Simple Class AB Stereo Amplifier Circuit

Audio amplification is an important part of electronics because it helps weak audio signals to power loudspeakers.

Among the different types of amplifiers Class AB amplifiers stand out as a good balance combining the efficiency of Class B amplifiers with the smooth sound quality of Class A amplifiers.

This article will look closely at a simple Class AB stereo amplifier circuit discussing how it works, the calculations needed through formulas, how to build it and what we can learn from the whole process.

Circuit Working:

Parts List:

The Class AB stereo amplifier circuit described here uses a clever setup of complementary transistors to provide both efficient and smooth amplification of audio signals.

This well designed circuit is great at reducing distortion while supplying enough power to drive an 8 ohm speaker effectively.

Important parts like the TIP31A and TIP32A transistors are key to boosting the output.

The input signal comes in through a potentiometer VR1, which is important for adjusting how strong the incoming signal is.

Plus, capacitor C1 is placed to block any DC signals ensuring that only the AC signals get amplified.

In the circuit, transistors Q1 and Q2 which are 2N3904 types act as a differential amplifier giving the first boost to the signal and helping keep the circuit stable.

Resistor R3 helps set the base of Q2 while capacitor C3 improves the circuits stability at high frequencies.

Transistors Q3 TIP31A and Q4 TIP32A work as driver transistors further increasing the signal and providing the needed current to the output stage.

To keep everything running smoothly resistors R4 and R5 control the bias current through the driver transistors.

The complementary push pull setup with transistors Q5 TIP31A and Q6 TIP31A is a key feature of Class AB amplifiers helping to cut down on crossover distortion while staying efficient.

Resistors R6 are used for sensing current and providing feedback, which is essential for keeping the circuit stable.

Capacitors C4 and C5 act as decoupling components which are crucial for stabilizing the power supply and filtering out any unwanted noise.

The quiescent current of the output stage can be adjusted.

Formulas:

Formulas for Simple Class AB Stereo Amplifier Circuit is mentioned below to design the circuit diagram

Bias Current Setting:

I_Q = V_BE / R_6

where,

• V_BE is the base emitter voltage of Q5 and Q6 which is around 0.7V

Voltage Gain:

A_v = R_C / R_E

where,

• R_C is the collector resistor R4 and R_E is the emitter resistor.

Output Power:

P_out = V_peak^2 / (2 * R_load)

where,

• V_peak is the peak output voltage and R_load is the speaker impedance for 8Ω.

How to Build:

To build a Simple Class AB Stereo Amplifier Circuit following steps need to be followed:

• Assemble all the components as mentioned in the above circuit diagram.
• Connect the collector of transistor Q1 to third leg of VR2.
• Connect the base of transistor Q1 to center leg of VR2.
• Connect the emitter of transistor Q1 to second leg of VR2.
• Connect the collector of transistor Q2 to emitter of Q1.
• Connect the base of transistor Q2 to capacitor C3 and resistor R3.
• Connect the emitter of transistor Q2 to GND.
• Connect VR1 pot center leg negative of capacitor C1, connect the upper leg to audio input, and connect the third leg of VR1 to GND.
• Connect the collector of transistor Q3 to positive supply of +30V.
• Connect the base of transistor Q3 to collector of transistor Q1.
• Connect the emitter of transistor Q3 to emitter of transistor Q4 through resistor R4
• Connect the collector of transistor Q4 to GND through resistor R5.
• Connect the base of transistor Q4 to collector of transistor Q2.
• Connect the collector of transistor Q5 to positive supply.
• Connect the base of transistor Q5 to emitter of transistor Q3.
• Connect the emitter of transistor Q5 to collector of transistor Q6 through resistor R6
• Connect the base of transistor Q6 to the collector of transistor Q4.
• Connect the emitter of transistor Q6 to GND through resistor R6
• Connect the resistor R1 and R2 from collector of transistor Q1 to positive supply.
• Connect the capacitor C2 between resistor R1 and R2 to resistor R3 to the base of transistor Q2
• Connect a capacitor C4 from the collector of Q6 and from emitter of Q5 transistor to one end of 8 ohm speaker and other end of speaker to GND.
• Connect from negative of capacitor C4 resistor R8 and capacitor C5 in series and GND.

Conclusion:

This Simple Class AB Stereo Amplifier Circuit is a smart and useful choice for those who need to boost audio without going overboard.

It shows how push pull amplification works and strikes a nice balance between being efficient and producing clear sound.

If you follow the step by step instructions and learn how it operates, you can create and tweak this amplifier for different uses, which will help you learn more about electronics and audio engineering.

References:

A simple class AB stereo amp