Bedienungsanleitung Marantz Model 2230 (Seite 15 von 19) (Englisch)

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generated by a local oscillator. This mixer converts

the carrier frequency to the 10.7MHz intermediate

frequency. Careful attention to its thermal and

electrical characteristics has minimized drift, thus

obviating the necessity for AFC. The 10.7MHz

converted signal is then fed to a phaselinear

ceramic IF filter, followed by an IC limiter. It is

then, in turn, processedthrough an FM discrimina-

tor. The output of the FM discriminator is fed to a

buffer amplifier which then drives the demodula-

tor.

IF STAGES

The IF section consists of four transistors and six

ceramic filters. The characteristics of this filter are

ideal in that the 200KHz passband is phase-linear,

with sharp cut-off slopes. Its exceptional phase

linearity assuresthe elimination of a major source

of high-frequency distortion and a loss of stereo

separation. The sharp cut-off slopes provide im-

proved selectivity, permitting reception of closely

spacedchannels.

LIMITER

The Model 2230 utilizes multi-stages (transistor

plus limiterdiodes and IC) limiter amplifier with a

very small dynamic symmetrical aperture, elimi-

nating the need for AGC circuit which introduces

low frequency distortion. Undesirable Amplitude

Modulation (AM signals, AM noise, AM distortion)

are removed from the IF signal within the limiter.

FM STEREO DEMODULATOR

The composite audio signal from the buffer am-

plifier is fed into the multiplex stereo demodulator

circuit consisting of 11 transistors and 6 diodes.

The 19kHz pilot signal contained in the composite

audio signal is doubled into 38kHz after two-stage

amplification and then the 38kHz signal is further

ampl ified to the level necessary to drive the diode

switching circuit. The composite audio signal is

split into the right and left channels by the 38kHz

switching signal in the diode matrix circuit. The

right and left channel audio signals are processed in

the crosstalk cancelling circuit which utilizes com-

plementary configuration with NPN and PNP

transistors. The audio signals are then fed into the

selector switch and the TAPE OUT jacks from

the low pass filters for filtering undesired 19-and

38kHz components and emitter followers for

10vI/

impedance output.

The stereo demodulator circuit has been designed

with the de-emphasis netlNOrk to provide flat

frequency response up to 15kHz. One hundred

percent air-tight coils and filters are incorporated

in the stereo demodulator circuit for improved

stabil ity and reiiability with good stereo separation

and frequency response. '

The multiplex stereo demodulator circuit has been

provided with an automatic stereo/monaural

switching circuit. The circuit checks the input

signal intensity and activates the stereo demodula-

tor circtlit and the stereo indicator lamp auto-

matically only when the input signal is powerful

enough to provide good quality stereo reception.

When t~e input signal strength is below the

threshold level, the FM stereo broadcast is process-

ed as monaural signal and improved signal-to-noise

ratio is obtained in this mode of operation.

MUTING CIRCUIT

In the absence of an FM carrier, all FM receivers

produce a peculiar noise. The muting circuit

eliminates this noise, providing you with noise-free

tuning from station-to-station.

A muting circuit, consisting of a two-transistor

noise amplifier and a three-transistor (including

one FET) switching circuit, has been incorporated

in the Model 2230. The muting circuit perfectly

mutes out all the ir'lterstation noise and also

completely mutes out the side slope spurious

response of the unit. The circu it has been designed

to minimize annoying "pop" noise for velvet

smooth tu ne in and tu ne out.

AM TUNER

The AM tuner portion of the Model 2230 has been

provided with a tuned RF amplifier incorporating a

three-section variable capacitor for improved

spurious responseratio.

The ceramic filter utilized in the AM IF amplifier

comes with high.er selectivity and wider bandwidth

for interference-free hi-fi AM reception.

Following the AM IF amplifier, the AM detector

recovers the audio modulation and provides this

signal to the selector switch.

The AM tuner and IF amplifier are subjected to the

action of an effective automatic volume control

circuit which maintains constant the level of all

stations in the AM band.

SELECTOR SWITCH

Your Model 2230 has the capability to operate

from a variety of program sources, e.g., AM or FM

broadcasts, turntable (PHONO), tape recorders

(TAPE) or any other source capable of providing

100 millivolts output level (AUX). The selector

switch connects the inputs of the TONE amplifiers

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Marantz Model 2230 Seite 15

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