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AVC Automatic Volume Control Circuit

This circuit functions similarly to a self adjusting volume knob.

It automatically adjusts the volume to a right level after listening to the incoming sound such as music or a voice.

Thus if the music is soft it becomes slightly louder.

Also it becomes somewhat quieter if the song is played at a high volume.

This is useful since one do not have to change the volume all the time.

Circuit Working:

Parts list:

CategoryDescriptionQuantity
Resistors (All resistors are 1/4 watt)
10k1
4.7k1
1k1
4.7M1
47k2
Potentiometer 100k1
Capacitors
Ceramic 0.015μF2
Ceramic 0.01μF1
Ceramic 0.1μF1
Electrolytic 100μF 16V1
Electrolytic 10μF 16V1
Semiconductors
IC LM3581
Transistors 2SC733 or 2N22222
Diodes 1N41483

Op amp A1 functions as an input signal buffer.

Removing diodes D1 and D2 transforms A1 into an amplifier.

R4 and C5 combine to generate A1s DC bias which enables A2 to cap the DC level at its input and limit amplification to a maximum of 100 times.

The offset bias remains relatively constant.

Through transistors T1 and T2 the amplified signal is sent to regulator diodes D1 and D2 with trimmer P1 controlling this sampled signal.

Increased signal strength leads to higher current flow through the diodes.

These regulator diodes show a non linear curve with decreasing resistance as current increases.

As the current flowing through the diodes increases the input signal is more or less grounded through the diodes which act as an attenuator.

Formula:

Automatic Gain Control AGC circuits depend on operational amplifiers to keep the output signal level mostly constant even when the input signals amplitude fluctuates.

This explanation shows how to make AGC using an op amp with the related formula.

Adjusting the op amp power constantly to the input signal level is the main aim of an op amp based AGC circuit.

This is often achieved by sending back some of the output signal to regulate the amplifier stages gain.

The particular formula for AGC gain control in a circuit is as follows:

Output Voltage = G * (Input Voltage)

where,

Correct gain adjustment and AGC control method could differ based on the requirements and specific design of the AVC circuit.

Actual designs often contain additional components such as diodes for rectification, capacitors for smoothing and resistors for adjusting the bias level.

For accurate AVC design, methods of simulation and thorough circuit analysis are commonly used to improve aspects of performance including reaction time, gain stability and noise performance.

How to Build:

To build a AVC Automatic Volume Control Circuit following steps are required for connection:

Op Amp A1 as Buffer for Input:

Bias in DC:

Diodes D1 and D2:

T1 and T2 transistors:

Trimmer P1:

Results:

Other Things to keep in mind:

Source of Power:

Values of Components:

Testing:

Range of Amplification:

Taking Noise into Account:

Note:

There are dangers involved in building electrical circuits thus safety measures must be taken.

If ack knowledge with electronics think about asking someone who knows a lot about circuit design for help or looking through relevant resources like online tutorials or electronics textbooks.

Conclusion:

AVC Automatic Volume Control Circuits are frequently found in audio equipment such as amplifiers, TVs and radios.

When shifting between radio stations or other audio sources this circuit helps to maintain a constant volume level and avoid sudden changes in loudness.

References:

Automatic Volume Control

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