A headphone amplifier is a basic electronic tool that boosts low audio signals allowing them to power headphones effectively.
This device is handy in various audio scenarios particularly when plugging directly into an audio source does not deliver sufficient volume or clarity.
The Simple Headphone Amplifier Circuit using Transistors, which we will discuss is a compact and efficient amplifier that operates on a 3V power supply and is designed to enhance sound quality.
Circuit Working:
Parts List:
| Component Type | Value/Specification | Quantity |
|---|---|---|
| Resistors (1/4 Watt) | 10k | 1 |
| 100k | 1 | |
| 68k | 1 | |
| 1.5k | 1 | |
| 3.3k | 1 | |
| 330Ω | 1 | |
| 4.7k | 1 | |
| 2.2k | 1 | |
| Capacitors | PPC 1µF | 1 |
| Electrolytic 100µF 25V | 1 | |
| Electrolytic 470µF 25V | 1 | |
| Semiconductors | Transistor NPN BC547 | 2 |
| Transistor PNP BC557 | 1 | |
| Other Components | On / Off Switch | 1 |
| Headphone | 1 | |
| 3V Battery | 1 |
The circuit has three transistors Q1 BC547, Q2 BC547 and Q3 BC557, which work together to create a small amplification stage.
The audio signal enters through the base of transistor Q1 capacitor C1 1µF, which acts like a preamplifier.
After this initial boost transistors Q2 and Q3 further amplify the signal in a push pull setup.
Q1 transistor is a voltage amplifier that strengthens the weak input signal.
Q2 transistor serves as a driver, giving additional current gain.
Q3 transistor is a power amplifier that provides enough power to drive headphones effectively.
C2 and C3 capacitors assist with signal coupling and help reduce noise.
All resistors from R1 to R8 are used for biasing and managing the gain.
3V battery and S1 switch supply the necessary power for the circuit.
The amplified audio output goes through the headphones ensuring the sound is clear and without distortion.
Formulas:
Below are the formulas for Simple Headphone Amplifier Circuit using Transistors:
Voltage Gain formula:
The voltage gain of the circuit can be estimated using the transistor Q1 gain formula:
Av = beta * (Rc / Re)
where,
- beta is the current gain of the transistor Q1
- Rc is the collector resistor R4
- Re is the emitter resistor R6
Biasing Formula:
Base voltage Vb is calculated using the voltage divider rule
Vb = Vcc * (R2 / (R1 + R2))
where,
- Vb is the base voltage f transistor Q1
- Vcc is the supply voltage of 3V
- R1 and R2 are resistors 10k and 100k to form a divider to set the biasing voltage at the base of Q1.
Collector current Ic can be estimated using:
Ic = (Vcc – Vce) / Rc
where,
- Ic is the collector current of transistor Q1
- Vcc is the supply voltage of 3V
- Vce is the voltage drop across the transistor which is around 0.7V for saturation
- Rc is the collector resistor R4 1.5k
How to Build:
To build a Simple Headphone Amplifier Circuit using Transistors follow the below mentioned steps:
- Assemble all the components as mentioned in the above circuit diagram
- Connect the base of transistor Q1 to one end of of resistor R1 and other end of R1 resistor connect to capacitor C1 and other end of capacitor C1 connect to audio input
- Connect one terminal of resistor R2 between resistor R1 and base of transistor Q1 and other terminal of R2 connect to GND
- Connect the emitter of transistor Q1 to GND through resistor R2
- Connect the collector of transistor Q1 to base of transistor Q2
- Connect the collector of transistor Q1 to positive supply through resistors R4 and R5
- Connect the collector of transistor Q2 to base of transistor Q3 and one terminal of resistor R7 and other terminal of R7 connect to positive supply
- Connect the emitter of transistor Q2 to collector of transistor Q3
- Connect one terminal of resistor R3 between between the junction of resistor R2 and resistor R1 and base of transistor Q1 and other terminal connect to collector of transistor Q3
- Connect positive of capacitor C2 between resistor R4 and R5 and negative of C2 connect between resistor R3 and collector of transistor Q3
- Connect the emitter of transistor Q3 to positive supply of 3V
- Connect the collector of transistor Q3 to one end of resistor R8 and other end of R8 resistor connect to one end of headphone and other end of headphone connect to GND
- Connect capacitor C3 positive to positive supply of the circuit and negative of C3 capacitor connect to GND of the circuit
- Connect S1 switch one end from positive supply of the circuit and other end to +3V battery and connect to negative of 3V battery to GND of the circuit
Conclusion:
This easy-to-make Simple Headphone Amplifier Circuit using Transistors is a budget friendly way to enhance weak audio signals.
Powered by a 3V battery, it is portable and can be built with parts that are easy to find.
You can use it for small audio projects, DIY tasks or as a preamp for your personal audio devices.