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.

Step 1 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

Comments

[codycool55]

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]

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).

[codycool55]

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?

[codycool55]

(removed by author or community request)

[codycool55]

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?

[codycool55]

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]

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.

[jarheadwithm16]

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]

Really? Thanks for pointing that out!

[Ritesh294]

noooooooooooooooooooo i cant read it

[aeronut01]

Would everyone like me to post a clearer picture of the schematic?

[NeMewSys]

yes please

[aeronut01]

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.

[jir3h]

can i ask somthing: what is the voltage of that polyester capacitor you use??

[aeronut01]

25 volts i think (not sure), but you could use 16 volt ones or higher.

[ninjatails]

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.

[suckafish]

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.

[kunchu]

Try using eagle for your schematic

[TheJ0y]

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]

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

[TheJ0y]

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]

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.

[roytoton2008]

ok.nice.very helpful

[MrLeitexxx]

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?

[aeronut01]

Are you sure that you have your signal and ground correctly hooked up? Try reversing these wires. Also, use a multimeter to check if the Battery is charged (though I'm pretty sure you already tried that). Tell me if that works

[MrLeitexxx]

just rebuilt the circuit and it works pretty well, but i have a lot of noise, any way i cn lessen this?

[aeronut01]

What do you mean by noise?

[MrLeitexxx]

like the bad kind, static if you catch my drift

[T0C]

That's because the LM386 isn't the best sounding portable amp (you could try a bigger cap on the output like 470uF) . if you want a better sounding amp try it with a TA7368p i made one of those a few months back and the sound is perfect. it's mono like the lm386, it has a little more power consumption but more power output, i run mine on one 9v battery and it lasted about 1 month on nearly full power (about 1-2 hours a day). i used 2.5W(max 5W that's what i t said on the speakers i think they were from an old boom box) 3ohm speakers and the sound was clear and verry loud. And if you want a longer battery life just build one of the amps and make a stereo to mono converter at the imput.....for more info (if you want to buld the amp) e-mail me at [e-mail]

[7654321]

nah, I made a 386 amp and it sounds really clear, try a different schematic

[T0C]

I've tried almost all schematics (+ 4 that i made), and well, the sound isn't with the highest quality (It still sounds great but i like it when it's with GREAT sound.) And also the speaker is big part of the quality , no matter how high the quality , if the speaker sucks you'll get nothin'.

[7654321]

Quite true

[Electrified Geek]

hey umm. i built this amplifer and checked all the connections and it didn't work. i turned on my input device, turned on a song, and tried attaching the speakers to the speakers to the 0.1uf polyester capacitor that was attached on the other end to the input

+audio in on this side_____[]_____speaker__
gnd audio in this side___________________|

i hope you can understand my diagram there. anyway it wouldn't work when it was connected so it seems that the 0.1uf polyester capacitor that i have doesn't work. what does it say on your caps?
do you think there is a problem with the rest 
i put in 3300uf cap at 16v is hat too big?

[aeronut01]

The speakers are not supposed to be attached to the 0.1uF capacitors. They attach from the negative side of the electrolytic capacitor to pin 4 (or gnd, pin 4 is grounded anyway).

[ixododae]

Thanks for this tut! I just soldered together one of the channels and it sounds pretty good! less joints, less interference :)

[mglsotto]

what sort of speakers can be used for this particular set up? right now i have two 4ohm 3 watt speakers and a 4ohm 10 watt speaker. Will this setup work for my available speakers? If so, how do I wire all three together?

[aeronut01]

4 ohm speakers would work, but you have to monitor the chip's temperature when you're testing it out (just touch the chip occasionally to make sure it's not burning your finger). I would recommend using only the two 3 watt speakers. If you wanted to include the 10 watt speaker as well, you would wire it in series with one of the 3 watt ones. That is, -----(speaker)--------(speaker)------. Then plug the two wires where one speaker normally goes. I'm not sure how well that would work because now you have an 8 ohm load on one channel and a 4 ohm load on the other (one channel would be louder than the other). You'll have to experiment. That's what the breadboard is for.

[sc4rzz]

Very nice. I'll probably be making one of these.
What type of battery do you use?
and if my jack only has 3 wires, that would mean it's a shared gnd ?

[aeronut01]

My battery is a 12 volt, 3 cell, 910mAh lithium polymer battery (the battery says it puts out 11.1 volts but I measured 12).  The 910mAh only refers to its charging capacity, the battery can actually put out 14.5 amps continuously.  As for your jack, you're probably right about it being a shared gnd.  You can check by cutting open ONLY the insulation at the point where your jack cable splits in two (one for each headphone speaker).  If you see one cable split in two, it's a shared gnd.

[what in the world]

hey i am new to electronics and i think i hooked everything up right but my 2.3 W speaker is really soft and you cant hear it unless u get really close to it. whats wrong?