Headphone Amplifier Circuit using Transistors make weak sound strong so headphones work well.
This circuit is useful when sound is direct from source which is not loud or clear.
In this post we talk about small 3V transistor amplifier for better sound.
Circuit Working:
Parts List:
| Component Type | Value/Specification | Quantity |
|---|---|---|
| Resistors (All resistors are 1/4 watt unless specified) | 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 | |
| On / Off Switch | 1 | |
| Headphone | 1 | |
| 3V Battery | 1 |
Circuit uses 3 transistors Q1 BC547, Q2 BC547, Q3 BC557 for small signal boost.
Audio is in through C1 1µF to Q1 and work as preamp.
Q2 and Q3 is in push-pull which gives more gain.
Q1 is voltage amp, Q2 is driver and Q3 is power amp for headphones.
C2 and C3 help signal pass and cut noise.
R1 to R8 set bias and gain.
3V battery and S1 switch powers the circuit.
Output goes to headphones with clear sound clear and with no distortion.
Formulas:
Formulas for simple headphone amplifier:
Av = β × (Rc / Re)
where,
- β is gain of Q1
- Rc is the collector resistor of R4
- Re is the emitter resistor of R6
Bias Voltage:
Vb = Vcc × (R2 / (R1 + R2))
where,
- Vcc is 3V
- R1 is 10k
- R2 is 100k
Collector Current:
Ic = (Vcc − Vce) / Rc
where,
- Vce is 0.7V
- Rc is the collector resistor of R4 is 1.5k
How to Build:
To build a Headphone Amplifier Circuit using Transistors follow the below mentioned steps:
- Connect base of Q1 to one end of R1 and R1 goes to C1 and C1 goes to audio input.
- Connect R2 between base of Q1 and GND.
- Connect emitter of Q1 to GND through R6.
- Connect collector of Q1 to base of Q2.
- Connect collector of Q1 to positive supply through R4 and R5.
- Connect collector of Q2 to base of Q3 and to one end of R7 and R7 goes to positive supply.
- Connect emitter of Q2 to collector of Q3.
- Connect one end of R3 between the junction of R1, R2 and base of Q1 and the other end to collector of Q3.
- Connect positive of C2 between R4 and R5 and connect negative of C2 between R3 and collector of Q3.
- Connect emitter of Q3 to positive supply of 3V.
- Connect collector of Q3 to one end of R8 and R8 goes to one end of the headphone and the other end of the headphone goes to GND.
- Connect positive of C3 to positive supply and negative of C3 to GND.
- Connect S1 between positive supply of the circuit and +3V battery and connect negative of 3V battery to GND.
Conclusion:
Headphone Amplifier Circuit using Transistors is cheap, easy to make and portable.
It is good for DIY audio, small projects or as a preamp.