Front End; Fm If Amplifier; Multipath Indicator; Fm Stereo Demodulator - Marantz 2210 Instructions Manual

FRONT END
FM antenna signals are applied through a balun
transformer and the antenna attenuator switch to
the antenna coil which drives a field-effect transis­
tor RF amplifier. When the ATTENUATOR push­
switch is placed in the "OUT" position, the attenu­
ator
circuit is cut off and FM signals are directly
fed to the FM antenna coil. With ATTENUATOR
switch placed in the "IN" position, the signals are
attenuated about 20dB by the
attenuator
circuit,
then fed to the antenna coil. The amplified signals
from the R F ampl ifier are fed through the triple­
tuned RF filter circuit to the FET Mixer stage,
which also receives the signal generated by the lo­
cal oscillator. This mixer converts the carrier frequ­
ency to the 10.7 MHz intermediate frequency. Care­
ful attention to its thermal and electrical characte­
ristics has minimized drift, thus obviating the neces­
sity for AFC. The 10.7 IVI Hz converted signal is then
fed to a phaselinear ceramic I F filter, followed by
an IC limiter. It is then, in turn, processed through
an FM discriminator. The output of the FM dis­
criminator is fed to a composite signal amplifier
which then drives the demodulator.
FM IF AMPLIFIER
The IF amplifier consists of 8 ceramic filters and 7
stages of I F amplifiers including limiter stages. The
characteristics of these ceramic filters are ideal in
that the 200KHz passband and phase linearity as­
sures the elimination of a major source of high fre­
quency distortion and loss of stereo separation. The
sharp cut-off slopes improve selectivity, permitting
reception of closely spaced channels. The Model
2270 utilizes symmetrical diode limiter cir­
cu its consisting of high performance Gold Bond
diodes and IC limiter amplifier with a very small
dynamic aperture. Thus, undesirable Amplitude
Modulation is removed from the I F signal within
the limiter and good capture ratio is also assured.
The amplified and symmetrically lim ited FM sig­
nalsarefed to the super-linear discriminator circuit.
The detected audio signals are, then, distr ibuted to
the QUADRADIAL jack, MPXDecordercircuit and
Noise Amplifier.
MUL TIPATH INDICATOR
The Multipath Indicator circuit is provided to aid
you to find the optimum antenna direction for a
desired station. Undesirable Amplitude Modulation
resulting from multipath reception is detected and
displayed on the multipath meter when the MUL­
TIPATH pushswitch is held "in". By orientating the
antenna for minimum meter deflection, minimum
multipath condition is obtained. The audible signals
detected are also fed to the Tone Amplifier through
the MULTIPATH switch, balance and volume con­
trol and the distorted sound due to the undesirable
Amplitude Modulation or the buzz-sound which are
proportional to the MULTIPATH meter deflection,
can be heard through the loudspeakers.
FM STEREO DEMODULATOR
The composite aud io signal from the composite
signal amplifier 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 amplified to the level
necessary to dr ive the diode switching circuit.
The composite audio signal is decoded 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 complementary
configuration with NPN and PNP transistors. The
audio signals are then fed into the selector switch
and the RECORD jacks from the low-pass filters
for filtering undesired 19-and 38KHz components
and emitter followers for low impedance output.
The stereo demodulator circuit has been designed
with the de -emphasis network 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
stability and reliability 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 demo­
dulator circuit and the stereo indicator lamp
automatically only when the input signal is power­
ful enough to provide good quality stereo recep­
tion . When the input signal strength is below the
threshold level, the FM stereo broadcast is processed
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 elimi­
nates this no ise, providing you with noise-free tun­
ing from station to station. A muting circuit, con­
sisting of all semi-conductor switching circuit inclu­
ding two EFTs, has been incorporated in the Model
2270. The muting circuit perfectly mutes out all
the interstation noise and also completely mutes
out the side slope spurious response of the unit.
The circuit has been designed to minimize annoying
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