Economical amplifier with lm386

In this tutorial, we’ll look at how to make a low-cost audio amplifier with the lm386 integrated circuit. We will look at the list of electronic materials and components, also the assembly of the board step by step and talk about some features of the lm386 integrated circuit. The printed circuit board is included completely free of charge.

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Overview

The LM386 is a power amplifier designed for use in low voltage consumption applications. The gain is set internally to 20 to keep the external parts count low, but the addition of a resistor and capacitor between pins 1 and 8 will increase the gain to any value up to 200.
The inputs are ground-referenced while the output is automatically polarized to half the supply voltage. The power consumption at rest is only 24 milliwatts when operating from a 6 volt supply, making the LM386 ideal for battery operation.

Features

Battery operation
Minimum external parts
Wide voltage supply range: 4V – 12V or 5V – 18V
Low standby current consumption: 4 mA
Voltage gains from 20 to 200
Ground-reference entry
Self-centering output quiescent voltage
Low distortion
Available in 8-pin MSOP package

Applications

AM-FM radio amplifiers
Portable tape player amplifiers
Intercoms
TV sound systems
line controllers
Ultrasonic controllers
Small servo controllers
Power Converters

Electronic diagram

LM386

The LM386 (also known as JRC386) is an integrated circuit consisting of an amplifier that requires low voltage, both in audio input and power. It is often used in amplifiers for computers (speakers), radios, guitar amplifiers, etc. Supplying 9 volts on pin 8 you can get 0.5 W of power, with only 0.2% distortion.

The TDA2822 shares several features of this integrated, works in stereo and is also used in the same class of electronics.

It is also a very used circuit to make home audio amplifiers.

Application Tips Gain

Control To make

the LM386 a more versatile amplifier, two pins (1 and 8) are provided for gain control. With pins 1 and 8 open, the resistance of 1.35 ko sets the gain to 20 (26 dB). If a capacitor is set from pin 1 to 8, without going through the resistance of 1.35 k, the gain will increase to 200 (46 dB). If a resistor is placed in series with the capacitor, the

gain can be adjusted to any value from 20 to 200. Gain control can also be performed by capacitively attaching a resistance (or FET) from pin 1 to ground.
Additional external components can be placed in parallel with internal feedback resistors to adapt gain and frequency response for individual applications. For example, we can compensate for a poor bass response of the speakers by shaping the frequency of the feedback path. This is done with an RC series of pin 1 to 5 (in parallel with the internal resistance of 15 ko).
For effective bass reinforcement of 6 dB: R ≅ 15 k, the lowest value for stable good performance is R s 10 k s if pin 8 is open. If pins 1 and 8 are omitted, then R can be used as low as 2 ko. This restriction is because the amplifier is only compensated for closed loop gains greater than 9.

INPUT BIASING The

scheme shows that both inputs are ground polarized with a resistance of 50 ko. The base current of the input transistors is approximately 250 nA, so the inputs are approximately 12.5 mV when left open. If the resistance of the DC source that drives the LM386 is greater than 250 k, it will provide very little offset (approximately 2.5 mV at the input, 50 mV at the output). If the DC source resistance is less than 10 k, then unused grounding will keep the compensation low approximately 2.5 mV at the input, 50 mV at the output). For DC source resistors between these values we can eliminate excess compensation by placing an unused input resistance to ground, equal in value to the resistance of the cd source. Of course, all compensation issues are eliminated if the input is coupled capacitively.
When using the LM386 with higher gains (without going through Resistance of 1.35 ko between pins 1 and 8) it is necessary to omit the unused input, avoiding gain degradation and possible instability. This is done with a capacitor of 0.1 F or a short ground depending on the resistance of the DC source at the driven input.

Typical applications