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  • Contents

I Description

Sometimes, if you can use the inexpensive LM386 and use it to make a stereo power amplifier, the effect should be considered ideal. Here, this blog will introduce the methods and experience of using LM386 to make a microcomputer stereo power amplifier.

lm386

Catalog

I Description

II Introduction

2.1 LM386 schematic

2.2 How to use LM386

III Installation and commissioning

FAQ

Ordering & Quantity

II Introduction

2.1 LM386 schematic

LM386 is a low-power high-gain power amplifier circuit. Its encapsulation form is shown as in Fig. 1.

lm386 pinout

 

Figure 1. LM386 Pinout

Because the audio signal amplitude of the "line output" of the sound card is large, it can drive the LM386  and then the speaker. And because it will be interfered by the video signal when playing VCD, it is not good to follow the typical circuit connection. At this time, we need to add some components and debug component values. The schematic diagram of LM386  is shown in Fig. 2.

 

Figure 2. LM386 Schematic

LM386 pin functions are as follows:

  • LM386 has two input terminals: non-inverting input terminal 3rd pin and inverting input terminal 2nd pin. The input signal can be input from any end, the other input end is grounded, the input end is connected in parallel with the capacitor C4, the purpose is to filter out the video interference when playing VCD. The value can be increased appropriately, but it can be with or without C4 when playing the CD.
  • Pins 1 and 8 are the gain control terminals, and the gain control network is composed of C2 and W2. The smaller the resistance, the higher the gain. Figure 2 Schematic diagram W2 is more appropriate to adjust the gain to about 150Ω, and the gain is too high to cause self-excitation;
  • Connect a 10μ capacitor to pin 7 to avoid self-excitation when the gain is too high;
  • R2 and C6 form a high-frequency component attenuation circuit to eliminate the "crack" sound from the speaker. Among them, the size of the C6 capacity is adjusted according to the actual effect;
  • A 0.1μ capacitor is connected to the 6th pin to ground to filter and eliminate the static hum of the amplifier;
  • The 5th pin is connected to the coupling capacitor C3. If only one cone speaker is connected to one channel (the author uses a cone speaker with a diameter of 120mm, impedance 8 ohms, and output power of 1W), the C3 capacity cannot exceed 470μ. Otherwise, the speaker will be blocked when playing low music. If the high and low frequency crossover technology is adopted, the C3 capacity can be increased to fully reflect the bass.
  • W1 is used to adjust the output volume, which is especially convenient when playing games or listening to CDs; the working voltage is 10 volts, and a bridge rectifier filter circuit can be made by yourself.

2.2 How to use LM386

LM386 is an audio power amplifier IC widely used in electronic products and home amateur production. Its typical application circuit is shown in Fig. 3.

lm386  circuit

 

Figure 3. LM386  Circuit

So, how should we use LM386 correctly?

1. Self-excited howling caused by the excessive input signal. For the howling caused by the excessive input signal, a resistance-capacitance network can be added between the 1 and 8 pins of LM386,  In batch application, the resistance of R can be determined by experiments, or R can be replaced by a trimming potentiometer W. If the signal is still too strong, LM386 pins 1 and 8 can be suspended.

2. High-frequency self-excitation. The principle of the anti-high frequency self-excitation circuit is shown in Figure 4. For howling caused by high-frequency self-excitation, a 4700pF~0.22μF ceramic capacitor can be connected between the signal input terminal and the ground, and a 1000~4700pF capacitor can be connected between the 8th pin and the ground. When making single-ended input, the idle input terminal should not be grounded.

lm386  circuit

 

Figure 4. LM386  Circuit

3. Low-frequency self-excitation. For howling caused by low-frequency self-excitation, you can try to connect a 68~22kΩ resistor between the input terminal and the ground, increase the filter capacitor of pin 8 to 1000μF, and make the LM386 as close as possible to the output terminal of the power supply when making the printed board.

4. When using other brand products (such as GL386, KA386, etc.), some ICs will affect the sensitivity of high-frequency audio. A 0.1μF ceramic capacitor can be connected between its 7th pin and ground, and a 0.1μF ceramic capacitor can be connected between the 4th and 6th pins (note: different from the 8th pin to ground).

III Installation and commissioning

According to the schematic diagram shown in Figure 2, we can make two identical power amplifier circuits, which are combined to form a stereo power amplifier.

Because there are few components, it is better to use double-core shielded wires without making printed circuit boards. Then, connect the stereo plug to the two amplifiers, and use the shield wire as the ground wire.

Do not connect the amplifier to the sound card after soldering. At this time, we should first check that the welding is correct and then turn on the power, and then tap the two input ends of the stereo plug with metal tweezers. If the two speakers can knock out normally, it indicates that the amplifier is working properly. At this time, after turning off the power of the amplifier and the microcomputer, we can connect it to the sound card.

The connection method is to insert the stereo plug into the line output jack (LineOut) of the sound card.

Finally, it is emphasized that you should avoid unplugging and plugging the stereo plug when the power is on (microcomputer or amplifier), or welding the circuit when the amplifier is connected to the sound card, so as not to damage the computer.


FAQ

  • What is LM386?

Low-power high-gain power amplifier circuit

  • How many input terminals does LM386 have?

Non-inverting input terminal 3th pin and inverting input terminal 2th pin.

  • How does an LM386 work?

The Lm386 integrated chip is a low power audio frequency amplifier, which uses low level power supply like batteries in electronic circuits. It is designed as 8 pin mini DIP package. This provides voltage amplification of 20. By using external parts voltage gain can be raised up to 200.

  • Is lm386 an op amp?

The LM386 is a type of operational amplifier (Op-Amp). ... In an amplifier circuit, the LM386 takes an audio input signal and increases its potential anywhere from 20 to 200 times. That amplification is what's known as the voltage gain.

  • What is lm386 IC?

The LM386 is an integrated circuit containing a low voltage audio power amplifier. It is suitable for battery-powered devices such as radios, guitar amplifiers, and hobby electronics projects.

  • How do you calculate lm386 gain?

Voltage Gain Analysis:
Without any external components, it has a gain of Gv = 2x15K/(150+1350) = 20 (26 dB).
With a capacitor (or shortcutting) between pins 1 and 8 , it has a gain of Gv = 2x15K/150 =200 (46dB).

  • Which IC is used in audio amplifier?

The IC LM386 is a low-power audio amplifier, and it utilizes low power supply like batteries in electrical and electronic circuits. This IC is available in the package of mini 8-pin DIP.

  • What are some projects that use the LM386 audio amplifier circuit?

LM 386 is an integrated class AB amp and is good for beginners small audio amplifier applications…for example in a RF receiver,small Stereo system,cheap low voltage amplifier etc…drawbacks is that it cannot handle much power and hence creates distortion when you crank up the volume too much.. So other ICs are used in practical.

  • How to make an LM386 audio amplifier circuit?

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