JVC M-7050 User manual

Table of contents

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JVC

Instruction

Book

&

Service

Manual

STEREO

POWER

AMPLIFIER

M-7050

i

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a

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ae

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ee

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Sea

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ea

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ee

WARNING:

TO

PREVENT

FIRE

OR

SHOCK

HAZARD,

DO

NOT

EXPOSE

THIS

APPLIANCE

TO

RAIN

OR

MOISTURE.

For

Customer

Use:

Enter

below

the

Model

No.

and

Serial

No.

which

is

located

either

on

the

rear

or

bottom

of

the

cabinet.

Retain

this

information

for

future

reference.

Model

No.

Serial

No.

Service

manual

No.

2469

July,

1979

E30580-804A

IMPORTANT

(In

the

United

Kingdom)

Mains

Supply

(AC

240

V~,

50

Hz

only)

IMPORTANT

Do

not

make

any

connection

to

the

Larger

Terminal

coded

E

or

Green.

The

wires

in

the

mains

lead

are

coloured

in

accordance

with

following

code:

Blue

to

N

(Neutral)

of

Black

Brown

to

L

(Live)

or

Red

\f

these

colours

do

not

correspond

with

the

terminal

identifi-

cations

of

your

plug,

connect

as

follows:

Blue

wire

to

terminal

coded

N

(Neutral)

or

coloured

Black.

Brown

wire

to

terminal

coded

L

(Live)

or

coloured

Red.

If

in

doubt

—

consult

a

competent

electrician.

Note

We

recommend

that

you

should

disconnect

the

AC

cord

from

the

outlet.

INTRODUCTION

Thank

you

for

purchasing

the

JVC

M-7050

stereo

Power

Amplifier.

You

are

now

the

owner

of

a

truly

sophisti-

cated

system

component

incorporating

many

advanced

features.

“Super-A”

high

efficient

150W

+

150W

power

output

stage

(is

equal

to

class

B

operation)

of

extra

low

distortion

(is

superior

to

class

A

operation),

high

slew

rate

(+300V/ysec),

un-

rnesurerable

TIM

distortion,

non

magnetic

alminium

chassis-

base

to

eliminate

the

magnetostriction,

and

high

capacitive

power

supply

are

just

a

few

of

the

host

of

features

which

combine

to

produce

the

best

possible

sound.

JVC

also

manufactures

the

EQ—7070

Stereo

Phono

Equalizer,

a

matching

preamplifier

and

the

SEA—7070

Stereo

Graphic

Equalizer,

a

matching

frequency

characteristic

controller

for

use

with

the

M—7050

Power

Amplifier.

Before

you

begin

using,

please

read

the

instructions

carefully

to

be

sure

of

getting

the

best

possible

performance

from

the

new

unit.

Wishing

you

memorably

enjoyable

listening.

WARNING

Dangerous

voltage

inside

CAUTION

(

To

prevent

electric

shock,

do

not

remove

screws,

covers

or

cabinet.

No

user-serviceable

parts

inside.

Refer

servicing

to

qualified

service

personnel.

CONTENTS

Instruction

Manual

page

Front.panel.):.:

si.

eh

a

ee

FA

ee

ee

g

Important

notes

2...

ee

5

Troubleshooting...

0.0.0.0...

eee

tee

ee

eee

6

Block

diagram.

6.2...

eee

ee

7

Performance

graphs...

2...

ee

ee

es

8

Technical

description...

0...

ee

ee

9

Specification

©...

6.

ee

et

ee

ees

10

Precautions

in

servicing

Adjustment

procedure

of

the

amplifier

Check

after

servicing

Exploded

views

Parts

list

of

exploded

views

Location

of

circuit

boards

Schematic

Diagram

(For

only

qualified

service

personnel)

cto,

et,

Instruction

Manual

FRONT

PANEL

PHONES

POWER

Switch

Headphones

jack

(PHONES)

Exclusively

for

monitoring

purposes.

Employ

this

facility

in

the

following

cases,

for

example:

1.

To

locate’the

beginning

of

a

particular

section

of

tape

when

no

speaker

sound

is

desirable.

2.

To

monitor

the

sound

to

be

transmitted

to

a

remote

place

when

the

amplifier

is

used

as

a

public

address

system.

(Note)

Plugging

in

the

headphones

does

not

switch

off

the

speaker

sound

automatically.

When

you

wish

to

listen

to

sound

from

the

headphones

only,

set

the

SPEAKER

switches

to

OFF.

POWER

switch

Press

to

turn

the

power

on.

The

red

indicator

lamp

in

push

knob

will

light

and

the

POWER

meters

will

be

illuminated.

To

turn

the

power

off,

press

the

switch

again

to

release.

Panel

IImination:

For

a

period

immediately

after

the

POWER

switch

is

turned

ON,

the

illumination

of

the

POWER

meters

is

red.

Wait

for

about

4

-

5

seconds

until

it

changes

to

white.

If

it

continues

to

be

red

for

a

longer

span,

the

protection

circuit

is

operating

for

some

reason.

Turn

the

POWER

switch

OFF

and

check

the

cause

of

malfunctioning.

——

Power

meter

SPEAKER

Switch

POWER

meters

The

output

power

is

indicated

in

wattage

on

the

compressed

logarithmic

scale

in

reference

to

the

8-ohm

load

impedance.

SPEAKER

switches

To

listen

to

the

speaker

system

connected

to

the

rear

panel

SYSTEM-1

terminals,

press

the

SYSTEM-1

switch.

To

listen

to

the

speaker

system

connected

to

the

rear

panel

SYSTEM-2

terminals,

press

the

SYSTEM-2

switch..

Both

speaker

systems

can

be

heard

by

pressing

both

switches.

When

a

SPEAKER

switch

is

pressed,

the

green

indicator

lamp

on

the

corresponding

switch

lights.

(Note)

If

the

load

impedance

is

lower

than

4

ohms,

the

protection

circuit

is

activated,

resulting

in

inter-

mittent

sound.

1.

If

a

single

pair

of

speakers

is

to

be

driven

at

a

time,

the

speaker

impedance

may

be

between

4

and

16

ohms.

2.

If

two

pairs

of

speakers

are

to

be

driven

simultaneously,

the

speaker

impedance

should

be

between

8

and

16

ohms.

CONNECTION

DIAGRAM

Refer

to

item

No.

3

in

page

5

Speaker

system

4

~

1622

Input

LEVEL

volume

Normally,

set

to

the

“MAX”

position.

If

the

preamplifier

produces

an

excessively

large’’

gain,

turn

the

control

counter-

clockwise

until

the

proper

adjustment

is

obtained.

Refer

to

item

No.

1

in

page

5

Refer

to

item

No.

2

in

page

5

Speaker

system

4

~

1692

SEA-7070

Graphic

equalizer

Pre-amplifier

Turn

table

Tape

Deck

a

IMPORTANT

one,

——

eeen

eoeow

Installation

Select

a

dry,

level

place

which

is

neither

too

hot

nor

too

cold

(between

—5°

and

40

°C/23°F

and

104

°F).

Leave

space

between

the

power

amplifier

and

the

wall

to

provide

good

ventilation.

Do

not

allow

a

curtain,

table

cloth,

etc.

to

block

the

ventilation

holes.

Keep

the

power

amplifier

away

from

direct

sunlight.

Do

not

place

close

to

a

heater.

Do

not

place

in

locations

subject

to

vibrations.

Do

not

place

in

locations

subject

to

dust.

Keep

as

far

from

a

tuner

and

a

preamplifier

as

possible

to

prevent

noise.

Power

cord

Do

not

handle

the

power

cord

with

wet

hands.

Do

not

bend

the

power

cord

double.

When

unplugging

from

the

wall

outlet,

always

pull

the

plug,

not

the

power

cord.

Malfunctions

Do

not

insert

any

metallic

object

inside

the

unit.

Do

not

allow

water

to

get

inside

the

unit.

Do

not

employ

thinner

or

benzine

to

clean

the

cabinet.

First

clean

with

a

neutral

cleaner

and

then

wipe

with

a

dry

cloth.

Power

switch

Do

not

plug

the

power

cord

into

an

AC

outlet

until

all

connections

are

complete.

Switch

the

power

off

when

connecting

other

components

to

it.

REAR

PANEL

1.

Connecting

with

other

components

may

result

in

trouble,

such

as

oscillation

or

hum.

Connect

ground

terminals

of

this

set

and

other

components

to

each

other.

SUBSONIC

and

DIRECT

INPUT

terminals

Do

not

connect

different

kinds

of

signals

simultaneously

to

input

terminals.

Input

cannon

connector

(for

professional

use)

(Unbalanced)

AC:

If

these

terminals

are

employed,

the

input

signal

passes

through

a

filter

having

a

cut-off

frequency

of

18

Hz

and

a

slope

of

6dB/oct,

which

results

in

a

reduction

of

ultra-low

frequency

noise,

such

as

that

encountered

with

warped

records,

and

prevents

speaker

intermodulation

distortion.

The

filter

also

eliminates

the

preamplifier

DC

leak

voltage,

thus

protecting

the

speakers.

DIRECT:

These

input

terminals

are

directly

connected

to

the

power

amplification

circuit.

Since

the

M-7050

employes

DC

amplifier

circuitry,

there

is

no

coupling

capacitor

between

the

input

circuit

and

the

power

amplification

stages.

Protective

circuit

When

the

protective

circuit

has

been

activated,

switch

off

the

power

and

determine

the

cause

as

follows:

The

speaker

load

impedance

Using

speakers

with

an

impedance

of

less

than

4

ohms

(or

a

short

circuit

across

the

speaker

terminals)

activates

the

protective

circuit

and

results

in

intermittent

sound

out-

put.

When

the

speaker

switch

is

at

the

“1

and

2”

position,

use

a

pair

of

speakers

having

an

impedance

of

8

or

high-

er,

at

“1”

or

“’2”

position,

use

a

speaker

of

4

or

higher.

Input

overload

The

speaker

produces

intermittent

sounds.

Detecting

the

offset

voltage

The

offset

voltage

of

+2

V

or

more,

activates

the

pro-

tective

circuit

and

results

in

no

sound

output.

Caution

indicator

When

the

protective

circuit

has

been

activated,

meter

illumination

changes

to

red.

TROUBLE

SHOOTING

What

seems

to

be

a

trouble

is

not

always

real

trouble.

{

Make

sure

first.

[

No

sound

]

Both

channel

Are

indicators

Yes

Does

the

relay

No

Is

the

speaker

switch

Yes

functioning?

operate?

set

to

ON?

One

channel

only

No

Reverse

the

L

and

R

Does

the

relay

Check

for

speaker

connections.

operate

connections

Does

the

channel

with

no

sound

shift?

No

Yes

Navsound

Yes

Is

the

input

level

volume

|

Yes

Check

for

trouble

in

the

preamplifier

IfOK......

set

to

maximum?

or

connected

component.

Both

No

channels

os

Does

the

replacement

of

the

preamplifier

or

connected

component

correct

distorted

sound?

|

|

Distorted

sound

only

Does

the

channel

with

distorted

sound

shift?

No

defect

in

the

M—7050

te

No

One

channel

Reverse

the

L

and

R

connections.

There

may

be

trouble

in

the

M—7050

it

self.

Consult

your

dealer.

BLOCK

DIAGRAM

YBLAW

8Y3MOd

ANddNS

YAMOd

39VLS

YSBAING

dWY

Y3M0d

A1ddNS

YAMOd

3OVLS

LNdLNO

TAA37

(00)

LOaYIa

@-WALSAS

Y3axVadS

(Ho

LINDYID

svia

v-y4adns

(Ov)

SINOSSNS

SANOHd

YOLINOW

Z2HOLIMS

LINDAID

SANILOSLOYd

Yy3ayvV3ads

LINDAID

Ssvig

(Sv)

SINOSSNS

(a4)

O

(10

(9q)

LOaYIa

T3A37

dWY

Y3aM0d

PERFORMANCE

GRAPHS

Wi

THD

vs.

Output

power

oe

|

;

=

&

0.03

=

|

|

ne

=a

{

c

Distortion

of

measurement

system

j

O

0.02

tae

4

1H

=

1KHz

0.0008%

7

6

20Hz

0,0011%

{

-_

20KHz

0.0014%

2

L.

pat

3

0.01

-

|

2

je

:

|

2

0.007

F

a

©

0.005

+

E

Ht

PS

0.003

g

0.002

°

ke

_——

|

KHz

0.001

-

+H

0.0007

=

1

rf

2

3

5

?

10

20

30

50

70

100

200

300

500

Power

output

(W/8

Q

}

@

Spectrum

of

harmonic

distortion

(dB)

(dB)

(dB)

—70

}

20K

100K

200K

}

20K

100K

200K

*

10

kHz

Fundamental

10

kHz

Fundamental

Measurement

System

Super—A

@

Characteristics

of

TIM

distortion

(Low

pass

filter

fe=100

kHz)

(dB}

3.18K

6.36K

9.54K

12.72K

15K

3.18K

6.36K

=

9.54K

=

12.72K

15K

19.08K

{He}

15.9K

(He)

15.9K

The

spectrum

of

input

signal

Output

signal

of

M-7050

(Same

as

input

signal)

af.

2

4

|

20K

100K

10

kHz

Fundamental

class

AB

3.18K

6.36K

9.54K

12,72K

15K

(Hz)

15.9K

An

example

of

TIM

distortion

(TIM

distortion

is

sum

of

components

less

than

15

kHz

which

showed

with

arrows.)

1g

O8K

TECHNICAL

DESCRIPTION

Super

A

power

amplifier

A

big

problem

has

remained

unsolved

in

the

progress

regarding

amplifier

technology:

how

can

class-A

operation

be

made

compatible

with

high

power

efficiency?

The

class-A

operation

is

best

in

terms

of

low

distortion;

its

critical

drawback

is

such

that

its

power

loss

is

greater

than

the

available

output

power.

Because

of

this,

class-B

amplifiers

have

generally

been

applied

for

power

amplification

because

they

offer

both

acceptable

distortion

and

power

efficiency.

However,

as

long

as

class-B

amplifiers

are

employed,

the

occurrence

of

crossover

distor-

tion

and

switching

distortion

is

inevitable.

Although

the

improvements

of

circuit

elements

have

realized

fairly

good

class-B

amplifiers,

when

their

values

of

distortion

are

referred

to,

the

‘‘nature”

of

distortion

is

still

detrimental

to

the

re-

produced

sound

quality.

To

solve

this

problem

by

improving

circuit

technology,

JVC

has

developed

its

new

‘’Super-A”’

power

amplifier.

The

Super-A

power

amplifier

consists

of

a

voltage

amplifier

stage

whose

distortion

is

minimized

by

compensating

for

the

non-linearity

of

semiconductors,

and

aclass-A

power

amplifier

stage

which

includes

a

bias

circuit

for

raising

the

power

effi-

ciency

to

such

a

degree

as

is

comparable

to

that

of

a

class-B

amplifier.

JVC’s

Super-A

power

amplifier

offers

the

following

features:

1)

Power

efficiency

is

extremely

high

despite

the

class-A

operation,

greatly

reducing

power

loss

and

heat

generation

compared

with

conventional

class-A

amplifiers.

2)

Switching

distortion

inherent

in

class-B

operation

is

com-

pletely

eliminated;

it

is

perfectly

zero.

3)

AVecE

distortion

*1,

ACob

distortion

*2

and

A

Vpe

dis-

tortion

“3

are

all

extremely

low

because

of

the

unique

non-distortion

circuit

configuration.

“1

Distortion

caused

by

non-linear

variations

of

current

gain

B

due

to

variations

of

collector-emitter

voltage

VCE.

*2

Distortion

caused

by

non-linear

variations

of

amplifier

gain

which

are

caused

by

non-linear

variations

of

feedback

capacity

Cob

due

to

variations

of

collector-emitter

voltage

VCE.

*3

Distortion

caused

by

non-linear

variations

of

base-emitter

voltage

VBE

of

power

transistor.

Distortion

of

measurement

system

Distortion

of

‘“Super—A”

Fig.

1

Output

and

residual

distortion

waveforms

of

measur-

ing

instrument

Fig.2

Output

and

distortion

waveforms

of

Super-A

am-

plifier

Fig.

3

Output

and

distortion

waveforms

of

class-AB

ampli-

fier

Voltage

amplifier

stage

utilizing

‘‘Super-A”’

performance

to

the

utmost

Fig.

4

shows

operating

characteristics

of

a

common-emitter

transistor;

8

varies

as

VCE

varies,

resulting

in

A

Vce

distortion

as

described

above.

Fig.

5

shows

a

variation

of

the

feedback

capacity

Cop

in

re-

lation

to

VCE.

This

non-linear

variation

of

Cop

due

to

varia-

tions

of

VCE

causes

a

non-linear

variation

of

the

amplifier

gain,

leading

to

the

A

Cob

distortion

mentioned

above.

Fig.

6

shows

operating

characteristics

of

a

common-base

transistor.

What

is

noteworthy

about

this

type

of

operation

is

that,

though

its

current

gain

is

O

dB,

its

output

linearity

in

constant-

current

drive

is

fairly

good

since

a

scarcely

varies

with

varia-

tions

of

VcE

(a=

1)

as

shown

by

the

equal

distance

between

adjacent

base

current

curves.

An

example

of

the

cascode-connected

amplifier

circuit

is

shown

in

Fig.

7.

The

features

of

this

circuit

are

good

frequ-

ency

response

(because

of

no

mirror

effect

due

to

Cob)

and

high

output

impedance.

This

means

that

this

circuit

eliminates

distortion

by

effectively

combining

the

advantages

of

common-emitter

and

base-emitter

configurations.

The

driver

stage

of

the

Super-A

power

amplifier

employs

an

applied

circuit

of

this

kind

and

a

drastic

reduction

in

distoriton

is

the

result.

Fig.4

Output

characteristics

of

common-emitter

amplifier

Fig.5

Cop

characteristic

Fig.6

Output

characteristics

of

common-base

amplifier

Fig.

7

Cascode

amplifier

Distortion

of

‘‘class

AB”

f=10

kHz,

THD=0.0008%

Fig.

1.

f=10

kHz,

Output

power=100W/8

QO,

THD=0.0009%

Fig.

2.

9

f=10

kHz,

Output

power=100W/8

Q

THD=0.0022%

Fig.

3.

IB1

Vee

Fig.

4.

Emitter

Configration

Vcs

Fig.

6.

Base

Configration

SPECIFICATIONS

Circuitry..........

Direct-coupled

DC

circuitry

with

F.E.T.

cascode

connected

double

differential

input

and

parallel-push

pull

output

SUPER-A

Output

power.......

150W

+

150W

892

Total

harmonic

distortion.........

0.0004%

(1KHz

150W

8&2)

(Mesured

by

Y.H.P.

HP-1B)

0.003%

(20Hz

~

20KHz,

150W

822)

0.03%

(20Hz

~

100KHz,

150W-822)

Inter

moduration

distortion.........

0.003%

(60

Hz:

7

kHz=

4:

1,8)

Power

bandwidth

....5

~

100KHz

(0.02%,

892,

IHF)

TIM

(Transient

Intermodulation

distortion)

........

unmeasurable

10

Fig.

5.

Cob

characteristic

Slew

Rate

........

Switching

distortion.

.

Hum

&

Noise......

Frequency

charactor

.

Subsonic

Filter.....

Input

sensitibity/

impedance.......

Output

..........

Power

suply.......

Power

consumption.

.

Dimensions

.......

Fig.

7.

Cascode

amplifier

+300V/p

sec.

.0

less

than

200

pV

(Short

circuit)

.DC

~

100KHz,

+0,

—0.2dB

18Hz

6dB/oct

.1V

(input

level

volume

max)

/47KQ

more

than

120dB

(1.H.F.A)

200(1KHz)

882

speaker-1

4Q.~

16Q

speaker-2

4Q.~

160

speaker

142

801~

162

Monitor

phone

Refer

to

page

30

.

Refer

to

page

30

160

m/m

(H),

425

m/m

(W),

415

m/m

(D)

22.4

kg

(49.3

Ibs)