Nakamichi High Com II Service Manual

Nakamichi

Service

Manual

Nakamichi

High-Com

Noise

Reduction

System

II

CONTENTS

General

2.

Principle

2.

1.

Be

See

2.

3.

3.

Removal

3.414

3. 2 Botton

Xe

3. 4 Front

3. 5 Main

3.

6.

3. 7 Meter

3. 8 Power

3. 9,

3.10)

Adjustments

Mounting

6:

Ten

5. 2.

Mechanism

6

1,

6...2,

6..

3...

6

4,

Block

Diagram

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Pin

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Measurements

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9

1.

1.1.

The

1.2,

Voltage

This

GENERAL

Control

Nakamichi

1.

2.

3.

4,

5.

6.

7.

8.

Voltage

selector

voltage

Functions

High-Com

Peak-Level

Switch

Mode

Switch

Filter

Output

Level

Inout
Master

Jack

GND

Jacks

Line

Tr

Wasiaraknd

Selactor

is

installed

selector

II

Meters

Contro!

Control

Level

Input

sigtt~Coni 1 poles

can

select

control

Control

Reduction

on

the

either

functions

7

Syareon

rear

panel

120 V or

are

shown

Fig.

Fig.

for

other

220-240 V at

below:

1.1

Front

1.2

versions

View

Rear

View

of

customer's

the

40.
+1.

12,
13,

14.

15.

Line

9.

Rec,

Rec.

Play

Play

Line

Power

Nakamichi

disposal.

In

Out

Out

In

In

Out

Jacks

Jacks

Cal.

Cord

High-

Cal,

Jacks

Controts

Jacks

Controls

-Com

Il.

2.

PRINCIPLE

2.1.

High-Com

The

Nakamichi

furnished

10

Hz

Following

{a)_

Compression
expansion

input
expander.

{b}

Frequency
reduction

is

Coloration

(c)

priate

Further,

ing

Fig.

2.1

Operation

and

the

Line

input

input

level

variable

L.P.F.

With

this

frequency

Next

to

permit

MPX,

or

At

the

posed

Input
Level

with

subsonic

are

the

to

output

of

about

20

attack-time

special

disturbance.

shows

the

of

the

Filter

Switch.

signal

control

master

L.P.F.,higher

over

L.P.F.

are a MPX

the

selection

MPX/Subsonic

further

stage,

of

U401B

Master

OF

OPERATION

Hi

Noise

Reduction

High-Com

peak

level

filter

and a built-in

outline

of

(encoding)

(decoding)

is

2:1

is

divided

noise

and

to

25

dB.

of

sound

is

or

release

measures

block

diagram

High-Com

is

fed

through

for L or R channel

control

for L and R channels

frequency

audible

frequency

filter

of 4 different

with

it

has a compressor

ICs

and

*

System

Ij

is

a-noise

meters, a 19

400

the

High-Com

is

made

at

playing

in

compressor,

into

two

the

noise

eliminated

time.

are

taken.to

of

this

done

independently

is

and a subsonic

stages

the

use

peripheral

[aoa

Hz

Osc.

reduction

kHz

Hz

tone

II:

at

recording

back.

bands

of

reduction

by

means

keep:

the

High-Com

by.

the

and

simultaneously

over

22

eliminated.

of

Subsonic,

of

Filter

or

expander

circuits,

system

MPX

filter,

oscillator.

The

ratio

vice

versa

area

for

as a whole

of

off

iesits

lt.

Mode

Switch

separated

and

reaches

kHz,

i.e.,

filter

Switch.

that

and

of

in

the

saad

the

which

Off,

com-

permit’

a

:

-

the

selection

{Decode)

At

recording,

Compressed

Jacks,

meters

For

playback,

the

expanded

Out

Jacks

Preceding
amp,

Frequency

and

tower

these

two

compressor

Compression

amplifying

_

Controt

output

the

frequency.

Following

U401B

of

with

select

line

while

the

and

at

Line

and

input

band,

bands

or

or

rate

Resistor).

in

correspondence

shows

__

18,

Cat.

the

use

input

original

Out

select

play

peak

signal

is

by

are

the

expander,

expansion

of

the

18

400

Hz,

of

Mode

Rec.

with

signal

signal

Jacks.

Play

input

signal

level

meters.

will

divided

H.P.F.

either

compressed

amplifier

The

VCR

block

20

Rec.

the

with

reach
into

and

is

performed

through

is

with

diagram

22

(Encode),

Switch.

Mode

will

wilt

the
will

two

L.P.F.

varied

the

Switch.

appear

appear

Mode
appear

L.P.F.

bands,

respectively,

or

expencen

by

the

by

input

of

the

24

Pass,
;

at

at

Switch.

on

and

higher

the

VCR

the

signal

iC

Rec.

peak

both

H.P.F.

changes

(Voltage

level

level

U401B.

Output

or

Play

Out

level

Then,

Line

band

and

by

sensor

and

ia

via

the

of

Filter

Mode

1,

2.

3.

A.

A.

8.

Switch:

Subsonic

Ott

MPX

Subsonic / PX

Switch:

Cae.

Record

C.

Poss

OC,

Playbock

+

:

400H2

Ag
Bo

c

con

Fig.

2.1

:

High-Com

I!

Biock

Diagram

.

H

-

io

Rec.

Output

(1)

Compressor

Fig,

2.2

is

the

V1

sand

V2

designed

that

gains

of

V1

at a constant

sent

through

This

function

The

gain

of

same,

therefore

Jine,

comes

For

instance,

pressed

to

—20

This

compression

are

equat,

then

input

PO.

“40

Pa

out

are

Vi

basic

and

level

the

is

~40

each

(Encoding)

circuit

variable

of

V2

are

by

the

level

sensor.

shown

in

and

V2,

as

seen

to

be

1/2

dB

dB

at

output

principle

the

output

input

-30

gain

them

Fig.

SP1

in

of

input

Fig.

-20

of

so

made

control

the

the

P1.

is

P1

(dB)

are

the

and

2.2

compressor.

amplifiers,

keeps

the

that

of

2.3.
AP2,

figure,

output

gradient

at

input

very

simple.

will

always

“19

and

same

P2

the

feedback

remains

of

PO

wo

is

PO.

will

if

be

o

they

gains,

always

always

Pt,

V1

1/2

Output

(dB)

the

be

are

signal

and

of

The

kept

the

thick

com-

the

PY

so

V2

The

2.4

circuit
to

obtain

basic

is

shown

of

-40

Pr’

circuit

V1'

the

reciprocal

1“¥

Le

:

-30

j

of

in

Fig.

is

connected

Input

V1

Fig.

(dB)

-20

Po’

Fig,

and

2.6.1.

of

as

V2’

ve

y

2.5

V2

On

shown

>

2.4

gain,

-10

of

the

eee

Fig.

other

in

Level

Sensor

2.2

Fig.

re)

and

hand,

2.6.2

Output

(dB)

V2’

the

Po

PZ

of

Fig.

basic

in

order

ities

aR

TE , Soh

dele

ak

pre

ee

er

(2}

Expander

Fig.

2.4

_

Compressed

V2'

is

Level

level

P2’
Level
1/V

and

panded

obtained

‘This

two

times

at

input

Po:

is

the

similar

sensar

at a constant

sensor

therefore

by

at

output

is

shown

the

PT’

is

(Decoding)

basic

signal

to

V1

and

V2’

output

V1’,

and

in

Fig.

gradient

expanded

circuit

is

fed

and

operate

level.

is

given

the

compressed

subsequently

PO’.

2.5.

of

Fig,

of

to

V1‘

V2

Pt’.

to

—40

2.3

the

expander.

and

amplifiers

so

as

to

V1‘

Output

For

dB

V2’

from

of

to

keep

as

well.

input

the

PO’,

instance,

at

output

-40

P1’.

the

compressor.

output

Gain

P1’

will

original

the

thick

—-20

PO’.

of

be

signal

line,

dB

signal

V1‘

ex-

input

oe

eee

Zt

Vq=~—~——

V3

21+

Ze

is

Fig.

is

2.6.2

is

Input

signal

independently
expansion,

and

the

lower

band,

This

division

approximately

higher

band

but

Further,

in

each

ent

time

constants

rate

so

as

to

band

and

to

venting

the

tone

Fig.

2.7

indicates

this

chart

you

accordance

with

sion

to

lower

frequency.

But

quency

band

As

the

frequency

point

of

compression

the

recording

the

saturation

on

the

tape

deck,

From

the

chart

level.

vs

output

is

divided

separated
subsequently

so

of

two

by

20

also

of

are

reduce

improve

quality

the

can

see

the

frequency

you

that

no

goes

level

at

level

of

level

Rec,

Out

Level

(dB)

into

two

in

the

called

breathing

bands

dB

in

both

in

the

lower.

these

two

used

for

the

distortion

the

response

from

compression

the

changes

frequency,

and

more

will

see

compression

up

to a higher

shifts

to

the

higher

into

consideration

the

Fig.

2.8,

characteristics

bands,

performing

modification

noise,

results

in

bands,

band

as

bands

of

frequency,

controlling

of

the

middle

at

the

deterioration.

characteristics.

of

compression

for

instance,
compression

the

limit

at

is

made

value,

the

lower

frequency.

at

you

can

of

each

of

which

compression

in

is

intercepted.

noise

reduction

not

only

well.

the

amplifying

and

higher

band,

less

compres-
to

the

higher

below

the

operating

level

and

This

is

the

higher

read

the

compression

noise

in

differ-

lower

From

fevel

higher

—40

lowers

to

the

pre-

fre-

dB.

put

band

input

and

is

expansion,

or 3 kHz
at

vi],

si

in

Output

Level(dB)}

Pee

i

Sy

and

See ee,

Fig.

2.8

with

10

the

parameter

kHz.

;

ae

ee

Compression

(Decode)

for

example

Se

ee

Input

Level(dB)

(Encode)

Characteristics

on

and

50

Hz,

eG

Expansion

400

aN

Hz,

ey

'

:

20

50 © 100

200

500

1K

2k

OK

10K

20K

Fig,

2.7

Compression

Frequency

(Hz)

{Encode}

Characteristics

2.2.

Subsonic

The

frequency

covers

the

Hz

with a peak
determined
ance

of

the
resonance
eccentric

or

In

extreme

level

of

disc

occurs

when

back

to

the

the

subsonic

of

inter-modulation

unclean

sound

especially
cover

lower
unsteadily
mentioned

The

turntable,

to

completely

proved

turntable,

subsonics.

using

commercially

te

subsonic

attenuation

can

not

sufficiently

fault

to

attenuate

Hz}.

The

subsonic

the

new

active

filter

characteristic,

Fig.

2.9

shows

portion

represented

filter,

Its

characteristics

shown,

the

to

50

Hz,

These

demerits

High-Com

Filter

response

subsonic

by

the

cartrige

frequency,

warped,

cases,

the

record

the

cartridge

effect

from

affects

frequencies

during

adverse

cartridge

eliminate

One

solution

fitters.

curves

filteration

the

curve

and

attenuation

have

II

as

foflows:

-
of

range.

of 5 to
mass,

compliances

and

the

or

the

resonance

playback

vibration

via

air

thus

produced

distortion,

amplifier,

such

systems

{note
playback
effect

can

and

etc.

could
of

available

But

of 6 dB/Oct.

eliminate

the

low

filter

used

technology,

subsonic

by

FT

are

of

the

twin T filter

been

ordinary

The

resonance

15

dB.

tone

arm.

disc

record

turntable

frequency

signals

caused

or

floor

the

speakers

whose

that,

of

disc

be

produced}.

tone

arm

subsonics.

not

this

problem

preamplifiers

most

of

or

subsonics.

frequency

in

the

filter

of

is

generatly

illustrated

at

below 5 Hz

smartly

hi-fi

phono

These

and

Further,

vibrates

(the

by

the

vibration).

is

not

subsonic

or

response

if

the

records,

must

However,

completely

so

them

12

dB/Oct.,

band

High-Com

can

the

High-Com

known

in

Fig.

rapidly

eliminated

point

factors

damping

is

likely

abnormally.

increases

worst

speaker

found.

effect

tape

woofer

the

be

far

achieved

that

shows

And

{near

II,

realize

as a twin

2,

drops

is

rather

cartridges

is

near

are

resist-

near

the

to

to

the

condition

is

fed

Usually,

Because

causes

decks,

curves
moves
above-

improved

even

im-

eliminate

incorpora-

poor

and

they

they

have

30

to

based

an

ideal

II.

The

10

(1).

at

small.

by

the

10

be

It

is

40
on

T

As

20

As

amplified

terminal.

non-inverting

—

‘This

Hz.

R110

and

asymmetric

achieved,

Improvement
The

|

subsonic

Hz,

Besides

C108

curve

the

and

-

Improvement

shown

greatly

For

is

to

change

curve

the

and

as

CR

filter

(3).}

“104

1

ri

Ny

oO

-304

ATTENUATION

(dB)

~404

-504

in

by

This

reduces

greater

added

curve

shown

filter

High-Com

R112

shown

1:

Fig.

OP-amp.

output

input

to

the

2:

Addition

except

by

curve

Improved

2.9,

the

|C302

provides

of

1C302

the

level

attenuation

lower

the

impedance

as

shown

of

in

Fig.

insufficient

1I

to

achieve a more

Fig.

2.10

and

{4)

-

Posbtaree

aac

Foe

3 5 10

FREQUENCY

Fig.

Twin T Filter

output

from

and

taken

positive

through

down

in

in

the

load

impedance

of

each

by

Fig.

.

CR

Filter

2.10

(2)

is

attenuation

uses a CR

{4}.

(In

is a combination

:

20

iHz}

2.10

with

the

twin T filter

from

feedback

C107

the

range

range

below 5 Hz,

of

element

2.10

satisfactory

filter

consisting

ideal

subsonic

Fig.

2.10

of

+

70

Boot

its

and

so

(2)

at

(3)

curves

20

the

that

below

can

Strap’

output

to

R109.

to

filter

for

filter

shows

100

the

the

the

50

(2)

is

be

5

of

pea

Input

680OP{N

C107

ctrog

O.OSbut)

Output

Rit2
120K

}

Fig.

2.9

Subsonic

Filter

Circuit

a

2,3.

Mute

Output

transient

the

mute

mute

signals,

2.3.1.

Power

Transformer
smoothed
tiat

appears

is

in

the

negative

where

the

voltage}

result,

Q403

from + V

the

mute

ON,

2.3.2,

Power

Transformer

C401

is

the

level

0401,

0401

discharged.

Signal

signals

noise

circuit

ON

output

by

at

cutoff

potential

voltage

of

402,

to

—12

time

output

charged

where

turns

Thus,

are

muted

when

and

capacitor

C401

state,

through

across

O402

turns

V,

depends

OFF

with
the

from

0402

i

Output

for a certain

power

is

Fig.

2.12

is

rectified

C401.

(transistor

while

C402

R404

C402

turns

ON

and

releasing

on

C402

becomes

negative

voltage

OFF

is

cut

ON

or

OFF,

shows a timing

through

Therefore,

O401

base},

(47

uF)

(2.2

exceeds

from

the

mute

the

mute

and

R404

zero,

as a result

potential

across

C401

to

ON

and

off

and

Q403

Mute

0403

280945

time

Fig,

diode

positive

is

MQ).

Vbe

OFF

signal

state.

through

exceeds

C402

)4-7K

That

after

is

to

prevent

2.11

shows

chart

of

the

D402

and

poten-

is,

0401

charged

with

At

the

level

{base-emitter

to

ON,

As

is

changed

This

means

power

of

which

R403.

At

Vbe

of

is

quickly

also

cut

off.

+V¥

D403

:

C403

2208

25V

Fig.

2.11

The

mute

signal

voltage

becomes

positive

to

mute

output

signal.

D403

acts

to

discharged

easily

Power

ON

Switch

:

OFF

c4o1

C402

0402

Coliecfor

Mute

Output

2

1OVILN)

Circuit

Open

-12V

-12V

pas

we

me

+V

OV

ov———

0402

—

©

a

is

47

Mute

when

Oe

Fig.

power

Q402

SS

'

2.12

R40)
270K

Vbe

1

Timing

prevent + V

is

OFF..

———S

Chart

the

from

being

\

Q401

t

Vbe\,

1

=

=

!

Los

.