Sansui AU-70 Troubleshooting guide

OPERATING INSTRUCTIONS
& SERVICE MANUAL
STEREO CONTROL AMPLIFIER
SANSUI AU-70
SANSUI ELECTRIC COMPANY LIMITED

This amplifier has a maximum output of 50 watts (25W-25W)
and features
an amazingly low distortion factor of not more
than 0.15% at 20W. A high-quality amplifier with many exci-
ting features, it
is delivered to you with Sansui's fullest confidence.
This booklet explains the steps necessary for operating and
caring for your new
the .AU-70. Read an the instructions
carefully and retain for future use.
CONTENTS
FEATURES. ......................................................... 3, 4
SPECIFICATIONS ..... ... ..... ... ...... ... ... ... ..... ........... . 5
CHARACTERISTICS. ............................................. 6
CONNECTIONS.......................................... .. ........ 7, 8, 9, 10
SWITCHES AND CONTROLS ........ . ..... .......... .... .. .. .. 11, 12
OPERATIONS.... ................ .. .. .... .. .. ...................... 13, 14
HI NTS ON USE ................ .. .............. .. .............. .. 15, 16
SERVICE NOTE ................ .......... ...... ...... ............ 17, 18
PAR TS LIST ...... ...... .. ..... . ... . ........................ .... .. 19, 20, 21
SCHEMATIC DIAGRAM .......... ........ ... . .......... . ...... . 22
PARTS LAyOUT ... ..... . ... ... . ............ ... .. ..... .. ..... ..... . 23
SUI
STEREO CONTROL
AMPLIFIER
AU-70

FEATURES
7189A P.P. PRODUCES 40W WITHOUT
PISTORTION ( MAX . 0.95% AT 30 CPS AND
·0.15% AT 1,000 CPS )
The 7189A power tubes operate in class AB,P . P.
(fixed bias) Jor high-fidelity reproduction. Their
combined . maximum output is limited to 50 W .
The amplifier incorporates a multiplex feedback
circuit (total negative feedback: 26 dB) for the
first time in this class of amplifiers in Jilpan.
This makes it extremely low in distortion over
the whole frequency range. Total harmonic dis-
tortion at 1 kc is 0.15%. At 30 cps, a very low
frequency at which it is extremely difficult · to
minimize ha r monic distortion, the distortion is
limited to
not more than 0. 95% . This is quite
a feat for a 50-watt amplifier. Another remarkable
feature is the damping factor of 18, a figure which
is lower than that of triode power tubes ' coupled
in P.P. This is why bass sounds come out with
su ch clarity .
- 3
NFB USED IN ALL AMPLIFIER CIRCUITS
,
FROM PREAMP TO POWER AMPLIFIER
The low distortion of the power amplifier is
meaningless if the preamplifier generates distor-
tions.
Your AU-70 uses a three - stage amplifier
circuit
in its interm ediate or cpntrol amplifier-
unlike conventional one-stage control amplifiers-
and has all its circuits in a single negative -feed-
back loop. These make your AU -70 free from
noise
and distortion.
SUPER-PRECISION TRANSISTOR PREAMP -
LIFIER ELIMINATES HUM AND NOISE
The exclusive Sansui four-transistor preamplifier,
which features a transistor circuit factor of 4-as
compared with conventional 5-1O-al1d a transistor
noise factor of 2
dB-as compared with conven -
tional 5 dB, eliminates
hum and noise, the enemy
of high -fidelity reproduction. The amplifier has
a
much better SIN ratio and a gain three times
larger than vacuum-tube amplifiers.
EACH CHANNEL CAN BE OPERATED IN-
DEPENDENTLY EQUIPPED WITH TONE
DEFEAT
Each channel has independent tone contro ls for
bass
and treble. This makes fine adjustment
possible. Moreover, each channel is equ ipped
with tone defeat which cancels the tone control
circuits.
You can easily obtain a flat frequency
response
without causing any undulation in
response
or redu ced gain in bass and treble as in
the case of conventional mechanical control by
means of a tone volume knob. Therefore, you
can
get an accurate, perfectly flat response from
your AU-70 just by flipping a switch.
BLEND CIRCU IT PERMIT CONTINUOUS
S HIFT FROM MONAURAL . TO STEREO
As you turn the "BLEND" switch clockwise,
y
our AU -70 gradually shifts from monaural to
stereop honic repr~duction. This feature enables
you to get full stereophonic effect by compensa-
ting program sour ces which give a, particularly
s
tron g effect of th e conce rt ha lL
EA S Y- TO- READ THREE - RAN GE OUT P UT
L EV EL METERS
Each output level meter can be switched over to
any of
the three scales of 5, 10 and 25 watts.
The meters not only give direct readings of both
ch anne ls, but also indicate any lack of balance
between the right and left outputs. These prove
very useful
in balancing the outputs .
THREE - DIMEN S IONAL P ERFORMANCE
POSSIBLE WITH CENTER - CHANNEL
OUTPUT TERMINAL
Y~ur AU -70 ha s an ou tput terminal for the
center -channel amplifier. Connect it to your
monaural amplifier to produce a three-dimensional
effect.
EQUIPPED WITH ADVANCED , HIGH-
PERFORMANCE ACCESSORY CIRCUITS
Your AU -70 is equipped with various advan ced
access
ory circuits such as loudness control, low
an d high filters, tape monitor, tone defeat, pre-
sence, blend, speaker switch and headphone jack.
- 4 -

SPECIFICATIONS
M
AIN AMP LI FI ER :
MAXI MUM OUTPUT : 25W-25 W ( SO W to tal)
HARMON IC DISTORTION:
Max. 0.15 % at 20W for 1, 000 Hz
Max . 0.95% at 20W for 30 Hz
INTERMODULAT IO N
D
IS TORTION: Max. 0.
85 % at 20W , (50 Hz
+ 5,50 0 Hz)
FREQUENCY RE SP ONSE: 10-
80 ,000 Hz
at
±1 dB
OU TPUT IMPEDAN CE : 8 and
16 ohms
G
AIN AND SENSITIVITY :
R
S
T
PHONO: MAG 84 d B ( Ou tput 2
0W at 1.1 mV in put )
x- T AL 54 dB (Output 2 0W at 36mV input)
TAPE: 86 dB (
Ou tput 2 0W a t 0 .9mV in put)
MIC: 86 dB (
Ou tp ut 20 W a t 0.9 mV in put)
AUX: ( TA PE MON) 51 d B (Output 2 0W a t 50 mV input)
TUNER: 51 dB (O utput
20W at 50 mV in put)
ESIDUAL NO I SE :
below 0.25 p. W
IN RATIO
52 dB ( at
T APE terminal)
ONE CONTRO L:
T ype CR
50 Hz + 11 to - 15 dB
10, 00 0 Hz + 12
to - 13 dB
E
QUALIZER :
Ty pe NF
TAPE:
NART B (50 p. s)
PHONO:
RIAA
A
CCESSORY CI RCU I TS :
PRESENCE CO NTROL: Turno ver a t
150 Hz
LOW FILTER: 5 0Hz - 12.5 dB
HIGH FILTER: 10, 000 Hz -13 .5
dB
LOUDNESS CONTROL
TONE DEFEAT
TAPE MONITOR
HEADPHONE JACK
TAPE RECORDER PLAYBACK CONNECTION (DIN)
TERMINAL FOR CENT ER · CHANNEL AMPLIFIER
LEVEL MET ER ( FOR OUTPUT ) Three ra n
ges
of 5,
10 and 2 5W
BLEND CONTROL
VA CUUM TUBES , TRANSISTORS AND DIODES:
7 18 9A X 4, 6AN8 X 2, 12 AX 7 X 3, OA - 91
ge rmanium
dio
de X 2, 2 5B - 381 tra nsis tor X 4,
50 -1 B silicon diode
X 2 5W- 0503 silicon dio de x l
TOTAL : 9 tu
bes
a nd 9 di od es
PO WER SUPPLY : 117V AC,
50 and 60 Hz:
P OWER CONSUMPT IO N:
150VA
DI MENSIONS : Wi
dt h 15" /6 /'.
D epth
12
19
/
32
/1.
Height 519/3/ ' .
W EIGHT:
30 lbs
- 5 -
~ "I..
CHARACTERISTICS
TONE CONTROL CHARACTERITICS
FREQUENCYRESPONSECHARACTE~ST~S
1111 I 1 1111111
NF: 26 dB LO AD RESISTANC E: 16 0HMS
20
r- M~X
M~X
6
-4
II)
~
~ 10 2
w
:---....
a;-
0
'"
.... TONE DEFEAT
~
z 0 w -2
0
......
en
,
"-
Z ....... A
'"
..."...
~ - 6
~ -10
~ - 8
-- OU
TPUT : I W
- ~
'"
0:: -10
---- OU
TPUT : 20 W
-
20
MIN I
II 1111
-12
1 I I I 11
11
100 I K 10 K 10 100 I K
10K lOO K
HIGH AND LOW FILTER CHARACTERISTICS
HARMONIC DISTORTION
I I I I I I I I I
10
I J
~Nt~t t~fE~T
10
-HARMONIC I Ke
;;;-
e
___ DISTORTION 1 00% ' LOAD RESISTANCE : 16 0HMS -
0 -
1- -z _ .-
10 Ke
~
r- 0
w ;::
~ -1 0
HIGH FILTER
Q:
0 5
0
LOW FILTER
...
"-
,
"\.
!!?
~ -20
\ c I
I)
Q:
I
:'J
-30 1 .,
-- - ,....
-
100
I K 10 K o I 5
10 15
20 25
I NPUT AND OUTPUT CHARACTERISTICS INTER MODULATION DISTORTION
I I I I I I I I
10 5
.5 Ke +50 %LOAD RES IS TANCE I6 0HMS
25
/'
e
INPUT : MAIN / z
NF : 26 db LOAD
Q
RESISTANCE: 16 0HMS
...
10
:5 5
...
-
!!?
II
~
c
...
::::>
1
"-
...
::::>
II 1 5
10
15
20
0
I
/
V
0. 3 I 2
- 6 -

CONNECTIONS
SPEAKER
STEREOPHONIC REPROD U CTION
Connect (+) of th e rig ht-hand s peaker to the
8- or 16 -ohm terminal of th e upp er R termin als
on the ba ck of the amplifier. Connect (- ) of
the rig ht-hand speake r to (C) of the upp er R
termin als. Connect (+) of the l ef t- hand speaker
to the 8- or 16-o hm termin al of the lower L
terminal s on th e back of the amplifier. Connect
(-) of the left-hand spea ker to (C) of the l owe r
L
terminal s.
MONAURAL REPRODUCTION
When you use an 8-o hm sp ea ker sys tem for mon-
a ura l reproduction, co nn ect th e upper and low er
16-ohm speaker termin als of your amplifier to
the (+) terminal of the speaker.
Conn ec t th e upp er a nd lower (C) s peaker term i-
~ 0 ,O' 0' 0' '0' 0' 0 15
~;::..,/-~-~~
P,)\,] 1'- =~~~ 'L'~t::' L' .~c .;.\
~ Q; O~ Q) 0; C' Q; C e
nals of your amplifier to the (- ) termin al of the
speaker.
THREE·DIMENSIONAL STEREO·
PHONIC REPRODUCTION
Your AU-70 is equipp ed w ith a t er min al for a
ce
nter-ch a nn el amplifi er so that it can be used
for three-dimensional reproduction.
To do this, connect th e input terminal of a
monaural amplifier (Either a main or co mbination
amplifier can be used) to th e pin-jack of the
ce nt e r-chann el o utput termina l at th e left of the
spea ker terminal b oa rd with a s hielded wire
Th e ce nt er-c hann el mix es the right a nd l eft
so und s to produce the thre e-dimensional effect.
Speakers suitable tor the AU-70 are 20 to 30-cm
coaxial s peak ers and, for the best mu sical re pr o-
- 7 -
duction, two or three-wa y speake r systems which
use different speakers for different fre qu ency
ranges.
In c hoo sing th e cabi net, t ake acco unt of ton al
quality in ad dition to design.
CAU TION:
If you find th at th e so und s from both sp ea kers
do not mix well, but l ea ve a sort of vac uum
midway be tw een th e spea kers, you ca n conclude
th at th e amplifier and the speake rs do not ma tch
in polarity (phase). In such a case, reverse the
(+) and (-) co nn ect ions of e ith er spea ker.
Wh en you use two pairs of spea kers for stereo-
phonic re prod uction, mak e s ur e th at the spea k er
output te rmina l connections do not cause con t act
between Rand L a nd that the terminals are
con nected prop e rly . If th e connect ions are faulty,
yo ur amp lifier will not wo rk normally and m ay
also go o ut of order.
i Pl ayer (magnetic)
P layer (c rystal)
RECORD PLAYER
1. Connect th e o utp ut te rmi na ls to th e "PHONO-
R" and " PHONO-L " terminals ( in the case
of mon a ur al reprodu ction, to eithe r of th ese
terminals) on the back of your amplifier with
sh ield ed wires.
2. Set the ca rt ri dge switch on th e back of your
amp li fier to "MAG" or "X -TAL " according
to the type of yo ur ca rtridge.
3. Connect the power- cord plug of the player
to the power plug r eceptacle on the back of
yo ur amplifier.
MICROPHONE
Connect th e m ic r ophone to R or L of the "M I C"
te rminals on the back of yo ur amplifier. When
you use two micr ophones, connect olle to Rand
the other to L.
, " Microphone
8 -
CARTRID GE SWITCH
S et this to MAG or X· TAL dep end .
ing on
your pla yer car tridge
(
ma gne tic or crys tal )
, '.

CONNECTIONS
TUNER
You can listen to broad casts eas il y by c onnecting
your amplifier to a tuner and MPX adapt or.
A) STEREO TUNER
Conn ect tun er output to the Rand L "T L:N ER"
te rmina ls on the back of yo ur am pi i fie r.
8) MONAURAL TUNER
Co nn ect tun er output to either R or L of the
"Te NER' - te rminal s on the back of yo ur amplifier.
C) FM MONAURAL TUNER AND
FM-M PX ADAPTOR.
Con nect monaur al tu n er outjJut to the input
te
rmin al of the F:\l-'\lPX adapt or a nc! connect
R
an d L of t he adapt or o utput te rmin als to R
AM / fM / MPX TU NER (SANSUI TU·70)
and L, respecti\'ely, ot the " AUX" terminals on
th e back of yo ur amplifie r.
TAPE RECORDER
1. SINGLE - CONNECTION TAPE RECORDER
( DIN STANDARD SPECIFICATION ):
Connect the " in , ld e-c onn ection connec tor to t he
"TAPE-I\E C ' receptacle on the back of your
amplifie r.
2. PIN - JACK TA PE RECORDER
a) Rec or d in g
Con nect the tap e rel' or cie r i nput ternlina is to R
and L (R
or L in th e l'ase of monaural opera-
ti on) of the "REC " te rmin als on the back of
yo ur ampli fie r \ \'i th shiel de d wires,
b) Pl
aybac k
e CENTER Ii rI Q It
o 16" eQ C
• "CHANOllT Ii ~ ~ G).
fM TUN ER (B) or (C)
MPX ADAPTOR (C)
9 -
Conn~ct the tape reco rder output termin al
( "LINE" ) to Rand L (R or L in the case of
monaural operation ) of the "TAPE MON"
terminal s on the back of y our amplifier.
3. Playing tapes on the tape deck
Connect the tape deck output terminals to R
and L (R or L in the case of monaural opera-
tion) of the "TAPE HEAD " terminals on the
back of your amplifier.
4. Monitoring with a three-head tape re-
corder
a) Single-connection tape recorder
Connect the single-c onnection
"T APE- REC" receptacle on the
amplifier.
b)
Pin -jack tape recorder
Tape-deck
plug to the
back of your
- 10 -
Connect the tape reco rder input te rminals to R
and L (R or L in the case of monaural opera-
tion ) of th e "REC" te rminals on the - back of
your amplifier. Also, c onnect the tape recorder
o utput terminal " LINE " to Rand L (R or L
in
the case of monaural operation ) of the
" TAPE MON " termin als on the back of your
amplifier.
• CENTER" .. Q •
o I~ Bll ~
"CHANOllT .. D ~ G).

SWITCHES AND CONTROLS
CD POWER INDICATOR
T his lights up yvhen power is being sup-
plied. It remains on whi le the amplifier
is in oper ation.
@ HEADPHONE JACK
When you want to avoid disturbing others
or when you use the ampl ifier as a monitor,
co nnect h ead phon es to this jack. You
can still enjoy s tereophonic reprodu ction
through the h ea d phone s. For thi s pur-
pose, you can use any type of headphones
or earphones if its plug fits into the jack.
But use dynamic headphones designed for
stereophonic reproduction, if possible.
@ SPEAKER ( SPEAKER OFF)
When you use headphones with the head-
phone jack, set this switch to "OFF " to
cut off sound to the speakers . This feature
enables you to enjoy stereophonic repro-
duction without disturbing others.
@ PRESENCE
If the Tone Control al one is used for bass
com pensat ion, slightly higher frequencies
are compensated at the same time. To
avoid this, turn this switch "ON" _ This
sets the turnover at 150 cps, changing
speaker damping and frequency re s ponse
ch ara cteristics to compensate bass. As a
resu lt, all s ounds become impressive and
you can enJoy clear, m ag nifice nt bas s.
@ POWER
This switch is used f or connecting and
disconnecting the power supply. Push the
. button for poweL Pu sh it again to shut
it off_ The switch also activates and de -
activates the power - supp ly plug recept acles
on the back of the amplifieL
CD
HE"O PHON
®
POWER
®
@
@
ow ..
TER
- 11
® OUTPUT LEVEL METERS
Th e right and left meters indic ate the out:
put l eve ls of th e right and left sp eake rs,
re spectively.
Since output is s hown se par ate ly for each
c hannel , the met e rs provide easy balance
adjus tment. Besides, you ca n wat ch c hang es
in th e o utput of each channel dur i ng ope-
ration . Each meter can be set to any of
th e thr ee range s of 5, 10 and 25 watts by
means of
th e output- level meter s witch on
the back of the amplifieL Choose th e
a ppropriat e range according to th e output
YOU want. \ '-h en the "MODE " sw itch is set
io R (or L), the meter for L (or R) does
not \york.
(J) LOUDNESS
\\ - hen so und \'olume is at a low level, you
ieel as if bass and treble are missing. In
such a case, turn this switch "ON " to
compensate bass and treble. Th is will
mak e you f ee l as if you were present at
an ac tual concert,
@ LOW FILTER (for eliminating
low-frequency
noise) .
Turn this 5w it ch "ON " to reduce phono "
motor and other unplea sa nt low-frequency
nOI ses.
® HIGH FILTER (for eliminat-
ing high-frequency noise)
Turn this sw it ch "ON " to reduce relatively
high-frequen cy noise, such as the sc ratch
from rec orel s made of poor mat erial or noise
du e to fluoresce nt lamp s in th e case of
th e tun er.
@) TONE DEFEAT
Turn this sw it ch " ON " to open the tone
co ntrol circuit s_ Then th e fre qu en cy re-
s pons e c ur\' e of the amp lifier wi ll be co me
perfectly flat.
,
1
® TAPE MONITOR
vVh en you mak e record in gs with a thr ee -
he ad tape record er, turn this sw itch "ON"
to use th e am pI ifi er as a mon itor. Then
th e s ounds rec ord ed on th e tape are re-
pro duced while yo u are reco rding. Keep
th is switch " ON " when you play the t ape
on the tap e .recorder.
Be s ure to k eep th e ~\\"itch "OFF" othe r-
wIse.
@ BALANCE
Th is knob is used to adjust the balan ce of
volume be tw ee n the right and left spea kers
for the best ste reoph on ic e ff ect. J\ , 1ake the
adjustment while watching th e o utput l eve l
met
ers and li s tening to the so und s of both
spea kers . \\Then the amplifier is adjusted
pr ope rly, yo u feel as if th e so und co mes
fr om a point midway between th e two
spea kers.
@ BLEND
Thi s knob permits continuous shift from
stereo phoni c to monaural reproduction .
Turn it co unter-clo c kwi se to brin g repro-
du ction closer to monaural ( R+L). For
co mp l ete mon aural re produ ction, turn it as
far co unter- c lo c kwi se as possible.
Th e so und s of the righ t and left sp ea kers
beco me sepa rated \"hen you turn th e knob
cl oc kwi se (R and L pe rform th eir respec tive
functions) . Th e best ster eop honic effect is
obtained when you turn it as far as possible_
@) BASS and @ TREBLE for L
Th ese control the tone of the left spea ker.
@ BASS and ® TREBLE for R
These control the ton e of th e right speaker.
@
®
@
-12 -
@) VOLUME
Thi s knob is used to co ntrol th e volume
of the tuner , rec ord s and tap es. Turn it
clockwise for louder reprodu ct ion. To
redu ce th e \'01 ume, turn co un ter-clockwise.
@ SELECTOR (input-selector)
TUNER: For receiving bro a dca sts through
the tuner.
PHONO: For playing reco rd s.
MlC: For us in g a mic roph one,
TAPE HEAD : For playing tapes on th e
t ape c1 eck (directly from the tape head).
AUX : For r epro du cing \'oice input or u si ng
the
MPX adaptor.
@ MODE (Stereophonic/
monaural switch)
Thi s s wit ch is used to shift from s ter eo-
phoni c · t6 mon a ur al re produ ction or vIce
versa .
STEREO: Set the switch at this po si tion
for
stereo reproduction. Signa ls f ed int o
A come
out of A's s peak er and tho se fed
into B come out of B 's sp ea ker.
STEREO- REV : Thi s position, too, is for
stereo reproclu ct ion. But signals fed into
A come out of B' s s peaker a nd tho se fed
into B come out of A's s peak er. Choose
this position when th e rig ht and l eft are
r e\'e rsed in r ep rodu ct ion.
L+ R: Signals fed into Land H. are bl e nd ed
into one (L+ R) in the amplifier befor e
th ey come out se paratel y from Land R.
Signals f ed into A and 13 become A+B
in th e amplifier and come o ut of the
spea kers of A and 13 in the form of tb e
co mbined so und A+B.
R (Mono R ): Signals fed into A come out
of A's and B 's sp ea kers. Use this pos i-
tion for reprodu cing mono broad casts and
tape s.
L (Mono L): Signals fed into B co me out
of A's and B's sp ea ker s.
Thi s position is rarely u secl .

OPERATIONS
RECORD PLAYING
1. Set the "SELECTOR" switch at " PHONO".
2. Set the "MODE" sw it ch at " STEREO " or
"S T EREO- REV " (at R or L in case of mon-
aura l operat ion ).
3. Sw itch on th e player, put on a record and
adjust the numb er of revolutions as ne cessa ry
before placing th e pickup on th e record.
4. Balance the so und s from both s peakers by
me ans of the "BALANCE" knob while wat c hing
the output level meters.
.
5. Adju st the amount of sound by means of the
"VOLUME" knob. Other adjusting knobs and
switches can be used to get the most satis-
factory repreduction .
When you play a monaural record on a stereo
record player, follow the same procedure as
for stereo re cord s. Thi s will give you better
re sults.
Catridg es are either ma gn et ic or crystal. Both
can be used with the AU-70, but, if possible,
use a
magnetic type for the highest fidelity.
If you feel that right and left are r eve rsed
when playing a st ereo record, turn the "MODE"
switch to "STEREO-REV". To balance th e
sound s from both speakers, play a monaural
record in
the sa me way as a stereo record an d
adjust
the "BALANCE" switch in such a way
that you feel th at the sound co me s from a point
midway between the rig ht and left speakers.
In this case, you can count on th e output l eve l
meters for a rough det er mina ti on of the balance.
Also,
make sure that th e "BLEND" knob is
kept at the point wh ere it ca nnot be turn ed
clockwise
any further.
When you supply power to the player from
the power-plu g receptacle on th e back of your
amplifier, do not fo rget th at the player is sw itch-
ed off when you switch off th e amp lifier.
BROADCASTS
In the case of A and B above:
1. Set the "SE LE CT OR" switch at "TUNER" .
2. Set the "MO DE " switch at "STE RE O" or
"STEREO-REV" in the case of A and at R
or L (according to the cha nnel selected) in the
case of B.
3. Tun e in with th e tun er.
4. Use other adjus ting knob s and switches to
get th e mo st sa ti sfac tor y performance.
In the case of C
1. Set the "SELECTOR" s witch at "AUX"
2. Set th e "MODE" switch at "STEREO" or
"STEREO- REV".
3. Tune in with the tuner.
4.
Prepare th e FM-MPX adaptor for stereophonic
re ception.
5.
Use other adjusting knobs and switches to
get the most sa ti sfac tory performance.
When you use a tun er or FM-MPX receiver, read
th e instru ctions for th em carefully. There should
be no mistakes in co nne ctions and operation.
When you usc o ur T U-70, follow the instruction s
for
A. Wh en you use an FM-tuner (without
Multiplex) and MP·2, fo ll ow the instructions for C.
USE A MICROPHONE
You can use microphones with yo ur AU-70
amplifier. Any hig h-imp e dan ce (50 kilo-ohm)
crystal, dynamic or velocity mic
rophone is accept-
able.
1. Set th e "SELECTOR" switch at "MIC".
2. Set th e "MO DE " sw itch at " STEREO"
(when you use only one micro phone for ste reo-
ph onic effect)
at R (when you use only one microphone for
mo
naural reproduc ti on),
or at L+ R (w hen you mix two different pro-
- 13 -
gram sources from tw o mi c rophon es.)
3. During stereophoni c operation, you can use
the "BLEND" knob for mixing purposes.
4.
Other adjusting knob s and switches can be
used for
the mo st satisf ac tory reproduction.
Remember that yo ur AU·70 accepts only high-
i mpedance micr ophones. You canno t get the
best perform ance if you use too long micro-
phone cord, whi ch causes \'arious problems and
re du ces treble. ·
Your amplifier ha s separ ate tone' co ntr ols for
right and left speaker s. You will find this
feature very useful wh en you use one micro-
phone for musi c and a noth er for voice. Furth er -
more, it gives added \, ersatility to yo ur amplifier,
particularly wh en you record on tape what is
pic
ked up by microphones.
RECORD AND PLAY TAPES
Your AU·70 can be sed with a tape recorder
for
recording and pl aybac k and can also play
tapes on th e tape deck. If you use a thre e ·h ead
t ape re co rder whi ch ha s separ ate record and
playback heads , you can make reco rding s while
li sten ing to a repr oduc ti on of the recordings . In
oth er words, yo ur amp lifier can be us ed as a
monitor which lets you know th e quality of your
recordin gs while th ey are being made ..
RE CORDING
Set th e' "SELECTOR " switch at the prop er
position according to th e program so urce (broad-
cas tor record) you are going to record.
2. Set "MODE" switch at "STEREO " (for
s
tereophonic recording ), at R or L (for monaural
recording), or at L+ R (for monaural recording
of a stereophonic so ur ce).
3. Prepare the tape re co rd er for recording.
4. Operate the recorder and amplifier adjusting
knobs and switches properly.
Amplifier adjusting knobs do not affect the level
and tonal quality of recordings, but only control
th ose ot the sound from th e spea ker s. Wh en you
record ' a broadcast
cir record, you can obtain
be tt er results by co nn ecting the tape . reco rder
directly to your amplifier in stead of picking up
th e sound from th e spea kers with micro phone s.
PLAYBACK
1. a) T ape deck
Set the "SELECTOR" switch at "TAPE".
b) Tape recorder
Set the " TAPE MONITOR " switch at "ON".
2. Set the tape recorder in the play position.
3. Other adjusting kn obs and switches can be
used for th e most sa tisfactory reproduction.
CAUTION
Wh en you use a Tape Recor der , keeping the
"TAPE MONITOR " sw itch at "ON" the "MODE"
switch is n ot operative.
If you wan t to use the "MODE" switch, connect
the recorder o utput to the "AU X" pin-j ackso n
th e back of your amplifi er and the " TAPE MONI-
TOR" switch at o ff .
T APE MONI T ORING
To use your amp lifi er as a monitor for a thr ee-
head t ape recorder, follow the same procedure as
the one for playing tapes on a recorder. Vvhen
yo u use a recorder, read the instruction manual
carefully to avo id errors in connect ion and oper-
ation.
U nl ess you use your amp lifier as a tape mon i tor
or for playing a t ape with a tape recorder, be s ure
to switch off the " TAPE MONITOR " switch.
Connecting a tap e reco rder can be done by
using either a single-co nnection connector or by
pin-jacks. The single-connection plug conforms
with German DIN standard specifications. It
makes it easier to connect the tape recorder
to your amplifier because it has a five-pin plug
for both record and playback. When you use
your amplifier as a tape moritor, turn on the
"TAPE MONITOR " switch if you want to hear
the sound you are recording.
- 14 -

HINTS ON USE
SPEAKER POLALITY
If the phase (polarity, viz. +and-) of the right
and left speakers is not co rre ct, so unds at the
center of the frequen cy ran ge beco me weak. You
will particularly sense an attenuation of bass. To
ma ke s ure that speaker polarity is all right , play
a
monaural record on a stereo record playe r. If
the polarity is reversed you will have the result
mentioned above. In such a case, reverse the
polarity of
either speaker. (Connect th e - lead-
wire to +.) When both speakers are thu s made to
agree in polarity, you , will feel as if the so und
comes o ut of a single spea ker placed midway
between the right and left speakers.
FUSE
The amplifier does riot work when th e fuse is
blown.
In such a case, disconnect the power
cord and replace the fu se on the back of the
amplifi er~ Use a 3 -ampere fuse encased in a glass
tube.
Never risk the dang er of usi ng fine wire
or a fuse of a larger capacity as a substitute. If
the fuse has burnt out because the amplifier is
out of order, locate th e tr ouble and repair it before
re
pl ac ing the fuse. The fuse , blows if you use
an AC plug receptacle lar ge r than the ' specified
· capacity (SO VA for t wo)_
HEAT GENERATED BY AMPLI·
FIER
The top of the amplifier case becomes considerably
hot after many hours of continuous operation_
But this should not worry you because air vents
are provided on the top and back of the case.
If you place something on the amplifier or put
it in a closed box, or keep its front panel facing
Fig. 1
up, it mi ght go o ut of order.
CONNECTIONS
Wh en you connect your amp lifi er to a tape
re corder or tun er, be s ur e to use an adequately
thick shielded wires. If you use untwi sted vinyl
cord like those used for lights, you will suffer
from
hum . Furthermore, do n ot ,use a wire longer
th
an 2 meters (about 6.5 ft.), bec ause the lon ger
the co nn ecting wire is, th e greater the a ttenuation
of tr eble beco me s. For connection to a tuner or
FM adap tor, use a wire 1 to 1.5 m ete rs (about
3.3 to 4.S ft.) long. When you use the amplifier
f
or mo naur al reproduction, it is easier for operation
to use th e upp er R terminal for connec tion. Be
s ur e to set th e "MODE" switch to the conne cted
ch
anne l.
HUM AND HOWLING
Wh en you pl ay a re cord or tap e, you may some-
time s h ear unpleasant hummin g or howling. This
,does not mean th at y our amplifi er is defec ti ve.
In mo st cases, hummi ng or howling is a result
of these causes:
If you place a r ecord player 0 11 or near th e
speaker box, th e vibrations of th e spea ker cabinet
caused by the sound waves from the s peaker a re
tran s mitted to the player and cause howling. To
prevent this, keep the record player away from
the speaker cabin et or put a thick cus hion be-
tween the player and the cabinet.
A low, buzzing sound wjll also be produced if you
do not use shielded wires for connection. If this
is
not the cause, exami ne the co nnections closely.
Make sure that the earth and live end~ are not
reversed so
th at the motor and arm a re inade-
quately grounded.
- 16 -
CONNECT
PERLY
LEADWIRES
Fig . 2
PRO·
Connect leadwires properly to the s peaker an d
oth er input and output termin al s. If co nnections
are loose or touch other parts, yo ur amplifier will
not wo
rk properly. Moreover, it may produce
noise. If you use your amplifier in s uch a way
for a long time, it ma y eve ntu a ll y break down.
Fin ally, read the ins truction s for yo ur tuner or
tape recorder carefully before you co nnect it to
yo
ur amplifier.
LEVEL METER SWITCH
Thi s is used to select th e most suitable meter
sensitivity from th e thr ee ranges of 5, 10 and
25 watts. The variable sensitivity is intended to
mak e it easier to watch needle movem en t.
high: up to 5 watts
medium: up to 10 watt s
lo\\': up to 25 watts (maximum o utput)
Choose the approp ri ate ran ge acco rding to volume
l eve l you want.
AC OUTLET
The AC OlJtlets on the back panel are connected
or disco nnected by the power switch on the front
panel. The total capacity is SOV A-30VA and
another 50VA- Be sure to lise them within
the limit.
WHERE TO BE PLACED
The amplifier should be installed to the place as
given below:
1. Easy to ground;
2. Floor not vibrated;
3. Not wet and dusty;
4. Not exposed to the sun;
5. Well ventilated.
- 16 -
Fig. 3

SERVICE NOTE
Symptom
No power when power switch is
pushed on
Probable Cause
1./ Defective power switch .
2.
Defective line cord .
Replace .
Replace .
What to Do
3. Loose contact betwe en plug and socket or R eco ndition or re pla ce .
defective plug .
4. Blown fuse. Replace .
Power indicator is lit when power
switch is pushed on. but;
A. the unit does not work at all. 1. Def e ctive tube.
2. Abnormal voltage in tubes and o ther parts .
B .
PNONO and TAPE does not
fu nction.
1.
Defective head amplifier ( transistor section ).
2.
Defective selector switch.
3.
Loose contact or short - circuit between input
terminal and pin - jack .
4.
Defective record pla ye r.
tape
recorder. or
others. connected to the
unit.
5.
Defective coupling condenser .
C. Weak sound
on
AUX . 1.
Abnormal
voltage
in power circuit and
PHONO and TAPE .
other parts.
A. Normal voltage at ' eve ry part 1. Defective fixed resistance .
but weak sound on AUX
2. Short -c ircuit in ou tput transformer.
3. Discharged capacitor.
4. Aged tube .
5.
Defecti ve slide switch or selector switch .
I
,
If again blown after replacing. check power
transformer ( T, ) & path condenser (Cs,) in
power circuit for short-circuit.
Check V , ~ V 9 and silicon diodes.
Check voltage in tube and other parts and
replace. if necessary . If voltage is OK. check
AUX input circuit and hereafter.
Rep l ace
transistor
head amplifier unit.
Replace
or
repair S2'20 and / or S2e. S 2f
Replace or
repair.
Replace .
Re
plac e C,
and / or Cs.
Check and repair .
Check R ,,~ R ,s . R 66~ R" and Compound part
CRS01. CRS02.
Check C 2 ' ~ C Z " C
a6
and Ca, tubular electro -
ly tic capacitor C2, . C
26
. C.
o.
C" .
-- -------------------+---------------- ------- ------ ~------------------------ -- ---
I
B. Normal voltage at every part 1. Defective selector switch .
but weak sound on PHONO
and TAPE . 2.
Abnormal input circuit :
between input terminal
defective shielded wire .
loose contact
and pin · jack:
3.
Defecti ve
record pla y er . tape recorder or
others. connected to the unit .
4.
Defecti ve coupling condenser.
5.
Discharged by pass condenser.
- 17 -
Replace or repair S 2" S 20. S 2e . Sz f. S". and
S JO
Repla ce or r epa ir.
Replace
Check C,. Cz•
C,.
C6• C,. and
Cs.
Check
Cs.
C,.
C9•
and C 'O .
Symptom
A . Distorted so und on AUX.
B. Distorted sound on PHO NO
and TAPE.
A . Hum on AUX .
Probable Cause
What to Do
1. Aged tube .
Check V ,~ V 9 '
2. Short -c ircuit In output transformer .
Check and repair T z and T 3
3. Defecti ve loudspeaker. Replace .
4. Defective record pla y er. adapto r or others. Replace
connected to the unit.
l. Defecti ve record pla ye r. tape rec order or Replace .
o
th e rs . connected to the unit.
2. De fecti ve tubular elect r oly tic capacito r.
3. Di
scon ne c tion at fixed resistance .
l. Electrol ytic capacit or di scharged .
2. D
efec t ive tube.
Replac e C, and / or C2.
Chec h R 2 , ~ R az . R•. R ,a. R ... R
15
• R '6 . R
17
• R'B.
R'
9. R
zo
. R2, and R
22
.
Check Ca ,. C66 ~ C' 3 . C76~C77'
Check V, ~ V 9.
3. Def ective record pla ye r. ada pt or or others. R ep lac e.
connected to the unit.
4. Hum balancer not properl y a dj uste d. Check VR .. a nd VR ".
5. Dis connected NF r esistor. Ch eck RS2 and Rs3.
B . Hum on PHONO and TAPE. l. D efec tive shielded wire and / or wrong con- Replace a nd connect correctly
nection of record pla ye r. tape reco rder or
others .
2. Audio system and shielded wire induced
from outside .
3.
Residual hum of audio sys tem co nnected
to the unit.
A . Noise on AUX and TUNER . 1. Fix ed resistor badly connected or touched
by a nother part .
Keep prop er dis tance between audio system
and inductor.
Replace or repair.
. 2. Capacitor nearly short- cir cui ted or touched Check C'6. C
S7
• C60 • C6, .
by another part.
3. Primar y coil of output transformer nearly Check T z and T a.
dis co nnected.
4. Defecti ve tube . Check V, ~ V 9.
B . Noise on RHONO and T A PE . 1. Fixed resistor defective or ne a rly discon- Check R 7~ R a2
nected.
2. Defecti ve capacitor. Check C ,~ClO
3. Noise or bad connection of audio system Replace or repair
connected to the unit.
--- 18 -