Bedienungsanleitung Marantz Model 2245 (Seite 17 von 28) (Englisch)

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generated

by a

local oscillator. This

mixer

converts

the carrier

frequency to the

10.71\,4H2 intermediate

frequency. Care{ul

attention

to its

thermal and

electrical characleristics

has minimized

drift,

thus

obviatinq

the necessity

for

AFC.

The 107[,4H2

converted

siqnal

is lhen

fed to a

phaselinear

ceramic

Jilter,

followed by an

lC limiter. lt is

then,

t.rn,

processed

lhrouqh dn

FIVI

drqcrim;na_

1or. The

output

of the

Fl\4 discriminator

is fed to a

buffer

amplifier

which then

drives the demodula

tor,

IF STAGES

The

lF section

consists

four traosistors

and

sax

ceramic

filters. The

characteristics

o{ this

filter

are

ideai

in thal

the 200KHz

passband

phase

linear,

with

sharp

cut-of{

slopes.

lts exceplional

phase

lineariry ässures

the ellminalion

ä malor source

high'{requency

distorlion

and

a loss o{

stereo

separation.

The

sharp cutoff

slopes

provide im

proved

selectivity,

permitting

reception

of closely

spaced

channels,

LI I\4ITE R

The l\,4odel

2245 utilizes

multi-staqes

(transistor

plus

lam;ter

diode and

lC) limiter amplifier

with a

very small

dynamic

symmetrical

aperture,

elirni_

nating

the need

for AGC circuit

which introduces

low

{requency distortion.

Undesirable

Amplitude

Modulalion

(AM

signals, AN,4

noise, AI\4 dislortion)

are

removed

frorn the

signal

wilhin the

limiter.

FIM STEREO

DEIV]ODULATOR

The composite

audio signal

{rom

the

bLrffer am-

plifier

is {ed inlo

the multiplex stereo

demodlllator

circuit consisting

of 11 transistors and 6

diodes.

lhe

l9lP1

pilot

siqaal conldin.d

Lhe

composrte

audio

signal is doubled

into 3BkHz after

two stage

amplification

and

then the 3BkHz signäl

is further

amplified

to the

level necessary

to drive the diode

switchinq

circuit. The composite

audio signal

split

into

the right

änd left channeis by the 38kHz

switch;ng

signal in

the diode matrix circuit.

The

right and

left channel audio

signals are

processed

the crossralk

cancellinq circuit

which L]tilizes com

plementary

configuration

with NPN and

PNP

transistors.

The audio

signals are then

{ed into the

selector

switch

anand the TAPE OUT

jacks

from

the low

päss

Jilters

for filtering undesired 19

and

3BkHz

components

and enritter

followers for low

impedance

oulput.

The stereo

demodulator circuit

has been designed

with the

d+emphasis

net\,vork to

provide

flal

frequency

response up to

15kHz.

One

hundred

percent

air'tight

coils and

filters

are

incorporated

the

stereo

demodulator circuit

for improved

slabilitv

and

reliabilitv with

good

stereo

separation

and

frequencv

response.

The multiplex

stereo

demodulator circuit

has been

provided

with an

automalic

slereo/monaural

switching

circuit.

The circuil

checks

the

input

siqnal

intensity

and aclivates

the stereo

demodula

tor circuit

and

the stereo indicator

lamp aulo-

matically

only

when the

inpul signal is

power{ul

enouqh

provide

good quality

stereo

reception.

When

the

input signal

strength is below the

threshold

level,

the FM stereo

broadcast is

process_

ed as

monaural

signal and

improved signal-to_noise

rätio is obtained

in this mode of operation.

IIIUTING CIRCUIT

ln rhp dbsence

ol dn FI\4 carrier, dll

f[4

recpivers

produce

peculiar

noise. The

mutinq

circuit

elirninates

this noise,

providinq

vou

with noise-free

tuning

from slation-to

station,

A muring circuil,

consistinq ol a two trdnsistor

noise amplifier

and a thre+transistor

{including

one FET) switching

circuit, has been incorporated

in the

lvlodel 2245. The muring circuit

perfectly

mutes out

all the interstation noise and also

complptely

mules oul thp side slope spurious

response

the

unit. The circuil has been designed

to minimize

annoying

"pop"

noise

for velvet

smooth

tune in and

tune out.

AM TUN ER

The Al\4 tuner

ponion

of the l\,4odel 2245 has been

provided

with a tuned

RF ämplifier incorporaling a

three-section

variable capacitor

for improved

spurious

response ratio,

The

ceramic

filter

utilized

in the Al\.4

ampliJier

comes

with higher selectivity

and wider bandwidth

for interference

{ree hi{iAI\l reception.

Following the

A[,4 lF amplif ier, tl're

Al\,4

detector

recovers

the audio modulation

and

provides

this

signal

to the

selector switch.

The Al\4

tuner and lF amplifier are subjected

the

action of an effective aulomalic

volume

control

circuit

which

maintains constant the

level

of all

stations

the Al\,4 band.

SELECTOR

SWITCH

Your

l\,4odel 2245

has the cäpability to operate

from a

variety of

program

sources, e.9., AM or

broadcasts,

tlrrntable

(PHoNoi,

tape recorders

(TAPE)

anv other source

capable of

providing

IOO

millivolts

output

level

(AUX).

The selector

switch

connects

the

inputs oJ the TONE amplifiers

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Marantz Model 2245 Seite 17

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