McIntosh MX 110 User manual

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CONTENTS

GENERAL

DESCRIPTION.

1

TECHNICAL

DESCRIPTION.

1

INTRODUCTION.

3

FM

ALIGNMENT.

4

MULTIPLEX

ALIGNMENT.

6

SCHEMATIC.

8

DIAL

STRINGING.

11

PARTS

LIST.

12

SPECIFICATIONS..

16

CHASSIS

LAYOUT.

.

18

OPERATING

CURVES.

20

M

AND

X

SERIES

SCHEMATICS.POCKET

2

CHAMBERS

ST.

BINGHAMTON,

N.Y.

WARRANTY

STATION

MX

110

SERVICE

MANUAL

nWntosh

mx

MX

110

TUNER

PREAMPLIFIER

GENERAL

DESCRIPTION

The

MX

110

combines

in

one

unit

an

extremely

low-distortion

preamplifier

with

a

highly

sensitive

FM

multiplex

stereo

tuner.

Every

desirable

feature

of

a

tuner

and

a

preamplifier

is

included

in

this

design.

Interstation

noise

suppression,

tuning

indicator,

FM

multiplex

indicator,

indi¬

vidual

channel

bass

controls,

individual

channel

treble

controls,

electronic

phase

switch

have

all

been

engineered

into

the

MX

110.

The

INPUT

SELECTOR

gives

you

a

choice

of

six

different

program

sources.

The

MODE

SELECTOR

is

a

newly

developed

control

which

makes

it

very

easy

to

balance

a

stereo

system.

It

is

designed

to

add

left

to

right

for

monophonic

operation,

to

control

the

left

to

right

stereo

perspective

or

to

compare

the

left

and

right

channels

of

a

stereo

program.

The

loudness

of

the

phono

channels

and

the

auxiliary

channel

may

be

balanced

to

the

TECHNICAL

The

radio-frequency

amplifier

of

the

MX

110

is

a

“cascode”

type

circuit.

The

circuit

is

specially

designed

to

amplify

weak

signals

with

less

noise

and

distortion.

By

carefully

tuning

this

RF

amplifier

during

manufacturing

and

controlling

other

circuit

constants,

spurious

response

rejec¬

tion

is

improved.

The

high-frequency

oscillator

mechanical

layout

is

engineered

for

minimum

response

to

temperature

variations.

In

fact

the

combination

of

mechanical

and

electronic

design

is

so

unusually

good

in

this

circuit

that

automatic

frequency

control

is

not

needed

in

the

MX

110.

The

mixer

output

is

amplified

by

four

inter¬

mediate

frequency

amplifiers.

The

transformers

used

in

the

I.F.

amplifiers

are

designed

for

max¬

imum

adjacent

channel

rejection,

for

electrical

stability,

and

for

electrical

and

mechanical

resistance

to

shock

and

vibration.

tuner

loudness.

These

adjusting

controls

are

located

on

the

top

of

the

MX

110

behind

the

front

panel.

By

releasing

the

PANLOC

buttons

on

the

front

panel,

you

can

slide

the

MX

110

out

of

its

mounting

until

the

second

latch

en¬

gages.

The

top

mounted

LEVEL

set

controls

are

now

available.

The

McIntosh

designed

PANLOC

system

is

the

first

professional

installation

technique

to

be

used

on

stereo

instruments.

The

PANLOC

sys¬

tem

gives

you

absolute

ease

of

installation,

operation,

and

maintenance.

The

McIntosh

MX

110

is

a

beautifully

engi¬

neered

control

center

for

the

finest

stereo

sound

systems.

The

extreme

care

in

manufacturing,

in

layout

design

and

in

thermal

engineering

prom¬

ises

the

usual

McIntosh

extra

values

of

reliability,

performance,

and

long

life.

DESCRIPTION

The

R.F.

and

I.F.

circuits

of

the

MX

110

are

completely

shielded

and

exceed

the

FCC

requirements

for

suppression

of

oscillator

radia¬

tion.

Either

a

300

ohm

or

75

ohm

antenna

may

be

used

with

the

MX

110.

A

VHF

television

antenna

which

is

suitable

for

FM

reception

can

be

connected

to

the

MX

110.

In

the

MX

110,

a

new

type

of

mechanical

tuning

assembly

gives

smooth

flywheel

tuning.

By

controlling

the

relations

between

mass

and

mechanical

resistance,

and

dividing

work

loads

in

the

dial

drive

system,

it

becomes

nearly

impossi¬

ble

to

detect

any

backlash.

Yet

the

entire

dial

drive

is

a

model

of

mechanical

stability.

For

smooth,

quiet

action

and

extended

life

with

virtually'

no

wear,

a

teflon

lined

dial

pointer

carriage

and

nylon

pulleys

are

used

in

the

dial

cord

assembly.

1

MULTIPLEX

DECODER

The

multiplex

decoder

uses

a

special

McIntosh

developed

detecting

circuit.

One

of

the

advan¬

tages

of

this

circuit

is

the

elimination

of

the

critical

adjustments

necessary

with

commonly

used

matrixing

methods.

This

circuit

detects

the

L+R

sidebands

and

automatically

matrixes

the

recovered

information

with

the

L+R

main

carrier

signal.

This

circuit

then

yields

the

left

and

the

right

program

with

maximum

separation.

A

temperature

stabilized

19KC

amplifier

locks-in

a

highly

stable

push-pull

synchronous

oscillator.

Apart

from

other

advantages,

this

method

provides

greatest

noise

immunity.

Bal¬

anced

detectors

cancel

the

38KC

component

in

the

output

and

insure

low

distortion.

A

three-section

sharp

cut

off

filter

rejects

SCA

interference

and

reduces

susceptibility

to

spuri¬

ous

signals.

The

MX

110

has

an

MPX

stereo

indicator

that

lights

when

the

dial

pointer

crosses

a

station

broadcasting

MPX

stereo.

A

unique

circuit

using

a

transistor

operates

the

MPX

stereo

indicator.

The

transistor

is

controlled

by

a

differential

detecting

circuit

that

amplifies

the

19KC

pilot

signal.

This

circuit

automatically

discriminates

between

the

19KC

signal

and

noise.

AUDIO

The

MX

110

audio

amplifier

consists

of

three

negative-feedback

amplifying

sections

in

dupli¬

cate

for

the

left

and

right

stereo

channels

and

a

separate

L+R

monophonic

amplifier.

The

first

section

in

each

channel

is

a

feedback

preamplifier

used

to

amplify

and

compensate

for

the

input

signals

coming

from

phonograph

pickups

or

tape

heads.

Level

set

controls

are

connected

into

the

output

circuit

of

this

preamplifier

section

when

the

INPUT

SELECTOR

is

switched

to

PHONO

1

or

PHONO

2.

These

controls

may

be

used

to

maintain

uniform

loudness

between

phono

and

tuner

inputs.

Skillful

layout,

grounding,

and

shielding

for

low-hum

pickup,

metal

film

resistors,

low-noise

tubes

and

extreme

care

in

manufactur¬

ing

combine

to

reduce

noise

and

hum

in

t

input

amplifiers.

octave)

rumble

and

high-frequency

filters

are

associated

with

this

section.

The

third

amplifier

section

is

a

two

stage

negative

feedback

amplifier.

The

variable

bass

and

treble

controls

are

included

in

the

feedback

loop

to

maintain

the

lowest

possible

distortion.

For

example

a

wave

meter

analysis

of

the

three

amplifier

sections

of

the

MX

110

shows

less

than

1/10

of

1%

distortion

at

3

volts

output.

The

MODE

SELECTOR,

balance

controls

and

left

and

right

outputs

are

associated

with

the

third

amplifier

section.

The

L+R

monophonic

amplifying

section

is

a

feedback

summing

amplifier.

It

supplies

mono¬

phonic

output

as

well

as

L+R

output.

The

second

amplifier

section

in

each

channel

is

a

cathode

follower.

The

sharp

cut-off

(18db

per

POWER

SUPPLY

The

power

supply

of

the

MX

110

has

received

very

special

design

attention.

Two

separate

rectifier

circuits

are

used.

A

full-wave

rectifier

supplies

D.C.

to

the

heaters

of

all

audio

stages.

A

bridge

rectifier

supplies

D.C.

to

the

anodes

of

the

audio

stages.

A

half-voltage

tap

on

the

bridge

rectifier

supplies

D.C.

to

the

tuner

stages.

This

elaborate

power

supply

design

insures

the

lowest

possible

background

hum

level

and

also

the

maximum

stability.

In

addition

to

this

care¬

ful

work

the

power

transformer

uses

special

magnetic

shielding

to

minimize

possible

hum

pickup

in

the

MX

110

as

well

as

in

any

other

equipment

used

with

it.

Hi

2

INTRODUCTION

All

McIntosh

tuners

are

carefully

aligned

and

tested

at

the

factory

using

the

finest

available

test

equipment.

All

McIntosh

tuners

will

meet

their

published

specifications

when

shipped

from

the

factory.

After

extensive

operation,

especially

when

tubes

have

been

replaced,

it

may

be

desirable

to

realign

the

tuner

circuits

for

best

performance.

This

manual

gives

complete

information

on

the

circuit

realignment

procedure

for

the

MX

110

tuner-preamplifier.

The

test

equipment

listed

below

(or

its

equivalent)

is

necessary

to

properly

align

an

MX

110.

The

accuracy

of

the

alignment

will

be

directly

related

to

the

accuracy

and

calibration

of

the

test

equipment

used.

FM

Signal

Generator

(Measurements

210A

or

equivalent)

VTVM

Multiplex

Generator

(RCA

WR-51A

or

equivalent)

10.7

MC

Generator

(Preferably

crystal

controlled)

Oscilloscope

(Hewlett-Packard

120B

or

equivalent)

Harmonic

Distortion

Analyzer,

desirable

but

not

essential—(Hewlett-

Packard

330B

or

equivalent)

If

the

necessary

test

equipment

is

not

available,

alignment

should

not

be

attempted.

You

may

contact

the

McIntosh

Customer

Service

Department

for

additional

information.

Customer

Service

McIntosh

Laboratory,

Inc.

2

Chambers

Street

Binghamton,

New

York

Our

telephone

number

is

723-5491

The

direct

dial

area

code

is

607

T

MX

110

FM

STEPS

TUNER

DIAL

SETTING

SIGNAL

GENERATOR

INDICATOR

FREQ

COUPLING

MODULATION

TYPE

CONNECTED

TO

Point

of

no

interference

or

signal

10.7MC

Through

external

.01

MF

cap

to

pin

7

of

12AT7

mixer

cw

VTVM

TP

#1

SAME

SAME

SAME

SAME

MX

110

tuning

eye

SAME

SAME

SAME

SAME

VTVM

TP

#2

or

(discriminator

output

on

"M"

series)

SAME

SAME

SAME

SAME

SAME

Pin

6

of

discriminator

transformer

105MC

105MC

300

ohm

antenna

terminals

with

*

matching

network

400

cycles

75KC

deviation

(100%

modulation)

VTVM

connected

to

TP1

and

scope

connected

to

L

or

R

audio

output

90MC

90MC

SAME

SAME

SAME

105MC

105MC

SAME

SAME

SAME

90MC

90MC

SAME

SAME

SAME

Point

of

no

interference

Scope

L

or

R

output

105MC

105MC

SAME

400

cycles

75KC

deviation

(100%

modulation)

attenuated

to

2.5

microvolts

output

VTVM

connected

to

TP

#1

and

Scope

connected

to

L

or

R

audio,

output

ANTENNA

MATCHING

NETWORK

FM

SIGNAL

GENERATOR

100

OHMS

-AAA—

-O

-AAA—

150

OHMS

TUNER

300

OHM

ANTENNA

°

TERMINALS

*

IF

SIGNAL

GENERATOR

HAS

OTHER

THAN

50

OHM

INTERNAL

IMPEDANCE,

USE

A

RESISTOR

OF

150

OHMS,

LESS

INTERNAL

GENERATOR

IMPEDANCE.

1

]

ALIGNMENT

ADJUST

TEST

LIMITS

REMARKS

Top

(secondary)

and

bottom,

(primary)

of

1st,

2nd

and

3rd

IF

transformers

Maximum

possible

negative

voltage

Shunt

to

ground

the

winding

not

being

adjusted

with

a

.01

MF

capacitor

in

series

with

a

1

K

resistor.

Attenuate

signal

generator

until

output

voltage

at

TP

#1

is

less

than

1.5

volts

with

one

IF

transformer

winding

shunted.

IF

transformers

have

terminal

#1

marked

with

a

green

dot

and

are

numbered

clockwise.

4th

IF

transformer,

top

and

bottom.

Eye

should

close

to

approx,

’/is”

with

strong

signal.

Make

additional

adjustments

of

eye

closure

by

varying

the

length

of

parallel

conductors

connected

to

pins

1

and

4

of

the

4th

IF

transformer.

(This

changes

the

capacitive

coupling

between

pins

1

and

4.)

Discriminator

transformer

upper

core

(secondary)

Adjust

for

0

volts

!

-

-

Discriminator

transformer

lower

core

(primary)

Maximum

negative

voltage

Repeat

step

3

if

a

large

change

is

made

in

the

setting

of

the

lower

core.

i

Oscillator

trimmer

cap.

Maximum

negative

voltage

As

output

increases,

attenuate

signal

generator

to

keep

maximum

output

at

TP

#1

to

less

than

2

volts.

Oscillator

coil

tuning

slug

SAME

Repeat

steps

5

and

6

until

dial

calibration

is

accurate.

j

Mixer

trimmer

and

RF

trimmer

SAME

1

|

Mixer

coil

tuning

slug

and

RF

coil

tuning

slug

SAME

Repeat

steps

7

and

8

until

output

is

as

high

as

possible.

Muting

adj.

control

Turn

muting

switch

to

"in''

position.

Adjust

muting

control

until

background

noise

just

disappears.

i

IHFM

sensitivity

2.5

microvolt

for

3

%

total

noise

and

distortion

Step

10

is

an

overall

sensitivity

check,

and

requires

a

distortion

analyzer

and

i

FM

signal

generator

with

attenuator.

With

2.5

microvolts

input

at

the

300

ohm

antenna

terminals,

TP

#1

voltage

should

be

.6

volts

or

more.

MX

IIO

MULTIPLEX

TUNER

SIGNAL

GENERATOR

_

INDICATOR

STEPS

DIAL

SETTING

FREQ.

COUPLING

MODULATION

TYPE

CONNECTED

TO

i

Point

of

no

interference

or

signal

Audio

generator

set

to

67KC,

0.5

volts

output

or

less

TP

H2

(MPX

input

on

"M"

series)

Audio

VTVM

Pin

6

of

38KC

transformer

(yellow

wire

connected

at

this

pin)

2

SAME

MPX

generator

with

19KC

pilot

attenuated

to

approx.

5%

level

(5%

level

is

14

of

normal

10%

level)

1

9KC

pilot

must

be

attenuated

for

correct

alignment

SAME

SAME

Pin

3

or

8

of

12AU7

MPX

oscillator

100MC

100MC

modulated

300

ohm

antenna

1

KC

100%

SAME

Pin

1

or

2

of

by

MPX

generator,

terminals

with

19KC

pilot

at

approx.

1000

normal

output

microvolt

signal

modulation

(34KC

deviation)

modulating

left

or

right

only

38KC

transformer

4

SAME

SAME

SAME

SAME

Audio

VTVM

and

scope

L

or

R

output

jack

5

SAME

SAME

SAME

SAME

SAME

SAME

6

SAME

SAME

SAME

SAME

SAME

SAME

7

SAME

SAME

SAME

Turn

off

1

KC

audio

modulation

SAME

SAME

8

SAME

SAME

SAME

Same

as

step

3

SAME

SAME

DECODER

ALIGNMENT

ADJUST

TEST

LIMITS

REMARKS

67KC

trap

Adjust

for

minimum

voltage

1

9KC

phase

coil

and

1

9KC

transformer

1.

Disable

local

38KC

oscillator

by

placing

a

jumper

wire

across

6.8K

resistor

connected

to

pins

1

and

6

of

12AU7

MPX

oscillator.

2.

Shunt

pin

2

of

19KC

transformer

to

ground

with

.01

capacitor

in

series

with

1

K

resistor.

3.

Adjust

19KC

phase

coil

for

maximum

output.

Proper

adjustment

places

core

approx.

%"

from

bottom

of

coil

form.

4.

Adjust

lower

core

of

19KC

transformer

for

maximum

output.

5.

Shunt

pin

3

of

19KC

transformer

to

ground

with

.01

capacitor

in

series

with

1

K

resistor.

6.

Adjust

upper

core

of

19KC

transformer

for

maximum

output.

7.

Remove

jumper

used

in

step

1

above.

38KC

transformer

bottom

core

Adjust

for

maximum

voltage

38KC

transformer

upper

core

Adjust

for

stable

scope

display

1.

Turn

off

19KC

pilot

on

MPX

generator.

2.

Adjust

upper

core

of

38KC

transformer

to

obtain

a

stable

and

uniform

1

KC

signal

scope

display.

This

adjustment

may

be

critical,

so

turn

core

very

slowly.

3.

Turn

19KC

pilot

back

on.

19KC

phase

coil

30db

separation

or

more

Modulate

left

channel

and

measure

right

channel

output.

Adjust

19KC

phase

coil

for

minimum

right

channel

output

(maximum

separation).

Remove

all

test

leads

from

TP

#2

for

separation

checks.

SAME

Modulate

right

channel

and

measure

left

channel

output.

Separation

in

steps

5

and

6

should

be

at

least

30db

This

step

checks

the

rejection

of

19KC

and

38KC

frequencies.

Residual

output

should

be

at

least

40db

below

modulated

output.

1

'

'

.

Check

for

MPX

indicator

light

1.

MPX

light

should

turn

on

with

MPX

signal

2.

Tuning

slowly

across

dial,

MPX

light

should

turn

on

only

with

MPX

signal.