50 Watt Audio Amplifier Circuit using IC LM3876

Audio amplifiers are super important in sound systems because they make weak audio signals stronger so that loudspeakers can produce sound.

The LM3876 IC is a handy and effective audio amplifier chip that provides great sound quality while needing very few extra parts.

This article will go over how to design, how it works and how to build a 50 watt audio amplifier circuit using the LM3876 IC.

Circuit Working:

Parts List:

The circuit diagram above for a 50 watt audio amplifier using the LM3876 uses basic components like resistors, capacitors and an inductor with the LM3876 integrated circuit as the main amplifier.

The LM3876 can work with a dual supply voltage that ranges from +/-12V to +/-49V DC, in this article we are going with +35V supply voltage.

The audio signal enters pin 10 of the LM3876 through coupling capacitor C7, which blocks any DC voltage from the input signal.

Resistor R5 helps with biasing and makes sure the impedance is matched correctly.

The amplifiers gain is determined by resistors R2 and R1 based on a specific formula mentioned below.

By plugging in the values we can ensure that the input signal is amplified enough.

Capacitors C1 and C3 help reduce high frequency noise from the power supply.

Capacitors C2 and C4 help stabilize the power supply by filtering out low frequency ripples.

R3 is the part that helps control the mute function by letting 0.5mA flow from pin 8 to turn the mute off.

S1 on off switch button you press to mute.

The inductor L1 and resistor R7 create a Zobel network, which keeps the circuit stable and reduces high frequency oscillations.

C8 also helps filter the output.

The amplified audio signal is sent to an 8Ω loudspeaker connected to output pin 3.

This circuit effectively powers the speaker with a clear 50 watt output.

The LM3876 has built in protection against overheating and short circuits making it reliable in different situations.

Steps to build L1 by winding over R7 resistor:

To create L1 by winding it around R7, you will need some enamel coated copper wire, also known as magnet wire in a suitable size like 26 to 30 AWG.

You will also need a 10Ω R7 resistor as shown in the circuit diagram.

To achieve an inductance of 0.7 μH the number of wire turns will vary based on the diameter of the R7 resistor and the wire size.

Generally, winding about 8 to 15 turns of the magnet wire around the resistor will give you an inductance between 0.5 and 1μH.

Start by taking the enamel coated wire and carefully winding it around the R7 resistor in a single layer making sure the turns are evenly spaced.

For your first test aim for around 10 to 12 turns.

Once you have finished winding use some glue or heat shrink tubing to hold the wire in place so it does not come undone.

After that check the inductance with an LCR meter to see if it is close to 0.7 μH.

If it is not right, you can adjust the number of turns by adding or removing some.

Just be careful that the wire does not touch the resistor leads or any other parts.

Finally, connect the R7 resistor with the inductor into the circuit according to your design.

Turns Calculation:

To calculate the number of turns required, you can use the formula for an air core inductor:

L = (N² × μ₀ × A) / l

where,

• L is the inductance in henries (0.7 μH = 0.7 × 10⁻⁶ H)
• N is number of turns
• μ₀ is permeability of free space (4π × 10⁻⁷ H/m)
• A is the cross sectional area of the coil (m²)
• l is length of the coil (m)

Formulas with Calculations:

Thee formulas with calculations are mentioned below for 50 Watt Audio Amplifier:

Voltage Gain (G):

The gain of the amplifier is calculated using the formula:

G = 1 + (R2 / R1)

Substitute the resistor values:
R2 = 20,000Ω (20k)
R1 = 1,000Ω (1kΩ)

G = 1 + (20,000 / 1,000)
G = 1 + 20
G = 21

Power Output (P):

The RMS power output of the amplifier is calculated using the formula:

P = (Vrms²) / R

Assume:
Vrms = 20V
R = 8Ω

P = (20²) / 8
P = 400 / 8
P = 50 watt

How to Build:

To build a 50 Watt Audio Amplifier using IC LM3876 following are the steps to follow for connections:

• Assemble all the required components mentioned in the circuit diagram
• Connect pin 1 of IC LM3876 to positive supply of +35V.
• Connect capacitor C1 from positive supply to GND.
• Connect capacitor C2 from positive supply to GND.
• Connect pin 3 of IC LM3876 to one end of 8Ω speaker through resistorR7 and connect other end of speaker to GND.
• Connect resistor R6 and capacitor C8 in series and GND between resistor R2 and R7
• Build and connect L1 inductor as shown in circuit diagram and text.
• Connect pin 4 of IC LM3876 to negative supply of -35V.
• Connect pin 7 of IC LM3876 to GND.
• Connect pin 8 of IC LM3876 to capacitor C6 and GND, connect resistor R3 and S1 switch in series from pin 8 to -35V supply.
• Connect capacitor C3 from -35V and GND
• Connect resistor R4 from -35V and GND.
• Connect pin 9 of IC LM3876 to GND through resistor R1 and capacitor C5 in series, connect resistor R2 from pin 9 and pin 3 of IC
• Connect pin 10 IC LM3876 to audio IN through resistor R4 and capacitor C7 in series.
• Connect resistor R5 between capacitor C7 and resistor R4 and GND.

Conclusion:

The 50 watt audio amplifier that uses the LM3876 is a dependable and effective choice for great sound quality.

It has few extra parts and built in safety features, making it perfect for do-it-yourself audio projects and home audio systems.

If you put it together correctly and follow the design instructions, it will work really well and last a long time.

References:

LM3876 Overture™ Audio Power Amplifier Series High-Performance 56W Audio Power Amplifier w/Mute