Crown D-150 User manual

D-150

SM-5

$1P1-21-0

crown

|

SERIAL

NO.

ISSUED

TO

SERVICE

MANUAL

D-150

DUAL:

CHANNEL

POWER

AMPLIFIER

~

Div.

of

INTERNATIONAL

RADIO

&

ELECTRONICS

CORP.

BOX

1000

ELKHART,

INDIANA

46514

|

Se

ome

TABLE

OF

CONTENTS

SECTION

i

INTRODUCTION

11

1.2

3

INSTALLATION

AND

OPERATION

4

CIRCUIT

DESCRIPTION

41

5

SERVICE

PROCEDURES

5.1

5.2

5.3

54

55

5.6

5.7

5.8

Scope

of

Manual

Equipment

Description

.

General

....

Unpacking

...

Mounting

Instructions

Accessory

Panel

Kit

Installation

Amplifier

Protection.

Mechanisms

Load

Protection

Methods

Operating

Precautions

...

Connecting

Output

Lines

Connecting.Input-Lines

.

Connecting

Power

..

Operating

Controls’.

Normal-Hi-Fi

Installation

Cleaning.

...

Principles

of

Operation

introduction

.....

Service

Policies

Warranty...........

Disassembly

for

Servicing

.

5.4.1.

Removal

of

Bottom

Cover,

Transformer

Cover

and

Wrap-around,

and

Board

and

Electronics

Cover

-

5.42

Removal

of

Control

Plate

Assembly...

5.4.3

Replacement

of

Components-of

Main

PC-Board,

7891

5.4.4

Replacement

of

Input

Level

Potentiometers

(R101,

R201)

5.4.5

Replacement

of

Thermal

Switch;

SW-L..

5.4.6

Replacement

of

Bridge,

DM-1

-....

5.4.7

Replacement

of

Filter

Capacitors,

C23

and

C24

5.4.8

...Replacement

of

Output-indactors;-L.102.and

k202

..

5.4.3

Replacement.of

Driver

and

Output.

Transistors

5.4.10

Replacervent

of

Power

Transformer,

11

.

Test

Equipment

000.0...

5.5.1

Calibration

of

Test

Equipme:

Test

Procedures.

Troubleshooting

5.7.1

Turr-on

Procedure

.

5.7.2

Qutput

Offset

Voltage

Check

.

5.7.3

Bias

Level

Check

0.

5.7.4

Checkout

Procedure

~

1

KHz

Input,

No

Load

.

5.7.5.

Checkout

Procedure

—

J

KM2

Input;

With

Load

5.7.6

Checkout

Procedure

—

Protection

Circuit

Tests

5.7.7

.

Checkout

Procedure

—

20.KHz

Sine

Wave

Input.

§.7.8

Checkout

Procedure

—

10

KHz

Square

Wave

input

.....

5.7.9.

Checkout

Procedure

—

IM

intermodulation)

Distortion

Test

-

5.7.10

Checkout

Procedure

~

20-20

KHz.

Hunvand.Noise

Test

....

5.7.11

Checkout

Procedure

—

Quiescent

AG

Power

Consumption

Bias

Level

Check

and

Adjustment

8

SCHEMATICS,

PARTS

LISTS

AND

COMPONENT

LOCATION

6.1

General

Information

...

6.2

Parts

Replacernent

.....

7

APPLICATION

NOTES

7.1

General

..

ae

Note

1.

v-l

Needs

of

2

Load

-

Note

2.

D-150

Morio

Conversion

..

Note

3.

PA

Adapter

Panel

installation

.

LIST

OF

ILLUSTRATIONS

DESCRIPTION

integrated:

Circuit.

Stereo.

D-150

Amplifier

D-150.

Mountinig

Dimensions’...

Panel

Kit

Mounting

Graph.

of

V-1

Operating

Range,

D-150

Output

..

Fuse

Selector

Nomiag

for

Loudspeaker

Protection:

Relay-Controlied.

Protector

With

Overload

Indicator

Peak:

Power

Limiting

Compressor

With

Qverdiive

Indicator...

Turn-On-Transient

Muter

for

Load

Protection

.

Rear View

of

Chassis

.

Seheniatic

tor-Full.

Benge.

Bectrostatic

Speaker

Connection

Schernatic

of

Ear

Phone

Pad

..

aie

Cw

OAD

Nw

om

Oo

Source

Resistance

and

Damping

Factor

¥

vs.

Length

and

‘Size

of

Output

Leads.

.

10

Graph

for

Selection

of

input

Capacitor

.

16

Low-Pass

Filters

for

Severe

RF

at

Inputs

..

li

Line

Voltage

Connections

(240

VAC)

~AL

Operating

Contrels

JL

Typical

Hi-Fi

Installation

....0..-

12

Test

Equipment

Complement

es

Typical

Protection

Clipping,

2-Ohm

Load

.

26

Typical

20

KHz

Sine

Wave

Test

Output

Waveform

. .

26

Typical

10

KHz

Square

Wave

Test

Output

Waveform

.

26

Bias

Level

Check

Components.....:

27

Schernatic

Diagrarn,

0-150

Ampiitier

.

34

Explodéd

View,

0-150

Chassis

Assanibly

33-34

Component

Location;

D150

Main.

PC

Board

7891

Exploded

View,

Contfal

Plate

Assembiy’

...

Exploded

View,

Output

Inductor

Assembly.

FIGURE

1-4,

INTEGRATED

CIRCUIT

STEREQ

2-150

AMPLIFIER

1.1

‘SCOPE

OF

MANUAL

This

matidal

is

intended

to

provide

the

User

and

sérvice

tech-

nician

necessary

technical

information

required

to

install,

oper-

ate

and

repair

the

CROWN

D-150

Dual-Charnel

Power

Amplifier

properly

and

to

maintain

the

unit

in

optirmum

operating

condition.

The

manual

is.

comprehensive;

containing

a

physical

description

of

the.0-150,

electrical

and

mechanical

specifications,

complete

installation

atid

operating

instructions,

a

detailed

circuit

descrip-

tion

and

service

procedures

to

include

troubleshooting

and

repair.

Also.

included

are.complete

parts

lists,.a

unit

schematic

and.ex-

ploded

view

drawings

to

assist

in

identification

of

parts

and

under-

standing

the

functional

operation

of

the

D-150.

amplifier.

A

thorough

reading

of

this

manual

and

strict

adherence

to

the

in-

structions,

procedures

and

cautions

will

assure

many

years

of

pro-

fessional

quality

service

and

listening

enjoyment

from

your

CROWN

D-156

Dual-Channel

Power

Amplifier.

1.2

EQUIPMENT

DESCRIPTION

Tre

0-150

isa

dual-channel

medium

power

amplifier

for

ultra-low

distortion

amplification

from

5Hz

to

20KHz

with

operation

into

loads

of

4-ohms:and

higher.

The-unit

features

extremely

tow

har:

monic

and

intermodulation

distortion,

very

low

noise,

highest

“damping

factor,”

and

quality

parts

and

workmanship.

The

unit

may

be

wired

to

produce

a

balanced

50

volt

monaural

output.

The

amplifier

is

fully

protected

against

misrretched

and

shorted

loads

by

a

resetting

V-1

(volt-ampere)

limiter

having

no

obnoxious

muting

or

program

delays.

A

thermal

switch

removes

power

from

the

unit

if

overheating

occurs

due

to

insufficient

ventilation.

The

power

supply

features

large

computer-grade

filter

capacitors

giving

over

20

joules

of

energy

storage.

A

total

of

24

discrete

transistors,

1

linear

IC

(dual

op

amp),

20

diodes

and

1

bridge

rectifier

are

utilized

in

a

CROWN-ploneered

Class

AB+B

output

circuit.

The

effective

number

of

semi-

conductors

is

40

transistors

and

30

diodes.

The

input

voltage-ampiifiers,

(IC),

are

powered

by

two

voltage-

regulated

supplies.

This

results

in

complete

channel-to-channel

isolation

and

independence

from

line

voltage

variations.

Two

level

controls

are

mounted

adjacent

to

the

inputjacks

to

allow

balancing

and

optirnizing

of

systern

levels.

ise

BRaEmnEnEgaNIRitR

ke

nsonannannsnnnnnnnssnnonimnossnnnenans

Me

Power

Output

Power

Bandwidth

Frequency

Response

LM.

Distortion

Phase

Response

Damping:

Factor

Hur

and:

Noise

Verification

Load

Impedance

Construction

input

Turon

.

Circuit

Protection

Power

Supply

Dimensions

‘Weight

Warranty

SECTION

2

SPECIFICATIONS

Power

output

not

less

than

75

watts

R.M.S.

per

channel

into

8

ohms

(both

channels

operating),

20-

20,000Hz

at

rated

distortion.

Typically

100

watts

R.M.S.

per

channel

into8

ohms,

180

watts

8.M.S.

per

charinel

into

4

ohms.

Power

bandwidth

+

1dB,

5-20,000Hz

at

75

watts

R-M.S.

per

channel

into

8

ohms.

+0.10B

20-20,000Hz

at

1

watt

into

8

ohms;

+

1dB

4-100,000Hz.

1M.

Jess

than

0.05%,

0.01

watt

to

76

watts,

60Hz

and

7,000Hz

mixed

4:1.

Harmonic

lass than

0.05%,

0.01

watt

to

75

watts;

20-20,000Hz.

+£15°,

20-20,000Hz

at

1

watt

into

8

ohms.

Gee

graphs)

Greater

than

200

orn

2676

te

1000Hz

into

8

chimes.

11008

below.75-watts:R.M.S.

output.

Each

unit

accompanied

by

its

individual

hand-entered

proof-of-perfarmance

report.

4

to

16-ohrns

(complete

stability

with

any

load);

dual

binding-post

outputs.

100%

American-made-with

industrial.

grade

construction-for

years

of

continuous

use.

Impedance

—~

Norninal

25K

ohm,

screwdriver

adjust

on

rear.

Input

sensitivity

1.2V

for

full

output.

Standard

°4”

phone-jack

on

rear.

:

J

Instantaneous,

with

no

program

delay,

and

minimum

thump.

Unique

wideband,

stable

design

utilizing

one

linear

iC

(dual

op-amp).

Total

equivalent

of

40

tran-

sistors,

24

diodes,

and

four

rectifier-diodes.

Amplitieris

short:

and

mismatch:

and

open-circuitproof.

Unique

V-1

limiting

is

instantaneous

with

no

thumps,

cutout,

ete.

Two

massive

capacitors

with

energy-storage

exceeding

20

joules.

Total

of

two

regulated

supplies

for

complete

isolation

and

stability.

No

fuses

except

AC

powerline,

17"

width,

544”

high,

9°

deep

Grom

mounting

surface).

All-aluminum

construction

with

massive

chassis,

and:

extruded

front-panel.

Amplifier

will

pane!-mount

in

a

16%"

x

5”

opening

(with

optional

front

panel).

With

adapters,

staridard

19°

rack

tieurit,

22

pounds

(24

pourids

tack

mount.

3-year

on

all

parts,

labor,

and

round-trip

shipping.

3.1

GENERAL

-

This:

section

contains:

instalistion

and

operation

instructions

for

the

D+150:

arhplifier.

Also

included:

are

destriptiaris

of

the

pro-

*

tective

mechanisms

forthe

amplifier

and

the

liad:

together

witha

list

of

operating

precautions

to

help

clarify

proper

operating

procedures.

3.2

UNPACKING

imamediately

upon:

‘peceipeot

the

‘arn

RE?

shipenenc

weber

the

unitforany

damage

incurred

intransit.

The

amplifier

was

carefully

inspected:-and-tested.

and

left

the

factory-unmarred.

Notify

the

————

comparty

immediately

ifany

damage

is

found.

Only

NOTE:

The

“basic”

D-180

shown

at

right

may

be

converted

for

rack-

or

cabinet-

(panel)

mounting

by

installing

the

front

panel

with

brackéts

or

end-caps

as

shows

below.

RACK

MOUNTING

INSTALLATION

AND_OPERATION

the

consignee

may

initiate

a

claim

with

the

carrier

for

damage

dur-

ing

shipment.

However,

CROWN

will

cooperate

fully

ini

Sich

ah

event.

Be

sur

to

Save’

thé

carton-a6

evidence

at

eerie

far

he

:

shipper's

inspaction.

CROWN

récommends

that

you

‘save

the

packing

|

materials,

even

it

the

unit

arrives

in

perfect

condition.

They

will

prove

valuable

in

preventing

damage

should

there

be

ovéas

1

Ship

the

unit.

Both

the

carton

end

internal

pack

are

specifically

de-

signed

for

protection

during

transit:

Do

not

ship

the

unit

without

this,

factory

pack”

Be

sure

to

returri

thewaerantyregistraticn

formtothe

CROWN

face

tory

within

ten

days

for

the

full

warranty

coverage.

ee

i

CABINET

MOUNTING

FIGURE

3-1.

0-150

MOUNTING

DIMENSIONS

%

The

D-150

may

be

custom

oF

rack-miounted

if

an

accéssory

front-

panel

kit

with

rack-mounting

brackets

was

purchased.

The

installation

of

this

kit

is

detailed

in

Figure

3-2.

Refer

to

Figure

3-1

for

mounting

dimensions.

Sufficient

ventilation

must

be

pro-

vided

forthe

unit.

Airmust

be

allowed

tocirculate

overthe

chassis,

atherwise.

the

amplifier.will-intenmitiently

tur

off

due

to

the

-

internal.

thermal.

protection.

feature...Applications

+-.other-than

standard

“Hi-Fi”

—

requiring

long,

sustained

signaisathigh

power

levels

may

require

the

use

of

a

cooling

fan.

3.4.

ACCESSORY

PANEL

pis

INSTALLATION

MODEL

PK)...

05

To

install

the

D-150

amplitier

ina

:

“custom

configuration’

ue

cessory

cabinet

(Model

5-D

or

5-R)

or

a

rack,

the

accessory

front

panelmust

be-attached:first:

Referto

Figure:

3:2eso2.0006

1.

Pull

four

rubber

feet

off

the

bottom

of

the

amplifier,

2.

Place

amplifier

on

bench

or

table:

stand

on

end

with

trans:

former.

down,

“Amplifier”

onthe

front

panel

should

foe

tb

cpanel

being-instalied:

sae

4.

Plastic

wedges

supplied

with

the

panel

kit

should

be

forced

inta

positions

Land

2or

Hoth

ends

of

the

unit

as

far

as

possible.

Clip

or

break

off

the

excess

part

of

the

plastic

wedges

~

5.

Align-end-caps-to-the-unit-so-holes.“A”-and

“B"

match

th

caps.

Use

6/32

x

%

socket

cap

screws.

(NOTE:

Socket

screws

may

look

as

though

they

are

cross

threading

but

willstraighten

approximately

half

way

through)

in.

a

“custom

installation”,

install

a

solid

shelf

to

support.the

amplifier..The

-shelf-top-surface

should:

be-

flush

with

the

bottom

edge

of

the

required

L6%,"

wide.x

5%"

high-panel

cutout.

When

using angle

brackets

for

rack

mounting

(Figure

3-2)

always

have

the

brushed

side

of

the

anglé-bracket

toward

you.

Simply

mount

the

end-brackets

in-place

of

the

end

caps

and

rack

mount:

as

shown

in

Figure

3-1.

FIGURE

3-2.

PANEL

KIT

MOUNTING

-on

to

Figure

2.3,

In

applications

where

the

load

is

a

loudspeaker,

amplifier

protection

will

be

evidenced

by

distortion

inthespeaker.

fatchtheend.

-

3.5

AMPLIFIER

PROTECTION

MECHANISMS

The

D-150

is

protected

against

all

the

common

hazards

which

Plague

highpower

amplifiers,

including

shorted,

open,

and

mis-

matched

loads;

overloaded

power

supplies;

excessive

temper-

ature;

chain

destruction

phenomena:

input

overiond

tetiee

and

high

frequency

overload

blowups.

é

Protection

against.

shorted

and

misrnatched-ioads

is:

‘provided:

by

an

instant-acting

Jimiter

which

instantaneously

linits

at

the

volt-

ampere

product

to

the

maximum

safe-stress.

value

eve

transistors...

“

The

area

in

which

the

amplifier

will

drive

the

load

without

being

V-i

limited

is

depicted

by

the

cross-hatched

areas

of

Figure

3-3.

if

a

load

initiates

protection

in

the

amplifi

it

can

‘be

detected

generally:

by.

watching:

the

wanster,

characteristics

ofthe

amplifier

Hy

The

audible

effect

ranges

from

something

resembling

cross-

overnatch

distortion

to

a

snapping

sound,

depending

on

the

overall

load

characteristics,

Speaker

systerns

which

are

truly

8

ohms.

or

greater

will

not

initiate

the

protection

system.

;

FIGURE

3-3.

GRAPH

of

V-1

OPERATING

RANGE

of

D-180

OUTPUT

&,

y

ea

os,

The:

AC.

line

for

120VAC

is

fused

with

a

4A,

250V.type

AG

fuse

for

240,

250VAC,

2A

type

AG).

The

use

of

any

other

type

of

fuse

will

in-

validate

the

warranty.

A

thermal

Switch

is

mounted’

onthe

Hones

10

protect

the

amplifier

against

insufficient

ventilation.

If

it

becomes

too

hot,

the

AC-line:

power

will

be

interrupted

until

the

temperature

fais

to

a

safe

level,

whereupon

power

will

automatically

be

restored.

When

such

an

event

occurs,

the’

external

symptorns

are:

no

output,

anda

wartn

anipiifier.

The

‘amplitier’s

voltage-amplifier

citcultry

is

designed

t

to.be.

in-

hereritly

current-intited.

1

any

of

the:

aevices

fail,

no

damage

occurs

to

the

rest

of

the

stages.

‘with

the

Vil

limiter,

protects

the

amplifier

foi

‘blowers

When

hod

large

RF

input

signals.

3.6"

LOAD

PROTECTION

METHODS

=

The

most

corrimon

ofall

protection

schemes

is

a

fuse

in

series

with

the

load.

The

fuse

may

be

singte;

fusin,

erallsystem.

Or,

in

the

case

of

a

multiway

speaker

system,

it

ey

‘be

rHUltiple

with

Orie

fuse

wit

éach

speaker,

SPEAKER

FIGURE.

3-4.

FUSE

SELECTOR

NOMOGRAPH

FOR

LOUDSPEAKER

PROTECTION

Fuses

help

to

prevent

damage

due

to

prolonged

Overload

,

but

pro-

vide

esseritially

no

protection

against

damage

that

may"

bé

large

transients

and

Such:

To

mininiize

this

problem,

high:

instrument

fuses

“such

“as

Little

fise

361000

Series

are’

mast

appropriate

for

siich

applications.

For

a

niomopgraph

showing

fuse

Size

¥s,

loudspeaker

ratings

refer

to

Figure

34.

;

Another

form

of

load

protector

is

shown

schematically

in

Figura

3.

5.

Whenever

the

load

is

overdriven,

a

relay

switches

a

jamp

in

Series

with

the

load;

smoothly

relieving

the’overload.

The

lamp

then

doubles

as-an

overdrive

indicator

as

it

glows:

If

overdrive

ig

unreasonably

severe,

the

lamip

will

serve

ag

2

fuse.

By

adjusting

the

relay.tension

adjustment

and

the

protéction

level

control,

this

system

is

useful

from

25

to

200

watts

for

a

typical

8

ohm

ioad.

Another

more

sophisticated

form

of

overload

protector

relieves

the

overload

by

controlling

the

ampliier’s

eu

sigral

which

is

eT

hise

; :

load:

but

also

eliminates

amplitie

possible

16

Operate

the

anipiifier

at

ids

maximum

level

with:

arain-

imum-of

chipping.

This

device

is

shown

schematically

in

Figure

3-

4,

It

features

an

overdrive

indicator,

distortionless

photo-optical

control,

and.a

Protection

Level

control

giving

adjustment

from

1W

to.

200W

when

driving

8

ohms.

.

FIGURE

3-6.

PEAK

POWER

LIMITING

COMPRESSOR

WITH

OVERDRIVE

INDICATOR

A

common

problem

which

causes

damage.and

irritation

is

the

turn-on

thump

problem

typical

to

many

signal

sources.

Figure

3-7

shows.

the

schematic

of

a

muter

which,

when.

inserted

inthe

input

signal

line,

mutes.

for

several

seconds

before

connecting

the

source

to

the

amplifier,

thereby

eliminating

turn-on

transients.

it

aiso

removes

turn-off

transients

occurring

after

the

relay

drops

See

00).

FOR

LOAD

PROTECTION

BO

this

imuter

ig

not

required.

rany

signal

source

NOTE:

When

using

the

CAO

whose

AC

power

is

switched

by

the

IC-160.

Followingare.

ey

number

of

operating

precautions

givenasanaidto

understandirig

proper-and

improper.

amplifier

usage:

1

Use

care

‘ine

taking

connections,

selecting

signal

sources,

and

Gontvalling

the

i

U

thay

bé

your

own.

CROWN

is:

‘any

damage

done

to

loads

“due

to

careless

ampliier

usage

or

deliberate

over:

powering.

For

pointers

on

load:

ibe

see

paragraph

3.6:

2)-Néver

parallel

the two

ou

OF

—

‘them

with

an

without

a

series

isglating

capacitor.

Such

operations

may

damage

the

device

and/or

needlessly

activate

the

V-Himiting

(see

Figure

3-3),

4.

Do-not

short.the.ground.

lead.of:an

output

cable

to

the

input

signal

ground

as

oscil

Fay

result

from

forming

such

a

grourid

loop...

=

8.

Operate

and

fuse

the

amplifier

only

as

set

forth

in

paragraphs

34.

6.

Operate

the

amplifier

from

AC

mains

of

not

more

than

10%

above

the

selected

‘fine

voltage

and

only

on’50,

60

or

400Hz

AG:

Falling

to

comply

with

these:

aes

will

sec

siyatate

ine

warranty.

7.

Never

connect

the

output

toa

power

supply

output,

battery;

or

power

main.

Damage

incurred

by

such

a

hookup

is

not

covered

by

the

warranty,

8.

Do

not

expose

the.

amplifier

to

corrosive

chemicals

eehs

as

soft

drinks,

lye,

salt-water,

ete.

~~

De

To

apt

rt

ecrmende

fr

ih

ower

industria

usage

at

frequencies

above

20KHz.

10,

Tampering.in.

the.

cireuit:-by

unqualified.

personnel

or

the

making

of

unauthorized

circuit

modifications

invalidates

the

warranty.

11.

Donotexpose

the

output

leads

to

areas

likely

to

be

struck

by

lightning.

Such

an:

installation,

could

invalidate

the.

amplifier.

3.8

CONNECTING

OUTPUT

LINES

input

and

output

connéctors

are

located

on

the.chassis

as

shown

in

Figure

3-8,

FIGURE

3-8.

REAR

VIEW

OF

CHASSIS

Rt

ig

always

wise

to

remove

power

from

the

unit

and

tum

the

input

level

controls

off

while

making

connections,

especially

if

the

toad

is

a

loudspeaker

system.

This

will

eliminate

any

chance-of

toud

blasts.

CROWN

is

not

liable

for

darnage

incurred

at

any

trarisducer

to

its

being

overpowered!

The

use

of

the

enclosed

speaker

fusesis

therefore

highly

recornmended:~

-

Before

making

connections,

it

is

recommnended

that

the

aperator

farniliarize

himself

wth

the

amplifiers

protective

system.

Reterence

paragraph

3.6.

Because

of

the

locations

of

the

output

connectors

(color-coded

binding

posts)

it

will

be

easiest

to

make

these

connections

first.

High-quatity,

dual

“banana”

plugs

are

the

preferred

connections

for

permanent

installations.

©

Because

the

output

wire

gauge

and

length

raises

the

resultant

source

impedance

or

lowers

the

Damping

Factor

by

adding

series:

«

resistance,

the

nomograph

(Figure..3-11)

is

provided

for

wire

selection.

For

dynamic

moving-coil

loudspeakers

the

valueRy

--

should

preferably

be.

that.

measured

by

an

ohmmeter

across

the

voice

coil,

rather

than

the

manufacturer's

rating.

For

elec

speakers

and

such,

theynanufacturér’s

rated

impedance

should

Pa

be

used

for

R,

-

ff

the

load

(matching.

teanstoriner,

inductance,

or

ibe

electrostatic

speaker

system)

appears

as

a

short-circuitatiow

freé

quencies,

a

large

non-pélarized:

capacitor’

(paralleled

with

a

resistor)-should-be-placed:in

series.

withthe.

jgad.

For

electrostatic

speakers

(if

the

manufacturer

has

not

provided

a

lar

Capacitor

oF

S90-

708

mitdand

4

ohn

power

resistor

should

be

placed

in

senes

with

the

plus

+)

speaker

lead.

This.

will

prevent

lerge

low-frequency

currents

from

darnaging

‘the:

electrostatic”

tansfortier

‘or

from

unnecessarily

activating

the

D-150's

protectivé.system.

An

effective

test

to

determine

if

such

parts

are-needed

is

to

measure

the

DC

re-

sistance

between

the

output-terminals

with

a

résistarice-is

tess

than

3

ohms,

the

parts

si

shown

schematically

in-Figare-

Ss

9.

40,200...

FIGURE

3:9.

SCHEMATIC

FOR

FULL

RANGE

ELECTROSTATIC

SPEAKER,

CONNECTION

should

nét

be

used.

A

cormmon

exariple

is

the

standard

3-

circuit

“inch

phone

jack.

and

lug

awen.

wired

-

for

stereo

sound.

.

4.

Connectors

having

low-current-carrying

capacity

are

“vers.

5.

Connectors

having

any

tendency

to

short,

or

having

shorted

leads,

are

unadvisabie.

on

Most

commercially-available-

headphones

employ

a

A-circuit

4%

inch

phone

plug

which

violates

condition

No.

2.

This

is

no

handi-

cap

if

#

pad

is

inserted

between'the

atip:

jack,

which

is

only

sensibie

when

such

a

large

amp!

is

coupied

to

such

a

small

HE

this

precaution

is

not

only

may

the

trans-

ducer

te-Gairned

out but

permanent

hearing

loss

could

result.

The

recommended

pad

is

shown

in

Figure

3-10.

“FIGURE

3-10:

SCHEMATIC

‘OF

EARPHONE

PAD

3.9

CONNECTING

INPUT

LINES

Connecting

the

inputs

will

require

observance

of

three

basic

pre-

cautions:

Undesirable

signals.to-the

inputs,

“ground

foops;“and

feedback

from

output(s)

to

input(s).

°

in

high

fidetity

audio

applications

any

good

vacuun?-tube

or

solid-

State

control

center

will

operate’successfully

into

the

25K

ohm

inputs

“of

the

D-150.

Occasionally

a

high-impedance

output

of

poorly-designed

preamps

will

be

encountered,

and/or

a

larger

_

output

coupling

capacitor

may

be

required

(o

prevent

excessive

—

fow-tr

quency

rolloff).

For.

joudspeaker-driving

applications,

the

vane

should-be

free

of

large

sub-audio

or

undesired

low

frequencies,

as

they

cause

over-

heating

and

overloading

of

the

loudspeaker.

To

remove

such

low

frequencies,

a

series

capacitor

may

be

placed

in

the

input

signal

line.

(The

graph

of

Figure

3-12

indicates

the

effectofthe

size

of

the

.

capacitor

on

the

frequency

response.

1)

Only

a

low-leakage

paper,

oF

cause

general

overload

‘sewing

-tate

stage

of

the

amip

(which

is

employed

to

provide

RF

overload

protection).

The

following

filters

are

recommended

for

such

applications

(Figure

3-13),

A

second

precaution

is

“ground

loops”

—

electronic

jargon

for

un-

desirable

circulating

currents

flowing

in

a

grounding

system.

A

commion

form

of

loop

(possibly

resulting

in

hurn

In

heoutpuld

is

a

pair

of

input

cables

whose

area

is

subjected

to

a

magnetic

hum

Crown D-150 User manual

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