12 Watts Amplifier Circuit using Transistors make sound louder in audio systems.
12W amplifier uses op-amp with NPN and PNP transistors.
It gives strong output for 4 ohm speaker.
This circuit is good for audio lovers and boost weak sound to loud, which is clear and with good quality.
Circuit Working:
Parts List:
| Component | Specification | Quantity |
|---|---|---|
| Resistors (All resistors are 1/4 watt unless specified) | ||
| 47k | 2 | |
| 10k | 1 | |
| 270k | 1 | |
| 1k | 2 | |
| Capacitors | ||
| Ceramic 0.01μF | 1 | |
| Ceramic 50pF | 1 | |
| Semiconductors | ||
| IC 741 | 1 | |
| Transistor Q1 BC547 NPN | 1 | |
| Transistor Q2 2N3055 NPN | 1 | |
| Transistor Q3 BC557 PNP | 1 | |
| Transistor Q4 2N2955 PNP | 1 | |
| Speaker 4ohm | 1 |
Circuit uses IC 741 op-amp in non-inverting mode to boost audio signal.
Op-amp controls two transistor pairs like Q1-Q2 and Q3-Q4.
They work like push-pull amp.
This design give good power and work efficient to drive the speaker.
Audio comes through resistor R4 to pin 3 of non-inverting input of 741 IC.
R5 and R6 make voltage divider for op-amp bias.
Op-amp boost signal and send it from pin 6.
Gain is set by resistor R1.
Capacitor C2 remove high frequency noise and keep circuit stable.
Op-amp output goes to base of Q1 and Q2.
Q1 NPN and Q2 NPN handle positive and negative parts of signal.
Q3 PNP and Q4 PNP give more boost to drive 4 ohm speaker.
Capacitor C1 blocks DC and send only audio to speaker.
Formulas:
Here are simple formulas for 12W transistor amplifier:
Op-Amp Voltage Gain:
Av = 1 + (R1 / R5)
where,
- R1 is the feedback resistor
- R5 is the input resistor
Power Output:
P = V² / R
where,
- P is the power in watts
- V is the RMS voltage on speaker
- R is the speaker impedance in 4 ohm
How to Build:
To build a 12 Watts Amplifier Circuit using Transistors follow the below mentioned steps for connections:
- Collect all parts as per circuit diagram.
- Pin 2 of IC 741 connect to Audio In through R4 and also to GND.
- Pin 3 of IC 741 connect to GND through R5.
- Pin 4 of IC 741 connect to -12V through R2.
- Pin 6 connect to speaker through C1 and other side of speaker to GND.
- Pin 7 connect to +12V through R3.
- Q1 NPN collector join with Q2 NPN collector.
- Q1 base connect between Pin 4 and R2.
- Q1 emitter goes to Q2 base and Q2 emitter goes to -12V.
- Q2 collector also connect to Q4 collector.
- R6 connect between R4 and Pin 2 to Q3 collector.
- C2 is in parallel with R6 with same points.
- Q3 collector connect between R6 and Q2 collector.
- Q3 emitter goes to Q4 base.
- Q3 base connect between pin 7 and R3.
- Q4 base goes to Q3 emitter, Q4 emitter goes to +12V and collector join with speaker and Q1/Q2 collector.
- R1 goes between pin 6 and pin 3 and also connects to GND.
Conclusion:
This 12 Watts Amplifier Circuit using Transistors is strong and clear for sound.
It uses op-amp and push-pull transistors.
If made right it gives loud and clean audio.
It is good for low ohm speakers which is great for upgrading our audio sound system.
References:
Recommendation for a single transistor audio amplifier circuit