This article talk about Class A amplifier which is good for small speaker or headphone, also amplifier make sound more loud.
Further, this Class A Amplifier Circuit uses near 20 milliamp power so it good for low power thing and we can show in this post how to make it using Q1 and Q2 transistor and this transistor work like tiny switch.
WARNING: Making electronic project is not easy, only do it with adult help.
What is Class A Amplifier Circuit:
Both output parts of Class A amplifier always work with full power all the time, because it is always ON, Class A amplifier is not so efficient.
Also, it usually give only 20% efficiency but sometimes maybe it goes up to 50% max.
Circuit Working:
Parts List:
| Components | Values | Quantity |
|---|---|---|
| Resistors | 5.6k CFR 1/4 watt | 1 |
| 47k CFR 1/4 watt | 1 | |
| 39Ω CFR 1/4 watt | 1 | |
| Potentiometer 100k | 1 | |
| Capacitors | Electrolytic 1µF 25V | 2 |
| Electrolytic 100µF 25V | 1 | |
| Electrolytic 220µF 25V | 1 | |
| Semiconductors | Transistor 2N2222 | 1 |
| Transistor TIP31 | 1 | |
| Speaker 65Ω | 1 |
To begin with, amplifier uses about 20 milliamp quiescent current and this current is important because it sets transistor bias and how amplifier works; also we can change quiescent current by changing resistor R3.
We can change the amplifier slightly to fit different needs and improve the working point.
Q1 and Q2 transistors work as common emitter amplifiers, and this Q1 output goes to Q2 input by making cascade to amplify more.
Amplifier gives about 80 dB voltage gain which means it makes signal strong.
Also, capacitor C3 blocks resistor R3, so R3 works as emitter load for Q2 and this makes amplifier stable by keeping Q2 emitter voltage near Q1 collector voltage.
Here, resistor R2 gives base bias to Q1 using voltage from Q2 emitter.
Furthermore, negative DC feedback keeps bias safe and amplifier stable and also volume can change by input potentiometer R4.
As a result, this resistor R4 lets user control sound volume and input signal level.
Formulas:
We call the collector current in a BJT the quiescent current (IQ), which is the current that flows through the transistor when no signal is present.
We can find IQ like this:
IQ = VCC / R3
where,
- We call the DC current in the collector with no input the idle current or IQ.
- VCC is positive voltage for BJT collector, measured from ground.
- R3 is resistor that connects BJT collector to VCC.
How to Build:
To Build a Class A Amplifier Circuit follow the below mentioned steps for connections:
- First, choose good transistors for Q1 and Q2 and they must match the amplifiers need like impedance.
- Next, place Q1 and Q2 on the PCB or breadboard, check the pin layout and be sure we put them in the correct way.
- After that, connect resistor R1 between Q1 collector and positive power of VCC.
- Then connect resistor R2 from Q1 base to Q2 emitter.
- Now connect resistor R3 from Q2 collector to VCC and to change amplifier idle current change value of R3 this help fix transistor working point.
- After that, connect capacitor C3 with resistor R3 which will help block DC and keep good bias, also this C3 help make Q2 emitter voltage follow Q1 collector average voltage and this will give better stability.
- Also, use resistor R2 to give base bias to Q1 from Q2 emitter.
- Next, connect potentiometer R4 to control volume.
- Join power supply wires like positive and negative to correct place on circuit.
- After that, turn ON the circuit and use speaker or oscilloscope with audio signal to check output.
- Lastly, adjust potentiometer R4 to change volume and check amplifier work proper.
Conclusion:
Overall, this Class A Amplifier Circuit is easy and flexible project, which uses common emitter setup, adjustable quiescent current and smart parts like capacitors.
Also, if required people can test and improve it, by learning how it works and they can make it fit for different audio needs.