Audio Circuit Diagrams

Audio Equalizer Circuit

The Audio Equalizer is used to alter the tune/melody to a different pitch level without losing any of the tune’s information. At different points in time, the signal’s properties may change. The melody generated by the melody generator IC can be delayed, and the tune’s pitch can be varied at different points in time. From a single tune, this can produce a variety of musical sounds.

The word ‘modulation’ is used to denote change of the tune by generating delay along with other effects.


  • Circuit Diagram of Audio Equalizer Circuit:
    • Components Description:
    • Working of Audio Equalizer Circuit:

Circuit Diagram of Audio Equalizer Circuit:

Audio Equalizer

Components Used in this Circuit:

  • IC
    • IC1, IC2(4046) – 2
    • IC3(NE555) – 1
    • IC4(CD4051) – 1
  • ResistorC1,C2(4.7uf) – 2
    • R1,R3(2.2K) – 2
    • R2,R4(220K) – 2
    • R5,R6(10K) – 2
    • R7(56K) – 1
    • VR1(10K) – 1
    • VR2(5K) – 1
  • C3(470uf) – 1
  • C4(.1uf) – 1
  • D1(1N4148) – 1
  • T1(SL100) – 1
  • UM66 – 1
  • Speaker – 1

Components Description:

1. Phase Locked Loop (for Voltage Controlled Oscillator):

IC for the Phase Locked Loop is linked with 220K ohm (R2 ae well as R4) at pin number 12.The offsets are mainly provided by these resistors. Large value of R2 or R4 implies that there is a merely a minute offset.To shun total silence at the time input is 0V, R2 resistor offsets the range of frequency.

The frequency at output from VCO(pin4) at the time when voltage at pin 9 is half the voltage given is calculated by

      f=1/ (R1*C1) = 1/ (2.2K*4.7u) = 96.71 Hz.

The frequency alter with the variation of the voltage at VCO’s input is altered by potentiometer.

2. 555 Timer: This IC works like a astable multivibrator.

The on-time is = R5+C3=10Kohm*470pF=47msec

Off-time is also equal to 4.7 m sec (R6*C3)

During off-time when discharging the capacitor, a diode is connected to block the route. The basic idea is to keep the on and off times consistent (50 percent of the duty cycle). C4 with a value of 0.1uF is utilised to filter out any noise in the circuit. It is not necessary to be online.

The 555 timer output is used as a selection line for the multiplexer, and it multiplexes both VCO outputs.

3.Multiplexer: The CD4051 operates as a 2.1 multiplexer, with both VCO outputs serving as inputs to MUX pins 13 and 14, and a selection line used to choose output from each of these PLLs with the same time period. A variety of effects can be added into the audio by concluding a few additional VCOs and multiplexing them, and the speaker receives it as an output. There are several different types of UM66T on the market, each of which generates a different tone. For example, the UM66T01 produced “Jingle Bells,” “We Wish You a Merry Christmas,” and “Santa Clause is Coming to Town.” Any melody can be used in place of UM66 in the circuit above to change the melodies.

Working of Audio Equalizer Circuit:

IC UM66 is used in the circuit to alter the melody which is produced by the melody generator. Oscillation is generated by the voltage controlled oscillator at the time when constant voltage is applied. For the purpose of the VCOs phase locked loop IC (i.e. 4046) which is IC1 and IC2 in the circuit is used. PLL chip comprises of VCO as well as Phase comparator.

The voltage supplied to VCOs can be modified with the help of the potentiometer. The circuit includes a 5K and 10K potentiometer for modifying the VCO input voltage. IC1 and IC2 are responsible for capturing this voltage. A CD4051 multiplexer IC time-multiplexes the output of VCOs at pin 4 of IC CD4046 (which IC 4 in the circuit diagram).

The signal for the multiplexer is generated by a 555 timer (IC3) that functions as an astable multivibrator. The time consumed by each high and low pulse emitted by the 555 timer is 4.7 seconds. Using a tiny signal diode like the IN4148, the duty cycle is guaranteed to be 50%. After that, the output is applied to the NPN transistor.

The melody generator UM66 (or any other IC for melody generation) receives its input from the collector terminal. The melody generator’s output is then connected to one terminal of a 4 ohm speaker (SP), and the speaker’s left terminal is connected to a 5 volt power supply.

The same music can listen to many different tones, heights, and pitches by making minute changes in the places of the potentiometer. Similarly, a variety of tunes can be changed by simply substituting another melody IC for UM66 in the aforementioned circuit.


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