Pioneer SA-9500II User manual

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MODEL
SA-95OOIICOMESIN FOURVERSIONSDISTINGUISHED
AS FOLLOWS:
This service
manual
is applicable
to the KU-type.
When
repairingthe KC-type,
HG-type,S-type,
please
see
theadditional
service
manual.
CONTENTS
1. SPECTFTCATIONS
.... 5
2. CONNECTION
DIAGRAM 6
3. FRONT
PANELFACILITIES.. 7
4. BLOCK
DIAGRAM 9
5. CIRCUITDESCRIPTIONS
5.1 Equalizer
Amplifier 11
5.2 Tone
Controls 11
5.3 PowerAmplifier 12
5.4 ProtectionCircuit 13
5.5 Power Supply
Circuit 14
6. LEVEL
DIAGRAM 15
7. DISASSEMBLY. 16
8. PARTSLOCATION
8.1 Front
PanelView 18
8.2 Front
Viewwith PanelRemoved. . 19
8.3 Top View 20
8.4 Bottom View . 21
8.5 RearView 22
ADJUSTMENT 23
EXPLODED
VIEWS 24
SCHEMATIC
DIAGRAMS,
P.C.
BOARD
PATTERNS
AND
PARTSLIST
11.1 Miscellanea 32
11.2 Schematic
Diagram 33
,}
'}tt
9.
10.
11.
3
UL (U.S.A.) approved
CSA (Canada)
approved
22OV and24OV (Switchable) SEMKO (Sweden),
NEMKO (Norway), DEMKO(Denmark)
and
El (Finland) approved
12OV.
22Ov and24OV
(Switchable) General
export model

11.3
'tI.4
11.5
11.6
11.7
11.8
12. PACKING
SwitchAssembly
(AWS-1
09)
SwitchAssembly
(AWS-1
02)
Phono
Jack
Assembly
(AWX-107)
Equalizer
Amplifier
Assembly
(AWF-024)
Control
Amplifier
Assembly
(AWG-045)
Power
Amplifier
Assembly
(AWH-052)
35
41
42
45
46
50
53

1.
SPECIFICATIONS
Semiconductor
Transistors 55
Diodes 33
Power
Amplifier Section
Circuitry . . . 2-stage
differentialamplil'ier
Parallcl
PPdirect-couoled
OCL.
Continuous
Power
Outputform20Hertzto20,000
Hertz
(Both
channelsdriven)
. . 80watts
per
channel
(8
ohms)
I00 watts
per
channel
(4
ohms)
TotalHarmonicDistortionat2jHertz.to20,000Hertz
Continuous
rated
power
output . . 0.05%
4Owatts
pcr
channel
power
output,8ohms . . . . 0.01%
lwattperchannel
poweroutput,
8ohms. . . . . . 0.01%
IntcrmodulationDistortion
Continuous
rated
powcr
output . 0.05%
4Owatts
per
channel
power
output,8ohms . . . . 0.0'l%
lwatt
per
channel
power
output,
8ohms . 0.01%
Frequency
Responsc 5Hertzto I00,000Hertz
ltdB
Input
(Sensitivity/l
mpedance)
POWER
Al\4PlN ]V/5Okohms
Output ... Speaker A,B,A+B
Headphone: Lowimpedance
DampingFactor
(2}Hertt
to20,000Hertz,8ohms)
. . . 30
Hum
andNoisc
(lHF,
short-circuired,
A network)
. . ll0dB
PreamplifierSection
Circuitry
Equalizer
amplifier:
1st stagedifferential
amplifier
3-
stage
direct-coupled
A class
SEPP.
Control
amplifier: .l
st stagcdifferential
amplif
ter 2-
stagedirect-coupled,
N
FBtype.
Input
(Sensitivity/l
mpedance)
PHONOl
.... 2.5mY110,25,50,10Okohms
PHONO2
.... 2.5mYl10,25,50,lOOkohms
CARTRIDGE
LOAD ... BothPHONOI
and2,
100,200,300,400pF
TUNER 150mV/50kohms
AUX 150mV/50kohms
TAPEPLAYI.... 150mV/50kohms
TAPEPLAY2.... l50mV/50kohms
PHONO
OvcrloadLevel
(
f.H.D.
:0.05%)
PHONO
| .... 300mV
(l
kHz)
300mV
(l
kHz)
PHONO2
Output
(Level/l
mpcdance)
sA-s|500II
Total
HarmonicDistortion
(20H2
to20,000H2) . 0.01%
Frcqucncy
Rcsponsc
PHONO
(RIAA
Lqualiz.rtion) .2OHt
to
20,000H2
10.2d
B
. . 5Hz to50,000H2
_,1d8
MAIN
t8dB(100H2)
suB
16dB
(SOHz)
MAIN
18dB
(10kHz)
SUB
16dB(zOrHz)
TUNER,
AUX,TAPE
PLAY
loncContrrrl
(2dB
stcp)
fREBLf
Filtcr
LOW
BASS
c
. . l50mV
......tu)io,,n.r,,oupoon,'.rt,t';Il
HIC,H.
Loudncss
Contour
(Volumc
controlsc1a1
-40dB position)
Hum and Noisc
(lHF,
shorl-circuilcd,
A network)
PHONO 75dB
TUNIR,
AUX,TAPEPLAY
. . . .95d8
Muting ..0,-20d8
Miscellaneous
Powcr
Rcquircmcnts . . . l20V60Hz
only.
Powcr
Consumption 230watts
(U
L)
490VA
(CSA),
560watts
(Max.)
Dimcnsions ....420(W)x150(H)x376(D)mm
16-9116
x5
118
x 14
13116in
Weight . Without
Package:l6kg
(351b
4oz)
With
Packagc: 11.9kg
(391b
7
ot)
Furnished
Parts
Operatinglnslructions ......1
Connection
Cord
with PinPlugs l
Hcx.
Wrcnch
(Used
for l'asteningVolumc
Knob). . . . . . 1
NOTE:
Specifications
and thedesign
subject to possible modifica-
lion utithoutnotice
due to improuements.
I5Hz
(6dB/oct.)
8kHz
(6dB/oct.)
+6dB
(100H2)
+3dB
(10kHz)
F
tr F'
9.,
Blt
E'
TAPEREC
1
TAPEREC2
PREOUT . .
5

2.CONNECTION DIAGRAM
TURNTABLE
1TUNER
UT-
PUT TURNTABLE
2
Connect
to
ground
terminals
of turntables,
tu
ner,
tape
deck,
etc. GROUND
LEAD
GROUNDING
TO EARTH
A SPEAKER
SYSTEM
CARTRIDGE
TAPEPLAYER
OUTPUTLINE
TAPE
DECK1
DECK
2
INE
OUTPUT
sA-95001I
ACCORD
LINE
INPUT
BSPEAKERSYSTEM
o o f-- -- jr)-
aJ tf
f,...:--.Tl-l
r ppr';l (-) rr
f-l f--l l.-l
tott.tL
r-r \-
lle{"r:,4ll E
o--.t-i g -J lr :
?
"l
[E
fNVEN
FI
lEl
,a,
FF
I ttI
lEl 16l
:E
OUTLE
a
-
:
C-D
(-D

3.FRONTPANEL
FACILITIES
POWER
SWITCH
Setto ON
position
toenergize
SA950011.After
settingto
ON, thereisa briefdelay
beforesoundis
obtained.
This
is due to the operationof the muting circuit which
prevents
noisewhenthePOWER
isswitched.
Thisfunc-
tion does
not indicate difficulty
and normalopcrating
conditionis
attaincdinafcw
seconds.ThePOWER
switch
alsocontrolsthe rear pancl
SWITCHED
convenicnce
outlets.
TONESWITCH
In theON position,
tone
adjustments
canbc
performcd
with
the
BASSandTREBLE
twin
controls.When
setto
the upper
(OFF)
position,
thetone
controlcircuits
are
disengaged
andfrequency
rcsponse
is
flat.
Thisfunction
is
convenient
for checking phono
cartridge
andspeaker
tone
quality
andlistening
room
acoustic5.
BASS
TWIN
CONTROLS
Controlsfor
adjusting
lowfrequency
tones.
l00Hz: Adjusts
frcquencies
below
400H2.
With
respect
50Hz: to 100H2,
ad
justment
range
is
:t8dB.
Provides
additional
adjustment
to the .l
00Hz
control
for the
band
below
200H2.
Adjustment
range
with
respect
t<t
50Hz
is
i6dB.
TREBLE
Controls
I
0kHz:
2OkHz:
TWIN CONTROLS
for adjusting
highfrequency
tones.
Adjustsfrequcncies
above2.5kHz.
With
respect
to10kHz,
adjustmentrange
is
t8dB.
Provides
additional
adiustment
to thc l0kHz
vol
Ad
att(
arb
bin
wic
PHONES
JACK
When
listening
w
this
jack.
NOTE:
Set SPEAKE,RS
headphones.
th stereo
headphones,
conncct
them to
switch to OFF when listening
only u..tith
controlfor the band
above5kHz.
Adiustment
rangewith
respect
to20kHz
is
t6dB.
r'
'' '"1
LOWFILTER
SWITCH
Setto 15Hz
position
in theeventthatturntablerumble,
recording
cuttingnoiseor other low frequencynoise
becomes
objectionable.
Attenuation
in the frequency
bandbelow15Hzis
6dB/octave.
HIGH
FILTER
SWITCH
Set
to 8kHz
position
if recordscratch
noise
orotherhigh
frequencynoise
becomes
objectionable.Attenuation
in
thc
frcqucncy
band
abovc8kHzis6dB/octavc.
BALANCE
CONTROL
Controlfor adjusting
stcreo
balanccbetwccnlcft andright
speaker systemsor hcadphoncs.Turn clockwisc from
ccntcrto incrcase
right
(R) channcl
volumc
andcountcr-
clockwisclrom ccntcr to increase left
(L) channcl
volumc
in order to obtainabalarrce
.
A:
tJ:
SPEAKERS
SWITCH
Selects
speaker
system
operation.
OFF: Sound
notobtained
fromspeakers(when
using
headphones).
Sound obtaincd
from spcakers
connected
to A
speakcr
terminals.
Sound obtained from speakcrs
connected
to B
speakers
terminals.
A + B: Sound obtained trom spcakcrs
connectcd to
both A and B speakcr
tcrminals.
NOTE:
Whenlisteningwith headphones
or to lemporarily inter_
rupt the speaker sound, set su,titch
to OFF or to an
u
nuse
d speaker p osit
ion.
r
I
I MUril
I*:i
|:*,r
I
Lrouo
When
enhanr
humar
switch

res.
.With
respect
B.
o thc .l 0kHz
VOLUME
CONTROL
Adlusts
speakerand headphonevolume.
Scaleindicatcs
attenuation
in dB with maximum volume
assignedan
arbitraryvalue
of 0dB.Control
canalso
be
usedin com-
binationwith theMUTING
switch
to orovidea finerand
widerrange
of adjustment.
CARTRIDGELOADSWITCHES
Select
phono input circuit resistanceand capacitance
according
to thespecificationsfor the employed
phono
cartridge.
(0 ProNCCn ,,
sA-s500[
MUTING
SWITCH
Switch
for reducingvolume
by 20dBfrom theVOLUME
controlsetting.Convenient
for temporarily
reducingthc
volume
whenchangingrecords
ortapes,sinceitcliminatcs
the need for continually readjusting
the VOLUME
control.
LOUDNESSSWITCH
Whenlisteningatlowvolumcscttings,setswitch
toONto
enhancelow and
highfrcquencies.The responscof thc
human
ear
to sounddiffcrsaccordingto loudncss.This
switchcomoensatcs
f
orthiseffect
atlow
volumcs.
siA-9sc,Otr
FUNCTIONSWITCH
Selects
desired
playbackprogram
source.
PHONO
2: To
play
recordsonaturntable
connectedto
thePHONO2 jacks.
To play recordsonaturntablcconnected
to
the
PHONO
1
iacks.
To listen
to broadcasts
with a tunercon-
nectedtotheTUNER
jacks.
To play acomponent
connected
totheAUX
jacks.
TAPE MONITOR SWITCH
Employfor tape
playback
or to monitora recording
in
progress.
.l
: Playback
or monitoringof a tape deck
connected
totheTAPE
.l
iacks.
SOURCE: Be surcto setto this oositionwhennot
usingthetape
deckfor playback.
2'. Playbackor monitoring
of a tape deck
connectedto theTAPE
2 iacks.
NOTE:
Whenlisteningto records
or broadcasts,besureto set
this stDitchto SOURCE.Sound will not beobtained
from speahersif setto 1or 2.
TAPE
DUPLICATE
SWITCH
Employ
whenusingtwo tapedecksfor duplicationor
editing.Besureto setto theOFF
position
atothertimes.
1
- 2: Duplication
of tapefrom TAPE 1 (playback
mode)tof APE 2 (record ingmode)
.
OFF: Setto this
position
when
notusing
theduplica-
tion featurc (this includessimultaneous
recordingwith two tapedecksandtape
play-
back).
2'1: Duplication of tape
from TAPE 2 (playback
mode)toTAPEI (rccording mode).
MODE SWITCH
REV: Reversesleftandrightchannelstereosignals
and
reproducesthemstereophonically.
STEREO: Setto this
position
for normalstereorepro-
duction.
L + R: Mixcs left and right channelsignals and
reproducesthemmonophonically.
L: Left channelsignal
is reproducedmono-
phonically
frombothspeakers.
R: Right channelsignal is reproducedmono-
phonically
frombothspeakers.
:.
Adiustment
tB. I
PHONO
1:
TUNER:
AUX:
\"
)
tablerumble,
truency
noise
1e
frequencY
orotherhigh
ttenuation
in
te.
lcftandright
rckwise from
and
countcr-
rannclvolume
a

4. BLOCKDIAGRAM
VRza,
b, BAL
ANCF
1C
AUX
TUNER
P
F.t
0
t.to
1
PHONO
2I
+=
Tir-;kl
iffi
Lffi
EQUALIZER
AMPLIF
'it-
tt"rApETpLA)
t '^''.*rJF
_.o*
ittl'tfG
'REcY--c
S+o S+. l-un, BASS
50Hz
BASS100H2
VRs
lro*rn
i
,0,
VRo
I
TER
o Ssu
VRza
o vnla
riRru
I VRt
' TREBLEl'kHz I
I vno,TREBLE
zok1z
L.- .--J
I
Sroa
VR+ VRs
TON
F
SPEAKER
1.
OFF
4. A+B
RE
LAY
POWIR
OFF-ON
R SFLE
CTOR
1.
r0kQ ? 25k4
3. soko -+ 100k4,
S
r+o
LEFT
CHANNEL
RIGHTCHANNEL
t
tVRra,u,
VoLuM, coNTROL
AMPLTFIER
AUX
TUNFR C
.r
5c
EQUALIZER
ANPLIFIER
Szr TAPE
TAPE
ITI
S\lIfCHES,
Sta-d
' FUNCTI0N
1.
PH0N0
2
3.
TU
NER
Sza,b
' C
SELEC]-OR
1.
100pF
3 300pF
S3o-a
, DUPL
lC
ATE
1 1,->n
J. I L
3 7- 1
s+o
S+a-d' TAPE
MONIr0R
1-IAPE1
2OFF
3.
TAPE
2
Sso-c
' 110DE
IREV 2.STEREO
3.L+3.
+.t 5 R
Ssa,u
'YIUTING OFF-
Sro,u
' LOUDNESS OFF
-
Seo,b
' HIGH
FITTER OfF
-
Sso,u
' [Ow FILTIR E -
Sqa
PH0N0
1(q--o
Pfl0N02
st+r
1b^.
S
PRE
POW
Ssu
Ssa
- PLAY
1
LREC
- PLAY
2
L
REC
2 PHONOI
4.
AUX
2 200pF
'1.
400
pF
2 OFF
-20d
B
ON
B
k
Hz
15Hz
Sioa,b '
Srta-d :
S,n
v tL
o
vtJ
Sr+a
,
u
OFF
- ON
2.A
3.B
CONTROL
AIlPLIFIE

BASS
50Hz
BASS
100H
z
VRs
-l**rn t*
:
lrnr
our
VRe
POWER
r--
L
AIlPLIFIER
I
Sroa
vR+
TREBLE
10kHz
TREBTE
20kHz
NTROL
A}lPLIFIER
ONTROL
AIlPLIFIE
TONE
SPEAKER
1.
OFF
4. A+B
RE
LAY
PO\NER
OFF
-ON
R SELE
CTOR
1. l0k0 7 25k0
3. s0kQ, -+ l00ka,
PROTECTTON
CIRCUIT
T
To Lch
powen
a[P
To contno
I amp
To power
amP
To egualizen
amP
To
pr-otection
clrcuit
To
power
amP
To
control
amP
fs eQua
lizen
amp
ss
oc
\
L
I
T
VRs
-J
1,'oNEs
L
FFT
CHANNEL
RIGHT
CHANNE
L
Q^
.L
rgr,
T
I
+
OUT
ERIN
Q.
* tso
L
PRE
POW
Stoa,b
:
Srto-d
S,"
Srs
St+a,b
- 0N
3B
OFF
z.A
-
,tP
SPE
AK
ER
P0WER
AMPLIIIIR
S
P
EAKTR
To
pnotection
crrcurT
'l-o
R
ch power

5.CIRCUIT
DESCRIPTIONS
FUNCTION
S|{IICH
7=l20(a
C
=100pF
PHONO
2
PHONO
'I
CARTRIDGE
LOAD
+
siA-s|5clcltr
OUT
Fig.
1. Schematic
diagram
for
equalizer
amplifier
5.1 EOUALIZER
AMPLIFIER
The circuit diagram for the equalizer amplifier is
shown
in Fig. 1. The two separate
phono inputs are
selected
by the FUNCTION selectoron the front
panel.The input resistanceand input capacitance
canboth beadjustedto 4 different levels
(R=l0kCl,
25kO,50kA and100kO, C=1-00pF,200pF, 300pF
and400pF) by meansof the CARTRIDGE LOAD
control knobs(R and C) which switchesin and out,
additional resistors and capacitors in parallel with
the input terminal. Hence, optimum load condi-
tions for different phono carbridges can be ad-
justed, as well as modifying the cartridge's fre-
quency response in the high frequency range and
thus producing variations in its characteristics.
Thefirst stage
of the equalizeramplifier (Q, & Qr)
isadifferential amplifier using PNPtransistors. The
next stage
(Q.) isa bootstrap circuit employing C1,
R1 to provide high voltage gain. The output stage
(Q+& Qr) is a complementary-symmetrical SEPP
circuit, whose high voltage utility factor results in
a high output voltage. This gives the equalizer
amplifier a very wide dynamic range, and a con-
siderable
overload input level of 300mV (RMS at
lkHz) with no more than 0.05V"distortion.
The equalizerelements(Cr, Cr, Rz and R3)consist
of polypropylene film capacitors (tolerance !2Vo)
and metal film resistors (tolerance xIVo). Phono
equalizer
RIAA deviation has been reduced to less
thant0.2dB (20H2 - 2OkHz\.
5.2 TONE
CONTROLS
The SA-9500 II featurestwo sets
of tone controls
(Tkin Tone Controls) with different turnover fre-
quencies for bass and treble. And each of these
controls may beusedindependently.
Incoming signalsare amplified to the required level
by the 2 stageamplifier which usesa differential
amplifier at first stage. T\vo tone control circuits
(C-B feedback NFB type) are connected together
in series. The second stage is the normal tone
control (MAIN), while the other is a seeondary
tone control at a different turnover frequency
(SUB). On the TREBLE side,this (SUB) tumover
frequency is higher than the MAIN, while on the
BASS side,it is lower.
The basicprinciples of the NFB type tone control
circuit areoutlined in Fig. 2.
R" YR" R,
TREBLE
Fig.2. Basic
circuitry of NFB type tone control circuit

Midrange Operation
The Cr and C2
reactances
are considerably smaller
than VRr at frequencies above midrange, effec-
tively shorting VRr. At frequencies
below mid-
range, C. reactance becomes large and in effect,
opens the circuit. Consequently,
the circuit be-
comes equivalent to that shown in Fig. 3 with
respect
to the midrange.In this figure,the circuits
parameters
are not changedby any changein posi-
tion of the VRr andVR2sliders.
TheNFB amount
is therefore fixed and the circuit gain is also fixed
without regard
to VRr andVRzslider positions.
R. IR. R.
Fig.3. Midrange
operation
of NFB type
tonecontrol
circuit
Low FrequencyOperation
The reactanceof C, and C, increases
at low fre-
quency to form a circuit asshown in Fig. 4. This
reactance
increases
in proportion to the frequency
declines. Also, the NFB amount varies greatly
according to VRr slider position. The circuit gain
at low frequencies
can therefore bevariedby VR1.
R. VR, R.
Fig.
4. Low frequency
operationof NFB type
tone
control
circuit
High Frequency Operation
The considerablysmallerreactance
of C1andC, at
high frequency in comparison
with VR1 effectively
shorts VRr to from an equivalent circuit such as
that shown in Fig. 5. C3 reactance decreases
in
the samedegreethat the frequency increases
and
the NFB amount is now mainly controlled by the
VR2 slider position. Consequently,
the gainat high
frequencies
canbevariedby VR2.
R" YR, R.
Fig.5. High
frequency
operation
of NFB type
tone
control
circuit
ToneDefeat
Circuit
By setting the TONE switch to OFF, the above
described
tone control circuit becomes
bypassed.
5.3 POWER
AMPLIFIER
The circuit diagramfor the power amplifier section
isshown
in Fig.6.
The input stage
(Q,) constitutes a differential am-
plifier, employing a dual transistor (a 2-in-1tran-
sistor "package" possessing
the functions of 2
separate
transistors). The second stage
(Qr, Q.) is
alsoa differential amplifier, but with the inclusion
of a current mirror (D,, Qo). Since
the Qabase-
emitterjunction corresponds
to adiode,thepoten-
tial on the anode of D1 and the emitter of Q+
will
be the same.Consequently,
the potential drops
across R' and R2 will also be equal. So if the
resistance
of these2 resistorsisthe same,
the same
current will flow through both sections.
And if the
hpE of the transistor is sufficiently large,the base
current can be neglected.
That is, the Q2collector
current and the Qo collector current will be the
same.Since Q2 and Q3operate out of phase
with
each other, Q3 and Qq will operateasa push-pull
amplifier. The bias voltage for the power stageis
supplied by the potential difference produced
across
the VR,-D1, where VRl is the variable
resistorusedto set
this potential difference.D2isa
varistorwhich compensates
for thermaldifferences.
The power stage (Qr-Q,o) includes a 2-stage
Darlington connection, with the final stage
(Q7-
Qro) forming two complementary symmetrical
parallel circuits. The output mid-point is main-
tained at 0V by a balanced
plus and minus power
supply anda LOOTo
DC NFB circuit.
le

+Vcc
z
-Vcc
z
5.4 PROTECTION
CIRCUIT
This circuit protects the power transistorsin case
of overload,the speakersin case
of power amplifier
malfunction, and alsoperforms a muting function
whenthe power supply is turned ON or OFF. The
protection circuit is composed of three sections
(Fis.
7).
' Power
amplifier
+Vcc
Fig.
7. Block
diagram
of protection
circuit
1.RelayDriver
Circuit
(Fig.
8)
The relay which connects the output circuits is
driven by this circuit. It also performs a muting
function to prevent unpleasant noise during ON-
OFF operation of the power supply as well as
opening
the output circuit on command from the
detectorcircuits.
Muting Operation
Whenthe power supply is turned ON, Qu baseis
reversebiased
through Duand R1e,turning Qu
OFF.
Qr base
potential risesasCachargesthrough Rr, &
R23,&nd Qr & Q* turn ON severalsecondslater.
siA-s|5c,cltr
+Vcc
r
OUTPUT
The collector current of Qu
then flows through the
relay coil, operatingthe relay to turn on the power
amplifier output circuit. Thereverse
bias
of eu base
from D6 & Rrg disappears
when the power supply
is set from ON to OFF. Q6remainsON however,
due to the residualpower supply voltage. Cavery
rapidly discharges,Q, base potential drops and
Qr & Qs turn OFF. The relay releases
and the
power amplifier output circuit turns OFF.
Note:
Q, is normally OFF due to base bias and does not
participate in the muting operation.
i
+ VCC
(
Detectors
{t
Fig.
8. Schematic
diagram
of
relay
driver
circuit
Operation by Detector Circuit Command
Command from the detector circuits pass
through
one of D., Do or D5 and areappliedin the form of
a current flow. Q, is normally reverse biased
through R,o, but when a large current flows
through on of these diodes, Qs base potential
declines according to the voltage drop at R,a.
Q5 then turns ON, Q6 base potential rises and
Q6 turns ON. C4 rapidly discharges
and Q, base
potential drops, turning Q, & Q, OFF. The relay
releases
and the power amplifier output circuit
becomes
cut off.
Fig.
6. Schematic
diagram
for power
amplifier
r€

2. Overload DetectorCircuit
Shorting of the power amplifier load or a load
impedance below the specified value causes a
command to be sent to the relay drive circuit.
This isillustrated in Fig. 9.
Fig.9. Basiccircuitryfor overloaddetector
With the output stagein classB operation, when
Qa is operating in the positive half cycle, Qb
becomes cut off and the signal current flows as
indicated by the solid arrows in Fig. 9. Point D
potential at this time is the point A potential
divided by Rt and R3. Also, point C potential is
the point A potential divided by RE1 and RL
(load). Point D is connected.to Qr base
and point
C to Qr emitter through R2 and REz. When RL is
extremely small, the point C potential becomes
considerably lower than point D. This potential
difference forward biases Qt. Qt tums ON and
current flows in D..
Qb operates in the negative half cycle and ea
becomescut off. The signal flows is indicated by
the broken line arrows in the center of Fig. g.
Qr is biasedby the potential difference between
point C and point E. If RL is extremely small,the
point C potential becomes considerably higher
than that of point E. Q, turns ON and current
flows in D..
If large current flows in Qa and Qb, Q, becomes
ON due to the RE1 and RE2 voltage drops, and
current flows in Dr. C, prevents faulty operation
dueto externalnoise.
3; CenterPointPotential
Detector
Circuit
If a DC potential isproduced at the junction point
of the power amplifier, a command is sent to the
relay drive circuit. Fig. 10 shows this operating
principle.
Q, and Qacomposea differential amplifier. When
the sameinput is applied to both input terminals
(Q. and Qobases),no output is present.However,
if there isadifference betweenthe terminal inputs,
the difference isamplified and becomes
the output
between the two collectors. During normal opera-
tion, an AC signal only is presentat the junction
point. As C2
reactance
issufficiently low, the same
signalis applied to Q. andQa
bases,
resultingin an
absence
of output at the collector sides.
When a DC potential is produced at the junction
point, it becomes the input of Q, only. If the
voltage is negative,Q, collector current declines.
and at Qa the collector current increasesand the
potential drops, causing current to flow through
Do.
If the DC voltage is positive, Q, collector current
increases
and the potential drops, while at Qathe
collector current decreases
and the potential rises.
Current therefore flows through Ds.
Power
ornpi
ifier
Fig.10. Basic
circuitryforcenter
point
potential
detector
5.5 POWER SUPPLY
CIRCUIT
In the power stage,power is supplied independ-
ently to both left and right channels, using 2
separate
power transformers.Separatebridgerecti-
fiers (one for eachchannel)and 1-2,000pF
(x 2)
capacitors to provide the plus and minus voltages.
Power for other sectionsis supplied via a bridge
rectifier connected in seriesto separate
windings
(not those used for the power amplifier) feeding
plusand minusvoltageregulatorcircuit.

sA-s'sclcltr
6.
LEVEL
DIAGRAM
Balance Volume PRE OUT
I vwrrtr vl
amplrfrer
1 amPlifier
I
11l
Iri
rrl
li
6zv
o
Z 1^
J
L!
U
_)
l
I
I
I
I
I
L SPEAKER
i i (26.8v/80
I
I
II
l
!
fr
ll
r'i
t;
li
28.
5dB
/Power \
\amolif
ier
/
PRE
(OU
rv)
T
TAPE,
AUX
-_
(
1
50mV) _+- rO'
5dB
r
I
| 20dB
35.5dB | (Mutine
oN)
/
Eoualrzer\ |
\"rpr'tli
i '----r---
P110NO
(2.
5mV)

7. DISASSEM
BLY
FrontPanel
Loosen the setscpews
of VOLUME knob with a
hexagonal wrench. Remove all the knobs by
pulling. Remove the four nuts (B).
BottomPlate
Remove
thetenscrews
(C).
Top Gover
Remove
thefour screws
(A).
16

Control
Amplifier
Assembly
Remove
the three screws
(D). Power
Amplifier
Block
(
L)
itchAssembly
sA-9E'ootr
PowerAmplifier
Block
(R)
Removethe three screws
(F).
AmplifierAssembly
Remove
the two screws
(H).
D
Remove
the sevenscrews
(J).
17

8.
8.1
PARTS LOCATION
FRONTPANEL
VIEW
Knob
(BASS)
AAB.116 Knob
(TON
E
)
AAD.1
,I7
Front
panel
ANB-480
Knob
(TREBLE)
AAB.l1
6
Knob
(CARTR
IDGE
LOAD)
AAB117
Knob
(VOLUI\4
E
)
AAB-1
14 Knob
(FUNCTION)
AAB.1
15
o,{ fr*
F''
'"'r'l
Knob
(SPEAKERS) Knob
(BALANCE)
Knob
(POWE
R
)
AAD,lI7 AAB.l1
6AABI16 Knob
(l\ilODE)
AAB.l16
Knob
(MUTING)
AAD ,I,17
Knob
(TAPE)
AAD,l
17
Phone
jack
(PHONES) Knob
(FtLTER)
AKN,OOS AAD.117
Knob
(LOU
DNESS)
AAD.l17

8.2 FRONT
VIEWWITH
PANELREMOVED
Variable
reststor
(BASS
100H
2
)
ACV 175
Variable
resistor
(BASS
50Hz)
ACV 176
Rubber
bracket
AEB.092
Variableresistor
(voLUr!1E)
ACV-171
siA-9500tr
Rotary
switch
(CARTR
IDGELOAD
)
ASD.O
55
Rotary
switch
(FUNCTION)
ASD,O52
Variable
resistor
(TREBLE
20kHz
)
ACV
173
Lever
switch
(TONE)
ASK109
Variableresistor
(TR
EBLE
1OkH
z)
ACV.174
f.f
'E-E'';
\nn./;)
t
I
nn. o
K; Larnpwithleads8V,50mA
AE1,069
Leverswitch
(POWE
R
)
ASK.124
Phone
jack(PHON
ES)
AKN.OOB
Variallleresistor
(BALANCE)
ACV
_112
Leverswitch
(H
IGHFILTER)
ASK 110
Leverswitch
(LOW
F
ILTER
)
ASK.1
1
O
Rotar
y swllch
(SPEAKERS)
ASD 054
Lever
switch
(TAPE
INONITOR
)
ASK,113
Lever
switch
{TAPEDUPLICATE)
ASK-
i13
Rotary
switch
(l\,4ODE)
ASD
053
Lever
switch
(t\4uTtNG)
ASK.
]1O
Lever
swrtch
(LOUDNESS)
ASK.
11O

8.3 TOP
VIEW
Equalizeramplifierassembly
AWF-O24
Variable
resistor
(vo
LUr\4E)
ACV171
Controlamplitier
assembly
AWG-045
Switchassembly
AWS-109
Power
amplifierassembly
AWH-052
Power
transJormer
(R)
ATT.375
Electrolyticcapacitor
12,000sF63V
ACH-065 Power
amplilier
assembly
AWH
052
Power
transformer
(L)
ATT,374

a
I
sA-s'5c,0II
8.4 BOTTOM
VIEW
Switchassembly
AWS 109
Leverswitch
(POWER
)
ASK 124
,--f, ",L ----' riL rlf
t
Power
amplifier
assemt)ly
AWH,O52
Electrolyticcapacitor
I
2.000!F63V
ACH065
Poweramplif
ierassembly
AWH 052
?1