Instructables

Simple Stereo Amplifier

Though it may not look like it, the circuit in this instructable is so easy anyone with even incredibly basic electronic skills can do this.  The circuit shown below is actually 2 mono amplifiers (mono is single channel, for those who don't know).  You don't even need to know how to solder and almost all the parts can be purchased at the nearest Radioshack. 


P.S.  The camera that I am using is old and close-up pictures are blurry.  Also the microphone on the camera sucks so the circuit will appear to be horrible-sounding, but it actually sounds good when you play it in your room or wherever.
 
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Step 1: Gather Parts

Picture of Gather Parts
What you'll need:

2-  LM386 audio amplifier IC
2-  220uf of greater capacitors
2-  0.1uf polyester capacitors
6-  jumper wires
1-  1/8" stereo headset jack
2-  speakers
1-  9 to15 volt battery
1-  connector for battery
1-  breadboard

Step 3: Build!

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Assemble.  Use the pictures as i put the notes on them:

1) Put the chips in.
2) Put in the polyester caps as shown.
3) Plug in the jumpers from pin 2 to pin 4 on each chip.
4) Attach jumpers from pin 6 to the positive side of your power supply.
5) Attach the 220uf caps as shown.
6) Connect the headset jack connections.
7) Top view of previous picture.
8) Hook up a jumper from pin 4 to the negative side of your power supply on each chip.
9)Add your battery connector observing polarity.
10) Connect your speakers.
11) Add battery and double check connections
12) Yay! You're done.

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argo714 days ago

im salvaging a samsung speaker system. left and right channel has 2x8 ohms speakers and a tweeter. the center channel has 2x4 ohms in parallel. i want to know how to integrate that to an existing stereo amp from an ihome cube speaker. is there any way to make it work? i have solderless breadboard and thinking of copying the parts layout there to test fit all components.

SyrioForel29 days ago

If I wanted to add several speakers or use bigger speakers, what modifications would I have to make? Is it just as simple as adding speakers symmetrically to each amp and upping the battery power while making sure that the components can still handle the voltage?

akki523010 months ago
I want to add a volume control to this circuit. What should I do? Thanks in advance...
Kharon akki52301 month ago

If I'm correct all you need is to wire a potentiometer to the circuit. All volume controllers are potentiometers that control how much power can go through it.

hunterakagman3 months ago
what is the point of the caps? Is it to get rid of noise?
aeronut01 (author)  hunterakagman2 months ago

The capacitors filter out DC signals from the output, so in a way, yea.

asimobot3 months ago
great instructable, wat is the output in watts and can i use the small 8ohm speakers
hkerr6 months ago

what ohm are the speakers

aeronut01 (author)  hkerr6 months ago

8-ohm speakers.

hkerr aeronut016 months ago

do you know a cheap place to get them they are like £3 on ebay

blogie hkerr6 months ago

You can find some good speakers in old (and new if you want to hack a new set open) computer multimedia-ish speaker sets.

hkerr blogie6 months ago
thanks i found some old speakers in my house so im using them.
aeronut01 (author)  hkerr6 months ago

My speakers came out of an old TV that someone abandoned on the side of the road. If you have junk lying around that used to make sounds, it may have a speaker in it which you can use.

etcmn10 months ago
Thanks, this is exactly what I needed! I have a pair of small speakers that I wanted to plug into my mp3 player so I can listen to it while working. Needed something simple as my knowledge of electronics is limited.
faziefazie1 year ago
can I using potensiometer for changing the volume of the speaker? where should i put it in ?
joshr1231 year ago
hey if you have a better camera can you get me some more shots that are blury im making one and its too confusing to see (close ups/over head/ bottom)preferable.
thanks
samaddon1 year ago
hi! it's awesome and simple but may i know that if i will supply only 9volts oto the amplifier instead of 12volts will it work??
codycool552 years ago
I got them working, but the sound quality is terrible. there is tons of a static at any volume, with any speakers i try. what can i do to fix this?
aeronut01 (author)  codycool552 years ago
This happened to some of these circuits I built. On one of them, the voltage affected the quality (as the battery drained, the quality of sound got worse). On another one, the chips being too close seemed to affect each other (they didn't hum separately, but together there seemed to be bad interference with each other? Anyway, they had a lot of static). Is everything connected correctly? What are you using as a power supply? What is the value of the capacitor on the speaker output (the larger one)? Is static coming out from only one amp, or both? If all else fails, try building each amp separately, to test each one. Some one here mentioned soldering the circuit together instead of breadboarding it helps reduce static. You might want to try that as well if nothing else is working and you haven't done so already (remember to use sockets).
As far as i can tell, everything is connected correctly.

Im using a 9.6v 800 mah ni-cad battery, off of a RC car. The battery hadn't been in use for around a year, but i charged it for the amount of time i was supposed to. I tried taking 1 of the chip circuits off, and that changed nothing.

Its a 1000 10v uf cap, but i have tried using a 220v 25v cap, and the only thing that did was make he humming higher pitched.

When you say sockets, you mean like a dot and solder board? would soldering it straight together work?

I've seen other instructables where they put the bread board in a altoids tin, claiming that is to help eliminate outside interference. Would that help with my problem?

Would putting a variable resistor on the gain pins, and adjusting it around help?
codycool552 years ago
Will this work well with a 9.6v battery from an rc car? What is your battery, and where did you get it? How is the sound quality? How loud does it get?
Also how long is the battery life? what kind of speakers did you use? how can i find out the information about my speakers, as far as ohms and wattage? i recycled them out of a car, and they have almost no information printed on them.
aeronut01 (author)  codycool552 years ago
Yes, this circuit will work from a 9.6v battery. My battery is a lithium polymer, 3-cell, 11.1V, 910mAh battery. The battery, along with the smart charger (not shown here) came from here: http://www.hobby-lobby.com/   .   Have a look around, they have much better batteries than mine.  Sound quality is decent, though sometimes I would hear strange noises (usually faint) coming from the amp when it was on but nothing was playing.  Maybe soldering the circuit together instead of breadboarding it would help this, but I wouldn't know (I have long since dismantled this circuit).  The sound distorts at high  volumes, but if you push it you can get loud enough to rip your diaphragm on small speakers like mine (look at my speakers, there's a picture annotation highlighting the ripped part I glued back together).  Battery life depends on usage, speaker resistance, battery used and volume.  At medium volume, 8 ohm speakers, and moderate usage, I got at least a week out of it before recharging (my battery capacity is rather small though).  I used two 8 ohm, 2 watt speakers.  I've also tried 4 ohm speakers and they work just as well.  To find resistance, use a multimeter set to ohms (use the lowest scale), and measure the resistance.  I wouldn't know how to find the wattage, however since they are car speakers, they will definitely hold up to the 500mW each chip outputs.
Not trying to be a jerk or anything but I just had to add that the capacitors that you called "polyester capacitors" are in fact not polyester. They are mylar. :)
aeronut01 (author)  jarheadwithm162 years ago
Really? Thanks for pointing that out!
Ritesh2942 years ago
noooooooooooooooooooo i cant read it
aeronut01 (author)  Ritesh2942 years ago
Would everyone like me to post a clearer picture of the schematic?
yes please
aeronut01 (author)  NeMewSys2 years ago
Ah, the wonders of better cameras. See if the new picture is any better (the lighting was ok, not great, but the pic should be a little better now). it helps if you view it in large or original size. Remember the schematic shown is for one channel, build two of them.
jir3h4 years ago
can i ask somthing: what is the voltage of that polyester capacitor you use??
aeronut01 (author)  jir3h4 years ago
25 volts i think (not sure), but you could use 16 volt ones or higher.
From what I know, the voltage written on a capacitor is simply its operating voltage (the maximum voltage it can with stand--I THINK... I might be wrong) So, you could probably get away with using one rated for just a few volts higher than whatever the incoming voltage is.
You are right. The voltage written on the side of the cap is its maximum rating. Its always good to go a few volts higher than the input voltage. I always recommend 10% more than the input voltage.
kunchu2 years ago

Try using eagle for your schematic
TheJ0y3 years ago
Real nice tutorial m8 !

But I have a question:
I made the circuit (mono) on a breadboard to test and it has good sound so i made a PCB (stereo). When I plug the speakers (without input) one side start to make some "tic" (like ticTICTICticticticTICTIC...) the other side is fine. With input, the sound is horrible and the "tics" are still present.

I was wondering if it could be the result of the PCB layout? or because the LM386 are really close to each other? or because 1 ic is a LM386 and the other is a LM386N-1... ?

Thank you !

aeronut01 (author)  TheJ0y3 years ago
What voltage are you using, I'm not sure if it's a problem, but if it's possible, try to use the same chip for both sides. Also, do you have the volume up too loud? This particular amp distorts at high volumes. Are you sure the pcb hooks up everything correctly
Hi again !

I'm using a 15V DC power supply ( wich was working quite nice on the protoboard) I also tryed every volume settings (on iphone) aslo tryed to decrease the gain with a resistor...problem is still there :P

I looked the PCB and could not find mistakes.... should i put diodes where i split the GND? or else

P.S.: seems i have problem with the website (pictures ans posting) forgive me if my post repeats...
aeronut01 (author)  TheJ0y3 years ago
Sorry for taking so long to respond. Been off the website for a while, busy with college prep/school work. Do NOT put diodes on the gnd. Audio signal are AC and you'll most likely chop the signal in half by adding diodes. You say sound quality is terrible on one amp, not both, right? Did you solder the circuit together with sockets? It's recommended so you can swap chips out if needed. You might have a bad chip. other than that, I don't know what else could be wrong.
ok.nice.very helpful
MrLeitexxx3 years ago
i am using a 2w, 8 ohm speaker and a 0.25 watt 8 ohm speaker, with both the sound is so little , even at full ipod volume with 12 v battery that you have to put your ear really close to hear it, what could be the problem?
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