The circuit shown here is based on the switching action of transistors.
Volume of a stereo deck can be controlled with the
help of a potentiometer which changes the resistance between the output
of the preamplifier and input of the amplifier. This can be done with
the help of decade counter, IC.4017 and some transistors.
The input is applied at collectors and the output is taken from emitters
of the transistors. Depending upon the output of IC 4017, the
corresponding transistor gets saturated. Output from the emitters is
taken through a coupling ” capacitor to block the DC components. When
pin 4 of IC 4017 ° goes high, the corresponding transistor (T2) gets
saturated and the input signal is directly fed to the output through the
To start with, press switch S1. The timer IC (IC 555) will start
generating pulses at equal interval of time which are fed to IC2.
Depending on the output of IC 4017 the transistor is selected. When
desired volume reached; release the switch.
To reset the counter, switch S2 is brought to position A. The time
period of the output pulses · can be set, using the formula Td: 0.693
(R1 +2VR1 + 2R32) C1 seconds.
Digital volume controller circuit diagram: