SMALL AMPLIFIER TDA7377 of 15W + 15W + 30W

I have developed an amplifier with the following characteristics: 15W + 15W + 30W in 4 ohms and TDA7377 as main component. This has 4 outputs that can deliver a power of 15W each, distributed as follows: first, we have 2 outputs of 15W, which form a stereo amplifier. On the other hand there is another mono amplifier, which is formed by the other 2 outputs in bridge mode, and delivers a power of 30W.

Another additional circuit is a low pass filter that is connected to the input of the 30W mono amplifier. So this one only delivers low frequencies, while the stereo outputs have a frequency response approximately, from 100Hz, to 20,000 Hz.

Another interesting feature of this design is that it is fed with a simple 12-15V supply. In addition, the amplifier, preamplifier and the low pass filter are all on the same PCB.

SPEAKERS SYSTEM

We take into account that the power of a speaker must be equal to or slightly above the power output of the amplifier. If the stereo outputs are 15W each, then the speakers must support 15W RMS or more.

POWER SUPPLY

The integrated circuit TDA7377 is powered by voltages between 12 and 17 volts DC. So is necessary to deliver a continuous voltage to the amplifier.

PREAMP AND TONE CONTROL

There are plenty of integrated circuits operational amplifiers like the TL072. All of them work in a similar way and many are compatible. The TL072 contains two amplifiers. So it’s used in stereo preamps. It can be replaced by JRC4558, TL082 or NE5532. Each one has its characteristic sound, without diminishing the merits of one or the other. The function that it does in this amplifier, is to amplify the signal a bit, since the TDA7377 comes with the fixed gain and is somewhat low. If for example is amplified the audio signal delivered by a cell phone directly with the TDA7377, the audio volume is somewhat low. However, when you first pass through the preamplifier with TL072, the sound is stronger. Not to mention that it can be modified the gain just by changing a pair of resistances. The gain is left in 10. This is determined by the division of 56K in 5.6K. If for example the user wants to increase the gain, it can raise the resistance of 56K. And if the idea is to lower the gain, this in case the player has a very strong output and there is distortion, it is enough to lower the value of those same resistances.

As I've mentioned at the beginning, our amplifier has a low pass filter. It receives the signal from the already amplified TL072, to be processed. The low pass filter is responsible for restricting the passage of high and medium frequencies, and only allows the passage of low frequencies. The TL081 is a chip that only contains one amplifier inside. Has to be taken into account that amplifier is called 2.1, since the two represents the stereo outputs and the third represents the mono output that only delivers low frequencies to the subwoofer. The cut of frequencies is done mainly by the two capacitors of 0.47uF, which are in parallel with each other, and which go between the input and output of the TL081. If is required more frequency cutting, just has to be raised the value of these two capacitors. The low response of TL081 is better than that of TL071, for this reason we chose this one.

I hope enjoy this project!