A transistor amplifier is a key part of audio systems that make sounds louder.
The 12 Watts Amplifier Circuit uses an operational amplifier along with NPN and PNP transistors to produce a strong output that can power a 4 ohm speaker.
This circuit is perfect for people who love audio and want to increase weak sound signals to higher volumes without losing clarity and quality.
Circuit Working:
Parts List:
| Component | Specification | Quantity |
|---|---|---|
| Resistors | ||
| 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 |
The circuit uses the IC 741 operational amplifier in a non inverting setup to boost the audio signal coming in.
This op amp controls two pairs of transistors Q1-Q2 and Q3-Q4, which work together as a complementary push pull amplifier.
This design helps the circuit run efficiently and provides enough power to drive the connected speaker.
The audio signal comes in through the coupling resistor R4 and goes into the non inverting input pin 3 of the 741 op amp IC.
Resistors R5 and R6 create a voltage divider that sets the op amps biasing.
The op amp increases the input signal and sends it out from pin 6.
The gain of the op amp is set by the feedback resistor R1.
Capacitor C2 helps keep the circuit stable by filtering out high frequency noise.
The output from the op amp controls the base of transistors Q1 and Q2.
Q1 NPN and Q2 NPN work together to amplify the positive and negative parts of the signal.
Likewise, Q3 PNP and Q4 PNP further boost the signal to ensure there is enough power to drive the 4 ohm speaker.
Capacitor C1 helps connect smoothly to the speaker making sure that DC components do not reach the load.
Formulas:
Below mentioned are the formulas for 12 Watts Amplifier Circuit using Transistors
Voltage Gain of Op-Amp:
Av = 1 + (R1 / R5)
where,
- R1 and R5 are the feedback and input resistors
Power Output:
P = V² / R
where,
- P is the power in watts
- V is the RMS voltage across the speaker
- R is the speaker impedance of 4Ω
How to Build:
To build a 12 Watts Amplifier Circuit using Transistors follow the below mentioned steps for connections:
- Gather all the components as mentioned in the above circuit diagram
- Connect pin 2 of IC 741 to through resistor R4 to audio in and GND.
- Connect pin 3 of IC 741 to GND through resistor R5
- Connect pin 4 of IC 741 to -12V supply through R2 resistor.
- Connect pin 6 of IC 741 through capacitor C1 to one end of 4Ω speaker and other end of speaker to GND.
- Connect pin 7 of IC 741 to +12V supply through resistor R3.
- Connect transistor Q1 collector to one end of collector of transistor Q2 as shown in circuit diagram, connect base of transistor Q1 between pin 4 of IC 741 and resistor R2, connect emitter of transistor Q1 to base of transistor Q2.
- Connect base of transistor Q2 to emitter of transistor Q1, collector of transistor Q2 to collector of transistor Q4, emitter of transistor Q2 to negative supply of -12V.
- Connect resistor R6 between resistor R4 and pin 2 of IC 741 to collector of transistor Q3.
- Connect capacitor C2 parallel of resistor R6.
- Connect transistor Q3 collector between resistor R6 and collector of transistor Q2, connect emitter of transistor Q3 to base of transistor Q4, and base of transistor Q3 between pin 7 of IC 741 and resistor R3.
- Connect transistor Q4 base to emitter of transistor Q3, emitter of transistor Q4 to +12V supply, and collector to one end of speaker and collector of transistor Q1 and Q2.
- Connect a resistor R1 from pin 6 to pin 3 and GND.
Conclusion:
The 12 Watts Amplifier Circuit using Transistors is a dependable and effective way to enhance audio signals.
It combines an op amp with pairs of complementary push pull transistors, which helps it produce clear sound and enough power to drive low impedance speakers.
If built correctly and with the right parts this amplifier can be a great upgrade for any audio system.
References:
Recommendation for a single transistor audio amplifier circuit