Block Diagram; Circuit Descriptions - Pioneer SA-708 Service Manual
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Also See for SA-708:
- Operating instructions manual (13 pages) ,
- Operating instructions manual (13 pages)
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3. BLOCK
DIAGRAM
35.5dB
[renee FUNCTION
PHONO
TAPE
=4kH:
16.54B
|
(f
MUTING
voune|"
27.548
[retin
O SPEAKER A
BALANCE
INTERFERENCE
MONITOR
MODE
SUBSONIC
TONE
POWER
PHONO
(©
6)
LS
(SX)
&)——&)
E ae
&)
Fs Fees
OT oO
&
O SPEAKER B
L
RFI
;
ATT
FILTER
ATT.
'a
'
art |
PHONES
Se,
i,
1
a
® Or[rve]
TUNER
© 6
LOUDNESS
eUaUeE
AUX
(6
TAPE DUPLICATE
protection | [\/
INDICATOR
>
TON
CIRCUIT
DRIVE
EREG
X9
CONTROL
/N
TAPE 1
H
H
1
i
Leray ©
|
+8
on
ie ||
| | FUNCTION
PREC
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!
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PHONO eu
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oe
00
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AC LINE
TUNER
AUX
REC
TAPE 1
LPLAY
pREC
TAPE 2
'pray
R
4. CIRCUIT DESCRIPTIONS
4.1 PHONO CIRCUIT
RF Interference Filter
Since the phono input circuit is extremely sensi-
tive, it is adversely
affected
by radio
frequency
interference. This interference is reduced by insert-
ing a resistor in series with the phono input circuit
by setting the PHONO
INTERFERENCE FILTER
switch on the rear panel to the ON position.
Equalizer Amplifier
The
equalizer
amplifier
is a
3-stage
direct-
coupled
amplifier
with
emitter-to-emitter
feed-
back.
An
S-N
ratio
of 86dB
(at 2.5mV
input,
IHF-A, PHONO INTERFERENCE FILTER switch
OFF) has been achieved by using a ultra-low-noise
PNP
transistor
(2SA978)
at the first stage, and
reducing the signal source resistance and equalizer
element impedance.
The
2nd stage load has been reduced, a large
F
O SPEAKER
A
R CHANNEL
(SAME
AS
L
CHANNEL )
O SPEAKER
B
POWER
AMP
INDICATOR
DRIVE, FUNCTION
INDICATOR
POWER
AMP
EQ AMP
TONE AMP
output
voltage
obtained,
and
the
output
impe-
dance lowered by using an emitter follower at the
output stage.
Metal
film resistors having a tolerance
of +1%
and polypropylene
film capacitors having a toler-
ance of +2% are used on the NFB circuit to obtain
an equalizer deviation of within +0.2dB
over the
20Hz
to 20000Hz range. The maximum
allowable
input
of this
circuit
is 200mV
(at 1kHz,
THD
0.01%).
4.2 TONE CONTROLS
The
tone
amplifier
is a 3-stage
direct-coupled
amplifier with emitter-to-emitter feedback.
Tone control (BASS, TREBLE)
is accomplished
by providing the tone amplifier
NFB circuit with a
frequency
characteristic.
The
NFB
circuit
is
changed
to a flat frequency
characteristic
when
the TONE switch is in the OFF position.
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