How to build a 25W amplifier using TDA2040

Amplifiers are the backbone of analog electronics. They are widely used in the electronics industry. Amplifiers are used in almost all audio-related applications.

A power amplifier is a part of audio electronics. It is designed to maximize the power f amplitude of a given input signal. In sound electronics, an operational amplifier increases the voltage of a signal but cannot provide the current required to drive the load. In this tutorial, we will build a 25W amplifier using a TDA2040 power amplifier IC and connect a 4 ohm impedance speaker.

Amplifier topology

In an amplifier chain system, a power amplifier is used as the last or final stage before the load. Typically, a sound amplifier system uses the following topology as shown in the block diagram

As shown in the block diagram above, the power amplifier is the last stage that is directly connected to the load. Usually, before the power amplifier, a preamplifier and a voltage controlled amplifier are used to correct the signal. Also, in some cases, if tone control is required, a tone control circuit is added before the power amplifier.

Know Your Load

In the case of audio amplifier systems, the load and load driving capability of the amplifier is an important aspect in the construction. The main load of the power amplifier is the speaker. The output of the power amplifier depends on the load impedance, so connecting an incorrect load may affect the efficiency and stability of the power amplifier.

The speaker is a huge load, acting as both an inductive and resistive load. The power amplifier provides an AC output, so the impedance of the speaker is a critical factor in proper power transfer.

Impedance is the effective resistance of an electronic circuit or component to alternating current, resulting from the combined effects associated with ohmic resistance and reactance.

In audio electronics, different types of speakers have different impedances and different wattages. Speaker impedance can be best understood by the relationship between water flow in a pipe. Just imagine the speaker as a water pipe and the water flowing through the pipe is the alternating audio signal. Now, if the diameter of the pipe is made larger, water will flow easily through the pipe and the amount of water will be greater, if we reduce the diameter, less water will flow through the pipe, so the amount of water will be less. The diameter is an effect created by Ohmic resistance and reactance. If the pipe diameter is made larger, the impedance will be low, so the speaker can get more wattage and the amplifier provides more power delivery scenarios, if the impedance is made higher, the amplifier will provide less power to the speaker.

There are different options and speakers for different market segments in the market, usually 4 ohm, 8 ohm, 16 ohm and 32 ohm, among which 4 ohm and 8 ohm speakers are widely available at cheap prices. In addition, we need to understand that an amplifier with 5 watts, 6 watts or 10 watts or even more is the RMS (root mean square) wattage delivered by the amplifier to a specific load in continuous operation.

Therefore, we need to pay attention to speaker ratings, amplifier ratings, speaker efficiency, and impedance.

Simple 25W amplifier structure

In our previous tutorial, we made a 10W amplifier using an operational amplifier and power transistors. But in this tutorial, we will build a 25W power amplifier which will drive a 4 ohm impedance speaker. For this purpose, we will use a specific power amplifier IC. We have chosen the TDA2040 power amplifier IC.

In the picture above, the TDA2040 is shown. It can be purchased in most general online stores as well as on eBay. The package is called the "Pentawatt" package and has 5 output pins. The pinout diagram is very simple and can be found in the datasheet,

The tab is connected to pin 3 or –Vs (negative power). Not to mention, the heat sink connected to the tab also gets the same connection.

If we look at the datasheet we can also see the features of this power amplifier IC

The functionality of the IC is very good. It provides short circuit protection to ground. Also, thermal protection will provide an additional safety feature due to overload conditions. As we can see, the TDA2040 is able to provide 25 Watt output into a 4 Ohm load if a split power supply with +/- 17V output is connected. In this case, the THD (Total Harmonic Distortion) will be 0.5%. In the same configuration, if we get 30 Watt power output, the THD will become 10%.

Additionally, there is another graph in the datasheet that provides the relationship between supply voltage and output power.

If we see the graph, we can achieve more than 15Watt output power if we use a split power supply that outputs more than 26V. So, let's make the power amplifier work with 25W into a 4 ohm impedance speaker without compromising THD.

Required components

To build the circuit, we will need the following components-

Vero Board (Anyone can use dashed lines or connect)

iron

Solder wire

Pliers and wire strippers tools

electric wire

Aluminum radiator

17V rail-to-rail power supply with +17V GND -17V power rails

4 ohm 25 watt speaker

4.7R Resistor 1/2 Watt

680R Resistor 1/4 kW

22k Resistor

10k Resistor

100nF / .1uF Capacitors 4 pcs

22uF capacitor

TDA2040

25 Watt Audio Amplifier Circuit Diagram and Description

The schematic for the 25 Watt Audio Amplifier is very simple; the TDA2040 is amplifying the signal and delivering 25 Watts RMS wattage into a 4 Ohm speaker. C4 and C5 are used as decoupling filter capacitors. C1 and R1 act as filters. R2, R3, and C2 provide the necessary feedback to the power amplifier. R4 and C3 are snubber circuits to clamp feedback from the inductive load (the speaker).

Testing the 25W amplifier circuit

We used Proteus simulation tool to check the output of the circuit; we measured the output in virtual oscilloscope. You can check the complete demonstration video given below

We power the circuit with +/-17V and provide an input sine signal. The oscilloscope is connected to the output with a 4 ohm load on channel A (yellow) and the input signal is connected on channel B (blue).

Amplifier Power Calculation

We use a simple formula to calculate the wattage of an amplifier -

Amplifier Wattage = V2 / R

We connected an AC multimeter to the output. The AC voltage shown in the multimeter is the peak-to-peak AC voltage.

We provide few very low frequency sinusoidal signals of 25-50Hz. As with low frequency, the amplifier will deliver more current to the load and the multimeter will be able to detect the AC voltage correctly.

The multimeter shows +10.1V AC. Therefore, according to the formula, the output of the power amplifier under a 4 ohm load is

Amplifier Wattage = 10.12 / 4

Amplifier Wattage =

25.50

(25W approximately)

Things to Remember When Building a 25W Amplifier

When building the circuit, the power amplifier TDA2040 needs to be properly connected with the heat sink. The larger the heat sink, the better the effect. In addition, it is better to use audio grade rated box type capacitors for better effect.

Using PCB for audio related applications is always a good choice. The best way to build the PCB is to refer to the IC manufacturer guidelines. A reference PCB design is provided in the datasheet of TDA2040.

In the above figure, a sample circuit with PCB layout is shown. It is best to stick to the reference layout and have a 1:1 ratio. It will reduce noise coupling in the output.

Also, try using 4 ohm high efficiency speakers with appropriate wattage to drive with this power amplifier.