In this tutorial, I’ll show you how to build a great sounding audio amplifier with the LM386 Low Voltage Audio Power Amplifier. IIt’s not a “minimal components” audio amplifier. I added a bunch of extra capacitors to reduce the noise, and I added a bass boost control as well to make it sound even better. But before we start building, it might be helpful to get a little background information first…
Step 1: Lm386 Basic
The LM386 is quite a versatile chip. Only a couple resistors and capacitors are needed to make a working audio amplifier. The chip has options for gain control and bass boost, and it can also be turned into an oscillator capable of outputting sine waves or square waves.
There are three varieties of the LM386, each with different output power ratings: LM386N-1: 0.325 Watts, LM386N-3: 0.700 Watts, LM386N-4: 1.00 WattsThe actual output power you get will depend on your supply voltage and speaker impedance. I used a 9V battery for the power supply and it works great, but you can go down to 4V or up to 12V.
Step 2: Gain Vs Volume
After you build this amp and play with the volume and gain controls, you’ll notice that both appear to raise or lower the intensity of sound coming out of the speaker. So what’s the difference then? Gain is the amplification of the input potential and is a characteristic of the amplifier. Volume lets you adjust the sound level within the range of amplification set by the gain. Gain sets the range of possible volume levels. For example, if your gain is set to 20, the range of volume is 0 to 20. If your gain is set to 200, the range of volume is 0 to 200.
Gain control can be achieved by connecting a 10 μF capacitor between pins 1 and 8 . Without a capacitor between pins 1 and 8, the gain will be set to 20. With the 10 μF capacitor, the gain will be set to 200. The gain can be changed to any value between 20 and 200 by placing a resistor (or potentiometer) in series with the capacitor.
Step 3: A MINIMAL LM386 AUDIO AMPLIFIER
Now that we have a little background information on the LM386, let’s start by building a bare bones LM386 amplifier with the minimum amount of components needed to make it work. That way you can compare it to the better sounding one we’ll build later on.
In the first diagram above, the audio input ground flows through the same path as the audio output ground. The output ground is “noisy” and will cause distortion in the input signal if it’s wired this way. The audio input ground is sensitive to any interference and any noise picked up will get amplified through the amplifier.
Make it a goal to keep the input ground separate from other ground paths as much as possible. For example, you can connect the grounds for the power supply, input, and output directly to the ground pin (pin 4) of the LM386 This will reduce the distance the input ground flows through the output ground. Connecting it like this should sound better than the first circuit, but you”ll probably still notice some noise, static and popping. We’ll fix that in the next circuit by adding decoupling capacitors and a couple RC filters.
Step 5: A GREAT SOUNDING LM386 AUDIO AMPLIFIER
Now that you’ve seen the bare minimum of what it takes to make an audio amplifier with the LM386, lets build a higher fidelity version with an adjustable gain control.
Note: Most of the component values in this circuit aren’t critical. If you don’t have a particular value, try substituting something close and it will probably work.
Several things in this circuit make it sound better:
1)A 470 pF capacitor between the positive input signal and ground, which filters radio interference picked up by the audio input wires.
2)100 μF and 0.1 μF capacitors between the positive and negative power rails to decouple the power supply. The 100 μF capacitor will filter low frequency noise while the 0.1 μF capacitor will filter high frequency noise.
3)A 0.1 μF capacitor between pins 4 and 6, for additional decoupling of the power supply to the chip.
4)A 10K Ohm resistor and a 10 μF capacitor in series between pin 7 and ground to decouple the audio input signal.
One thing to keep in mind when you’re wiring any audio amplifier is that the cleanest sound will result from keeping all wire connections and components as close to the chip as possible. Keeping the wires as short as possible will also help.
Step 6: THE LM386 AUDIO AMPLIFIER WITH BASS BOOST
A cool feature of the LM386 is the option to add an adjustable bass boost to the amplifier. You’ll probably find that this is the best sounding circuit. The bass boost is basically just a low pass filter, and it removes most of the noise not taken out by the decoupling capacitors. All you need for the bass boost circuit is a 0.033 μF capacitor and a 10K Ohm potentiometer in series between pins 1 and 5
Step 7: Items Needed
2) 2×10 MFD capacitor
5)0.1 MFD ceramic capacitor
6)470 of ceramic capacitor
7)0.033 MFD ceramic capacitor