This AVC Automatic Volume Control Circuit work like auto volume knob, as it hears the sound coming like music or talking and then change volume by itself.
Also, if the music plays at a low volume, the circuit makes it louder and if the music becomes very loud, the circuit reduces the volume slightly.
Hence, it also helps because users do not need to adjust the volume again and again.
Circuit Working:
Parts list:
| Components | Values | Quantity |
|---|---|---|
| Resistors (All resistors are 1/4 watt) | 10k | 1 |
| 4.7k | 1 | |
| 1k | 1 | |
| 4.7M | 1 | |
| 47k | 2 | |
| Potentiometer 100k | 1 | |
| Capacitors | Ceramic 0.015μF | 2 |
| Ceramic 0.01μF | 1 | |
| Ceramic 0.1μF | 1 | |
| Electrolytic 100μF 16V | 1 | |
| Electrolytic 10μF 16V | 1 | |
| Semiconductors | IC LM358 | 1 |
| Transistors 2SC733 or 2N2222 | 2 | |
| Diodes 1N4148 | 3 |
Op-amp A1 work like input buffer for signal, and if we remove diodes D1 and D2 and then A1 become amplifier.
Here, 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.
Furthermore, this bias stay almost same all time and transistors T1 and T2 send big signal to diodes D1 and D2.
Also, trimmer P1 control this signal amount and when signal get strong more current connects through diodes; as these diodes are not normal and they change resistance.
When current goes up, the resistance then goes down; so when more current goes through then diodes kind of short the input signal to ground like volume to go down, also 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, also 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 and 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:
Hence, 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 follow the below steps for connection:
Op-Amp A1 as Buffer for Input:
- First, to use Op-Amp A1 as input buffer just connect it direct.
DC Bias:
- Next, use capacitor C5 and resistor R4 to make DC bias.
Diodes D1 and D2:
- After that, connect diodes D1 and D2 together and these diodes regulate the signal.
Transistors T1 and T2:
- Then connect T1 and T2 transistors in circuit and these help to control current going through diodes.
Trimmer P1:
- Now, the trimmer potentiometer P1 adjusts the sample signal.
Results:
- After all the connections, the circuit boosts and amplifies the output signal.
Other Things to Keep in Mind:
Power Source:
- Always, be sure power supply is good and use stable power inside range of circuit parts.
Component Values:
- Also, choose resistor, capacitor, diode values based on what circuit need, as different design need different values.
- Do not solder parts to PCB before testing and always try on breadboard first to see if all is working.
Amplification Range:
- If amplification is too high or low change resistor values and we can add more parts if needed.
Noise Control:
- Also, try reduce noise like mostly for good sound system for hi-fi and keep wires short and clean layout.
Note (Important):
- Making circuit with electricity can be dangerous, so be careful if anyone is not sure ask expert or read books or watch online video for help.
Conclusion:
Overall, this AVC Automatic Volume Control Circuit used in many audio device like radio, TV and amplifiers; as it keeps volume same level and stops sudden loud sound when changing station or input.