AVC Automatic Volume Control Circuit

This AVC Automatic Volume Control Circuit work like auto volume knob.

It hears the sound coming like music or talking and then change volume by itself.

If music is played low then it makes little louder.

If music is very loud then makes it little quiet.

This helps because there is no need to change volume again and again.

Circuit Working:

Parts list:

Op-amp A1 work like input buffer for signal.

If remove diodes D1 and D2 and then A1 become amplifier.

R4 and C5 together make DC bias for A1 and this bias help A2 to block DC and ensures signal does not amplify too much which is max around 100 times.

This bias stay almost same all time.

Transistors T1 and T2 send big signal to diodes D1 and D2.

Trimmer P1 control this signal amount.

When signal get strong more current connects through diodes.

These diodes are not normal and they change resistance.

When current goes up the resistance also goes down.

So when more current goes through then diodes kind of short the input signal to ground like volume to go down.

It work like signal reducer.

Formula and Function:

AGC (Automatic Gain Control) circuit uses op amps to keep output signal same level, even if input get big or small.

This idea show how to make AGC using op-amp and give formula.

Main goal of AGC is to change op-amp gain automatic and depending on input level.

This work by sending some output back to control gain of op amp.

Formula for AGC is:

Output Voltage = G × Input Voltage

here,

• G is the gain factor and it can change live depending on output and control signal.

How to control gain and AGC depends on circuit design and what we need.

Actual circuits use extra parts like:

• Diodes: to change AC to DC
• Capacitors: to smooth signal
• Resistors: to set bias voltage

For better AGC design people use simulation and deep circuit check to make performance good like fast response and stable output.

How to Build:

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

Op-Amp A1 as Buffer for Input:

• To use Op-Amp A1 as input buffer just connect it direct.

DC Bias:

• Use capacitor C5 and resistor R4 to make DC bias.

Diodes D1 and D2:

• Diodes D1 and D2 must be joined together.
• These diodes work like regulator for signal.

Transistors T1 and T2:

• Connect T1 and T2 transistors in circuit.
• These help to control current going through diodes.

Trimmer P1:

• Trimmer potentiometer P1 is used to adjust sample signal.

Results:

• After all connection the output get boosted means amplified the signal.

Other Things to Keep in Mind:

Power Source:

• Be sure power supply is good.
• Use stable power inside range of circuit parts.

Component Values:

• Choose resistor, capacitor, diode values based on what circuit need.
• Different design need different values.

Testing:

• Do not solder parts to PCB before testing.
• Try on breadboard first to see if all is working.

Amplification Range:

• If amplification is too high or low change resistor values.
• We can add more parts if needed.

Noise Control:

• Try reduce noise like mostly for good sound system for hi-fi.
• Keep wires short and clean layout.

Note (Important):

• Making circuit with electricity can be dangerous.
• Be careful if anyone is not sure ask expert or read books or watch online video for help.

Conclusion:

AVC Automatic Volume Control Circuit used in many audio device like radio, TV and amplifiers.

It keeps volume same level and stops sudden loud sound when changing station or input.

References:

Automatic Volume Control