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:
| Category | Description | 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 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,
- G the gain factor can be changed in actual time based on the output levels AVC control signal.
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:
- For use as an input buffer connect Op Amp A1.
Bias in DC:
- For DC biasing use capacitor C5 and resistor R4.
D1 and D2 diodes:
- One should see the diodes D1 and D2 are joined
- Diodes serve as regulators by doing so.
Transistors T1 and T2:
- The transistors T1 and T2 should be connected.
- Such transistors control the current that flows through the diodes.
Trimmer P1:
- In order to regulate the sample signal connect trimmer potentiometer P1.
Results:
- The output receives the enhanced signal after that.
Other Things to keep in mind:
Power Source:
- Check that there is a enough supply of electricity in the circuit.
- Use a steady source of power that falls within the working range of the component.
Values of Components:
- Choose the values of the resistor, capacitor and diode according to the required features of the AVC circuit.
- The values of the components are based on the particular needs of the application.
- Soldering components onto a PCB is not the same as testing the circuit on a breadboard.
Range of Amplification:
- If necessary modify the resistor values and maybe add more parts to adjust the amplification range.
Taking Noise into Account:
- Reduce noise as much as possible particularly if the circuit is meant for high fidelity applications.
Note:
There are dangers involved in building electrical circuits thus safety measures must be taken.
If anyone lacks 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:
Audio devices like radios, TVs and amplifiers commonly have in them AVC Automatic Volume Control Circuits.
This circuit helps to keep the volume level constant and to avoid unexpected changes in loudness while switching between radio stations or other audio sources.