12 Watt Audio Amplifier Circuit using IC LF351

An audio amplifier is an important component of any sound system because it strengthens weak audio signals to power 8 OHMS speakers.

The 12 Watt Audio Amplifier Circuit is designed with an operational amplifier IC LF351 and a complementary push-pull transistor stage.

This circuit runs on a dual ±12V power supply providing sufficient power for small to medium-sized speaker systems.

Circuit Working:

Parts List:

The circuit shown below is a basic audio amplifier that can provide 10 to 12W of power to an 8 Ohm speaker.

In this design the LF351 op amp IC serves as the preamplifier.

This is the first section where an IC LF351 operational amplifier is used to make the incoming signal stronger and more stable.

How much stronger the signal gets depends on the resistor values of R4 and R6.

Next, the output from the operational amplifier passes through capacitor C2 to reach the base of the Q1 TIP127 transistor.

This transistor works together with the Q2 transistor TIP122 to create a complementary push-pull driver stage.

Finally, in this last section the push-pull design increases the current providing enough power to drive an 8 ohm speaker.

To ensure the output remains stable feedback resistors R2 and R3 along with capacitor C1 are used.

Formulas with Calculations:

Below are the formulas with calculations for 12 Watt Audio Amplifier Circuit using IC LF351:

Voltage Gain Calculation (Pre-amplifier Stage):

Av = 1 + (R4 / R5)

Av = 1 + (47k / 4.7k)

Av = 1 + 10

Av = 11

The input signal is amplified 11 times.

Output Power Calculation:

Assuming an 8-ohm speaker and a peak voltage swing of 12V:

P = V² / (2 * R)

P = 12² / (2 * 8)

P = 144 / 16

P = 9W

Output power voltage is approximately 10W to 12W.

How to Build:

To build a 12 Watt Audio Amplifier Circuit using IC LF351 follow the below mentioned steps:

• Gather all the components as mentioned in the above circuit diagram:
• Connect pin 2 of IC1 LF351 between resistors R4 and R6 of inverting input
• Connect pin 3 of IC1 to GND through resistor R5
• Connect pin 4 of IC1 to negative power supply -12V DC through resistor R3
• Connect pin 6 of IC1 to one end of 8 ohm speaker and other end of speaker connect to GND
• Connect pin 7 of IC1 to positive power supply +12V DC through resistor R2
• Connect one terminal of resistor R4 and capacitor C3 in parallel from pin 6 and other terminal connect to pin 2 of IC1
• Connect one terminal of resistor R6 from pin 2 of IC1 and other terminal connect to one leg of VR1 pot and other leg of VR1 pot connect to Audio input and GND
• Connect one end of capacitor C2 between the junction of pin 7 and base of transistor Q1 and other end connect to pin 4 of IC1
• Connect emitter of transistor Q1 to +12V DC power supply and connect collector of transistor Q1 to collector of transistor Q2
• Connect resistor R8 and LED1 in series between emitter of transistor Q1 and +12V DC power supply and GND
• Connect capacitor C1 and resistor R1 in series from pin 6 of IC1 and GND
• Connect capacitor C4 and resistor R7 between the junction of capacitor C1 and one end of 8 ohms speaker and GND
• Connect base of transistor Q2 to pin 4 of IC1 and emitter of transistor Q2 connect to -12V DC power supply

Conclusion:

This 12 Watt Audio Amplifier Circuit using IC LF351 is a great option for those just starting out and for hobbyists.

It delivers solid performance while using only a few parts which makes it affordable and simple to assemble.

With an LF351 op-amp and matching power transistors, it provides dependable amplification and good sound quality.

This design works well for small speaker setups and various audio uses.

References:

LF351 Single Operational Amplifier (JFET)