If Stages; Limiter; Fm Streo Demodulator; Muting Circuit - Marantz 2230 Handbook Of Instructions

generated by a local oscillator. This mixer converts
the carrier frequency to the 10.7M Hz 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, processed through 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 I F 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 h igh-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 I F 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 rei iabil ity 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 u nit. 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 response ratio.
The ceramic filter utilized in the AM I F amplifier
comes with high.er selectivity and wider bandwidth
for interference-free hi-fi AM reception.
Following the AM I F amplifier, the AM detector
recovers the audio modulation and provides this
signal to the selector switch.
The AM tuner and I F 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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