Audio Section - Pioneer SX-1250 Service Manual

I
4 . 2 A U D I O S E C T I O N
Equalizer Amplifier
The equalizer amplifier is shown in Fig. 7. The ftst
stage (Ql & Q2) is a PNP transistor unbalanced
differential amplifier. High voltage gain is provided
in the following stage (Q3) by a bootstrap circuit
(C1 & R1). The output stage (Q4 & Qb) is a com-
plementary symmetrical SEPP circuit. The high
voltage utility
factor of the SEPP circuit provides a
high maximum output voltage. Dynamic range of
the equalizer amplifrer is therefore wide and over-
load input lettel at O.lVo distortion is 500mV (rms
at lkHz).
Equalizer elements (C2, C3, R2, R3) are polysty-
rene film capacitors with tolerances within 117o
and metal film resistors with tolerances better than
i1%. These lead to a deviation with respect to the
RIAA playback standard within t0.2dB. Due to
the balanced plus and minus power supply, the
input and the output points become essentially 0V,
reducing click noise during FUNCTION switch
operation.
Tape and Adaptor Circuits
With the DUPLICATE switch OFF, the program
source selected by the function switches are ob-
tained at the TAPE REC jacks (Fig. 8).
The TAPE MONITOR 1 switch selects between the
program source selectd by the function switch
and the input at the TAPE 1 PLAY jacks (Fig.9).
The TAPE MONITOR 2 switch selects between the
signal selected by the TAPE MONIIOR
1 switch
and the input at the TAPE 2 PLAY jacks (Fig.9).
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F i g . 9 . T a P e m o n i t o r c i r c u i t
When the DUPLICATE
switch is set to ON, the
TAPE 1 REC jacks are connected to the TAPE 2
PLAY
jacks, and the TAPE 2 REC jacks to the
TAPE 1 PLAY jack's (Fig. 10).
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Fig. 10. Tape duplicate circuit
The signal selected by the TAPE MONITOR 2
switch appears at the ADAPTOR OUT jacks (Fig'
11). The ADAPTOR switch selects between the
signal selected by the TAPE MONITOR 2 switch
and the input at the A-DAPTOR IN jacks (Fig. 11)'
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Fig. 1 1. ADAPTOR iacks
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MODE Switch
When the MODE switch is set to the MONO posi
tion, the left and right channels are shorted in the
stage following the tape and adaptor circuits.
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Fig. 7. Schematic diagram for Equalizer amplifier
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Fig. 8. TAPE REC jacks