Simple 70 Watt Audio Amplifier Circuit

This article explains an amplifier circuit that uses special transistors called MOSFETs to make sounds louder.

These transistors are good for amplifiers because they:

Let a weak electrical signal coming in control a strong outgoing signal like turning up the volume on a radio.

Do not waste much power themselves and;

Can handle strong signals for loud noises.

Note: This project might be more complex than some others.

Circuit Working:

Parts List:

This 70 watt audio amplifier circuit utilizes the TL071C operational amplifier along with two MOSFETs IRF9530 and IRF530, capable of delivering up to 45W on an 8Ω speaker or 70W on a 4Ω speaker.

The schematic is derived from siliconix application and incorporates variations in voltage on two resistors serially inserted into the voltage supply of the operational amplifier driver.

It is crucial to mount the MOSFET transistors on a heatsink with a thermal resistance of at least 1k/W to ensure optimal performance.

The efficiency of this amplifier is rated at 70% and distortions at the cutoff frequency were measured at a maximum of 0.2% at 20Hz on an 8Ω load and 10W power.

With a power supply of ±30V, the MOSFET audio amplifier can deliver 45W on an 8Ω speaker and 70W on a 4Ω speaker.

It is important to note that this audio amplifier lacks short circuit protection.

Therefore, exercise caution each time you switch it on and verify whether the speaker is properly connected to prevent potential damage.

Formula:

To calculate power dissipation of the MOSFETs formula below is mentioned:

P_D​ = V_DS​ × I_D​

where:

• P_D: Calculate the power dissipation in the MOSFETs
• V_DS:​ is the drain source voltage.
• I_D: is the drain current.

Load Line: The load line aids in determining the amplifiers maximum output swing and Q point.

Gate Drive Voltage: Ascertain the gate drive voltage necessary to completely activate the MOSFETs, taking into account the threshold voltage V th and making sure there is enough headroom for complete conduction.

To make sure the amplifier can give the required peak-to-peak output voltage without clipping, figure out the maximum output voltage swing.

Realistic Aspects:

Thermal Management: To ensure that MOSFETs dissipate heat effectively, make sure they are properly heatsinked.

Feedback: To increase linearity and decrease distortion, use feedback systems (such as emitter degeneration or feedback resistors).

Protection Circuitry: to defend against overcurrent, overvoltage, and other possible problems that might affect the MOSFETs and other components.

To design a MOSFET output stage for a power amplifier that has the required performance characteristics such as low distortion, high efficiency, and reliability a mix of theoretical knowledge, circuit simulation, and hands on experience is required.

How to Build:

Building the 70 watt audio amplifier circuit requires careful attention to detail and adherence to the schematic.

Gather Components:

• Collect all the required components based on the schematic.

Prepare the PCB or Breadboard:

• If using a PCB, follow the layout design specified in the schematic.
• If using a breadboard ensure it has adequate space for all components.

Connect the Operational Amplifier TL071C:

• Connect the TL071C operational amplifier according to the schematic.
• Pay attention to the variations in voltage on the two resistors serially inserted into the voltage supply of the operational amplifier driver.

Connect the MOSFETs IRF9530 and IRF530:

• Mount the MOSFETs on the heatsink with a thermal resistance of at least 1k/W.
• Connect the MOSFETs as per the schematic ensuring proper orientation.

Connect Resistors and Capacitors:

• Integrate resistors and capacitors as specified in the schematic.
• Use the correct resistor values to achieve the desired performance.

Connect Power Supply:

• Connect the power supply with a voltage of ±30V to the designated points on the circuit.

Verify Connections:

• Double check all connections to ensure they match the schematic.

Connect the Speaker:

• Connect the speaker to the output of the amplifier, either 8Ω or 4Ω based on your preference.

Power On and Test:

• Turn on the power supply, and carefully monitor for any anomalies.
• Use a signal generator to input an audio signal and test the output on the speaker.
• Gradually increase the input signal and check for distortion and performance.

Exercise Caution:

• Since the amplifier lacks short circuit protection always verify the speaker connection before powering on to avoid potential damage.
• Remember, safety is crucial when working with electronic circuits.
• If you are not experienced consider seeking assistance from someone with expertise in electronics or consult with professionals.

Conclusion:

It is important to note that the specific design and characteristics of a MOSFET audio amplifier can vary based on the intended application, power requirements and desired audio quality.

Engineers and hobbyists often design and build MOSFET audio amplifiers for use in various audio systems, such as stereo systems, home theaters or musical instrument amplifiers.

References:

Datasheet ICTL071

Datasheet IRF9530