Simple 70 Watt Audio Amplifier Circuit

An amplifier circuit that boosts sounds using special transistors known as MOSFETs is described in this article.

The reason these transistors work well in amplifiers are as follows:

• Turn increase the volume of a radio by allowing a weak electrical signal to control a powerful outgoing signal.
• Avoid wasting too much power alone.
• Able to manage loud noises with strong signals.

Note: Compared to other projects this circuit is quite challenging.

Circuit Working:

Parts List:

The TL071C operational amplifier and two MOSFETs IRF9530 and IRF530 are used in this 70 watt audio amplifier circuit which can provide up to 45W to an 8Ω speaker or 70W to a 4Ω speaker.

The design which is based on a siliconix application includes voltage fluctuations on two resistors that are in parallel connected to the operational amplifier drivers voltage supply.

To guarantee maximal efficiency the MOSFET transistors must be mounted on a heatsink with a thermal resistance of at least 1k/W.

With an 8Ω load and 10W of power distortions at the cutoff frequency were measured at a maximum of 0.2% at 20 Hz and the amplifiers efficiency rating is 70%.

The MOSFET audio amplifier can provide 45W to an 8Ω speaker and 70W to a 4Ω speaker using a power supply of ±30V.

It is important to remember that there is no short circuit protection on this audio amplifier.

To avoid any damage be careful each time to turn it ON and make sure the speaker is connected correctly.

Formula:

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

PD​ = VDS​ × ID​

where:

• PD is to calculate the power dissipation in the MOSFETs
• VD is the drain source voltage.
• ID is the drain current.

The line of load:

The load line helps in identifying the amplifiers Q point and maximum output swing.

Gate Drive Voltage:

Calculate the gate drive voltage required to totally activate the MOSFETs by using the threshold voltage Vth and allowing enough headroom for full conduction.

To be sure the amplifier can supply the required peak-to-peak output voltage without clipping find out the maximum output voltage swing.

Realistic Aspects:

Control of Heat:

To provide effective heat dissipation be sure MOSFETs are heatsinked correctly.

Feedback:

To improve consistency and reduce distortion use feedback systems such as emitter degradation or feedback resistors.

A protective circuit:

By protecting the MOSFETs and other parts from risks such as overcurrent and overvoltage.

To construct a MOSFET output stage for a power amplifier with the required performance features such as low distortion, high efficiency and dependability a mix of mathematical knowledge, circuit simulation and practical experience is required.

How to Build:

To build a Simple 70 Watt Audio Amplifier Circuit following steps are required for connections:

Gather Components:

• Gather all of the necessary components according to the schematic.

Prepare the PCB or breadboard:

• If using a PCB follow with the layout design given in the schematic.
• If using a breadboard be sure it has enough room for all of the components.

Connect the operational amplifier (TL071C):

• Connect the TL071C operational amplifier using the schematic.
• Pay attention to the voltage changes on the two resistors that are in parallel introduced into the operational amplifier drivers voltage supply.

Connect the MOSFETs IRF9530 and IRF530:

• Mount the MOSFETs on a heatsink with a thermal resistance of at least 1k/W.
• Connect the MOSFETs as shown in the circuit diagram keeping them in the right position.

Connect the capacitors and resistors:

• As mentioned in the above circuit schematic connect the resistors and capacitors.
• To get the desired performance use the right resistor values.

Connect the power source:

• Connect the power supply at ±30V to the circuits proper spots.

Check for Connections:

• Check that every connection match to the schematic.

Connect the speaker:

• Based on ones personal desire connect the speaker to the amplifiers output (8Ω or 4Ω).

Turn on and give it a try:

• Switch ON the power supply and pay close attention to any odd activities.
• Use a signal generator to receive an audio signal then listen to the output through a speaker.
• Increase the input signal slowly and keep an eye on the circuits performance and noise.

Take Care:

• Because the amplifier lacks short circuit protection always check the speaker connection before turning ON to avoid any damage.
• Remember that safety is essential while working with electrical circuits.
• If anyone lacks experience try receiving advice from someone who knows electronics or consulting with experts.

Conclusion:

The characteristics and design of a MOSFET audio amplifier could differ based on the desired usage, power requirements and audio quality.

Engineers and electronics fans often build and develop MOSFET audio amplifiers for their use in many kinds of audio systems including stereos, home theater systems and musical instrument amplifiers.

References:

Datasheet ICTL071

Datasheet IRF9530