Specifications

CONSTRUCTION
tact with terminal 3 (Q3 output of IC7
high), normal gain is provided for the
high-frequency components (treble) and
higher gain is available for a wide range
of low frequencies (including some mid-
range frequencies). This is termed as the
X-BAS mode. The gain of the amplifier
for different frequencies, in each of the
above-mentioned modes, is also dependent
on VR3 and VR4 potmeter settings.
In the actual circuit diagram, the bi-
polar analogue switcher (CD4066) replaces
switch SW. The LEDs D6, D7, and D8
are used to represent the sound modes—
low-boost, hi-fi, and X-BAS repsectively.
Switch S2 is used to select variouse sound
modes. At power on, Q0 (pin 3) of IC7 is
high and therefore normal sound mode
is on.
Section III (Fig. 6). This section com-
prises an audio power amplifier, a 12V
dual power supply, and an audio level in-
dicator. The power amplifier used is the
popular IC-TA7230, which delivers up to
7-watt (RMS) power per channel into a
4-ohm load. This IC has in-built short cir-
cuit protection and over-temperature cut-
off. A suitable heat sink must be connected
to the IC to prevent thermal run-away.
Potmeters VR8 and VR9 are volume con-
trols for left and right channels respec-
tively, while VR7 is the balance control.
A dual power supply is used for the
circuit. The +12V section uses a π filter
with capacitors in the parallel arms and
an inductor in the series arm. However,
for the – 12V supply, the inductor of the
series arm (as used for +12V supply) is
replaced by a resistor. Filters are provided
to reduce the ripple factor and thereby
reduce hum (noise). Please refer inductor
details in parts list.
The audio level indicator is built
around IC KA2281. LEDs D14 through
D23 are connected at its outputs to show
the audio level of each channel in five
steps. The input to this audio level indi-
cator is derived from the output of the
power amplifier. The gain of this level
indicator can be varied by changing the
values of resistors R49 and R50.
Assembly
The complete circuit, with the exception
of the audio level indicator, can be as-
sembled on a single PCB. A separate PCB
is used for the audio level indicator
and for mounting LEDs (D2 through
D8). Single-sided, actual-size PCB for the
complete circuit is given in Fig. 7. The
component layout for the PCB is shown
in Fig. 8.
Use sockets for all ICs except IC1 and
IC9. Shielded wires must be used for con-
nections to stereo head and all potentio-
meters. The PCB must be mounted away
from power transformer and DC motor.
Inductor L2 should also be placed
away from the power transformer. If in-
ductor L2 is difficult to procure or fabri-
cate, it may be substituted with a 5-ohm,
5W wire-wound resistor.
A suitable cassette drive mechanism
and cabinet may be used to assemble the
stereo cassette player. Readymade cabi-
nets and cassette mechanisms are avail-
able in the market.
Adjust potmeters VR1 and VR2 for
minimum distortion at higher volume
level. Use separate aerials for FM trans-
mitter and FM receiver.
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