Circuit Description; Signal Path - Pioneer SX-1010 Service Manual

CIRCUIT DESCRIPTION

SIGNAL PATH

1. The FM broadcast signal waveform from the
antenna is fed to the two dual-
field-effect transistors in the front end for
radio frequency amplification. This
converted into an intermediate frequency by
gate MOS FET mixer stage in com-
the dual-
signal from the local oscil-
bination with the
lator.
2. The
intermediate frequency signal
verted within the front end
ceramic filters and three ICs , where it is
tuned , amplified
, and detected
audio frequency (composite) signal.
The composite signal following detection is
fed to the 4 CH MPX terminal jack
multiplex decoder stage.
3. The multiplex decoder stage uses one IC for
three functions: to
posite signal into the left and right
, to
operate the automatic
stereo signals
mode switching between stereo/mono , and
stereo indicator lamp appro-
to switch the
priately.
The
decoding system uses a phase locked
loop (PLL) circuit , which assures continuous
stable operation and excellent
ration with low
susceptibility to external
as
car
noise (such
ambient temperature changes.
After decoding, the
transistors and one LC filter
residual carrier component (38kHz , 19kHz
and SCA) is rejected , and then to the audio
amplifier section.
4. The FM muting circuit consists effectively of
two circuits
, designed to reduce the pulse
noise which can so
muting circuit is operative.
The one circuit is an
corporated into the IC , so that the de-
modulated circuit is switched off and on in
, and the other short-
the IC
signal by means of a reed relay.
5. The AM tuner section
lithic IC which functions as radio frequency
amplifier
, frequency converter
lator , intermediate frequency amplifier , and
detector. The output is a pure
6. The signals which are applied to the MIC and
PHONO terminal jacks are selected by the
FUNCTION switch before being fed to the
first stage of the three-
direct- coupled equalizer amplifier by which
the signals are amplified.
In order to reduce the
circuit configuration employed enables the
potential at the input and output terminals
to be set at near zero volts.
gate MOS
signal is
, con-
, is fed to four
, becoming a
and the
demodulate the com-
channel
stereo sepa-
ignition noise) and
signal is fed to four
, where the
when a
easily arise
electronic switch in-
circuits the audio
employs one mono-
, local oscil-
audio signal.
stage differential
switch noise , the
It incorporates an
circuit in the first
amplifier whose DC supply uses twin plus
and minus.
7. The output from the
together with that from the
, the audio signal from the AM tuner
jacks
and the audio signal from the FM tuner
all selected by the FUNCTION switch
pass through the switch circuits for TAPE
DUPLICATE , TAPE MONITOR , 4 CH
ADAPTOR DOLBY NR ADAPTOR
the
BALANCE and VOLUME
circuits for
controls
, before being fed to the
amplifier.
8. The control amplifier has an extremely high
, using PNP and NPN tran-
input impedance
direct-coupled two-
sistors in a
This greatly reduces the influence of the
performance inherent in equipment
nected externally.
The output from
coupled circuit is
divided into two circuit
systems.
TONE switch via the twin
One goes to the
tone control circuit
directly and unmodified in any way .to the
TONE switch. The TONE switch
between them.
9. The amplifier section of the twin control has
closed loop NFB
amplifiers for both the
main and sub circuits
own transistor
, eliminating mutual
ference.
10. The control amplifier output is fed to the
power amplifier after passing through the
LOW FILTER , HIGH FILTER and AUDIO
MUTING circuits.
The first
stage of the power amplifier is a
differential amplifier element with constant
current load , and the second stage
a differential amplifier element
potential drift is prevented.
On the other hand
uses two power transistors in parallel in both
the upper and lower circuits
collector dissipation is possible.
Again
, in order to reduce the
which occurs at low
current has been set at a standard
100mA.
11. The power amplifier output is fed to
three push buttons which form
SPEAKER switch. This selects A
speaker system terminal connection.
If
all three speaker systems were to
connected
simultaneously, the
speaker impedance might be less than 4il.
To guard against this possibility, when all
three buttons are
three systems are
amplifier.
12. The power amplifier circuit board includes a
SX-
1 01 0
independent differential
equalizer
stage of the
equalizer amplifier
AUX terminal
, are
, and
, and
control
stage circuit.
con-
stage direct-
this two-
, and the other goes
selects
, each of which has its
inter-
, too
, uses
, so that DC
, the final output stage
, so that large
distortion
signal levels , the idle
level of
the
the
, B , and C
effective
depressed together
, all
disconnected from the