Pioneer SX-3800 User manual

Sefvice nual
FM Ouartz Locked
STEREO
RECEIVER
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MODEL
SX.38OOCOMES
INFOUR
VERSIONS
DISTINGUISHED
AS
FOLLOWS:
Type Volt4e Remarks
KU 120Vonly U.S.A.model
s/G 1
10V, 120V, 22QV,
and
240V (Switchable) U.S.Militarv model
s110V, 12OV,
22OY
, and
24OV(Switchabte) General
exDortmodel
KC l20V only Canada
model
r This
servicemanualisapplicable
to theKUtype.
When
repairing
the
S/Gand
SWpe,
please
see
theadditional
servicemanual
lp 47 -p571.
Whenrepairing
theKCtype.
olease
seethea-
dditional
service
manual
(ART-519).
CONTENTS
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1.SPECIFICATIONS
2, FRONT PANELFACILITIES
3. BLOCKDIAGBAM
4. CIRCUITDESCRIPTIONS
4.1 FM Tuner
4.2 AMTuner
4.3 Display
Circuit
4.4 EqualizerAmplifier
4.5 ToneControl
Amplifier
4.6 Power
Amplif
ier
. . .
4.7 Power
Indicator
Circuit
4.8 Protection
Circuit
DISASSEMBLY....
PARTS
LOCATION
DIALCORD
STRINGING
ADJUSTMENTS
8,1 FM
Tuner
8.2 AMTuner 22
8.3 PowerAmplifier... 23
8.4 FL Indicator
Circuit 24
9. EXPLODED
VIEW 25
10.
SCHEMATIC
DIAGRAM,
P.C.
EOARD
CONNECTION
DIAGRAM
ANDPARTS
LIST
10.1 Schematic
Diagram 3l
10.2 P.C.
Board
Connection
Diagram 35
10.3PartsList ...,...41
11.PACK|NG.... 46
ADDITIONAL
SERVICE
MANUAL
I.SPEC|F|CAT|ONS .....47
2. CONTRAST
OFMISCELLANEOUS
PARTS
. . . . 48
3. SCHEMATIC
DIAGRAM,
P.C.
BOARD
PATTERNS
ANDPARTS
LIST
3.1 SchematicDiagram 49
3.2 SwitchAssembly
{AWS.148) 57
5.
1
8.
3
5
7
I
o
o
12
12
12
14
14
16
17
19
20
e

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1.
SPECTFTCATIONS
Power
AmplifierSection
Continuous
Power
0utputof60watts*
per
chan-
nel,
min.,
atSohmsfrom
20Hertzto20,000
Hertz
with
n0m0rethan0.005%total
harmo'
nicdistortion,
Total
Harmonic
Distortion
(20
Hertzto 20,000
Hertz,
I ohms)
continuous
rated
power
output . . Nomorethan
0.005%
30
watts
per
channel
power
outputNomorethan0.005%
Intermodulation
Distortion
(50
Hertz:7,000Hertz
=
4 : 1)
continuous
rated
power
output Nomorethan 0.0057o
30
watts
per
channel
power
outputNomore
than0,005%
Frequency
Response
. . . . . 5 Hertz to 200,000
Hertz
l! OA
lnput
Sensitivity/lmpedance
(POWER
AMP
lN)
or,rri 1v/50
kilohms
Speaker A,B,A+B
"-: ::::"::'': 1*:": 1o
i* He*z'
8
0hms)
Hum and
Noise
(lHF, short-circuited,
A network)
115d8
Preamplifier Section
Input
(Sensitivity/l
mpedance)
PHONO 2.5mV/50
kilohms
AUX,TAPE
PLAY
1,2 . . .. . . . 150mVl50kilohms
Phono
Overload
Level
{T.H.D.0.005%,
1,000
Hertz)
PHONO .. .. . 250mV
Output
(
Level/l
mpedance)
TAPERECI,2
.. ..,. 150mV
PREAMP
OUT
(Rr_:
50
kilohms)
-....1V/l kilohms
{Volume:
max.}
Total
HarmonicDistortion
(20
Hertz
to 20,000
Hertz)
ToneControl
BASS. tSdB
(100H2)
TREBLE ..... r',l0dB(10,000H2)
Subsonic
Filter
. 15Hz
(-6dB/oct.)
Loudness
Contour
(Volume
controlsetat *40d8 position)
. . . . +6dB
(100H2),+3dB
(10,000H2)
Hum
and
Noise
(lHF,
short-circuited,
A network)
PHONO. .....82d8
AUX,TAPEPLAY
1,2..,. .
.
. 11OdB
Attenuator. ....-20d8
FM
TunerSection
PHONO
(REC
OUT)
AUX,TAPE
PLAY
1,2. .. .
.
.
Frequency
Besponse
PHONO
(RIAA
Equalization)
or", iori ,ro" i
,';'o^u"' to20'000
Hertz
t0'2dB
UsableSensitivity
(lH
F
)
50dB
OuietingSensitivity
MONO
STEREO
Signal-to-Noise
Ratio
MONO
STEREO
Distortion
(at
65dBf)
MONO l00Hz.
lkHz.
6kHz .
STEREOIOOHz.
lkHz .
6kHz -
Capture
Ratio.,
Alternate
Channel
Selectivity
400kHz ..,..,7ft8
StereoSeparation
1kHz. ......45d8
30H2to15kH2. ...... 35dB
Frequency
Response ....2}Hzto15kHz1!loe
SpuriousResponse
Ratio, . . . . . . 65dB
lmageResponseRatio ... 65dB
lFResponseRatio.. .... 90dB
AMSuppressionRatio ... 55dB
SubcarrierProduct
Ratio. . . . . . . 50dB
SCARejectionRatio .... 64dB
MutingThteshold 19.2dBf
(5pV)
Antenna
lnput . 300ohmsbalanced,
75
ohmsunbalanced.
10.3dBf
{1.8itv)
16.2dBf
(3.6sV)
37dBf
(39pV)
83dB
(at
65dBf)
78dB
(at
80dBf,
0.1o/o
a.a7%
0.15%
O.2Yo
0.15%
0.25%
r.odB
No more than0.005%
{10V
output}
Nomorethan
0.005%
(10V
output)
7Hz
to
8o,0oo
Hertz
]f aa

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AM Tuner Section
Sensitivity
(lHF,
Ferrite
antenna).
. 300pV/m
{lHF,
Ext.antenna}
. . . 15pV
Selectivity .....30d8
Signal-to-NoiseBatio .... 50dB
lmageResponseRatio ... 40dB
lFResponseRatio.. .... 40dB
Antenna .... Ferritelooostickantenna
Audio Section
Output
(
Level/l
mpedance)
FM(100%Mod.). ..... 650mVl1 kilohms
AM(3O%Mod.)
. ..... 200mV/1kilohms
Semiconductors
fCs... .......17
FETs. .......6
Transistors ...,.71
Diodes .......58
Miscellaneous
PowerRequirements .... ACi20V,60Hz
PowerConsumption. ... 200W(ULl
Dimensions ....506{W}
x164{H)x
434{D}mm
19-15116(W)
x6-7/16
(H)
x 17-1116(D)
in
Weight
(withoutpackage) 16.2k9
(351b
12oz)
Furnished
Parts
Operatinginstructions
. . . . . . . . . 1
FMT-typeantenna ..... I
* Measured Dursuant to the Federal Trade Commission's Tnde
Regulation rule on Power Output Claims for Amplif iers,
NATE:
Specifications and the design subject to poisible modifications
without notice due to improvements.

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2.
TRONT
PANEL
FACILITIES
c POWER
SWTTCH
Setthisswitch
to ONto supply power
to thereceiver.
There
will be
a short
delay
when
it is
set
to ON,
because
the muting
circuit hasbeen
actuated
to suppress
the
unpleasant
noise
that issometimesgenerated
when
the
power
is
switched
on
and
off
.
O spERrER
swtrcHEs
Depress
the switch
corresponding
to the speakers
con-
nected
to the
SPEAKERS
terminals
(AorB)
ontherear
panel.
You candepress
both of these
buttons
to listen
to the
sound
from two pairs
of speaker
rystems
at the same
time.
@ gnlcHrNEss sELEcroR
Use
this switch
to select
the brightness
of the power
meter
and
the
frequency
displav.
BRIGHT: When
using
thereceiver
indaylight
orother
DIM: brightlocations.
At night
or in
dark
locations
when
the
exist-
ing
brightness
is
toohigh.
CI POWER
METER
This
meter
allows
you to read
out therated power
level
on the fluorescent
display
tubewhen
speakers
with a
nominalimpedance
of g ohms are connected
to the
speaker
terminals.
@ orel PoINTER
This
pointer
indicates
the
broadcasting
stations.
@ bunnrz
LocKED
tNDtcAToR
This
indicator
lights
upafter
theoptimum
tuning
point
has
been
obtained
anddisplays
that
thereceiving
stateis
stabilized
bythe
built-in
quartz
lock
circuit.
O TTU
STEREO
INDICATOR
This indicator
lights
up when receiving
an FM stereo
program
if theFM
muting
off switch
is
released.
,o SIGNAL
INDICATOR
Thisindicator
lights
in sequence
from left
through
right
during
thetuning
of anAM or FM broadcast
in
accord-
ancewith the strength
of the signals
being
received.
The optimum tuning point is where
the maximum
number
of indicators
light.
@
rururruc
tNDtcAToR
When
tuningin an FM station,
theoptimum
reception
point is indicated
when
the center
indicator
lights
up.
When
the left indicator
has
come
on.rotate
thetuning
knob
slightly
clockwise.
When
theright
indicator
comes
on,
rotate
theknob
slightly
counterclockwise-
@ rnEouENCY DTSPLAY
Thisindicates
thefrequency
which
is
tuned.
With FM reception,
theletters
,,FM.,
appear
on the
left
of thedisplay
and
',MHz,'
onthe
right.
With
AM recep.
tion,
"AM" appears
onthe
left
and
,,kHz..
on
theright.
These
change
when the function selector
position
is
changed.
0 rururruc
KNOB
Use
thisknob
to tune
into broadcasting
stations.
c} FM
MUTTNG
OFF
SWTTCH
When
this
switch
isreleased
and
an
FMbroadcast
tuned
in,
themuting
circuit
is
activated
inside
to suppress
the
annoying
interstation
noise
between
the broadcasting
frequencies
for noise-free
reception.
When
thebroadcast-
ingstation
isfar away
or when
receiving
a station
in a
fringe
area,
setthe
switch
to theOFF
position
and
then
tune in. lf there
is
a broadcasting
station
with a strong

r--
signal
level
on the airnextto astationwhose
program
you wantto receive.
you may not be ableto tune in
satisfactorilv
becausethe soundwill be drowned
out
by the strongersignals. ln caseslikethis,
setthe FM
MUTING
OFF switch
to OFF
{depressed
position)
and
tunein. The mutingcircuit
doesnot workwhen
the
tuner is receivingAM broadcasts.lf tuninghasbeen
performed
aftertheFM MUTING
OFF switchhas
been
depressedand a stationselected,the quartz locked
circuit is set to the OFF mode
and the LOCKED
indicator
does
not
light.
{"} FUNCTTON
SELECTOR
Depressthe function
switch
whichcorresponds
to the
program
source.Turn the volume
control down first
beforeselectinga differentfunctionswitch whilethe
sound
fromone
program
sourceis
being
reproduced.
FM:
AMr Depressthis
switch
for FMbroadcasts.
Depress
thisswitchfor AM broadcasts.
AUX: Depress
this switchwhen listening
to an
audio componentconnected
to the AUX
jacks.
PHONO: Depressthis switchwhen
playing
a record
on the turntableconnected
to thePHONO
jacks.
NATE:
Only one function swirch should be deplessedat a time.
@volunnEcoNTRoL
Use this control to adjustthe output levelto the
speakersand headphones.Turnit clockwiseto increase
theoutput
level
. No soundwill beheardif you setitto
"o."
(} MUTING
SWITCH
Setthisswitchto the*20d8 position
to attenuate
the
audio
output by 20d8.
There
is no needto adjust
the
volumecontrolif you thisswitchwhenturningdown
the
audiooutput
temporarilyand
when
changingover
records
ortapes.
LOUDNESSSWITCH
When listeningto a performance with the volume
control
turned
down,depressthis switch andthe bass
andtreble
willbeaccentuated.
Whenthevolume
islow,
the
humanear
finds
itharder
to
hear
thebass andtreblethanwhenthe
volumeis
high.
Theloudness
switch
is
thus
designed
to compensate
for
this
deficiency.By depressingthisswitch,thebassand
treblecomethrough
much
morestronglyandthesound
takes
on a punch
evenwhen the volumecontrolis
turneddown,
@ gRl-Rr\cE
coNTRoL
Use
thiscontrolto balancethe volume of theleftand
rightchannels.
First,however,set
the modeswitch
to
MONO. lf thesoundappears
to belouderon theright,it
meansthat the volume of the right channel
is higher.
Turn the balancecontrol to the left and adjust.Con-
versely.if the soundappears
to be louder
on the
left,
it
meansthat the volume of the left channel is higher.
Therefore, turn the balancecontrol to the right and
adjust. After adjusting. return the mode switch to
STEREO.
@)
TAPEMONTTOR
SWTTCHES
Employ for tape playbackor to monitor a recordingin
progress.
1: Playback
or monitoring
of atapedeck
connected
to
the TAPE 'l jacks.
2:, Playback
or monitoring of a tapedeck connectedto
the
TAPE 2 iacks.
NOTES:
l. 8e sure to set the switches
to the upper IOFF) position
when
playing
records
or listeningto broadcasts.
2. When recording
with tvvotapedecks
simultaneausly.do nat
operate
the tape monitor I switchasthiswill interrupt the
signatto the T,APE
2 deck.
G} MODE
SWITCH
Use
this switch
for selecting
monoor stereo
perform.
ances.
STEREO:
Setto this
position
for normal
operations.
MONO: Whensetto this
position,
theleft
and
right
channel
signalswill be mixed and repro-
duced
monophonically
from both speaker
systems.
AD
LOWFILTER
SWITCH
When
thisswitchis
set
to 'l SHz,a 6dB/octattenuation
can be provided {or frequencies
below 15H2.
This
meansthat you cancancelout noisein theultra-low
frequencies
which is generated
by low-pitched
rumble
from a turntableand other forms of distortion.
Although
thisnoise cannotbe heard, it can
generate
intermodulation
distortionanddamagethespeakers.
@ BASS
AND
TREBLE
CONTROLS
When turned clockwise
from the OFF position,
the
responsein the bass
and treble range, respectively,
is
boosted. Turning counterclockwise attenuates the
reSponse.
At the OFF position
the
tonecontrolcircuitisbypassed
andfrequencyresponseisflat.
€} HEADPHONE
JACK
Plug
the headphonesinto this jack when you want to
listen
throughyour stereoheadphones.
Release
both speaker switches
if you want to listen to
thesound
through
your headphonesonly.
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4. CIRCUIT
DESCRIPTIONS
4.1 FM TUNER
Front
End
The FM front end of SX-3800 includes a 3
gangedtuning capacitor, a dual-gateMOS FET-
equipped L-stageRF amplifier, and a modified
Clapp circuit local oscillator. This oscillator is a
voltage controled oscillator employing a vari-cap
(variable
capacitancediode). Whenthe quartz-lock
system (refer to "Quartz-lock system") is not in
operation, a constant voltage is applied to the
diode.
lF AmplifierandDetector
Theseemploy 3 ICs and 3 dual-elementceramic
filten. The IC (HA1201) of the first 2 stagecon-
stitutes a single-stagedifferential amplifier current-
limiting limiter. The IC (PA3007-A) in the third
stage,an
improvementon the former IF system
IC
(PA3001-A), includes an IF limiter amplifier,
quadrature detector, meter drive, and other cir-
cuits. Performance in terms of distortion, S/N
ratio, delay characteristics,and other parameters,
shows a marked improvement in comparison to
thePA3001-4.
MultiplexDecoder
The recently developed multiplex decoder IC
(PA4006-A)
combines
MPX decodingwith muting
functions in a single IC, thereby handling the
functions of the more conventional MPX IC
(PA1-001-A)
and
AF MUTING IC (PA1002-A).
Distortion ratings and SIN ratio have been
further improved by incorporating a chopper type
MPX decoder.The chopper type switchingcircuit
(see Fig. 4-1) operates by switching the signal
either to ground or to the through circuit, thereby
eliminating the generation of unwanted noise or
distortion. Furthermore, sincethe PA4006-A fea-
tures DC direct-coupledswitchingwith the detec-
InOut Output
JU1IIIUIJIJUUI .^ I
Switchins
,is".rc-1q/ - |
thL
Fig.4-1 Choppertype switching
circuit
ouartz-Lock
system
The quartz-lock system
featured
in the SX-3800
stereoreceiveris a frequency servocontrolsystem
employingacrystal
resonator.
Any displacement
in
the intermediate
frequency(iF) isdetectedasaDC
voltage by the discriminator (equipped with a
crystal resonator),resulting in the local oscillator
frequency being corrected and subsequently
locked. This extremely stable frequency servo-
control systemthusensuresthat tunedfrequencies
remaintuned securely
for aslongas
required.
Whenthe IF signal
appears
at pin no.l? of the
IF system IC (PA300?-A), it is amplified and
applied to crystal detector (seeFig. 4'2) which
consistsof diodesconnected
in parallel
in a series
resonance
circuit equipped with a crystal resona-
tor. The resonance
frequency is the same
asthe IF
frequency
(10.?MHz),
which
means
theimpedance
at this time will beminimal, resulting
in the output
beingreduced
to aminimumlevel.
If the input fre-
quency increases,the reactance of the capacitance
CRYSTAL DTTECIOR
OCAMP
WITH LIMIiER LPF
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Fig.4-2 FM
quartz-lock
sYstem
tor, there is no deterioration
in separation
at the
low frequencyend.
Besidesthe decoder and muting circuits, the
PA4006-A
also
incorporates
thepilot signal
cancel-
ler, stereo auto selector,VCO killer circuit, ivluT
amplifier,andMUT control circuit.
Composite
signal
dhllL'
T
E}
FM FRONTENO

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stage
(C) is reduced,
and the reactance
of the in-
ductance stage (L) increased,
resulting in AM
detection
by D2 which leaves
the positive
portion
of tlieIF signal. If theinput frequency
decreases,
L
stagereactance
is decreased
and C stage
reactance
increased,
resulting
in AiVl
detection
by D1 which
leaves
the negative
portion of the IF signal.TheL
stage
and C stage
reactances
increase
asthe deglee
of detuning in the respective
directions is in-
creased,
resulting in a subsequent
increase
in the
detector output. By thus attaining S-curve
charac-
teristics,FM detection
becomes
possible.
Since
the
IF signalis an FIvI
signal
frequency deviation due
to modulationwill besymmetrical
aboutacentral
axis, And if the central frequency is equalto the
resonance
frequency,
the detector
output DClevel
will be zero.If, however,
there
is
anydisplacement
in the central frequency,frequency deviation in
respect
to the detector
will become
asymmetrical,
resultingin the generation
of a DC voltage.
This
DC voltage
ispassed
throughLPF1 (IF filter) and
LPF2 (AC filter) to form a correction voltage
which is applied
to the variable
capacitance
diode
in tlre iocal oscillator, thereby correcting the
oscillator frequency
to obtain a constanttF (i.e.
aconstant
tuned
frequency).
Sincethe central frequency of the crystaldetec-
tor is regulated
by the crystalresonator,
tuned fre-
quencies
of extremelyhigh stability are
obtained.
r Limiting the Locking Range
If lhe quartz-lock range is too wide, it will
overiapwith strong adjacentbroadcasting
frequen-
ciesand result in considerable
tuning difficulties.
A DC amplifier is therelore used as a limiter
(limiter actionby NFB circuitzener
diodes)
which
restrictsthe voltageappliedto the variablecapaci-
tance
diode,
therebylimiting thequartz-lock
range.
A DC voltageappea$ at pin no.L3 of the IF
system IC (PA3007-A) when the antenna
input
level drops below 5pV, or when the tuned fre-
quency
hasbeen
detuned
by more than r100kHz.
This DC voltage(FM muting signal)
is applied
to
the gate
of Q2 (fET) via a Schmittcircuit, result-
ing in the FET beingturned on, and the quartz-
Iockcircuitbeing
turnedoff.
sx-gaoo
4.2 AM TUNER
The AM tuner section consists of a 2-ganged
tuning capacitor plusan IC (HA119Z) which con-
tains a l-stage RF amplifier, converter,2-stage
IF
amplifier,
detector,
andAGCcircuit.
The AM STEREO OUT terminal on the rear
panel is for connecting to an AM stereo broadcast
decoder adaptor. The signal appearing at this ter-
minal is the converter output passed
via a buffer
(
emitterf
ollower) stage.
4,3 DISPLAY
CIRCUIT
Frequency
Display
Frequencies
received by the SX-9800 are dis-
playedin digital form by fluorescent
indicator tube
(FL tube). Eachdigit employs up to ? segments
(a
- e) (see
Fig.4-3) to display
all numerals
from
0 to 9 (with the exception
of the left handdigit
whichemploys
only 2segments
b and
c).
o
fi'
Fig.4-3
7-segment
digit
display
The signal
source
during both AM and FM recep-
tion is the local oscillator. The signal
is passed
via
a buffer amplifier (FET) to the prescalar IC
(M54451P) where it issubjected
to frequencydivi-
sion (1/8 for AM and L/80 for FM) beforebeing
rFRlied to the frequency counter IC (pDb0Og).
This IC is responsible
for the dynamic driveof the
?-segment
S-digit display (eachdigit being turned
on according
to time-shared
sequential
scanning).
An outline of the composition of pDb009 is
given in block diagramform in Fig. 4-b. With the
FL tube a- g segments
(anode)for each
digit con-
nected in parallel,the D1 - Db time divisionpulse
signals(see Fig. 4-6) apptied to each grid (inde-
pendent grid for each digit) result in the digik
being lit up in succession
from the left hand side.
Eachdigit is lit up for lms during each bms
inter-
AM
LOCAL
osc.sr6NAL
FM LOCAL
OSC.SIGNAL
FM"aM sELgcrroN FLTUBE a
SIGNAL
Fig.
4-4 Frequency
display
block
diagram
a
rc(M5445rP)

OIGIT
ORIVER SEGM€NT
DRIVER
MU
!TI PLE XER
PRESETAEL€ 5-DIGIT
OECIMAL COUNTER
22-8lI r 16 ROM
GND
Fig.4-5 Blockdiagram
of PD5009
I
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t
t
t
val. Pin no.? of PD5009
is the brightness
selector
terminal. The time division pulse width is set to
8009s for H level input signals,and to 200psfor
L level signals,thereby varying the degree
of FL
tube brightness(by varying the segmentlighting
period). Note that sincethe pov.er indicator FL
tube is driven by static drive, the degree
of bright-
ness
may bevaried
by changingthe gridvoltage.
The 5.12MHz crystal oscillator generates
the
basic signai used in the preparation of the time
division pulse signaland the counter gate circuit
control signal.
TerminalsS1
- S4 (pin nos.3 - 6) areusedin
designating reception mode. The 2 reception
modesemployedin the SX-3800
(see
Table1) are
designatedby varying the combination of input
levels
(H and L). The 3 different IFs during FM
mode are required in coping with IF offset in the
IF ceramic filter stage, 53 and 54 being preset
during FM mode according to the ceramic filter
characteristics.
Although the SX-3800 FM stagequartz-lock
system
is capableof locking any frequency within
the FM band,the L0kHz digit (digit in thesecond
decimal place)in the FM frequency
displaywill
appear
only as5 or 0.
The frequencydisplayFL tube alsoincorporates
the TUNING and SIGNAL indicators. And al-
though the segments
(anode)
for theseindicators
are static driven by the correspondingdrive cir-
cuits, the edd is driven accordingto the D3 time
division
pulse
timing, thereby
placing
thesegments
10
Inl
lttr-
o,w
ooM
*l-w
,,iw
-'l'*i*iill
t{-- tm3 +
8C= L (DlM)
Fig.4-6 D1-D5 timedivision
pulse
signals
under
dynamicdrive.In addition,the AM and
FIW
indicators in the frequency display section arelit
accordingto the Db timing, while the kHz and
MHzindicatorsare lit accordineto theD1 timine.
MODE s1 S2 s3 IH
L
H
lF {MHz)
FM
H L L 1073
HL H
H
10.70
H L 't 0.67
AM LH H L450kHz
Table
1

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SIGNAL
lndicator
Circuit
sx-g€too
Fig.
4-7 SIGNAL
indicator
drive
circuit
The SX-3800SIGNAL indicator consists
of an
FL tube5-point
indicator
display.
The
signal
meter
drive signalobtainedfrom the FM IF system
IC
(PA300?-A) and AIVI
tuner IC (HA119?) is first
amplified and then applied to the indicator drive
IC (HA12010).
This
IC contains
12pairs
of voltage
comparatorssimilar to those employed in the
powerindicatorcircuit, b of these
pairs
being
used
to drive
the SIGNAL indicator.
TUNING
lndicator
Circuit
The TUNING indicator consists
of a center
tuning indicator (which lights up when a broad-
casting
station frequency is properly tuned) and
2 detuning
directionindicators
which indicate
the
directionin whichthestation
has
been
tuned
awav
from. The corresponding
drivecircuitsare
outlinei
in Fig.
4-B
below.
The TUNING indicator is activated
once the
station hasbeentuned to within t100kHz of the
center
frequency.
This is because
e16 is
turned
on
and Q21 turned off (resulting
in the detector
dif_
feren^tial
amplifier le19 & e20J being
tumed off
andQ24 being
turned
on) by the FM muting
signal
appearing at pin no.lB of the IF system IC
{PA3007-A) and passed
via the Schmitt circuit
(Q17 & Q1B) rvhenthe station istuned awayby
more
than
t100kHz.
The DC voltage
on pin no.4 of pAB007_A
de-
scribes
an S curve
when
tuning
to and
away
from a
particular broadcasting
frequency,
the voltage
on
pin no.2 serving
as the reference
level.
This DC
Fig.
4-8 TUNING
indicator
drive.circuit
voltage is amplified by the differential amplifier
(Q19 & Q20) andthen applied
to apolaritydetec_
tor switch
circuit(eZZ & e2g).
When tuning to a frequency from the high fre_
quency side (or tuning away from the frequency
to a higher
frequency),
thevoltage
on pin no.4will
be higher
than that on pin no.2.
Thee20 collector
voltagewill thus be lowered andthe e1.gcollector
voltage raised, resulting in e2B being tumed on,
andthe higher frequency (right hand side)detun-
ing direction indicator also
being
turned on. When.
SCHMITT
CIRCUII
rc
(PA30(r/-A
)

on the other hand, the broadcasting
frequency is
approachedfrom the iow frequencyside(or when
tuning away to a lower frequency) the pin no.4
voltage
will belower,resultingin Q22 beingtumed
on to light up the lowerfrequency
(lefthand
side)
detuningdirection indicator.Wheneither Q22or
Q23 is on, the Q24 basevoltage
will be high,
resulting in Q24 beingtumed on and Q25 tumed
off, which meansthat the center tuning indicator
will not belit up,
Oncethe broadcasting
frequencyhas
been
tuned
properly, the voltages
on pin nos.2 & 4 will be
equal.Consequently,
q22 and Q23 will both be
turned off, which means
that neitherof the detun-
ing direction indicatorswill be on in this case.And
sinceQ24 is tumed off because
of the decreased
basevoltage,
Q25 will beturned on, andthe center
tuning indicator light up. Furthermore, C77 is
charged
up via R99, resuiting
in Q26 being
tumed
on, thereby lighting up the Quartz Locked indi-
cator
LED.
4.4 EOUALIZER
AMPLIFIER
?his circuit is an NFB type equalizer
amplifier
with newly developed high performance IC
(HA1201?P).
This IC is a low-noise
andlow distortiontype,
andprovide
an openloop
gain
of 105d8.
Themain
performance specifications
for this circuit include
a voltage gain of 35.5d8 (at lkHz), a phono
dynamic margin or maximum allowable
input level
of 250mV (1kHz, 0.}Abc/oTHD), S/N ratio of
82dB (at 2.5mV input, IHF-A), and equalization
within t0.2dB (20H2
* 20kHz).
4.5 TONECONTROLAMPLIFIER
This circuit is an NFB type tone control ampli-
fier with newly developedhigh performanceIC
iHA12017P).
4.6 POWER
AMPLIFIER
Amplifier
Circuit
The basic circuit arrangementof the power
amplifieris shown in Fig.4-9.The first stageis a
differentialamplifiercomprising PNP
twin transis-
tor (Q2), the load circuit of which is a current
mirror employing an NPN twin transistor(Q3).
The currentmirror providespush-pull
operationin
this stage,which seruesto cancel
evenharmonics
andfurtherincrease
gain.
Q1 in the input circuit absorbs
outflorv of base
currentfrom Q2, andprevents
the generation
of a
DC voltage.
Because
Q1 follows any temperature
drift in Q2, temperature
drift of the center
point
voltage
isprevented.
The pre-driver
stage
(Q4, Qb) is a Darlington
arrangement,
the load circuit of which employs
a
constant-current
source
(Q6) resultinga high volt-
age
gain.
The power stage
biasvoltage
is supplied
by the
high speed bias servocontrol circuit. The high
speed bias servocontrol circuit provides non-
switching operation in the power stage(refer to
"High SpeedBias
ServocontrolCircuit").
The powerstage (Q13- Q16) is a 2-stageDari-
ington arrangement,
the last stage is SEPPcircuit
employing an SL RET (Super Linearit5' Ring
Emitter Transistor).
The RET is a kind of IC con-
sisting
of a numberof smail transistors
on asingle
chip, with each transistor being connected ir"r
parallel via an emitter resistor. This provides
t
t
t
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H
H
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;
+
I
+
I
td
Fig.
4-9 Power amplifier

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T
T
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f,
F
t
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t
F
F
F
excellenthigh frequency
characteristics
compara-
ble lo thoseof a small-signal
transistor.
Further-
more,becanse
lhereisno time clonstant
in theNFB
circuit ir-r
the lorv-frecluency
region,
amplification
is
possibie
dorvn
to DC (DCinputs
willbe
cutoff,
hor,vever,
by theinput coupling
capacitor).
'I'hecircuit features
described
above
provide
an
extremely wide polver frequency range (60W
+ 60W,101-lz
to ZOkHz,THD 0.005Va,
Bdl).
High
Speed
Bias
ServocontrolCircuit
By operatingthe power stage
only within the
activeregion(no possible
cut-off) andwith mini-
mr-rm
idlecurrent,
the highspeed
biasservocontrol
circuit prevents
the generation
of switchingdis-
tortion and
reducesheafloss.
OperatingPrinciple
Since
idle currentflows throughnormalclass
B
SI)PP
porver
stages
(see
Fig.4-10)whenno signal
is appliecl,
the DC level
isshiftedby D andVR by
a fixed amount (w'itirthe voltage
across
pointsX
ancl
Y sen'ingasa bias).Thevoltages
across
points
X and Z, and Z andY at this time will be equal.
Whenthe positve
portion of a signalis appliedto
this circuit, the porver
stagecurrent on the NPN
sideisincreased,
andthevoltage(Vn1) acrossboth
ends
of RB1 alsoheing
increased,
resultingin the
voitage across point X and Z being increased.
However, sincethe voltageacross
points X and Y
is practically constant, the voltage acrosspoints
Z anrlY (PNPpower stagebias)will bedecreased,
resultingin thePNP
power
stage
being
cut off.
'I'he high speed bias servocontrol
circuit in-
creases
the voltage
across
points X and Y by the
same
amount asthe voltage
increase
across
points
X and Z, thereby cancelling
the voltage
decrease
across
poinls Z and Y, and preventing
the PNP
polver
stagefrom being
cut off.
This high speed
biasservocontrol
circuit is out-
linedin Fig.
4-11.lVhen
thereisno signalapplied
to the crrcuit, Q1 and Q2 are almost cut off,
while Q3 and Q4 u'ill be on. The voitage
across
fhe collector
andbase of both of these
transistors
(Q3 andQ4) at thistime maybedisregarded.Con-
sequently,
rvith the power stagebiascircuit con-
sistingof ,tr
PN junctions
formed
by Q3,D3, and
Q4, and VR1. this circuit is equivalent
to the
previous
circuil
shownin Fig.
4-10.
With R1 and
D1 ensuring
aconstant
flow of cur-
rent,the base
of Q1 and
point Z may be
brought
to the samelevel
on anAC basis
(level
fluctuations
due to the signal)by a simpleshift in DC level.
Furthermore, Qf may be considered emitter-
follower
lvitli R3 astheemitterresistance.
sx-3aclo
When the voltage
across
points X and Z is in-
creased
by tl're positive portion of the signalap-
plied to this circuit, it becomes
the input signal
of this emitter-follower (Q1). Since the emitter-
follower voltage gain is practically 1-,a voltage
more or lessequalto that of theinput signal
(that
is, the voltageincreaseacross
points X and Z) is
produced
at R3. And the R3 voltageis
thevoltage
appliedacrossthe baseand collectorof QBwhich
forms part of the power stage
biascircuit. So the
biasvoltageapplied to Q3 will be in excessby the
sameamount that the voltageacross
points X and
Z is increased (by positiveportion of the signal)
above the voltagelevel when no signalis being
applied. Consequently, the increasein voltage
across
points X and Z cancels
the decrease
in volt-
age acrosspoints Z and Y, thereby maintaining
the idle current without cutting the PNP power
stageoff (noting that there actually is a slight
decrease
in current). For the negative
portionsof
the signal,
Q3 and Q4 are operated
in the same
rnanner,
thereby preventing the NPN powerstage
from beingcut off.
In other words,
the highspeed
biasservocontrol
circuit actsto preventany "poler stagecut-off"
signals
from being
appliedto thepolyer
stage.
Fig.4-'l
0 Normal
power
stagebiascircuit
PRE-
ORIVER
PFE.
ORIVER
Fig.
4-11 High
speedbiasservocontrol
circuit
IJ

ic ('tA73t8P) t/?
HOLO
&
OCAMP
L€VEL
SHIFI
OFFSET
COM.
PENSAIOR
t
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Fig.
4-12 Power
indicator
circuit
4.7 POWER ]NDICATORCIRCUIT
s16NAL
rN
o*-l
F/LAMENT
The SX-3800 output power indicators feature
fluorescent
indicator
tube (FL tube).In this tube,
thermionic emissionsfrom the cathode are ac-
celerated into the fluorescent substanceof the
segmental
anodes,resulting
in the emission
of light.
Thistube is usedto indicate
numerals,letters,
and
other
symbols.
An outline of the FL tube drivecircuit isshown
in Fig.4-12.
The output circuitsj"tnalisappliedto
pin no.6 ( ) of the IC (TA?318f
-A).
TheIC con-
tains a detector circuit, conpressor (40d8), and
peak hold circuit for both left and right channels.
The dynamic rangeof the signal
isthuscontracted
by 40dBto obtaina"peakheld" DCvoltage.
The output pou'er
indicator
segmentsof tireFL
tube aredrivenby the HA12010ICs
(one
for each
channel) equipped rvith 12 pairs of differential
amplifiers.Theseamplifiers
arebiasedat increasing
levels,
soeachamplifier
lvill commence to operate
separatelyasthe input level increases.
And since
theseamplifiers apply the voltagesto the output
power indicator segmetrts,eachsuccessivesegment
will light up in turn as
the input levelrises.
4.8 PROTECTION
CIRCUIT
The purpose of this circuit is to protect the
speakers
andthepower amplifiers.
Therelayin the
output circuit is automatically opened
in any of
thefollowingcases:
L. During the "transient operations" lvhen the
power
supplyisturnedon andoff.
2. Upon detection of an overload, causedby a
shortcircuitin theioad.
3. Upon detectionof a DC voltage
in the output
causedby componentfailureor accident.
Muting
Operationwhen
Power
SupplyisTurned
OnandOff
With reference
to Fig. 4-13 when the porver
supplyis turnedon, Q3 turns off due
to *81 (l'he
time constantof the *81 circuit is very sma11.).
If thereis
no input (DC)on Qb and
Q6, theywill
be off, and the timing capacitorC1 charges
up
through R8 and R6, and thus Q4 turns on. \Vhen
Q4 condr,rcts,
tire relay operates,and the output
muting
onthepower
amplifier
will be
removed.
Whenthe polver supply is turned off, -81 rvill
abruptlydecay,andQ3 will conduct owingto the
resiclualcomponent of +81. As a result,C1 rvill
rapidlydischarge,
Q4 will ceaseto conduct,rvhere-
upon the relay will become de-energizedand
restore
mnting.
14

J
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Overload
Detector
The overload detector circuit incorporates
the
load(RL) in oneside
of aWheatstone
bridge.
The
base
and emitter of a sensing
transistor(e1) are
connected
to the opposite
corners
of the bridge,
so if RL decreases,
Q1will become
forward
biased.
If RL falls below a prescribed
value,e1 will turn
on, thereby C1 will rapidly discharge.
As conse-
quence,
Q4 will turr on and the relaywill become
deenergized,
thus causing the output circuit to
open.
DCVoltage
Detector
The output circuit isconnected
to thee6 emit-
ler and Q5 base
via a low-pass
filter (Rg, C2).
Any DC voltages
appearing
the output circuit of
the porveramplifier,it wil] be applied
to the e6
emitter andQ5 base.
If the voltage
ispositive,
eb
turns on. C1 will rapidly discharge.
If the voltage
is negative,
Q6 turns on. C1 will rapidly discharge.
As conseqnence,
Q4 will turn on andthe relaywill
become de-energized,
thus causingthe ourpur
circuit
to open.
six-gaoo
F
ig.
4-
13 Protection
circu
ir
15

5.DISASSEMBLY
Bonnet
Case
Removethe two screws O ot each
sideof the
bonnet
case.
Bottom Plate
Remove the fifteen screws O to detach the
bottom plate.
Front
Panel
Remove the all control knobs except push
knobs. Remove the two screws @ and two nuts
Q from the front Panel.
A\
s\$ Front
panel
Bottom plate
i
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t
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I
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tI
Bonnet
case
f\,.\
$\
to

!
I
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I
6. PARTS
Front
Panel
LOCATTON
Front
panel
assembly-
AN8.851
AAD,226
FrontViewwith PanelRemoved
Fluoresc€ntindicator
tube
AAV.OO9
Remote
push
swirch
-
sx-gEloo
: The fi marh found on sotnecamponent parts indicates
the importance of the sofety factor of the part. There-
fore, when replacing, be sure to use parts of identical
designation.
Push
knob B
AAD-227
AAA.O66
Knob
AAB.24O
AAB-239
Fluorescentindicatortube
AAV-OO7
Dial
shaftassembly
AXA.264
Pushswitch
(FMMUTINGI
ASG-230
ASK-181
Variableresistor1M {EALANCE)
ACT.021
Remoielever
switch (TAPEMONITORI
ASX-128
erminal
{lNPUI, PFIE
AMP
OUT,
POWEF
AMP lN}
AK8{63
erminal
(SPEAKE
BS)
AKE.O54
AAC socket
(AC
OUTLETS)
'AKP-O42
.ii\AC power cord
ADG.O23
Lever
knob
(SPEAKE
RS)
ASX,135
Push
switch
(BR
IGHTNESS)
ASG,230
; Leve'
swrrch
(POWER)
-...
ASK-507
t7
Phone
jack
lPHONES)
AKN.O30
Varrable
resislor
'l
0k (BASS)
ACT-135
Vilnable
resistor
10k
(TBEBLE)
AcT-136
Leverswitch
{N4ODE,
LOW
F
ILTE
R)
ASK.,]52
Rear
Panel
Terminal
(AM STEREOOUT) -
AK8.076
Bar Jntenna ilssenrblY
-
ATB.624
Slicie
swrtch
iDE-EMPHASISi
ASH.O15
Termrrtal
(ANTENNA)
-- --
AK
A.013
TPr
rrrrr;rl
(TAPE
1
.2) -
AK8"063
_l ,l
t
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17

sx-3Etoo
P.C.
BOARD
CONNECTION
DIAGRAM
UE TUNER
Ass'y
GWE-133
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The counter IC (PD50A
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values by appropriate co
or L leuel signals) applier
the wiring (connecting
within the equalizer ass
differ slightly from the ci
the grade of the FM cet
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to ,
The R28 and. R29 resist
(
AWM-227
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match the counter IC (PI
assembly) with the FM I
haue been arranged accor
mic filter Fl - F3 (color
in the following table.
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