Technical Description; General; Functional Description; Front End - Marantz 4300 Owner's Manual

TECHNICAL DESCRIPTION
GENERAL
Figure 14 is a block diagram of the model 4300
Stereo 2
+
Quadradial 4 Receiver showing main
functional elements and input and output signal
routing. PHONO INPUT jacks are provided for
the front pair of channels.
FUNCTIONAL DESCRIPTION
FRONT END
FM antenna signals are applied through a balun
transformer to the antenna coil which drives a
field-effect transistor RF amplifier. The signals
from the RF amplifier are fed through the double-
tuned RF tank circuit to the
F
ET Mixer stage,
which is also fed by the signal generated by a
local oscillator. Carefu I attention to its thermal
and electrical characteristics has minimized drift,
thus obviating the necessity for AFC. The 10.7
MHz converted signal is then fed to a phase-linear
ceramic
I
F filter, followed by the limiter. The
output of the FM discriminator is fed to a buffer
amplifier which then drives the demodulator.
IF STAGES
The IF section consists of six transistors and
three stages of dual element ceramic filters.
The characteristics of these filters are ideal in that
the 200KH.z. passband is phase-linear, with sharp
cutoff slopes. This exceptional phase linearity
assures the elimination of a major source of high-
frequency distortion and a loss of stereo separa-
tion. The sharp cutoff slopes provide improved
selectivity, permitting reception of closely spaced
channels.
LIMITER
The Model 4300 utilizes symmetrical diode limit-
er circuits consisting of high-performance Gold
Bond Hot Carrier type diodes and I F limiter
amplifier with a very small dynamic symmetrical
aperture, eliminating the need for an AGC circuit
wh ich introduces low frequency distortion. Un-
desirable amplitude modulation (AM signals, AM
noise, AM distortion) are removed from the IF
signal within the limiter.
FM STEREO DEMODULATOR
The stereo composite signal obtained from the
buffer amplifier is first led to the FET muting
circuit; then to the phase locked loop stereo
demodulator IC circuit and decoded into both
left and right channel signals. Each left and right
channel signal is then applied to the 16KHz low
pass filter (LPF) and de-emphasis networks to
remove the undesired switching carrier signal in
the audio signals. Next, each audio signal is ap-
plied to the audio amplifier consisting of NPN·
PNP direct-coupled transistors and amplified to
the required signal level of about 775mV RMS.
Finally, each amplified signal is led to the
SELECTOR Switch.
The multiplex stereo demodulator circuit con-
sists of a phase locked loop
Ie
and is equipped
with a separate automatic Stereo/Monaural switch-
ing circuit. The circuit checks the input signal
intensity and actuates the stereo demodulator
and stereo indicator lamp automatically, when the
input signal is of sufficient strength to provide
high quality stereo reception. When the input
signal intensity is insufficient for this purpose,
the stereo signal is automatically changed to a
monaural signal to insure reception with a high
quality signal-to-noise ratio.
MUTING CIRCUIT
In the absence of an FM carrier, all FM receivers
produce inherent noise. The muting circuit elim-
inates this noise, providing noise - free tuning
from station to station.
A muting circuit, consisting of a two-transistor
noise amplifier and a three-transistor (including
FET) switching circuit, has been incorporated
in the Model 4300. The muting circuit perfectly
mutes out all the inter-station noise and also com-
pletely mutes out the side slope spurious response
of the unit. The circuit has been designed to
minimize annoying "pop" noise for velvet smooth
tune-in and tune-out.
AM TUNER
The AM TUNER portion of the 4300 is compos-
ed of one IC circuit (including RF amplifier,
local oscillator, mixer, IF amplifier, detector and
a signal strength indication amplifier) and one
transistor amplifier to amplify the detected audio
signals. A three-section variable capacitor im-
proves spurious response ratio.
The ceramic filter utilized in the AM IF amplifier
comes with high selectivity and wide band-
width for interference-free hi-fi reception.
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