Akai AT-2650 User manual

BAHN
ae a

I.
iit.
IV.
VI.
Vil.
VII.
IX.
XI.
XI.
For
SECTION 1
SERVICE MANUAL
TABLE OF CONTENTS
TECHNICAL
DATA
2.0.
0c
ne
eee
eee
eee
ne
eee
2
EEMODEELMAT-2650
4
ses
wraton
teat
eneres
g
Get
GM
Ris
vot
aca
alent
9
GARE
Sie
ener
ale
ae
Me
pipe
elas
2
2.
MODEL
AM-2650
201
ee
ee
eet
ee
eee
eee
te
eee
3
DISMANTLING
OF
UNIT
2.0.0.0
ee
ee
es
4
1
MODEL-AT-2650..c422
seek
na
PAG
eRe tee
Poe
Bae
ee
Ae
de
ee
Ee
4
2.
MODEL
AM-2650
20...
ee
te
eee
ee
eee
een
es
$
CONTROUS.
soccer
tis
eat
ES
A
Se
DE
ERR
TN
eG
EATS
GE
SES
6
1.
MODEL
AT-2650
000
ee
eee
ee
eS
6
2.
MODEL
AM-2650
2.02.
ce
ee
ee
ee
nee
eee
ee
7
PRINCIPAL
PARTS
LOCATION
2.0.2...
0.
ec
ee
te
ne
ee
8
1.
MODEL
AT-2650
20.
Ee
ee
eee
ee
ee
ee
8
2.
MODEL
AM-2650
2...
ee
ne
ee
Ee
ns
9
OPERATING
PRINCIPLES
OF
QUADRATURE
DETECTION
SYSTEM
........-
20-0
ee
eres
10
OPERATING
PRINCIPLES
OF
PLL
CIRCUIT
EMPLOYED
IN
STEREO
DEMODULATION
CIRCUIT
..
2.0...
00.
ee
eee
12
1.
PLL
CIRCUIT
OPERATION
.......
0.0.0.
ce
ee
12
2,
STEREO
DEMODULATION
CIRCUIT
2.2...
0.
es
13
OPERATING
PRINCIPLES
OF
FM
NOISE
CANCELLER
CIRCUIT
....
2.2...
0.
eee
ee
eee
15
1.
BASIC
CIRCUIT
FOR
PULSE
NOISE
SUPPRESSION
........
0.20
e
eee
ees
15
2.
OPERATION
PRINCIPLE
WITH
STEREO
SIGNALS
..
0.0...
0.2
ee
ee
ees
15
3.
ADJUSTMENT
METHOD
FOR
THE
PILOT
SIGNAL
GENERATING
CIRCUIT
.......------
16
LEVEL
DIAGRAM...
0...
en
ee
ee
ES
17
TUNER
ADJUSTMENT
(AT-2650)
2.00
en
ee
18
1.
FM
TUNER
SECTION
ADJUSTMENT
..
0.0.
0
ee
19
2,
AM
TUNER
SECTION
ADJUSTMENT
...
2.2.00
ee
20
AMPLIFIER
ADJUSTMENT
(AM-2650)
200.6
ee
21
1.
IDLING
CURRENT
ADJUSTMENT
.......
2.06.
eee
21
2,
LEVEL
METER
INDICATION
ADJUSTMENT
...
2.2.0.0.
6-2
ee
es
22
TUNING
CORD
THREADING
...
2.1.
0
ee
nee
23
CLASSIFICATION
OF
VARIOUS
P.C
BOARDS
...
2.0...
ee
ee
ee
24
1.
P.C
BOARD
TITLE
AND
IDENTIFICATION
NUMBER
.....
22...
ee
eee
ees
25
2.
MODEL
AT-2650
COMPOSITION
OF
VARIOUS
P.C
BOARDS
.......
2.
ee
eee
ees
28
3,
MODEL
AM-2650
COMPOSITION
OF
VARIOUS
P.C
BOARDS...
--
0.
0-0-6
ee
ee
52
SCHEMATIC DIAGRAM
basic
adjustments,
measuring
methods,
and
operating
principles,
refer
to
GENERAL
TECHNICAL
MANUAL.

I. TECHNICAL DATA
1. MODEL AT-2650
FM TUNER SECTION
FREQUENCY RANGE
87.5 MHz to 108 MHz
SENSITIVITY (IHF) 1.6 UV
CAPTURE RATIO 1.2 dB
SELECTIVITY (IHF) More than 80 dB
IMAGE REJECTION
More than 110 dB (98 MHz)
IF REJECTION
More than 110 dB (98 MHz)
SPURIOUS REJECTION
More than 110 dB (98 MHz)
AM SUPPRESSION 55 dB
SIGNAL TO NOISE RATIO 75 dB
HARMONIC DISTORTION MONO Less than 0.1% (100% modulation)
STEREO
Less than 0.15% (100% modulation)
FM STEREO FREQUENCY RESPONSE
20 Hz to 15 kHz +1 dB, —3 dB
MUTING
Level Control (1 #V to 100uV)/Switchable to ON-OFF
STEREO SEPARATION
More than 45 dB (1 kHz)
SUB CARRIER SUPPRESSION
More than 65 dB
OUTPUT VOLTAGE
Controllable from 0 mV to 2V (100% modulation)
ANTENNA INPUT IMPEDANCE
300 ohms balanced, 75 ohms unbalanced
AM TUNER SECTION
FREQUENCY RANGE 520 kHz to 1,605 kHz
SENSITIVITY
(IHF)
80
uV/m
(bar
antenna),
13
uV
(external
antenna)
SELECTIVITY
(IHF)
More
than
30
dB
IMAGE REJECTION
More than 80 dB (1,000 kHz) _
IF REJECTION
More than 70 dB
SIGNAL TO NOISE RATIO
More than 50 dB
OUTPUT VOLTAGE _|_ Controllable from 0 mV to 2V
ANTENNA Built-in ferrite bar antenna
MISCELLENEOUS
SEMICONDUCTORS
| Transistors: 12, Diodes: 15, FETs: 3. 1Cs: 5
POWER REQUIREMENTS
120V, 60 Hz for U.S.A. and Canada
220V, 50 Hz for Europe except UK and Australia
240V, 50 Hz for UK and Australia
110V/220V/240V. 50/60 Hz internally switchable for other
countries.
DIMENSIONS
440 (W) x 144 (H) x 368 (D) mm, (17.3 x 5.7.x 14.5”)
WEIGHT
1
1 7.5 kg (16.5 lbs)
*
For
improvement
purposes,
specifications
and
design
are
subject
to
change
without
notice.
bh

i
2. MODEL AM-2650
POWER AMPLIFIER SECTION
RATED OUTPUT POWER
2-CHANNELS DRIVEN
65
watts
per
channel,
minimum
RMS,
at
8
ohms
from
20
to
20,000
Hz
with
no
more
than
0.08%
total
harmonic
distortion
POWER BANDWIDTH (IHF)
6 Hz to 60 kHz / 8 ohms (Total Harmonic Distortion: 0.08%)
6 Hz to 60 kHz/8 ohms (Total Harmonic Distortion: 0.08%)
SIGNAL TO NOISE RATIO (IHF) PHONO
Better than 75 dB
AUX | Better than 95 dB
RESIDUAL
NOISE
Less
than
0.5
mV
at
8
ohms
CHANNEL
SEPARATION
(IHF)
PHONO
Better
than
$5
dB
at
1,000
Hz
DAMPING
FACTOR
More
than
30
(1
kHz,
8
ohms)
OUTPUT
SPEAKERS
A,
B
(4
to
16
ohms)/A+B
(8
to
16
ohms)
HEADPHONE 4 to 16 ohms
PREAMPLIFIER SECTION
INPUT SENSITIVITY/IMPEDANCE
PHONO PHONO 1: 3 mV/33/47/100 kohms
PHONO 2: 3 mV/47 kohms
AUX 150 mV/100 kohms
TUNER 150 mV/100 kohms
TAPE
MONITOR
PIN:
150
mV/100
kohms,
DIN:
150
mV/100
kohms
OUTPUT LEVEL/IMPEDANCE
TAPE REC PIN: 150 mV/1 kohms, DIN: 30 mV/30 kohms
FREQUENCY RESPONSE
PHONO (RIAA EQUALIZATION)
TUNER, AUX, TAPE MONITOR
30 Hz to 15 kHz +1 dB, —1 dB
10 Hz to 60 kHz +1 dB, —1 dB
TONE CONTROL BASS +9 dB at 100 Hz
TREBLE +9 dB at 10 kHz
LOUDNESS
CONTROL
|
+10
dB
at
100
Hz,
+5
dB
at
10
kHz
(Volume control set at —30 dB position)
FILTER HIGH —3 dB at 10 kHz
LOW —3 dB at 30 Hz
AUDIO MUTE —20 dB attenuation
MISCELLANEOUS
SEMICONDUCTORS
Transistors:
33,
Diodes:
17,
ICs:
4
POWER
REQUIREMENTS
|
120V,
60
Hz
for
U.S.A.
and
Canada
220V. 50 Hz for Europe except UK and Australia
240V, 50 Hz for UK and Australia
110V/220V/240V, internally switchable, 50/60 Hz for other
countries.
DIMENSIONS
440
(W)
x
144
(H)
x
345
(D)
mm,
(17.3
x
5.7
x
13.6”)
WEIGHT
10.9
kg
(23.5
Ibs)
*
For
improvement
purposes,
specifications
and
design
are
subject
to
change
without
notice.

Ht. DISMANTLING OF UNIT
1. MODEL AT-2650 In case of trouble, etc. necessitating dismantling, please dismantle in the order
shown in the photographs. Reassemble in reverse order.
j 5
SCREW & KNOBS
SCREWS
Ww
On
SCREWS
UPPER COVER
SCREWS
i
FRONT : PaxtL SCREWS.
2
tt mare
f
Eee Ee at
yer ee og
e
@
1
| } |
| :
Ben, —e |
TRALEE it “ita
<__TUSRAENUURULETTATU RUE
BOTTOM Pi.ATE

2. MODEL AM-2650
Ht
iL iE
m Ce ae a ee aces
TUES ALLL LL
wey, TN ILUELNUNLG incHELIDALI HL
_& eee a e _ JS
d BOTTOM PLATE e
SCREWS
1 5
4A & Cc
| i
a \
NS
J * Gti
AKAL : ¢ { { { {
D E F
SCREWS CONTROL KNOBS
|
2 16
SCREWS
|
S | 7
BEPERCEUVER
|
i
|
i
|
|
'
SCREWS
Ly SCREWS.
FRONT PANEL
4 ° 8
wa

ili, CONTROLS
1. MODEL AT-2650
AEALT cai an svenco Tunes moan AT- 2660
© 2) ©
|
(9) GQ)
“900A BALAES ~ 98 BET OPEN!
‘SACU BE LOR - ME NS ERE /
seabenanceetae ~ mace OE |
pa cides ae ee ARON>O©
WNHAARWN>
Fig. 1 Controls AT-2650
FM DIAL SCALE
AM DIAL SCALE
SIGNAL STRENGTH METER
FM TUNING METER
POWER INDICATOR LAMP
FM STEREO INDICATOR LAMP
TUNING KNOB
POWER SWITCH
OUTPUT LEVEL CONTROL
NOISE CANCEL SWITCH
FM MUTE SWITCH and LEVEL ADJUSTER
INPUT SELECTOR
ANTENNA TERMINALS
AM FERRITE BAR ANTENNA
OUTPUT TERMINALS

2. MODEL AM-2650
OMNDGRYN>
ee ee ee ee
go RaON>O
aid tains Mobs ceca
i
‘E14 f
ee oe
POWER PHONES FILTER roue ease TREBLE
TAPE MONITOR:
SOURCE
Py a 4g ter tp
ea es er ;
ps)
@
q
f
f
-
is
Ns
a
_
. -E = ade 2 Ei ee cae i
AK AL erento miccn are AMPLRER moan! AM-2850
— i | i
i
|
| |
i
— | |
®
©
OU®
©
(8)
G
—SPEAKER Ao B (4-ehme)
Aend 8 (8-wotans)
canyen
* dn cese of une gutside Of indicated |
+ SROCK HAZARD 00 WAT TREKS
RISREE HK SBE - WE PAS SRLEVEE !
“SeRMETERESoATANR ~ 9x00 OFFA!
Fig. 2 Controls AM-2650
SPEAKER SYSTEM SELECTOR 16. TAPE MONITOR SWITCH
OUTPUT POWER LEVEL METERS (Left and Right) 17. IMPEDANCE SWITCH
AUDIO MUTE SWITCH 18. PHONO 1 TERMINALS
MODE SWITCH 19. PHONO 2 TERMINALS
LOUDNESS SWiTCH 20. TUNER TERMINALS
VOLUME CONTROL 21.. AUX TERMINALS
INPUT SELECTOR 22. Aand B SYSTEM SPEAKER TERMINALS
POWER SWITCH and POWER INDICATOR LAMP 23. EXTRA AC OUTLETS (some models not equipped
HEADPHONE JACK with this facility)
LOW FILTER SWITCH 24. GROUND TERMINAL
HIGH FILTER SWITCH 25, TAPE 1 SYSTEM DIN JACK
TONE SWITCH 26. TAPE 1 SYSTEM REC JACKS
BASS TONE CONTROL 27. TAPE 1 SYSTEM PLAY JACKS
. TREBLE TONE CONTROL 28. TAPE 2SYSTEM REC/PLAY JACKS
.
STEREO
BALANCE
CONTROL
29.
AC
CORD
(AC
Iniet
for
UK
and
some
other
countries)

IV. PRINCIPAL PARTS LOCATION
1. MODEL AT-2650
FRONT END BAR ANTENNA
FB824UI4 FILTER P.C BOARD ANT 901
T3-6501C
POWER TRANSFORMER
AT - 2650T -70
POWER SUPPLY P.C BOARD
T3- 4502
POWER SWITCH __
Sw}
TUNER PC BOARD
T3- 6501A
ti
Fig. 3 Top View
POWER INDICATOR
D2
rFM STEREO INDICATOR Di
; &
{
: ;
{oo
me ' Hl | ~
i i i
POWER SWITCH | | : TUNING SHAFT SELECTOR SWITCH
Sw | i i ! Swi
i |
OUTPUT LEVEL CONTROL ~ i i CMUTE LEVEL CONTROL
VR2 5SOKB | : VR3 2CKB
NOISE CANCEL SWITCH — “FM MUTE SWITCH
SW 3 swe
Fig. 4 Front View

2. MODEL AM-2650
WER TRA
a
BE
TR
NSr
Oe
MER
ELECTROLYTIC
CAPACITORS
risuiene:e
GARD
: 903,904 4000 52wv a
=
|
:
‘i
e202
|
lel
ea
M3-65014
: i
MAIN AMP PC BOARD
M3-E6504A
” 1
PEE.
MAIN VOL, & BALANCE P.C BOARD
M3-6502 A/B
Fig. 5 Top View
rAUDIO MUTE SWITCH SW3
;MODE SWITCH Sw!
i - LOUDNESS SWITCH SW2
| H
|
|
|
EA
L
KER SYSTEM ’ :
CTOR Ae ane LEFT RIGHT
m
|
H | |
‘ i
‘ ad : i
ee
per
es
Oe
i
ee
.
es
=
ob.
of.
of.
“
:
ot
See
|
i
{
LED PC BOARD
M3-6504C
1
1am
~
i:
i
pees
ean
“
a
S
cngeeels
woot
seat
i
4 i
Seerice
Si
ponte
ere
sis
betes
:
oiled
fia
=
POWER
SWITCH
|
Low
HiGH
=
|
i
|
i
'
SWw3O0!
sws
sw2
BASS
CONTROL
BALANCE
CONTROL
Sade ite | ! VRI SOKC VR2 250KMN
coe
|
|
TONE
SWITCH
TREBLE
CONTROL
TAPE
MONITOR
SWITCH
evel
:
sw}
VR2
S5SOKC
sw3
|
FILTE® SWITCH
Fig. 6 Front View

V. OPERATING PRINCIPLES OF QUADRATURE
DETECTION SYSTEM
PHASE CIRCUIT
DETECTED
OUTPUT
Fig. 7 Quadrature Detection Block Diagram
OUTPUT
INPUT OUTPUT
INPUT =
E | :
It
7 it} |
Fig. 8 Single Tuning Type
Fig. 9 Double Tuning Type
SINGLE TUNING TYPE
Se ee ee
lod —
DOUBLE TUNING TYPE
a $2
ss ffi As
Af
eae
Fig. 11 Output at Non-modulation
Fig. 10 Tuning Curve
Fig. 12 Output at Modulation Time
10

Jo
Fas
bag
Ss
ee
ee
SS
SS
Se
The
Quadrature
Detection
Circuit
is
comprised
of
a
Phase
Circuit,
a
Multiplier
Circuit
and
a
Low
Pass
Filter
(L.P.F.)
as
shown
in
Fig.
7.
There
are
two
types
of
Phase
Circuits,
the
Single
tuning
type
shown
in
Fig.
8
and
the
Double
tuning
type
shown
in
Fig.
9.
However,
because
with
the
double
tuning
type
there
is
less
frequency
deviation
in
relation
to
carrier
frequency,
linearity
is
improved
as
shown
in
Fig.
10
and
phase
distortion
is
reduced,
this
type
of
phase
circuit
is
employed
in
the
AT-2650.
Input
signal
S1
is
divided
into
the
part
which
enters
the
direct
multiplier
circuit
and
the
part
which
passes
the
phase
circuit
and
enters
the
multiplier
circuit.
The
signal
supplied
to
the
phase
circuit
is
always
90°
phase
delayed
at
L1.
Also
because
at
Non-modulation
time,
L2
is
tuned
to
10.7
MHz,
if
modulation
is
applied
and
$1
is
changed
from
10.7
MHz,
phase
deviation
at
L2
will
take
place
proportionately
in
relation
to
this
changed
part
and
this
becomes
S2
signal
which
is
delayed
in
relation
to
S1.
At
Non-modulation,
because
as
shown
in
Fig.
11,
the
input
signal
S]
and
90°
phase
delayed
(by
means
of
Ll)
signal
S2
are
switched
by
means
of
the
multiplier
circuit,
the
output
signal
becomes
S3.
Because
this
$3
passes
the
low
pass
filter
and
becomes
S4
fixed
direct
current,
the
detector
output
is
zero.
Then,
when
modulation
is
applied,
because
the
switched
output
is
varied
according
to
the
degree
of
modulation,
and
the
output
which
passed
the
low
pass
filter
becomes
the
pulsating
current
part
as
shown
in
Fig.
12,
detector
output
is
obtained.

Vi.
OPERATING PRINCIPLES OF PLL CIRCUIT
EMPLOYED
IN
STEREO
DEMODULATION
CIRCUIT
INPUT SIGNAL fs
VvcO OUT
LEFT CHANNEL
SIGNAL (L)
RIGHT CHANNEL
SIGNAL (R)
DIFFERENCE
SUB CARRIER
To separate the FM stereo broadcast signal received to
date into left and right signals, a 19 kHz pilot signal was
successively multiplier to form a 38 kHz signal and
ste
reo separation was effected from this. However, with
this multiplier system, change in coils due to wear
occurred and adjustment points were numerous, etc.
Therefore, this model employs a newly developed PLL
cir
SW
1.
cuit which produces an exceedingly accurate 38 kHz
itching signal.
PLL CIRCUIT OPERATION
PLL circuit is a kind of feedback circuit and is com-
prised of a Phase Comparator (PC), a Low Pass Filter
(LPF), a Direct Current Amplifier (DC Amp) and a
Voltage Control Oscillator (VCO) as shown in Fig.
13. The PC compares input signal Fs and VCO
oscillator output and generates the difference in
signal voltage Ve(t) proportionately to this phase
deviation. This Ve(t) passes LPF and the DC Amp
and becomes control voltage. This control voltage
supplied to VCO and VCO oscillation frequency is
DC controlled. When there is no input signal Fs,
because there is also no Ve(t), control voltage Vd(t)
becomes zero, and VCO maintains a *Free-running
oscillation frequency. When a signal enters, VCO
oscillation frequency Fo is controlled to narrow the
difference between Fs by means of feedback as
described above, and the PLL circuit assumes a
synchronous condition. This is referred to as input
signal lock. (When the difference between Fo and Fs
is too large, the differential signal frequency becomes
MAIN CHANNEL SIGNAL
MODULATOR
Fig. 13 PLL Circuit
ANTENNA
WIDE BAND
FREQUENCY TRANSMITTER
MODULATOR
SUB CHANNEL SIGNAL
Fig. 14 FM Broadcasting System Diagram
high and is reduced at the LPF. However, because the
VCO control voltage does not change, PLL will not
stay within the *lock range).
Because of the ability of the signal interference
removing LPF to accumulate the previous voltage
when the PLL deviates from within the lock range
due to certain interference, the original condition is
quickly reinstated.
* Free running frequency: Oscillating frequency
when there is no input signal.
* Lock range: At the condition in which the VCO
oscillation frequency is locked to the input
signal, the lock range is the oscillating fre-
quency in which when the input signal
changes, the PL:. maintains its input signal
lock condition.
Accordingly, in case Fs is changed inside the
PLL lock range, VCO oscillation frequency
always follows this, and ano frequency devia-
tion and no phase difference signal is ob-
tained. In other words, VCO oscillation
frequency can be locked to Fs.
ea ee
12

.
STEREO
DEMODULATION
CIRCUIT
As
shown
in
Fig.
14
for
FM
broadcasts,
the
sum
signal
(L+R)
consists
of
left
signal
(L)
and
right
signal
(R)
and
the
audio
frequency
band
of
this
signal
in
its
original
form
is
frequency
modulated.
On
the
other
hand,
the
difference
signal
of
both
(L—R)
is
changed
to
high
frequency
through
the
use
of
the
sub
carrier,
and
is
referred
to
as
the
sub
channel
signal.
The
carrier
is
further
frequency
modulated
and
sent
to
the
FM
stereo
transmitter.
es
os
5
eS
SSS
SS
Accordingly, for composite stereo signal demodu-
lation, the sub carrier used for demodulation at the
transmitter must be the same uniform 38 kHz signal
as the frequency and phase. If the 38 kHz waveform
is asymmetrical, channel separation will become poor,
At the PLL employed MPX stereo demodulator
circuit, as shown in Fig. 13 first a 76 kHz signal is
oscillated and when this passes the divider, a sym-
metrical 38 kHz signal is obtained.
COMPOSITE STEREO o
SIGNAL.
MAIN CHANNEL SIGNAL
+
SUB CHANNEL SIGNAL
MAIN CHANNEL SIGNAL
SEPARATION ADJUSTMENT
Fig. 15 MPX IC Function
L+R
SUB CHANNEL SIGNAL
38KHz SUB-CARRIER
LEFT CHANNEL SIGNAL
RIGHT CHANNEL SIGNAL
Fig. 16 Multiplex Decoder
1
2

ST-MONO SW &
VCO STOP LOOP FILTER
on} OSC RC, NETWORK
LOOP FILTER
pf
W
nm] DETECTOR INPUT
SWITCH FILTER SWITCH FILTER
ST LAMP &
19KHz MONITOR
vco PHASE LOCK
vexxz | |_| oerecror
PILOT
PRESENCE
DETECTOR
STEREO
nes SWITCH
LAMP DRIVER
ST-MONO, SW
VCO STOP SW
76KHz TO 38KHz TO
38KHz ISKHz
DIVIDER DIVIDER
38KHz TO
ISKHz
DIVIDER
me |
PRE AMP NF AMP
BUFFER
AMPLIF
| BUFFER
AMPLIFIER
STEREO
DEMODULATOR B
Vec
PRE AMP OUTPUT | ~
OUTPUT
PRE AMP INPUT '|®
L ch. DEMODULATOR
This 38 kHz sub carrier is supplied to the multiplex
decoder together with the sub channel of the
composite stereo signal. At the multiplex decoder,
left and right channel audio signals are separated in
order as shown in Fig. 16.
The 38 kHz sub carrier composited with the sub
channel signal of which the carrier part was removed
when sub channel signal and sub carrier passed R1,
R2 produces the regular AM wave. Then, because this
envelop is detected by mutually reverse polarity
connected diodes D1 and D2, L—R signal is emitted
at point@and R—L signal at point®.
14
ee aor el a =
SD wD uid z
Ea wo rene ro)
S65 $585
2° 20 26
fs) 2a S
= os “J
i xt
a
<
Oo
a
Fig. 17 wPC1173C Block Diagram
Also, because the main channel signal (L+R) is
supplied to R3, R4 center point, @®)point voltage is
added and subtracted and becomes
(L+R) + (L—R) = 2L (left channel)
(L+R) + (R—L) = 2R (right channel)
The level of the main channel signal (L+R) can be
adjusted by means of the variable resistor VR (VR1)
for optimum separation.
However, please refer to Fig. 17 for the Block
Diagram of PLL IC uPC1173C used in the model
AT-2650.

VIL
OPERATING
PRINCIPLES
OF
FM
NOISE
IC
LA2100
used
in
this
model
is
a
monolithic
IC
for
FM
noise
canceller
use.
Situated
between
the
FM
detector
and
the
stereo
demodulator,
this
circuit
features
effective
elimination
of
pulsive
external
noise
such
as
engine
noise.
CANCELLER
CIRCUIT
(1)
(2)
Det
Vin
'
(GATE)
1
|
|
H(NOISE)
|
I
!
I
(SIGNAL)
|
|
we
ON
=
+
za
Fig.
19
Basic
circuit
for
pulse
noise
suppression
and
wave
forms
1.
BASIC
CIRCUIT
FOR
PULSE
NOISE
SUPPRESSION
The
composition
of
LA2100
is
made
up
of
a
gate
circuit
and
a
holding
condenser
to
eliminate
pulse
noise.
When
the
gate
is
closed
as
in
Fig.
19(1),
condenser
Co
is
driven
by
a
low
impedance
(emitter
follower
TRI)
and
therefore
the
output
signal
is
the
same
as
the
Vin
input.
When
pulse
noise
enters,
the
gate
opens
immediately,
and
condenser
Co
maintains
the
signal
level
prior
to
noise
input.
When
the
noise
stops,
the
gate
closes
and
the
wave
form
returns
to
normal.
The
output
wave
form
Vout
becomes
similar
to
the
wave
form
of
Fig.
19(3).
Interms
of
noise
alone,
it
means
that
the
noise
(2)
is
suppressed
as
in
(3).
2.
OPERATION
PRINCIPLE
WITH
STEREO
SIGNALS
When
the
aforementioned
circuit
is
used
on
the
stere
0
signals,
the
pilot
signal
is
cut
out
while
the
gate
is
open
and
distorts
the
stereo
composite
signal
to
generate
irritating
noise.
To
prevent
this
distortion,
during
the
time
gate
is
open
a
19
kHz
sine
wave
of
the
same
amplitude
and
phase
as
that
of
the
plot
signal
is
generated
from
the
pilot
signal
generating
circuit
(19
kHz
sine
wave
generating
circuit).
Thi
is
added
to
the
holding
condenser
Fig.
19(1)
eleciric
potential
while
the
gate
is
open
and
compensit
€s
the
pilot
signal.
i
15

| DUMMY NOISE
{
(1) OPTIMAL ADJUSTMENT
AA
LAT AN
LOOP GAIN= |
(2)MISS ADJUSTMENT
LOOP GAIN => |
Fig.
20
Pilot
signal
generating
circuit
adjustment
and
pin
wave
form
(non-modulated stereo signal)
STEREO SIGNAL
GENERATOR
40 to 6048
NON MODULATED
STEREO SIGNAL
FM-VHF
OSCILLATOR
PULSE
OSCILLATOR
PULSE tus, !Vp
lto 3KHz
VY
AT-2650
vuP STEREQ A
DEMODULATOR
; O OUTPUT
O
VR
“ep
OSCILLOSCOPE
5 [SYNC
Fig. 21 Pilot signal generating circuit adjustment method
. ADJUSTMENT METHOD FOR THE PILOT
SIGNAL GENERATING CIRCUIT
(Refer to Figs. 20, 21 and 23)
To compensate the pilot signal, the 19 kHz sine wave
amplitude must be equal to the amplitude before the
gate is opened. To do this, set the loop gain of the
pilot signal generating circuit to 1 with the adjust-
ment volume as in Fig. 20 (1).
Actual adjustment involves the following: make con-
16
nections as in Fig. 21 and switch the noise cancel
switch on. Oscillate non modulated stereo signal and
pulse, and observe the wave forms on the oscillo-
scope. Next, adjust the adjustment volume VR5 5 kB
so that the amplitude at the gate is equal to the
amplitude before and after.
Although the adjustment can be made as above, it
has been fully adjusted at the factory and should
not need readjustment unless it has been touched
otherwise.

Vil LEVEL DIAGRAM
IN 4B
LEVEL
TUNER
= AUX
= TAPE -1 (PIN)
© TAPE -I(OIN)
5 TAPE -2( PIN)
Cae ews eee
Lo en ae
L\
EHONO=2
HEADPHONES
'
—€Q
AMP
!
'
CONTROL
}
'
MAIN
AMP!
! ! AMP | 1
H
t
1
!
1
\
:
}
|
TAPE
REC(PIN
|
' i
1
|
Ss
;
' i
{
|
}
:
:
|
[TAPE
REC(DIN)
|
|
|
{
H
:
| |
I
1
I
]
|
t
1
i
1
i
I
I
\
H
1
1
40
|
\
|
1
'
|
1
I
{
l
I
!
I
|
!
l
30
!
!
SPEAKER
OUTPUT
:
ie
24V
78
OHMS
(30d)
I
i
1
\
7
i
aa
oe
eee
10
ia
0
1(5dB)
|
HEADPHONES
OUTPUT
0.85V/8
OHMS(1d8)
\
;
{
! |
-10
!
TUNER,
AUX,
TAPE
1,2(PIN,
DIN)
TAPE
_REC(PIN)
36
150mv
(-14dB)
:
f
(CONTROL
AMP)
(MAIN
AMP)
150
mv{-14dB)
1 ne
| | TAPE REC (DIN)
-30 $$$ —_—_——
3 30 mv (-28dB)
| ra
= i
40 | BHONO !
3mv(-48dB) (EQ AMP) FREQUENCY I KHz
-50
Fig. 22 Level Diagram AM-2650
17

IX. TUNER ADJUSTMENT (AT-2650)
NOISE € iia
Fi NOISE CAN L
NOISE CANCEL Xo)
0s
Pp
A]
OSC
LEVEL
[S|
[o|
C LEVEL T.
Tone!
AM!
eee
FM DISTORTION
T6(BLU)
Te
ee
I9KH2
TPL
D1
ye4
soxa
; hay
VR6
5KB
Beisel
|
Boat
ee
METER
SENS
I©|
FO: PLL I9KHz T5(WHT)
yRI 20KB v~
iS ®
SEPARATION nN
@
FM TUNING ne T4(BLK)
AM IF
AM TCR2 AM TCO AM TCRI
Fig. 24 Front End FB824U 14
18

Se
a
1.
FM
TUNER
SECTION
ADJUSTMENT
(Refer
to
Figs.
23,
24)
Step
Adjustment
Item
Adjustment
Point
|
Result
Remarks
Maxi
SELECTOR
to
FM
MONO,
FM
:
Front
End
IF
Coil
ae
MUTE
and
NOISE
CANCEL
to
IF
Coil
(Front
End)
“
OFF.
Tune
only
noise
without
Level
:
;
interference
of
broadcasting.
,
Centered
W
2
Tuning
MeN
a5
(EY)
Tuning
Meter
Same
as
above.
Centering
(Tuner
P.C
Board)
Bes
Indication
|
Dieter
T6
(BLU)
Less
than
0.1%
98
MHz,
60
dB
(mono)
input.
3
Ne
(Tuner
P.C
Board)
Distortion
Less
than
0.1%
on
both
channels
:
Factor
See
NOTE
1.
Conteaton
If
Tuning
Meter
Indication
is
not
of
Tuning
.
4
centered
re-adjust
Step
2
and
Mee
3
above
Indication
,
High
Range
verre
108
MHz,
60
dB
(mono)
input.
5
Scale
TCo
(Front
End)
mie
a
TUNING
INDICATOR
to
108
Indication
-
MHz.
Error:
Within
+250
kHz.
Pearee
ste
88
MHz,
60
dB
(mono)
input
6
ee
5
a
a
TUNING
INDICATOR
to
88
ie
MHz.
Error:
Within
+250
kHz.
Indication
GF
High
Range
TCA,
TCR1I,
TCR2,
TCR3
Pees
ar
ld
108
MHz,
Less
than
4
dB(mono)
;
Sensitivity
(Front
End)
Distortion
input
Factor
me
f
ie
a
7
an
Sy
8
Low
Range
Lr1i,
LR2,
LR3
—
nae
98
MHz,
Less
than
3
dB(mono)
Sensitivity
(Front
End)
-
‘
input.
See
NOTE
2.
a
actor
Cont
reHon
Ss
shat
eG
98
MHz,
Less
than
4
dB(monc)
9
of
Mid
Range
Distortion
:
ae
input.
See
NOTE
2.
Sensitivity
Factor
PLL
Free
FM
SELECTOR
to
FM
AUTO.
;
VR6
5
kB
FM
MUTE
to
ON.
Connect
10
Running
19.00
kHz
:
Peauend
(Tuner
P.C
Board)
frequency
counter
to
Test
Poi.
adil
See
NOTE
3.
Confirmation
]
98
MHz.
60
dB
(stereo)
input.
of
Stereo
ey
ee,
{1
.
Unlet
stereo
indicator
indicatts
Indicator
mere
feed
Lighting
no
stereo
separ
;
Stereo
VR120kB
Msieaian
FM
MUTE
to
OFF.
98
Mik,
12
Separation
(Tuner
P.C
Board)
45
dB
60
dB
(stereo),
Lech
input
(Left>Right)
:
Minimum
output
of
R
ch.
a
Rees
VRI
20kB
More
than
98
MHz,
60
dB
(stereo),
Rih
(Right>Left)
(Tuner
P.C
Board)
45
dB
input
Minimum
output
of
L
ch.
|
;
|
5
Signal
Meter
VR4
50
kB
Indicator
:
i
Sensitivity
(Tuner
P.C
Board)
L
at
“4.5”
oo
Mae
TOU
enon
ap
Ciar
t-1
NOTES:
1.
When
the
distortion
factor
is
not
less
than
0.1%
in
Step
3
adjust
by
turning
the
Front
End
lic
oil
core
but
not
more
than
1/2
turn.
;
2
In
the
event
that
distortion
factor
in
Step
9
is
not
less
than
3%,
re-adjust
step
7
&
8
obtan
3%
distortion
factor.
3.
PLLIC
free
running
frequency
must
be
an
exact
19.00
kHz.
19