LM386 Help

Advantages of the LM386 audio amplifier chip:

• Simplicity: It's a very easy-to-use chip, requiring few external components to build a basic audio amplifier circuit. This makes it ideal for beginners and hobbyists.

• Low cost: The LM386 is readily available and inexpensive, making it a cost-effective solution for various audio projects.

• Good sound quality: Under appropriate conditions, the LM386 can produce decent sound quality with minimal distortion.

• Versatility: It can be used in various applications, from driving small speakers in guitar amps and portable radios to headphone amplifiers and even line-level preamplifiers.

• Adjustable gain: The gain can be adjusted from 20x to 200x using external components, allowing you to tailor the power output to your specific needs.

• Wide operating voltage range: The LM386 operates on a wide range of power supply voltages (4V to 12V), making it suitable for battery-powered devices.

• Small size: The compact package size allows for easy integration into small, portable projects.

Disadvantages of the LM386 audio amplifier chip:

• Low power output: While usable for small projects, the LM386's maximum output power is around 0.7W, which wouldn't be suitable for larger applications requiring more volume.

• High idle current: Even without an input signal, the LM386 consumes a significant amount of current, leading to higher battery drain in portable devices.

• Low efficiency: The class-AB design results in lower efficiency compared to more modern amplifier types, leading to more heat generation.

• Limited features: Although versatile, the LM386 lacks some features commonly found in modern audio amplifiers, such as tone control.

• Susceptibility to noise: The chip can be susceptible to noise interference, requiring proper grounding and shielding techniques for optimal performance.

Overall, the LM386 is a classic and easy-to-use audio amplifier chip that's perfect for simple projects where cost, size, and ease of use are priorities. However, its limitations in power output, efficiency, and features might make it less suitable for more demanding applications or battery-powered projects requiring longer runtime.

Stability Issues

1. The LM386 is often use with the minimum number of external components which is the cause of many instability problems. 

2. It is also an old design with poor reasoning about the internal resistance of the power supply and the resistance of the supply rails.

3. It has excessive bandwidth, extending far beyond the audio frequency range, far up into the radio frequency range which can cause serious problems with radio circuity. 

External Components

Naturally the supply voltage to the chip should be decoupled with an electrolytic capacitor (eg. 220 uf) in parallel with a (eg. 100 n) ceramic capacitor (to remove RF noise). And those should be located very near the LM386.

The chip should be decoupled via a 50 uf capacitor from pin 7 to ground. This is very important to reducing the effect of hum and noise and feedback on the supply rails.

Pins 2 and 3 should not be directly connected to ground, instead a capacitor (eg. 100 n) should be connected in series with both.  This prevents early clipping of the output signal (distortion), especially at lower supply voltages. 

A Zobel Network (resistor 10 R and capacitor 100 n) should be connected from the output pin (pin 3) to ground to prevent instability driving the inductive loudspeaker load.

Supply Rails

• The LM386 does not respond well to power supplies with significant internal resistance such as ordinary batteries or unregulated transformer and diode based supplies. Likewise using very thin supply conductors to supply the chip with power can cause problems. A 1 amp audio signal load through a supply rain conductor with 10 milliohm resistance creates a 10 millivolt change in voltage which is enough to cause feedback problems.

Alkaline batteries, lithium cells and voltage from a voltage regulator chip all have low impedance and are suitable to power a LM386. 

Bandwidth

The LM386 unfortunately has a very high voltage gain bandwidth extending to several MHz, the power gain bandwidth is even higher.  This makes the LM386 problematic for use with radio circuits. By far the best solution is to completely remove any RF component from an audio signal before allowing it to enter the LM386.  This may require several stages of low pass RC filter sections.