Specifications

CIRCUIT IDEAS
CIRCUIT IDEAS
VIVEK SHUKLA
BASS AND TREBLE FOR
STEREO SYSTEM
M
odern audio frequency amplifi-
ers provide flat frequency re-
sponse over the whole audio
range from 16 Hz to 20 kHz. To get faith-
ful reproduction of sound we need depth
of sound, which is provided by bass (low
notes). Hence low-frequency notes should
be amplified more than the high-frequency
notes (treble). To cater to the individual
taste, and also to offset the effect of noise
present with the signal, provision of bass
and treble controls is made. The combined
control is referred to as tone control.
The circuit for bass and treble control
shown in the figure is quite simple and
cost-effective. This circuit is designed to
be adopted for any stereo system. Here,
the power supply is 12-volt DC, which
may be tapped from the power supply of
stereo system itself. For the sake of clar-
ity, the figure here shows only one chan-
nel (the circuit for the other channel be-
ing identical). The input for the circuit is
taken from the output of preamplifier
stage for the left as well as right channel
of the stereo system
Potentiometer VR1 (10-kilo-ohm) in
series with capacitor C4 forms the treble
control. When the slider of potentiometer
VR1 is at the lower end, minimum treble
signal develops across the load. The low-
est point is referred to as treble cut. As
the slider is moved upward, more and
more treble signal is picked up. The high-
est point is referred to as treble boost.
Bass would be cut if capacitive reac-
tance in series with the signal increases.
Thus, when the slider of potentiometer
VR2 is at the upper end, capacitor C1 is
shorted and the signal goes directly to
the next stage, bypassing capacitor C1.
Hence, bass has nil attenuation, and it is
called bass boost. When the slider is at
the lowest end, capacitor C1 is effectively
in parallel with potentiometer VR2. In this
position, bass will have maximum attenu-
ation, producing bass cut.
Bass boost and bass cut are effective
by ±15 dB at 16 Hz, compared to the out-
put at 1 kHz. Treble boost and treble cut
are also effective by the same amount at
20 kHz, compared to the value at 10 kHz.
After assembling the circuit, we may
check the performance of the bass and
treble sections as follows:
1. Set the slider of the potentiometers
at their mid-positions.
2. Turn-on the stereo system.
3. Set the volume control of stereo
system at mid-level.
4. Set the slider at the position of op-
timum sound effect.
This circuit can be easily assembled
using a general-purpose PCB.
G.S. SAGOO
H
ere is a very low-cost circuit to
save your electrically operated
appliances, such as TV, tape re-
corder, refrigerator, and other instruments
during sudden tripping and resumption of
mains supply. Appliances like refrigera-
tors and air-conditioners are more prone
MALAY BANERJEE
PROTECTION FOR YOUR
ELECTRICAL APPLIANCES
G.S. SAGOO
to damage due to such conditions.
The simple circuit given here switches
off the mains supply to the load as soon
as the power trips. The supply can be
resumed only by manual intervention.
Thus, the supply may be switched on only
after it has stabilised.
The circuit comprises a step-down
transformer followed by a full-wave recti-
fier and smoothing capacitor C1 which acts
as a supply source for relay RL1. Initially,
when the circuit is switched on, the power
supply path to the step-down transformer
X1 as well as the load is incomplete, as
the relay is in de-energised state. To
energise the relay, press switch S1 for a
short duration. This completes the path
for the supply to transformer X1 as also
the load via closed contacts of switch S1.
Meanwhile, the supply to relay becomes
available and it gets energised to provide
a parallel path for the supply to the trans-
former as well as the load.
If there is any interruption in the
35