Know Your IC: LM386

Welcome to the next installment of "Know Your Integrated Circuit"!

Know Your IC seeks to demystify common Integrated Circuits and allows people to understand them to a point where they can use them in their own projects.

This episode will feature the LM386 a popular op amp chip. We will go over the chip functions and a bit of history.

And we will teach you how to build a simple amplifier with the chip!

Step 1: Introducing Op Amps

Op-amps are a little hard to explain, but essentially they take something small and make it big!

Op-amps are perfect when you need to take a signal and have it go much higher than the original, for example doing audio amplification.  Wikipedia has a great history of the op-amp and it's development. 

LM386 is made specificly for low voltage applications. Different op-amps will have different requirements, always check out the data sheet! The LM386 can take 4V-12V or 5V-18V depending on the wiring and pump that up 20 to 200 times.

You can use this chip to build any of the following:
AM-FM radio amplifiers
Portable tape player amplifiers
Intercoms and
Small Servo Drivers

Step 2: Pin-Outs

The pin-out of the LM386 is as follows:

Pin 1: Gain
Pin 2: Input -
Pin 3: Input +
Pin 4: Ground
Pin 5: Vout (Output)
Pin 6: Vs (Power)
Pin 7: Bypass
Pin 8: Gain

The input obviously goes to pins 3&2. The most interesting part about this chip i feel is the gain function. If you put a capacitor between pins 1 and 8, you can control the amount of gain the amp has. The bypass allows you to access the input un-amplified, if you so desire.

Step 3: Project: Audio Amp

Our project we will be doing to demonstrate the LM386 is a simple audio amp. A similar design is used in "cracker box" amps.

This version is completed using minimal parts, you will need:
1 LM386
1 10 Ohm Resistor
1 220uf Electrolytic Capicitor
1. .047uf Film Capicitor
1 9v battery
1 10k Ohm Potentiometer
1 8ohm Speaker
1 1/8" mono audio jack
some solid hook up wire
1 breadboard

Step 4: Project: Layout

Once you have the parts layout the circuit, please review the circuit and the layout pictures i've included. If any parts smell like burning or are hot, disconnect the power right away!

Pin 1: Unused
Pin 2: Ground of audio plug
Pin 3: To the Potentiometer  and to the audio plug
Pin 4: Ground
Pin 5: Power of speaker
Pin 6: Power from Regulator
Pin 7: Unused
Pin 8 Unused

Once its together plug in your iPod and rock out. You can control the volume with the knob. 

Step 5: Final Thoughts

Now that you have your own little amp you can easily make projects like the cracker box amp. Using Integrated circuits can be fun and easy once you get into it!

Hope you enjoyed this latest Know Your IC installment. Feel free to do you own as well, and maybe we can get a full guide together.

Thanks for Reading!

Comments

[Jimbo724]

I tried to make this amp for use with an electric guitar. I'm an electronics noob (and beginner at guitar).

Before finding this design, I tried several almost identical LM386 designs with no success, using a 9V battery supply or 12 DCV power supply from a Sony BlueRay/DVD player. Yours is the first I have found with detailed wiring of the 10K linear pot used for volume. However, I get absolutely no sound from any version tried; not even a buzz, hum, snap, crackle, or pop. I'll stick to your version for this post.

My build is shown in the attached photos. Apart from the 10K linear volume pot and the mono 1/4" jack for the guitar plug, it uses only an NTE823 chip (apparently identical to an LM386), a 220uF 50V cap (I could not find a 250uF), a 0.047uF 100V cap (I could not find a 0.050uF), and a 10ohm 1/4W resistor. The speaker is 8ohm 1/2W.

When I use my MM to test voltage, the numbers are all over the place and usually drop to zero after a split second. I have to take the leads off and wait a bit before getting significant numbers. My guess is that I'm discharging a cap when I touch + and ground, but that's just a guess. Two things that I know for sure are that (1) with the pot "ON" all the way, I see varying measurements of 5V, 8V, 10+V, etc. measured on the back leg of the 220uF cap, promptly dropping to zero; and (2) with the pot "OFF" all the way, I see about 0.050V, constant, measured on the back leg of the 220uF cap.

I have been trying to get amp sound out of my Les Paul electric, which has passive pickups in parallel and uses a 9V battery to deliver a 15db boost with one of the knobs pulled up. I have also added a Danelectro Billionaire (Texas Trouble) stompbox, powered by a 9V wallwart. I hear a volume increase on my main Marshall amp when I use the 15db boost and also when I use the stompbox. Even using both with the breadboard, no sound whatsoever comes from the speaker. The MM readings in the preceding paragraph are taken with both the 15db boost and the stompbox ON.

The pin layout of the NTE823 and LM386 are the same. The NTE823 specs are attached.

Any help would be greatly appreciated.

[craigmskillings]

It appears to me you have your "tip" going to pin 2 ...and your "ring" going to pin 3.....connect your "ring" lead to ground......connect your "tip" to the potentiometer.....and ground either pin 2 or 3......the unused input has to be grounded......

[Jimbo724]

Thank you.

I replaced the 3-prong mono jack with a 2-prong mono jack. Since then, I've taken a closer look at the removed 3-prong jack. It seems the 3rd prong is in constant contact with the tip-prong. IIUC, with the 3rd prong connected to ground, the tip-prong is constantly grounded, both when the guitar plug is in and when it is out. IOW, with the 3-prong jack, the tip-prong is connected to the tip, pot, AND ground when the guitar is plugged in, and to ground only when the jack has nothing plugged in. The 3rd prong does not lift off the tip-prong when the guitar plug is in.

It seems strange - to my noob mind - to have a 3rd prong for constant grounding of the tip-prong (when the guitar is plugged in). Since the tip-prong and 3rd prong are constantly in contact (whether or not the guitar is plugged in), I wonder why the 3rd prong isn't removed and the tip-prong doesn't just have 2 lugs, one as it now has and a second for ground. If I put the 3-prong mono jack back in, would it be a problem to have the tip-prong connected to both the pot (directly) and ground (indirectly, via the 3rd prong) at the same time?

I seem to recall reading somewhere that always grounding the jack protects against a sudden in-rush of energy (surge?) when the guitar plug is inserted and contacts the tip-prong. But why not just 2 lugs on the tip-prong?

[jdoeson]

What's the point of the .047uF capacitor and the resistor coming off pin 5? They don't seem to be necessary in my setup (part of the GND line?)

I'm using the 250uF film capacitor, but I tried using a few electrolytic capacitors that also worked fine (though had small volume differences): 100uF, 470uF and 1000uF.

I'm actually using this for a "HDD speaker". It sounds ok, and I can make the HDD actuator move pretty well with this, though I think I need to boost the voltage to make that sucker really dance.

[oliverb76]

The extra parts prevent high frequency oscillation. At extreme frequencies the inductance of the speaker means it doesn't load the circuit, and the IC needs load resistance to operate correctly.

[foggy34]

Hey, im wondering the same question as you about the 250uf cap. i have a set of plans that says to use a 10uf cap. but i cant get the thing to work...grr. when you tried the 1k and the 100 which was louder? thank

[jeet_]

hi , what is the need for two capacitors in the output plz reply

[oliverb76]

FWIW the 250uF part prevents DC flowing through the speaker, as the IC output will be at half the supply voltage. It has to be at half supply so it can output AC waveforms.

The 0.05uF and 10R network is needed to suppress instability (oscillation) at frequencies above the audio range. It isn't always needed but as the oscillation is difficult to diagnose it is safest to just fit them to be sure.

[oliverb76]

For clarification the LM386 is not an op-amp, and it may cause unnecessary confusion to describe it as one.

Unlike an op-amp the LM386 has built in bias that allows it to accept a ground-referenced AC signal when running from a single DC supply (one battery), and output AC voltage offset to half the DC supply without the need for an input capacitor or external gain-setting resistors.

The special input configuration has more in common with an instrumentation amplifier.

[ElvisT]

I am doing a project that involves converting sound energy to electrical energy. my greatest worry is how to use the ics without powering them. please can you help me out?

[congobill]

Hi could you please tell me if I have to read the IC number legs (any IC) from the top or from the bottom ?

Thank

Guillaume

[makeosaurus]

To a str

[makeosaurus]

How would you connect rt

[yaser_e_]

Excellent

[abreldoronio]

But I used TBA820M amplifier instead of LM386.

.Is there any difference?

[abreldoronio]

Hi! I'm making my project like in this picture.It used LM386 board amplifier..But it doesn't show where the terminal of input is connected..Can you help me with this?..Thank you..

[Dr_momo]

Hi All,

I'm buying the parts to get started with this instructable, one thing is confusing me, what voltage is the .047uf film capacitor supposed to be? There are a bazillion options and I am totally new to electronics...help!

Many thanks.

[bilden]

Hi!

There is a 9Vbattery in the picture so buy one suitable for that range of voltage. Buy several if youre uncertain!

[Dr_momo]

Thanks Bilden!

[Bozho]

Hi, I have a question regarding the LM386. I saw some schematics online that feature this amplifier, and in most of them pin 2 (- input) was grounded, and input signal with a 10k potentiometer is hooked up to pin 3 (+ input). I was wondering, why is pin 2 always grounded, and can we use this IC in a negative feedback configuration as we do with a standard operational amplifier, such as LM741? Thanks in advance.