Pioneer SA-8500II User manual

D(t;
t-
(Dr:roruecn

t
sA-a5C,Cltr
^ MODEL
SA-8500IICOMES
lN FOURVERSTONS
DTSTINGUISHED
ASFOLLOWS:
re
A
This
service
manualisapplicable
to theKu-type.
WhenreparingtheKC-type,Hc'typeorS-type,
please
seetheadditionalservice
manual.
CONTENTS
l.
2.
3.
4.
5.
6.
7.
8.
11
11
12
16
18
l9
20
CONNECTIONDIAGRAM
SPECIFICATIONS
BLOCK
DIAGRAM
5,2 ToneControls
LEVELDIAGRAM
5
6
7
9
13
14
15
21
22
23
24
FRONT
PANEL
FACILITIES
CIRCUITDESCRIPTIONS
5.1 EqualizerAmplifier
a.
*r: 5.3 Power
Amplifier
5.4 Protection Circuit
5.5 PowerSupplyCircuit
PARTSLOCATION
8.1 FrontPanelView
DISASSEMBLY
8.3 Top
View
8.5 RearView
ADJUSTMENT
4.2 FrontViewwith PanelRemoved
8.4 Bottom
View
9.
10.
Type Voltage R€marks
KU 120V only UL {U.S.A.)
approved
KC 120Vonly CSA (Canada)approved
HG 22OV and 24Ov (Switchable) SEMKO
(Sweden),
NEMKO
{Norway},
DEMKO
(Denmark)
andEl {Finland} approved
s11OV. 12OV. 22Ovand
24OV
{
Switchable
}Generalexport model
t\ EXPLODEDVIEWS

11. SCHEMATIC DIAGRAMS.
P.C.
BOARD
PATTERNSAND
PARTS
LIST
11.1 Miscellanea
11,2 Schematic Diagram
.
11.3 SwitchAssembly
(AWS-108)
11.4 Phono JackAssembly
(AWX-I07)
11.5 EqualizerAmplifierAssembly
(AWF-023)
11.6 Control AmplifierAssembly
(AWG-044)
11.7 Power
AmplifierAssembly
(AWH-05I
)
12. PACKING
-l
32
33
35
41
42
46
50
53
-
)a
@
\

I
a
)1.
SPECIFICATIONS
Semiconductor
Transistors .....47
Diodcs.. ......29
Power Amplifier Section
Circuitry
. 2-stagcdifferenrial
amplifier
parallcl
PPdirect-coupled
OCL.
ContinuousPower
Outputform 20Hertzto 20,000Hertz
(Both
channelsdriven)
. . 60watts
per
channel
(8ohms)
75watts
per
channel
(4
ohms)
TotalHarmonicDistortion
at20Hertzto 20,000Hertz
Continuousratedpoweroutput .... 0.O5o/o
3owatts
per
channcl
power
output,8ohms
. . . . 0.01y.
Iwatt
per
channel
power
output,8ohms
. . . . . . 0.01%
lntermodulationDistortion
Continuousrated
power
output . . . 0.05%
3owatts
per
channel
power
output,8ohms
. . . . 0.01%
Iwatt
pcr
channel
power
output,8ohms
. . . . . . 0.01y.
Frequency
Respon5c
.. . . . 5Hertzto100,000Herrzl0,dB
lnput
(Sen
sitivity/
lm
pedance)
POWERAI\4PlN
..... ... 1V/5Okohms
Output.. .. Speaker: A.B,A+B
Preamplifier Section
Circuitry
Equalizer
amplifier:lst stagedifferential
amplifier
3-
stagedirect-coupled
A classSEPP.
Controlamplifier: lst stagedifferential
amplifier2-
stagcdirect-coupled,NFB
type.
Input
(Sensitivity/l
mpcdance)
PHONOl . . . 2.5mV/50kohms
PHONO2 . . . 2.5mV/50kohms
CARTRIDGELOAD. . . . . BothPHONO
I and2,100,
200,300,400pF
TUNER
. .. 150mV/50kohms
AUX ... .. 150mV/50kohms
TAPEPLAY1...... 15OmV/5Okohms
TAPEPLAY2........ l50mV/5okohms
PHONO
OverloadLevel
(T.H.D.
:0.05%)
PHONOL ...250mV(1kHz)
PHONO2 ....250mV(1kHz)
Output
(Level/
lm
pedance)
TAPEREC1...... 150mV
TAPEREC2...... .........'l50mv
PRE
OUT lv/2kohms,
6V/2kohms
(Max.)
TotalHarmonicDistortion
(20H2
to
20,000H2)
...... ..... o.o2.A
FrequencyResponsc
PHONO
(RIAA
Equalization)
TUNE
R,AUX,TAPEPLAY
Filter
LOW
......
....
H|GH..........
Loudness
Contour
(Volume
controlsetat
sA-a5ClC'II
20Hzto20,000H2
t0.2dB
.5Hzto 50,000H2
j
?dB
ToneControl
BASS... ... r10dBl25Hzl5l9zll01Hz)
TURNOVERfrequency1Q0Hzl200Hzl4O0Hz
TREBLE. ...i10d8(8kHzl'l6k9zl32k1z)
TURNOVERfrequency2kHzl4kHzlSkHz
... 15Hz
(6dB/oct.)
. . 8kHz
16d
B/oct.)
40dB
position): +6dB
(100Hr)
+3dB(1okHz)
Hum
and
Noise
(lH
F,
short-circuited,
A network)
PHONO.
TUNER,
AUX,TAPEPLAY
. . .
l\4uting
..
Miscellaneous
Power
Rcquiremcnrs 120V60Hzonly.
Powcr
Consumption l80watts (UL)
390VA(CSA),
490watts
(Max.)
Dimensions . a20(W)
x 150
(H)
x 376
(D)
mm
16-9116x 5-118x 14-13116
in
Weighl . . WithoutPackage:
13.9kg
(301b
l0oz)
With
Package: 15.8kg
(341b
13oz)
Furnished Parts
Operating
Instructions .......1
Connection
Cord
with
PinPlugs ........1
Hcx.Wrench
(Used
for fasteningVolume
Knob). . . . . . 'l
NOTE:
Specificotions
ond thedesign
subjectto possible modifica-
tionu,ithoutnoticedue
to improuements.
...75d8
. ..95dB
0,20d8
I Headphone: Low
impeddnc
c
r DampingI dclor
(20Hert1
lo 20.000Hcrt./,
8ohm:) . . . 30
Hum
andNoise
(lHF,
short-circuited,
A network). . 110d8
!
p

2.
CONNECTION
DIAGRAM
TURNTABLE1 TUNER
TURNTABLE
2
'r'l
CARTRIDGE
TAPEPLAYE
R
TAPEDECK2 JU
-n
Connectto
ground
terminals
etc. GROUND
LEA
D
GROUNDING
TOEARTH
F
@
A SPEAKE
RSYSTEM B SPEAKER
SYSTEM
I

3.
FRONT
PANEL
FACILITIES
BASSTURN
OVERSWITCH
Selects
thefrequency
below
which
theBASS
controt
tonc
adjustments
apply.
Ser
swirchto 100H2,
200H2
or 40OHz
accordingto listening
room
andspeaker
system
character-
isticsorpersonalpreference.
TONE
SWITCH
ln theON pos;tion,
toneadjustments
canbe
performed
with the BASS
and
TREBLE
controls.
When
setto the
upper
(OFF)position,
the tone
control
circuits
aredis-
engaged
andfrequency
response
isflat.
Thisfunction
is
convenient
for checking phono
cartridge
andspeaker
tone
quality
andlistening
room
acoustics.
Setto ONposition
to energize
54-850011.
Aftersetting
to
ON, there
isa brief
delay
before
sound
isobtained.
This
is due to the operation
of the muting circuit which
prevents
noisewhen
the PowER is
switched.
Thisfunc-
tion does
not indicate
difficulty
and normal
operating
condition
isattained
inafew
seconds.
ThePOWER
switch
also controls
the rear panel
SWITCHED
convenience
outlets.
PHONES
JACK
When
listening
withstereo
headphones,
connect
them
to
this
jack.
NOTE:
SetSPEAKERS
switch to OFF when listening
only with
headphones.
SPEAKERS
SWITCH
Selects
speaker
system
operation.
OFF: Sound
notobtained
fromspeakers (when
using
headphones).
A: Sound
obtained
from speakers
connected
to A
speaker
terminals.
B: Sound
obtained
from speakers
connected
to B
speakers
terminals.
A+B: Sound obtainedfrom speakers
connected
to
both
A andB
speaker
terminals.
NOTE:
When listening with headphones or to temporarily inter-
rupt the speaher sound, set switch to OFF or to an
unusedspeaher position.
BASS
ANDTREBLE
CONTROLS
Controlsfor adlusting
lowandhigh
frequency
tones.
With
the TONEswitch
setto ON, turningthe BASS
control
clockwise
from
centerenhances
thefrequency
bandbelow
the point selected
by the BASS
TURN OVER switch,
while counter-clockwise
rotation
attenuates
this band.
In a sinrilar
manner,
the TREBLEcontrol
adjusts
the
frequency
range
above
the
point
selectedby the
TREBLE
TURN OVERswitch.
TREBLE
TURN
OVER
SWITCH
Selects
thefrequency
above
which
theTREBLE
control
tone adjustments
apply.
Set to 2kHz, 4kHzor SkHz
according
to listening
roomand
speaker
systemcharacter-
istics
or personal
preference.
t'-""1
LOWFILTER
SWITCH
Set
to 15Hz
position
in the
event
thatturntable
rumble.
recording
cutting noise
or other low frequency
noise
becomes
ob
jectionable.
Attenuation
in the frequency
band
below
15Hz
is
6dB/octave.
HIGH
FILTER
SWITCH
Set
to 8kHz
position
if record
scratch
noise
orother
high
frequency
noise
becomes
objectionable.
Attenudtion
in
thefrequency
band
above
8kHz
is
6dB/octave.
BALANCE
CONTROL
Control
for
adjusting
stereo
balance
between
left
andright
speaker
systems
or headphones.
Turn clockwise
from
center
to increase
right
(R)
channelvolume
and
counter-
clockwise
from center
to increase
left(L) channelvolume
in
order
toobtain
abalance.
VOLUI
Adf
usts
atten
ua
arbitrar
binatior
wider
r
CARTR
Switch
match
I{
t--
I MUflN(
I SwitchI
I control
I volume
I the ne(
I controt.
I
I
LLOUDN
When
lis
enhance
numan
(
switch
c(
7
POWER
SWITCH

lones.
With
SScontrol
)andbelow
5R
switch,
thisband.
idjusts
the
ETREBLE
LE
control
zor 8kHz
Icharacter-
f'-"''r
ablerumble,
uency
noise
e frequency
rrother
high
tenuition
in
left
andright
ckwisefrom
andcounter-
lnnelvolume
CARTRIDGE
LOAD
SWITCH
Switch
for selecting phono
circuit
match the load capacitance
of theinputcapacitance
to
employed
cartridge.
VOLUME
CONTROL
Adlusts
speaker
and headphonevolume.
Scale
indicates
attenuation
in dB with maximum
volume
assignedan
arbitrary
value
of 0dB.
Controlcanalso
beusedin com-
bination
with theMUTING
switchto Drovide
afiner
and
wider
rangeof adjustment.
sA-A5Clcltr
FUNCTIONSWITCH
Selects
desired
playbackprogram
source.
PHONO2: To play
recordson aturntableconnectedto
the
PHONO
2 jacks.
PHONO1: To play recordson a
turntable
connected
to
thePHONO
1
iacks.
TUNER: To listen
to broadcasts
with a tunercon-
nectedto theTUNER
iacks.
AUX: To play
a
component
connectedtotheAUX
iacks.
TAPEMONITORSWITCH
Employfor tape
playback
or to monitora recording
in
progress.
1
: Playback
or monitoring
of a tape deck
connectedto theTAPE1
jacks.
SOURCE: Be sureto setto this position
whennot
usingthetapedeckfor playback.
2: Playback or monitoring of a tape deck
connectedto theTAPE2 iacks.
NOTE:
Whenlisteningto recordsor broadcasts,be
sureto set
this switch to SOURCE.Sound will not be obtained
from speahersif setto I or 2.
TAPEDUPLICATE
SWITCH
Employwhenusingtwo tapedecksfor duplicationor
editing.Besure
to setto the OFFpositionatothertimes.
1 --> 2: Duplicationof tape
from TAPE1(playback
mode)
to TAPE2 (recording mode).
OFF:
)
T'"-'-l
(0rrrorueen IEREO AMPL $A-8500
[
MUTING
SWITCH
Switchfor reducingvolume
by 20dBfromthe VOLUME
control
setting.Convenient
for temporarily
reducingthe
volumewhen
changingrecords
of tapes,
since
iteliminates
the need for continuallyread
justing the VOLUME
control.
OUDNESS
SWITCH
Whenlistening
atlowvolume
settings,
setswitchtoONto
enhance
low andhighfrequencies.
The response
of the
human
ear
to sounddiffers
accordingto loudness.This
switch
compensates
for
thiseffectatlowvolumes.
Set to this position when not using
the
duplicationfeature
(this
includessimultane-
ousrecording
with two tapedecksandtape
playback).
Duplicationof tapefromTAPE
2 (playback
mode)toTAPE1 (recording
mode).
SWITCH
Reversesleft
andrightchannelstereosignals
andreproducesthemstereophonically.
2- 1:
MODE
REV:
STEREO: Setto this
position
for normal stereorepro-
duction.
L + R: Mixes left and right channelsignals
and
reproducesthemmonophonically.
L: Left channelsignal is reproduced
mono-
phonically
frombothspeakers.
R: Right channel signalis reproduced
mono-
phonically
frombothspeakers.

4.BLOCK DIAGRAM
Ssa o
S+a-d
' TAPE
MONITOR
1.TAPEI 2 OFF
3. TAPE
2
Ssa-c
,X0DE
1 REV
3. LrR
.5
R
2 STEREO
I oncc I POwrn
BA
SS
PRE
OL
TREBLE
CONTROL
AMPLIFIER l-
L
PRE
POWEF
tt
SV'JITCHES
,
Sra-d'FUNCTI0N
t.
PH0N0
2
3 TUNER
Szo,b,C
SELECIOR
1.
100pF
3. 300pF
S3o-d,DUPLICATF
l.
l*2
3.2*1
sqc
s+a Ssa VRza,b
,BA
LANCE
VR
ra,u'
V0LUIIE
6 VRru
c^
rbo,b
Sra,
s
Sao,
u
Sso,
o
Stoo,
u
' IlUTING
: TOUDNESS
' HIGH
FITIER
' LOW
FILTER
.TONE
'SPEAKER
] OFF ?
3 B 4.
OFF
- -20d8
OFF
_.
ON
OFF
- BkHz
OFF 15Hz
OrF
- 0N
A
A+B
Srz RE
LAY
S13
. POWEROFF
-
S1a
' BASSTUR
N
0V
I 100H2
7.',
a / ^^ |
J..tLrul.'17
Sl5,TREBLE
TURN
1.
Tk\z l.
z
3 BkHz
PHONO
1
PH(')NO
2
AUX
TU
NFR
LEFT
CHANNEL
RIGHT
CFIANNET
EQUALIZER
AI'lPLIFIER "l
-"
1t1
vTAPE
|PLAY
LREc
-PLAY
TAPE
2
LREC
J
q^^
Sno
5+u
"9
o6b
I
I
vRto
I
c
J2i) .PLAY
TAPE
1
.REC
. PLA'l
TAPE2
LREC
2. Pr-10N0
1
4.
AUX
2 200pF
4.
400pF
2. OFF
EQUA
LIZER
AIlPLIFIER CONTROL
AHPLIFIER
4 L Srra-a

. RE
LAY
..
POIIEROFF
- ON
. BASSTURNOVER
1.
l00Hz
2.200H2
3.400H2
TREBLF
TURNOVER
1.
LkHz 2. 4kl,z
3.
BkHz
PO
r-WER
AI1PLTFIER
L
PROTECTION
CIRCUIT
To
pnotection
clr^cuit
To
pnotection
circuit
Toequalizer^
amp
Tocon
fr-oI amp
Topowen
amp r
To
L
ch powenampl
proteclron
circuit
eguallzen
amP
Contr0
I amP
T
To
R
ch powenampL
e
u9o
c
JIo
o8a
ls
I
TJJ
T
FIER LEFT
CHANN
EL
I
I
RIGHT
CHANNEL
f rloru,s
SPEAKFRA
?e
* "sb
I
e
ISeu
T
I
)-
PRE
OUT
POWER
IN
Topr
otection
cir-cuit ;I
c
e13
CP
AC LTNE
Srz
Srs
a
u14 r0
To
To
i
I
i
I
,
POWER
AIlPLIFIER
Srs

A5.CIRCUIT
DESCRIPTIONS
z=50Krt
c) c=roopr
PHONO
2
PHONO
I
CARTRIDGE
LOADSWITCH
sA-El5ClClII
-vcc
+
lr.
rl
Fig.
L Schematicdiagram
of equalizeramplifier
,li 5.1 EOUALIZER
AMPLIFIER
The circuit diagram for the equalizer amplifier is
shown in Fig. 1. The two separatephono inputs
are selected by the FUNCTION selector on the
front panel. The input capacitanceon the PHONO
terminals can be adjusted to 4 different levels
(100pF, 200pF, 300pF, and 400pF) by meansof
the CARTRIDGE LOAD control knob which
switchesin, or out, additional capacitorsin parallel
with the input terminal. Hence, the load capaci-
tance of the phono cartridges can be changed,
greatly effecting the cartridge's frequency response
in the high frequency range, and thus providing
considerablevariation in its characteristics.
The first stage
of the equalizer amplifier (Q' & Qr)
isadifferential amplifier usingPNPtransistors.The
next stage
(Q.) is a bootstrap circuit employing C' ,
R1 to provide high voltage gain. The output stage
(Qo & 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 an over-
Ioadinput level
of 250mV (RMSat lkHz) with no
morethan 0.05%distortion.
The equalizerelements
(Cr, C.,,
R, andR.) consist
of polypropylene film capacitors
(tolerance127o),
and metal frlm resistors
(tolerancet1%). Phono
equalizer
RIAA deviationhasbeen reduced
to less
than10.2dB (2OHz
- 2OkHz\.
5.2 TONE CONTROLS
Incoming signalsareamplified to the required level
by the 2 stage amplifier which usesa differential
amplifier at first stage.The tone control circuit is a
collector-basenegative feedback circuit (NFB) and
features 3 tumover frequencies for both bass
and
treble.
The basic principles of the NFB type tone control
circuit areoutlined in Fis. 2.
'fl
h
rl
0d0ut
hI|lt n, vn, n,
L.-
,,,
-{P
c.
Rl
,c. d
Fi1.2.
t, vR, R,
Basiccircuitryof NFB typetonecontrolcircuit
iri

Midrange Operation
The Cr and C, 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
respectto the midrange. In this figure, the circuits
parameters
are not changedby any changein pos!
tion of the VR, and VR. sliders.
The NFB amount
is therefore fixed and the circuit gain is also fixed
without regard
to VRr and VR, slider positions.
Fig.
3. Midrange
operation
ofNFB type
tonecontrol
circuit
Low Frequency Operation
The reactance of C, and C, increases
at low fre-
quency to form a circuit asshown in Fig. 4. This
ipactance increases
in proportion to the frequency
declines. Also, the NFB amount varies grea y
according to VR1 slider position. The circuit sain
at low frequenciescantherefore bevaried by Vh1.
Capacitance of C1 and C, is changed by BASS
TURNOVER switch (by adding acapacitor to each
in parallel). This a.llows
selection of the frequencv
at which VR, begins
to take effect.
that shown in Fig. 5. C. reactance decreasesin
the same de$ee that the frequency increases
and
the NFB amount is now mainly controlled by the
VR, slider position. Consequently,the gain at high
frequencies
canbe
variedby VR:.
C. capacitance is changed by TREBLE TURN-
OVER switch (by adding another capacitor in
series) to provide selection of the frequency at
which VR: begins
to take effect.
Fiq.
5. High
frequency
operation
of NFB
type
tone
control
circuit
5.3 POWER
AMPLIFIER
The circuit diagram for the power amplifier section
isshown
in Fig.6.
The input stage(Q1) constitutes a differential am-
plifier, employing a dual transistor (a 2-in-1 tran-
sistor "package" possessing
the functions of 2
separatetransistors). The second stage(er, e.) is
also a differential amplifier, but with the inclusion
of a current mirror (D1, Qr). Sincethe ea base-
emitter junction conespondsto adiode, the poten-
tial on the anode of D, and the emitter of eo will
be the same. Consequently, the potential drops
across R, and R, will a.lsobe equal. So if the
resistance
of these 2 resistors
is the same,
the same
current will flow through both sections.
And if the
hpg of the transistor is sufficiently large, the base
current can be neglected.That is, the e. collector
current and the Qa collector current will be the
same. Since Q, and Q3 operate out of phasewith
each other, Q: and Qo will operate asa push-pull
amplifier. The bias voltage for the power stage
is
supplied by the potential difference produced
across VR1- D3
- D, , where VR1 is the variable
resistor usedto setthis potential difference. D, is a
varistor which compensates
for thermal differences.
The power stage (Qs- Q16) includes a 2-stage
Darlington connection,with the fina.l
stage
(e7-
Qto) forming two complementary symmetrical
parallel circuits. The output mid-point is main-
tained at 0V by a balanced plus and minus power
supply and a 700% DC NFB circuit.
f)
I
'l
l
fr
vn.
Fig.
4. Low
frequency
operation
ofNFB
type
tone
control
circuit
High Frequency Operation
The considerably smaller reactanceof C, and C" at
high frequency
in comparison
with VR, effectivelv
shortsVR, to from an equivalent
circuit such as

-r
''r
i
sA-aE'ootr
+vcc1
OUTPUT
+vcc2
INPUT
ft.'f
r\i'^
5.4 PROTECTION
CIRCUIT
This circuit protects the power transistors in case
of overload,the speakers
in case
of power amplifier
malfunction, and also performs a muting function
when the power supply is tumed ON or OFF. The
protection circuit is composed of three sections
(Fis.7).
Por!r.r||0lili!r
Fig.7. Blockdiagram
of protection circuit
1.RelayDriver
Circuit
(Fig.
8l
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
detector circuits.
04
Fig.6. Schematicdiagram of power amplifier
Muting Operation
When the power supply is tumed .ON, Qu baseis
reverse biased, through D6 and R26, turning Qo
OFF. Q? basepotential risesas Cacharges
through
R22
& Rz3, and Q?turns ON several
seconds
later.
The collector current of Q7then flows through the
relay coil, operating the relay to tum on the power
amplifrer output circuit. The reversebiasof eu base
from Du & R2o
disappears
when the power supply
is set from ON to OFF. Quremains ON however,
due to the residual power supply voltage. Ca
very
rapidly discharges, Q, base potential drops and
Q? tums 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 operction.
{tr- Fig.
8. Schematicdiagram
ofrelaydrivercircuit

Operation by Detector Circuit Command
Command from the detector circuits pass
through
oneof D., Do or D, andareappliedin the form of
a current flow. Q5 is normally reverse biased
through R1a, but when a large current flows
through on of these diodes, Q, base potential
declinesaccording to the voltage drop at R,a.
Q, then becomes ON, Qu base
potential risesand
Qu becomesON. Co rapidly dischargesand Q,
base potentia.l drops, tuming Q? OFF. The relay
releasesand the power amplifier output circuit
becomescut off.
2. OverloadDetecto?Circuit
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 is illustrated in Fig. 9.
Qa emitter is connected to Q, base
through R, and
the junction point to Q, emitter. When RL is
extremely small,Iargecurrent flows in Qa,Q, turns
ON due to the RE, voltagedrop, and current flows
in D.. C1preventsfaulty operation due to extemal
norse.
oirplifier
eq
Fig.
9. Basic
circuitry
of overloaddetector
3. CenterPointPotential
DetectorCircuit
If a DC potential isproduced at the junction point
of the power arnplifier, a command is sent to the
relay drive circuit. Fig. 10 shows this operating
principle.
Qr and Qocompose a differential amplifier. When
the same input is applied to both input terminals
(Q. and Qo
bases),
no output is present.
However,
if there is adifference between the terminal inputs,
the difference is amplified and becomesthe output
between the two collectors. During normal opera-
tion, an AC signal only is present at the junction
point. AsCrreactanceissufficiently
low, the signal
is not applied to Q3, resulting in an absenceof
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 Qo the collector current increasesand the
potential drops, causing current to flow through
If the DC voltage is positive, Q. collector current
increases
and the potential drops, while at Qo the
collector current decreases
and the potential rises.
Current therefore flows through D. .
Fig-10. Basiccircuitryof center
point
potential
detector
5.5 POWERSUPPLY
CIRCUIT
The power stage
providesvoltage independently to
both left and right channels, using 2 separate
power transformers. Separate
bridge rectifiers (one
for eachchannel)and 10,000gF (x 2) capacitors
provide the plus and minus voltages. Positive
voltage for other sections is provided by full-wave
rectification from the samewinding on the power
transformer that is used for the left channel, anda
negative
voltage from the corresponding winding of
the right channel transformer. Both are supplied
via voltageregulator circuits.
There is only one pair of secondary windings in each the
lcfl and righl channel
powcr lrans[ormcrs.
t
{

6.
LEVEL
DIAGRAM
siA-E'5clclil
SPEAKER
't A
PRE
OUT
PREOUT
(
1V)
- -SPEAKEF
(23.7v,
&))
amp1er
f\il |
[*i
.D
1
d
J-
20
10
0
10
-20
30
50
-60
27.5dB
/Power l
\afn0lrlrer/
lf
35.5dB
iEqual
zer
\
\amplrfrer
/
r (Muting
ON)
17dB
APL. AU\ .r0 5oB
/r5O,rV) ./ /Control\
\am
plif
rer
/
(2.
5mv)
tzel
Irer
FREOUENCY
AT lKHZ
rtf

7.
DISASSEMBLY
TopCover
Removethefour screws
(A).
Front Panel
Loosen the setscrewsof VOLUME knob with a
hexagonal wrench. Remove all the knobs by
pulling. Removethe four nuts (B).
BottomPlate
Removethe ten screws
(C).

ControlAmplifierAssembly
Remove
thethreescrews
(D).
PowerAmplifier
Block
(L)
Remove
thethree
screws
(E).
CtA-E'5clC'tr
PowerAmplif
ier
Block
(Rl
Remove
thethreescrews
(F).
Equalizer
AmplifierAssembly
R€move
thetwo screws
(G).
SwitchAssembly
Remove
thesevenscrews
(H).
17

8.
8.1
PARTS LOCATION
FRONT
PANEL
VIEW
Knob
(TR
EBLE)
AAB.116
Front
panel
ANB.481
Knob
(TONE)
AAD-117
Knob
{BASS)
AA8.1r6
Knob
(VOLU|\ilE)
AAB114
Knob
(CART
RtDG
E
LOAD)
AAB117
Knob
{
FUNCTION}
AAB.11
5
;'ry;[
::|l -iiq'
tr'
;l
(
I
o
Knob
(POWE
R
)
AAD-1I7
Phone
jack
(PHON
ES)
AKN-OO8
Knob
(SPEAKERS)
AAB.l
16
.: ..r
FF
.,,,,
..".,, ile5001
,l .r"'.1
il[
-.Frl-"F! tn
]L.",,!
Knob
(TApE)
AAD-117
Knob
(l\4ODE)
AAB.116
Knob
(MUTING)
AAD.1
17
Knob
{LOUDNESS)
AAD.l17
7
(
Knob
(F
ILTE
R
)
AAD.117
Knob
(BALANCE)
AAB.I16
I

a-
I 8.2 FRONTV|EWWtrH
PANELREMOVED
SA-BSOOII
Rotaryswitch
(CARTR
IDGELOAD)
ASD,065
(ASD-055)
Rotaryswitch
(FUNCTTON)
ASD,052
Leverswitch
(TO
NE)
ASK
109
Variableresistor
(BASS)
ACV136
Rotaryswitch
(BASS
TURNOVER
)
ASD057
Rubberbracket
AEB-092
Rotaryswitch
(TREBLE
TURNOVER
)
ASD.O56
Variable
resistor
(VO
LU
I\4
E)
ACV,171
I
Variableresistor
(TREBLE)
ACV-136
a),
)
'f;. J r:
'ar,r,o,, 'g)
tt E.E./.iJ
nno.(, I T
E.
nsl
Lever
switch
(POWER)
ASK.1
24
Lamp
withleads
BV,
50mA
AEL081
Phone
jack(PHON
ES)
AKN
OOB
Rotaryswitch
(SPEAK
E
RS)
ASD
054
Variableresistor
(BALANCE)
ACV.l72
Lever
switch
(TAPE
tVtON
tTO
R)
ASK-1
13
Lever
switch
{TAPE
DUPLICATE}
ASK,'l13
Rotary
switch
([4ODE)
ASD.053
Lever
switch
it\,1uItNG
)
ASK-
11O
Lever
switch
{LOUDNESS}
ASK11O
Lever
switch
(LOW
FILTER}
ASK1
'IO Lever
switch
(H
IGHFILTER)
ASK11O

8.3 TOP
VIEW
Equalizer
amplifier
assembly
AWF-023
Variable
resistor
(VOLUI\4E)
ACV-
r71
Control
amplifier
assembly
AWG-044
Switch
assembly
AWS.108
Power
amplifierassembly
AWH-05'1 Power
amplifierassembly
AWH-051
Power
transformer
(L)
ATT.366
Power
transformer
(R)
ATT.367 Electrolytic
capacitor
10,000sF
50V
ACH-064

IsiA-a50clu
8.4 BOTTOMVIEW
Ceramic
capacitor
0.01sF250V
ACG-001
Lever
switch
(POWER)
ASK-124
Switch assembly
AWS.108
Power
amplifier
assembly
AWH.05I
Electrolytic
capacitor
10,000l1F
50V
ACH-064
21