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11. CIRCUIT DESCRIPTIONS
The
DC-221Z/220Z
is a stereo
amplifier
which
incorporates double cassette tape decks, namely; an
exclusive playback unit (Deck I) and a recording and
playback unit (Deck II).
11-1.
Cassette Tape Deck Section
DOLBY
NR
Section
The
DOLBY
NR
section
employs
HA12045
which
incorporates Type
BDOLBY NR Encoder/ Decoder in its
L and R channels.
During the COPY mode (Deck I is set to PLAY and Deck
II is set to REC),
the DOLBY
NR
operation
stops
independent of the DOLBY NR switch, and the playback
signals of Deck I are recorded into the Deck II without
being DOLBY
NR decorded or encoded. (Fig. 11-1)
MS (Music Search) Section
Music interval detecting IC TA7341P is used in the MS
section. When
Deck I becomes
into MS
mode (CUE
operation), the INH terminal becomes H level, and it
starts the music interval detection operation. When the
playback signals due to CUE operation are stopped for a
specified time length, pulse signal is output from the PO
terminal.
Due
to this pulse
signal,
MS
solenoid
is
operated
to turn
MECHANICAL
mode
into PLAY
mode.
FUNCTION
TAPE
ON
REC
SOURCE
PLAY
DET
(PLAY:
ON)
>—oO—o-
Automatic
Tape Selector
The automatic tape selector is designed for both metal
tape and normal tape uses by detecting the CrO2 tape
discrimination hole of the cassette half, and it enables to
perform simultaneous switching of both record/playback
equalizers and recording bias.
Accordingly, when CrO2 tape is used in playback, no
particular problems will occur; however, when recording,
the frequency characteristics tend to become over-bias.
This results in much reduction of frequency characteristics
in the higher ranges.
Fig. 11-2
Music
Search
circuit
DOLBY
NR (HAI2045)
O
TAPE
OUT
Fig. 11-1
Signal route in COPY
mode
37
11-2.
Integrated Amplifier Section
Phono
Equalizer Amplifier
It uses a low noise operation amplifier IC (M5218P).
Graphic
Equalizer Section
In order to vary the frequency characteristics, it provides
five resonance circuits (to obtain equalized inductance
by the transistors) in the feedback loop of the operation
amplifier, and creates five poles in its playback signal
frequency band.
In each of these circuits, IC (BA3812L) is used. The IC
(BA3812L) forms a five-pole graphic equalilzer by adding
a capacitor for resonace circuit and a variable resistor to
it
Power Amplifier Section
It uses IC (STK4171-2S)
which
incorporates
a power
amplifier for 2 channels and gains of 40Wx2 THD 0.3%
at 1 kHz.
Protection
Circuit
It uses a relay to switch the output cirucit of the power
amplifier ON and OFF, and prevents the transient noise
output due to cutoff by the DC voltage detection at the
center of the output, and the delayed connection when
the power is turned ON and cutoff when the power is
turned OFF.
38
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