for adapting this to a two-wire system if neces­sary.

The amplifier offers five standard line-voltage connec­tions: 100, 120, 200, 220, and 240VAC. The tag attached to
the line cord indicates for which voltage the amplifier is
connected. Most units are connected for

12OVAC.

When

changing the voltage to 200V or above, the external fuse,

Fl,

should be changed from 1 OA to 5A. Relabel the line tag

to indicate the proper voltage.

When testing the amplifier, the line voltage must be the

peak equivalent to a sinusoid of the indicated line voltage
when at full load. Line regulation problems can introduce
serious errors in the measurements on an amplifier of this
size.

Only a competent technician should attempt alteration of
the line voltage connections.

In order to change the voltage, it is first necessary to
carefully detach the bottom cover from the unit. On the back
of the board-mount subchassis a terminal stripwith solder-

ALL VIEWS WITH BOTTOM PLATE REMOVED

on jumpers is used to make the line-to-transformer

primaries connections (see Fig. 2-10).

1oov

120v

See Note

2oov

220

v

I

I

I

I

L

I

240 V

See Note

NOTE: The 120V and 240V connections require the changeover of the RED

wire from TB-3 to TB-2. Therefore the front panel, control circuit-board and

shield must be carefully removed for access. When replacing shield, use
care so that on-off switch locates properly in front panel opening!

I

FIG.

2-10

TABLE OF LINE VOLTAGE CONNECTIONS

1

Section 3

3.1 CONTROLS AND ADJUSTMENTS

OPERA TING CONTROLS

OPERATING INSTRUCTIONS

The DC-300A contains all the facilities essential for a

high performance amplifier.

On the front panel are located independent level controls,

a power switch, and pilot light. There is an AC line fuse
on the rear of the unit.

The level control should be adjusted for the desired

amplifier gain or output level. When the control is fully
CW, the gain is 26db as determined by precision 1%
resistors in the

The DC balance controls located behind the front panel

seldom, if ever, need adjustment.
critical applications will they need adjustment (not

“hi_fi”

balance controls, use the following procedures (see
Circuit Board layout in Section 4):

1.

Make sure amp has been allowed at least 15 minutes
of warm-up.

Set corresponding level control fully CCW.

2.

3.

Remove input signal from corresponding input.

Place sensitive DC voltmeter across output.

4.

5.

Adjust output balance control using small

bladed screwdriver for zero reading on voltmeter.

6.

Turn level control CW to 12 o’clock.

7.

Adjust input balance control using small

bladed screwdriver for zero reading on voltmeter.

The DC balance controls are now adjusted.

DC-300A’s

or similar applications). To adjust the DC

feedback loop.

Only

in the most

flat-

flat-

3.2 THE PROTECTION MECHANISMS

The DC-300A is protected against all the common
hazards which plague highpower amplifiers, including
shorted, open, and mismatched loads; overloaded power
supplies; excessive temperature;
phenomena; input overload damage; and high frequency
overload blowups.

Protection against shorted and low impedance loads is

provided by the Signal Programmed Automatic Current

Executor (SPACE control). It functions as an automatic
current limiter at audio frequencies whose value of
current limiting threshold is dependent on the history
of the output signal. Output current causes the threshold
to decrease while output voltage causes the threshold to

increase. The no signal threshold is high enough to
allow tone bursting, (even into 4 ohms) without premature
limiting as is found in some recent products of other manu-

facturers

Since the limiter has no instantaneous response to output
voltage, flyback transients do not appear in the output
when limiting occurs on inductive loads. Flyback
transients are a necessary response of a VI limiter
(sometimes misnomered an “Energy Limiter”) when

limiting drive to an inductive load. The actual response

of the flyback pulse is that the amplifier yields to the

load resulting in a pulse emanating from the load which

returns the inductive energy of the load to the opposite

polarity power supply of the amplifier as that supply

that produeed the excessive output. The audible effect

of flyback pulses is to produce a rasping, popping sort

of sound which is not pleasing.

chain destruction

19

A current limiter will

not

yield to the load butwill sustain the

constant current demands of the inductive load without

flyback.

Early amplifier designs frequently employed fixed current
limiters but had serious difficulty with obtaining reliable
low frequency output while being capable of full-voltage 4
ohm output. Also, many earlier designs used fragile

epi-

base or triple diffused outputs, which for reliable per­formance are poor mates for a current limiter protection
scheme. The

DC-3OOA

uses eight 150W silicon power

transistors per channel, chosen for their combination of

current, voltage and response characteristics to allow wide
operating safety margins. The safe operating area of each
transistor is specified by the manufacturer and individually
tested by CROWN. Their toughness allows the reliable use
of a current limiter which when rendered signal variable
permits larger power outputs than would be safely allow­able with a current limiter of fixed type.

At subsonic frequencies, the SPACE control behaves as

a

VI

limiter and provides the increased protection needed at DC
to prevent destruction due to heat buildup in the half of the
output stage that is being driven.

The fuse inherently protects the power supplies against
overload. The AC line for 100,
250V type A6 fuse (on 200, 220,
250V).

The use of any other size fuse will invalidate the
warranty.

Never change fuses with power applied!
On each heat sink (see Fig. 2-2) is mounted a thermal

switch which protects the amplifier against insufficient
ventilation. If either heat sink becomes too hot, the AC

line power will be interrupted until the temperature falls

to a safe level, whereupon power will be automatically

restored. When such an event occurs, the external
symptoms are: no indication of AC power (by the pilot),
and a warm front panel.

All of the amplifier’s voltage-amplifier circuitry is de-

signed to be inherently current-limited. Thereby, if any
of the devices should fail, (which is extremely unlikely),
no damage will occur to the rest of the stages.

The input stage is protected against overdrive damage
by a series limiting resistor should the input signal level
ever become very excessive.

120VAC

240VAC,

is fused with a 1 OA

5A type MTH

The amplifier features a controlled slewing-rate which,
coupled with the SPACE controller, protects the ampli­fier from blowups when fed large RF input signals.

3.3 OPERATING PRECAUTIONS

The following are a number of operating precautions

given as an aid to understanding proper and improper
amplifier usage:

1. Use care in making connections, selecting signal

--7

Emmpl.: z:sn

a-9

--10

N

”

a

W;;

..14 y

E

43

..16 g
UJ

e-20

AllStir:

2 ; .;

IL-

l--

d--

.4--

.a-

t

400

300

200

A common problem which causes damage and irritation is
the turn-on thump problem typical to many signal sources.
Fig. 3-5 shows the schematic of a muter which, when

inserted in the input signal line, mutes for several seconds
before connecting the source to the amplifier, thereby
eliminating turn-on transients. It also removes turn-off
transients occurring after the relay drops open

(=O.l

sec.).

..25

--30

--At3

.2- -

.15..

.l--

.oa-

FIG. 3-3

FUSE SELECTOR NOMOGRAPH FOR

LOUDSPEAKER PROTECTION

Another form of load protector is shown schematically

in Fig. 3-4. Whenever the load is overdriven, a relay
switches a lamp in series with the load, smoothly
relieving the overload. The lamp then doubles as an
overdrive indicator as it glows. If overdrive is unreason­ably severe, the lamp will serve as a fuse. By adjusting
the relay tension adjustment and the protection level
control, this system is useful from 25 to 200 watts for
a typical 8 ohm load.

to

Load

FIG. 3-5

TURN-ON- TRANSIENT MUTER FOR

LOAD PROTECTION

3.5 CLEANING

The CROWN
for life-time service. The panel can be cleaned with a
moist cloth and mild detergent. Never use steel wool,

scouring powder, lye solution, or any strong abrasive

cleaner as these will damage the panel’s finish.
The back chassis should require no more cleaning than

periodic dusting with a clean dry cloth. The use of de­tergents, abrasives or other cleaners may remove the
fine film of oil from the black anodized chassis which

is used to increase its surface lustre.

DC-3DDA

has a rugged anodized front panel

FIG. 3-4

RELAY CONTROLLED PROTECTOR

WITH 0 VERLOAD INDICA TOR

Section 4

CIRCUITRY

4.1 PRINCIPLES OF OPERATION

The DC-300A has two totally direct-coupled amplifier
circuits which employ a dual IC op amp and silicon
transistors in all stages. The CROWN-designed and
developed circuit represents a level of quality and per-

formance presently unequaled in the field of audio am-

plifier design.

As is implicit in the term “totally direct-coupled,” the

300A has a perfectly flat frequency and phase response
extending to
only low frequency amplification with absolutely no phase-
distortion, but also in perfect overloadcharacteristics.
symmetrical waveforms (such as music) cause overload

thumping in all currently produced AC amplifiers. These

same amplifiers may, however, show no signs of thumping

when fed a symmetrical test waveform such as a sinusoid.

DC frequency response combined with ultra-low noise and
IM distortion results in the closest approach to a “straight
wire with gain.”

Another characteristic of a DC amplifier is the thump or pop

produced at turn-on and turn-off. For example, at turn-on

the input amplifier requires a finite period of time to reach

operating levels. During this time the output could be driven
to large DC offsets resulting in annoying thumps.

A supply voltage detector virtually eliminates this problem

in the
supply voltages to the output stages during these turn-on
and turn-off periods, thus not allowing the DC offsets at the
output to occur.

The dual IC op amp is of a low noise type having a large gain
bandwidth. The result of using it for the input voltage
amplifier is that a maximum amount of feedback is applied
reducing distortion to record low values. This has been
confirmed by measurement with an elaborate test setup
employing CROWN-developed solid-state variable filters
and wave analyzing equipment. No other presently avail­able harmonic distortion test apparatus is capable of
such low residuals. The 300A’s low distortion is achieved
by employing multiple feedback loops to allow a max-

imum of total feedback.

The lack of noise is evidenced by a typical 20Hz-20KHz ef­fective input noise of

effective 8 ohm output of 80 micro-micro (pica) watts.
The output stage is a quasi-complementary format em-

ploying the CROWN class

OHz

DC-BOOA.

or DC. Flat to DC response results in not

The detector disconnects the regulated

1.25~

volts which produces an

AB+8

technique which uses no

DC-

Non-

bias current in the output transistors. The result is
maximum efficiency with minimum crossover notch dis­tortion and amplifier idling-heat. Thus there is no bias
current adjustment,

temperature-tolerance critical. Temperature drifts of bias

are further controlled by bias servos which are mounted on
the heat sinks.

In the

AB+8

output circuit, the driver transistors carry the
bias current, while the output transistors serve only as
boosters. The output transistors
sensewhen the driver transistors are delivering significant
current to the load and take over and deliver the large load
currents.

Protection against shorted and low impedance loads is
provided by the CROWN-developed SPACE (Signal Pro­grammed Automatic Current Executor) control circuit. It

functions as an automatic current limiter at audio fre-

quencies and as a VI limiter at subaudio frequencies. The

threshold of current limiting is dependent on the history of

the signal, yet the no-signal threshold of current limiting is
high enough to allow full power tone bursting. The net
result is total protection with a maximum of headache-free
output power requiring neither an inventory of special fuses
or cumbersome load matching techniques.

The monolithic input amplifier stages result in extremely

low DC drift. The input terminal bias current is offset by a
unique temperature compensated source resulting in a
laboratory amplifier needing no user-accessible offset
controls.

The input amplifiers are powered by zener-regulated power

supplies. The bias regulators are also powered by zener-
regulated current sources with the result that line voltage

variations do not cause noise or distortion due to misbias-

ing.

The power supply is a continuous-duty type, capable of

1 KW loading. The power transformer, weighing 25 pounds,
is constructed of special grain-oriented steel. The main DC
supplies arefull-wavecapacitor inputtypewith heavy-duty,

chassis heat-sinked diodes. Computer grade
furnish over 48 joules of energy storage. A higher voltage at

low current is derived from a half-wave voltage-doubler cir-

cuit. This voltage is used in the amplifier’s driver circuit.
The DC-300A represents nothing short of the highest

quality in both circuitry and components. It should provide a

lifetime of trouble-free service for the most discriminating
users.

as the output circuit is not

(12OOW

dissipation/Ch)

electrolytics

23

24

4.2 TEST PROCEDURES

The sole function of this section is to list precautions
essential to obtaining accurate measurements when deal-

ing with high-power, high-purityamplifierssuch
300A.

Use the proper line voltage, which is the one for which

1.

the amplifier is connected. The voltage should be

measured throughout the testing with a peak reading

meter, and adjusted to the RMS equivalent voltage (to
compensate for line voltage regulation errors during
the course of the measurements). All measurements
should be taken at the power amplifier’s plug. When
testing for IHF music-power measurements, the line
voltage is to be set at 12OV when the amplifier is con-

nected to 12OV, (IHF standards). If the amp is con-

nected otherwise, the equivalent test may be given by
applying the appropriate voltage.

The load should be resistive, having less than 10% re-

2.
active component at any frequency up to five times the
highest test frequency. The resistor should be capable

of continuously dissipating the full output of the

amplifier while maintaining its resistance within 1% of
its rated value. The load should employ only

current connectors (if any), and be connected to the

binding-post output terminals. All output measure­ments should be taken at the amplifier output ter­minals, and not anywhere along the output cable

through which the load current is flowing.

The input level controls should be set to maximum for

3.
all distortion tests to assure repeatability of all meas­urements.

4.

When measuring hum and noise, all inputs should be
disconnected from the amplifier and the level controls
set to minimum or to maximum, preferably minimum.

5.

Whenever possible avoid ground loops in the test
equipment caused by connecting the output ground to
the input ground. Never connect the ground of the
cable going to the load back to the input ground.

Ground loops are especially obnoxious when measur-

ing distortion. An I-M distortion analyzer, for example,
has its input and output terminals tied to a common

ground. Such a test should use an ungrounded output

return, with the output lead(s) wrapped around the

well-shielded and grounded input cable.

Always monitor the test oscillator when measuring fre-

6.
quency response. Use a wide-band AC voltmeter; or

use the same meter for both input and output level
measurements, if the meter’s frequency response is
known not to be dependent on attenuator settings.

Accuracy in measuring voltages for computing wattage

7.

is critical. For example, a 2% voltage error together with
a 1% resistance error can result in an error of
power into 8 ohms.

astheDC-

high-

lOwatts

Residual distortion and noise levels should be fully

8.
known for all the test equipment in order to accurately
evaluate the amplifier.

9.

Never attempt to measure damping factor by placing

abnormal loads on the output. D-F measurements
taken during clipping, or any other form of overload, are

meaningless. The preferred method is to apply an

externally generated current to the output terminals
and measure the resultant voltage at the terminals. A
convenient current is one ampere - as the resultant
voltage will read

Factor is defined as
ohms. A convenient

amplifier channel not under test. A non-inductive

resistance of 8 ohms - coupled between both
channels’ output terminals -will provide 1A when 8
volts are impressed across the resistor (by that channel

not under test).

Never measure hum and noisewhen in the presence of

10.
strong magnetic fields. The amplifier should be at least

4 inches away from any large metallic objects or shield

plates for a reading to be meaningful.

11

Noise measurements should be taken with a bandpass

filter of

ment of noise above

20.20KHz.

direc;ly

For audio purposes the measure-

in ohms for

w

gengrator

20KHz

[Zd.

Damping

,

where

is meaningless.

IZLI

is typically 8

for the 1A current is that

4.3 SERVICE

Should service other than routine fuse replacementever be

required, it is recommended that the unit be returned to the

factory in the original packing (or replacement, if damaged).

For warranty service the machine must be returned to the
factory or warranty service station. The CROWN warranty is
detailed on page 12.

Because of the level of circuitry sophistication of the DC-

300A,

only the most competent technicians should be

allowed to service it.

Many of the parts are standard items stocked by most
supply houses. However, there are several which appearto

be standard parts but are actually different. Although
standard parts may be used in an emergency, best results
will be with factory parts. A number of the parts are
available only from CROWN.

When ordering parts, be sure to give the amplifier serial

number as well as the part number and description. Rated
firms will be billed, otherwise shipments will be C.O.D.

Before returning an amplifier to the factory for service,
authorization should first be obtained from the service

manager. Shipments may be sent UPS or truck freight,
prepaid and insured at total value. The factory will return
your serviced unit by UPS or truck freight, collect. and will
add C.O.D. charges in the event that the cost is not covered
by registered warranty.

Section 5

APPLICATION NOTE NO. 1

V-l LIMITS OF A LOAD

Evaluating the V-l (volt-ampere) needs of a load: Many
loads exhibit large

which limits a power amplifier’s ability to deliver a

maximum power. If a load stores energy, which in turn

flows back into the amplifier, it is clear that the max-

imum power efficiency of the system is not being

achieved. Power that flows back into a linear amplifier
must necessarily be dissipated in the form of heat. A
pure reactance is not capable of dissipating any power;
therefore to drive such a load would only cause power
amplifier heating.

In practice all loads exhibit some energy dissipation
however large their energy storage characteristics may
be. The ideal coupling to any load is one that optimizes

the desired dissipation component while minimizing the

reactive or stored-energy component that is seen by

the amplifier’s output terminals.

reactances

(or energy storage),

-

APPLICATION NOTES

In applications where the input is sinusoidal and of small
proportional frequency deviation, a relatively stable load
may be resonantly tuned to present a real value of im­pedance to the amplifier.

Any load, no matter how complex its behavior, has a
V-l operating range which may be mapped by the follow­ing test.

The maximum voltage and amperage excursions in all
directions about zero (center of scope screen) define
the volt-ampere operating range of the load. If a load is
known to be linear over its operating range it is not nec­essary to supply the maximum desired power to the load.
The test may be conducted at low signal levels and the

current-sensing resistor (indicated as 0.1 ohm) may be
enlarged to a convenient value for the oscilloscope’s de­flection sensitivity. The resulting plot may be then linearly
scaled to the desired operating level.

cl

scope

LOAD

under

ted

Note: Scope and amplifier grounds are not common.

Vertical input reads (-) amperes vertically. If scope
has an inverter, invert to read (+) A.

AMPLIFIER LIMITS OF VI OUTPUT

. . .

AC LINE

F”SE

[DC

SINGLE

AT

10A

DC IF BOTH AREA OVER
CHANNELS ARE DRIVEN

EDUALLY

BLOWS

CHAN.l

SLOWS

V

out

- - MID-FREDVENCY BURST

SHORT CIRCUIT CONTINUOUS LIMIT

X

“ARIES (SIGNAL DEPENDENT)

-MAX AC LIMIT
MAX.)

MAX. CONT. AC POWER

-

----

,ZA = 2.75*)

HlGH FREDVENCY LIMIT

WHICH

It‘,

V OUT

LIMIT

LIMITER (AC)

ISINEI

AT

25

APPLICATION NOTE NO. 2

VFX-2

The CROWN VFX-2 is a dual-channel variable electronic
filter-crossover. When used with a power amplifier it can
greatly add to the total system capability. In combination
with the

useful functions.

The connections are made with the VFX-2 quickly and
easily. If a balanced line is to be used with the unbalanced

input of the DC-300A. the VFX-2 can serve asthe interface.
While maintaining these functions the output can be
shaped by selecting variable high-pass, lo-pass, or
pass filters. As a filter, the VFX-2 can be used as a cross-

DC-300A,

the VFX-2 adds several convenient

band-

over or ahead of several amplifiers in a bi- or
system.

Overall noise and distortion are extremely low, with IM
distortion less than .Ol% at rated output (2.5V into 600
ohms), and noise more than 1

OdB

gain.

For further information please request the VFX-2 spe­cification sheet or for a nominal fee, purchase a VFX-2 in­struction manual.

OOdl3

below rated output with

tri-amped

29

APPLICATION NOTE NO. 3

WARNING

POWER AMPLIFIER PROTECTION SYSTEMS PRO-

TECTAMPLIFIERS BUT NOT SPEAKERS! YOU, AND/

OR YOUR SPEAKER MANUFACTURER ARE RESPON­SIBLE FOR SPEAKER PROTECTION!

Except in unusual sets of circumstances, the circuitry in­cluded in power amplifiers designated as “protection”,

whether made up of transistor limiters, circuit breakers,
fuses, SCR’s, or whatever, is designed primarily to pro-
tect the amplifier from damage and will only protect
speakers incidentally. There are some exceptions to this
rule, which allow the user to vary the output power limits
of his amplifier to match the power rating of his speak­ers Even this, however, is a far from perfect speaker

protection scheme. The reason why this holds true is

simple: each make or model speaker has its own unique
operating capabilities. As a rule, a speaker system (in­cluding all electronics parts such as crossover parts and
electrostatic element transformers, as well as voice
coils) will be able to
continuously without burning up. This depends on the size,
quality, configuration, etc., of those parts. The same
speaker will be able to handle a somewhat
level for a short period of time (in the millisecond range)

without being destroyed by heat, but may then be endan-

gered by such phenomena as extending moving elements
beyond their normal range of travel (bottoming, torn dia-

phragm, etc.), overvoltaging electrostatic panels (arcing),
or other such suddenly disabling events. Since the points
at which these disastrous happenings will occur, differ for
different speakers, a speaker protection system must be
completely adjustable if it is to be useful for more than a

narrow range of speakers. Furthermore, if the user is to

be able to do adequate adjustment on a protection system
external to his speakers, he must receive accurate in­formation about the speaker power handling capabilities
from the speaker manufacturer. Speaker protection sys­tems embodied in amplifiers are comparatively useless,
therefore, unless the following things are true:

(1) The protection system can be accurately adjusted

by the user.

(2) The power handling capabilities of the speakers

are clearly stated by the manufacturer.

(3) The information about the speaker protection and

speaker power handling are stated in common
terms so that the user can adjust the protection
properly for the speaker.

These three things are rarely true simultaneously. It is

for this reason that CROWN takes the approach that
speaker protection is the responsibility of the speaker

manufacturer. Amplifier manufacturers have long been

required to provide protection in their products for any
faults

occuring

as speaker short circuits, open circuits, etc. In order to

drssipate

externally to the amplifier outputs, such

a certain amount of power

hrgher

power

fairly share the responsibility, and since the protection
cannot be exhaustively provided any other way, we feel
that speaker manufacturers should provide protection
tailored to their individual products. At CROWN we have
done this with our own speakers, simply because it is the
only comprehensive means of providing worthwhile pro­tection for all of our speakers.

Increasing power available from modern amplifiers in­creases the danger of speaker damage. Although occa­sionally an internal amplifier malfunction can contribute
to speaker failure, it is much more likely that speakers
will be overpowered by inadvertant use of too much
power. In the absence of internal protection in most
speaker systems, CROWN recommends very strongly
that in-line speaker fuses be employed in all systems.
The fuse selection nomograph reprinted in each CROWN
amplifier manual can be an invaluable help in choosing
fuses of the proper size. However, the effectiveness of
fuses in protecting speakers is limited in two important
ways

(1) Fuses as a rule protect only against prolonged

overpowering, and can only prevent speakers from
being driven with more than their RMS or average
power rating. Fuses cannot protect against sudden
high level transients of short duration. The use of
high-speed instrument fuses will give the best pro­tection available from fuses, but musical tran­sients can have an effect before the fastest fuses
blow.

(2) An appropriate fuse can only be selected if the

manufacturer’s specifications for hrs speaker are
accurately and clearly stated. If a speaker can
handle 100 watt peaks and 30 watts continuously,
but is advertised, and therefore fused, as a 100

watt speaker, then the speaker will destroy itself

before the fuse can protect it under a continuous
power level above 30 watts.

There are more effective (also more complicated and ex-

pensive) methods of protecting speakers than fuses. Some
of these, including methods similar to those employed in
CROWN speakers, are illustrated in the load protection
section of CROWN amplifier manuals. But these systems,

as all others, must still be adjusted in accordance with
the power-handling capability of the speakers In use, and
this can still be most readily done by speaker manu­facturers.

Your speakers have probably cost you at least as much

as any other part of your audio system. And since speak­er sound continues to be the most subjective area of com-

ponent selection, you may also have devoted more time

and effort to selecting your speakers than you have de­voted to any other part of your system. With these facts

in mind, be extremely careful in providing for adequate

protection of these often fragile, but most important, ex-

pressions of your audio taste.

Schematic
Designation

ClOO,

PARTS LIST, DC-300A Page 1

PARTS LIST, DC-300A Page 2

Schematic
Designation

RllO,

R210

RlO
R112,

R212

R5

R113,

R213

R114,

R214

R115, R215

R121, R221

R116,

R216

R117,

R217

R118,

R218

R119,

R219
R124, R224
R125, R225

R120,

R220
R123, R223

R122, R222
R3

R126, R226
R127, R227
R128, R228
R129, R229
R130, R230
R146, R246
R147, R247
R148, R248

Description

10K

ohm

V’Z

8.2K

ohm

5.6K

ohm
68K ohm
820 ohm

82 ohm

l/4

l/4

l/s

watt 1% Film

l/4

watt 10% 2877

l/4

watt 10% 3220

watt 10%

watt 10%

watt 10%

Part #

2343

3620
3301

3300

470 ohm VI watt 10% 2626

Crown

120 ohm

15K

3.3K

15 ohm

2.2K

750 ohm ‘A watt 5%

V’Z

watt 5% Film

ohm

Y’z

watt 10% 1064

ohm 1 watt 5%

l/4

watt 10%

ohm X watt 5% Film

3837

3617

3614
3145
3509

Sel

47 ohm

2.4K

ohm
100 ohm
56 ohm

l/4

watt 5%

j/4

watt 5%

l/4

watt 10%

l/4

watt 10%

1011
3616
2872
3511

Other Information

R149, R249

Rl

R2
R4
R6
R7
R8

R9

Rll

0103,0203
Q119, cl219
Q12O.Q220

180K

ohm VI watt 10%

1K

ohm 1 watt 10%

2.2K

ohm % watt 10%
200K ohm

91K

ohm VI watt 5%

6.2K

3.9K

l/4

watt 5%

ohm

l/4

watt 5%

ohm 1 watt 10%

2.7 ohm % watt 10%

75 ohm ‘A watt 5%
Semiconductors

2N4125

2884
3615

1036
3622
3621
3619

3618
2857

3798

3625

Wired between main board and
terminal strip on main shield

PARTS LIST, DC-3OOA Page 3

Schematic
Designation

QlOO,

Q200

0101,

Q201

Q102,0202
Q105,0205
01

Q104,0204
Q106.0206
0107,0207
02
DlOO,

D200

DlOl,

0201

D102,

0202
D103, D203
D104, D204
D105, D205
D106, D206
D107, 0207

Dill,

0211

Description

MPSA93

2N3859A

(selected)

NSDI 28

RCA 61061 (selected)

2N4929 SS7304
PN4250A
lN4148

Crown
Part #

3578

2961

4061
3348

2923
3786
3181

Other Information

Positive pre-driver
Negative pre-driver

D108, D208

Dl,

D2

D3, D4, 05

IC-lA,8

LlOO,

200

L102,

202

lN270

1 N4003

lN9616 1OV

zener
Integrated Circuits

~A739 or
~A749

Coils

.5

mhy axial lead

Miscellaneous
Main PC board

TO-5 mounting pad

TO-5 coolers

IC

socket,

14-pin

DIL

TO-92 dual cooler

PC receptacle

3447
2851
3549

3231
3643

3510

9605
1250

3175
3450

3493

3519

R

107,

207

omitted

R

107,

207 is 2629

Used to mount pre-drivers (QlO6,
206, 107, 207)

Mount on pre-drivers

Used on Ql 01, Q201

LlOl,

201

#8 x

5/s

hex WHSMT screw
OUTPUT INDUCTOR ASSY.
Torroid form

Magnet wire,

#14

(13” lg)

2757
41206
2850
3630

Fasten main board to shield

Wound on form 2850

PARTS LIST, DC-300A Page 4

Schematic
Designation

Cl 15. C215

Cl 17, C217

Description

Captive stud,

Nylon washer

Nylon spacer

#lO

internal star lockwasher

Hex nut,

Solder lug 806,

HEATSINK

DC-300

Heatsink

Capacitors

.Ol MF Ceramic Disc

.22

MF,

Diodes

#lo

lo-32

BOARD

heatsink

PC board

1OOV

Filmatic

x 1

#lO

l/4

ASSY.

Crown

Part # Other Information

3636 Used to mount coil assy.

3609 One used on each side of coil

2762 Used in center of coil; over stud 3636

2279 To mount coil

2170 To mount coil

3312

41207

3561

7954u

1751

3218

Mounted under nut; under coil

On PC board

On

heatsink

0109,

0209

DllO.

D210

R131, R231

R138.

R238

R132, R232
R139. R239

R133,

R233
R134, R234
R135, R235

R136,

R236
R137, R237

R140,

R240
R141, R241
R142, R242
R143, R243

SW-2
SW-3

0108,0208

1

N4003

Resistors

180 ohm

5.6

12

.33

Thermal switch SPST NC 1

Transistors

2N3859A

l/4

watt 10%

ohm1watt

or

ohm 2 watt

ohm 5 watt

(selected)

5%

1%

5% Wire

60°F

2851

2873

2355

3931

3583

2799

2961

On board

On board

On board

See chart on schematic

On board

One mounted on left heatsink,
one on the right

Attach to

heatsink

with 2162 compound

0109, 0209

Q114,

Q214

TIP558 (selected)

4025

Driver transistors

PARTS LIST, DC-300A Page 5

Schematic

Designation

QllO,Q210
0111,0211

0112, Q212

Q113,0213
0115, 0215
Q116.0216
0117,0217
0118,

Q218

Description
Sel. 1605 (RCA)

or

2N5631; 1 OOV (Motorola)

Miscellaneous
TO-3 anodized insulator
TO-3 insulator

Heatsink

#6 internal star lock washer

6-32 hex nut
6-32 x 3/ BHP screw

#6 solder lug, 505

FRONT PANEL ASSY.

compound, 340

Crown

Part #
3937

3990

4039
407 1

2162

1823

1889
2135
3163

Other Information
Output transistors

Mounts outputs and drivers
Mounts outputs and drivers
Mounts outputs and drivers
Mounts outputs and drivers
Mounts outputs and drivers
Mounts outputs and drivers
Used as terminals on board and

heatsink

RlOO,

R200

DC-300A Chassis cover

1 O-32 x
6-32 x

%

internal star lockwasher
Cable ties
,375 hole solder lug
Front panel extrusion
Front panel overlay
Knobs

Xi’ bright nut

Bright washer
Carrier strip
25K ohm audio ZF3448
Rack ears

SHIELD ASSY.

5/l

6 captive stud

l/4

BHP screw

9561s

3635
1954

2188

1811
2828
4087
4088
4080
1288 NIC
2189 NIC
3638
2942
20030

41202

Level controls

Main board shield
Brass shield spacer

8-32 x % THP screw

95928

3581

2155

Mounted on spacers
Mounted on transformer screws

(1 O-24)
To mount shield on transformer

spacers

PARTS LIST, DC-300A Page 6

Schematic
Designation

Added after
SN A71 14

Cl. c2

Description
Brass tube

6-32 x 1

j/4

BHP screw
G-6-G terminal strip
6-32 x % BHP screw
6-32 hex nut
G-6-G insulator

#6 internal star lockwasher
l/4”

expansion nut

#8 x

5/e

SMT hex screw

13,500 MF, 70V
,218 solder lug

lo-32

x

l/2

THP screw

Fiber shoulder washer

Crown

Part #
3637

3634
3503
2134CAD

1889

3600

1823
2544
2757

3436

2934

2049

3320

Other Information
To mount power switch

To mount power switch

Mounted on shield
To mount terminal strip
To mount terminal strip

Under terminal strip

To mount terminal strip

Mounted on shield in square holes

Used to secure main PC board to

shield
Mounted on

heatsink

Positive capacitor uses 2 on each
terminal; on top of 3320

Used to mount capacitor

Mounted inside 1309 to

insulate screw

Nylon washer
Flat metal washer

TRANSFORMER ASSY.

Tl

Power transformer

#lO

solder lug, 806

46P6E

1647
3830

41204
4004
3312

Mounts over capacitor terminals

Mounts between 3320 and 2934

Supplied with mounting screws (10-24)

Used under 3581 spacer and 2829 nut

for gnd. lug (3 position only)

#lO

internal star lockwasher

2279

Used over transformer screws; one in

position not having 3312 lug, 4 on top of

2829 nuts

#lo-24

hex nuts
Panel washer
Solder lug

2829

3830
3664

To mount transformer

Used between 2829 nuts and 3581 spacer
Used over one 3581 spacer to secure

input cables

Foam tape

120V serial plate

CHASSIS COVER ASSY.
Chassis cover

1152

3883
41209

9561 S

DMI

c3

Bridge, SDA9903, 30A

.l

MF, 200V Filmatic

Heatsink

compound

3526

2938
2162

On chassis cover
On bridge assembly
Use to mount bridge

Schematic
Designation

PARTS LIST, DC-300A Page 7

Description

#6

internal star lockwasher

Crown

Part #
1823

F2

Fl
Fl

6-32 hex nut
6-32 x % BHP screw

1 O-24 x 3/ self-tap screw
ABC

12A

internal fuse (CSA)
HTA fuseholder
Fuse block

1 OA 3 AB fuse

5A ABC fuse

Strain relief

112A

2-conductor hi-D

3/8”

fiber shoulder washer
Fiber flat washer
Dual binding post

#6 solder lug, 505

250

faston

terminal

250

faston

terminal housing

1889

2176

4035

jax

C116,

Cl 18,

R144,

R145,

SW-1

216

218
244

245

5 MF,

7OV

.l

MF, 200V Filmatic

5.6 ohm 1 watt 5%

1 ohm

‘/2

watt 10%
Power cord 3 #18 male
8-32 hex nut

8-32 x

3/e

RHS screw

#lo

solder lug

Power switch

250

faston

flag