Instructables

Pocket Protest (a LM386 amp in a 9v battery casing)

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Whether your working on electronics, want to test that speaker, checking out a cool looking radio at a swap meet, want to soapbox the evils of soapboxing, or sit on the street corner singing your blues ...

Well, darnit, sometimes you just need a simple easy to use amp!

I bring to the world Pocket Protest (a LM386 amp in a 9v battery casing)

Pocket Protest runs on a standard rectangle type 9 volt battery for a couple hours and can power a 4 - 8 ohm speaker fairly easily, while all along being enclosed in a 9 volt battery casing

The wattage is low, but since theres no filtering or enhancement the sound that comes out is quite brash...

Its a can running off of a 9V battery, and it sounds like it too! Even if the wattage is low the "bullhorn" quality sound gets loud enough that normal people have to talk to almost shouting levels in order to speak over the device

Here is a video of the breadboard test mentioned in step 9, with a really flat tiny 25 watt 8 ohm speaker, it was around 30% volume, which was enough to overdrive the mic on the camera and my wife on the other side of the apartment

http://cheesefactory.us/filecenter/PDR_0002.mpg
 
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Ploopy3 months ago

Cool!

Nice intructable 50+ pictures Now that`s a nice job!

Keep It Up

Ploopy3 months ago

Cool!

Nice intructable 50+ pictures Now that`s a nice job!

Keep It Up

verrry veerrry good project for me i buit it with the gain of 20 because for me the clearness of the amp's audio output sound is important but still verry good project very nice i modified it a little bit i throw a switch and the led i put it outside but the pot still in the back part of the 9v battery and verry good instructable good job!!!! clear instructable easy to understand and im only 13 years old i will post pics of the amp soon!!! im from philippines thanks for this great instructable

baikaa7 months ago
i modified it a bit on the one i built, i lost the pot and built it with a gain of 20, but i managed to make it stereo.. works really good..
Very cool instructable and I'm amazed that you had the vision to fit all of the parts into a 9v battery case. Crazy creative and useful, it's impressive. I'll add that in the LM386 Datasheet, it says that a potentiometer can be used in series with the capacitor to create a gain level control. If you are trying to keep this pocket sized, you could mount a tiny trimpot on the side instead of a large style potentiometer, though for the intended uses this may be just an extra step.

Source:
http://www.ti.com/lit/ds/symlink/lm386.pdf
under "extra steps"
Kralya1 year ago
Thank you! Works good
hcaz-3013 years ago
What size speaker would this drive, i mean how many WATS ?
700mW
7r3k5t3r2 years ago
Hey,

can i also switch the two clips (the output) with a 3,5mm jack output?
(sry im german my english is bad)
MROHM 7r3k5t3r2 years ago
(removed by author or community request)
Genau, Ihre Deutschkenntnisse ist sehr schlecht, aber mein Kompliment für den Versuch :-)
jakas981 year ago
i have problems with bass... becuose there is no bass.. what i should do?
put a 15 k resistor between pin 1 and 5. Gives you an extra 6dB of bass
Hey bro, awesome project. Love how you fit it in something so small. I was very interested in building this too, but had a few questions. Is it suitable for a passive microphone or would i need something else for that?. By passive i meant the mic isnt powered and goes directly to input. I read the distrotion is quite large, but for speaking uses is it good enough and loud enough? Im trying to use this as a mini megaphone for school club uses. I'd appreciate any help and again awesome project.
and additionally, what are the watt ratings on the resistor?
TSC4 years ago
You miss spelled building
snowpenguin TSC4 years ago
You misspelled misspell.
... grammar nazi-nazi? nice!
art.z2 years ago
This idea is awesome!!
I've just built a amp using a LM386, but I couldn't find capacitors and potentiometers that small! So I ended up soldering everything to a perfboard.

Could you explain to me why there is a capacitor to pin 7?
I'm asking because most projects like this don't even ground pin 7..

About the noise, you could put more capacitors to the circuit!
I'm pretty sure you could still fit a ceramic 47kpF between pin 5 and ground!
And you could get rid of the 10uF leaving pins 1 and 8 open! (and use the room to put a 100uF between pin 6 and gorund.
Anyway, it's just an idea..

I'll definetly try this in the future.. I just have to find smaller components!
rahulhari3 years ago
Where is the audio in

Vin (pin 3).

thesoloman2 years ago
this is very small than others that i have seen, what if you make a video of it , so we can see how it works......
prabhu88853 years ago
Thanks it is very usefull for me.. great job... but i like to connect bass / treble volume controller in this amp.. pls help me how to connect the controller in this amp. and also kindly provide me the clear picture for this job.. (I have seen in previous amp. the bass / treble connecter is there but there is some ceramic capasitor and resistor is there. I dont know the ohm's for that. I have attached the picture for u. so pls refer the picture and help me).
Picture1.jpg
pcacesam5 years ago
first of all I'd like to say this is awesome. I was wondering if you know were I could pickup a pair of the alligator clip arms you are using in this. thnks :)
osgeld (author)  pcacesam5 years ago
I had previously picked up a 10 pack of them from radio shack for 4-5 bucks and thats where i got mine, and I got them originally to make clip jumpers 3 red, 3 black, 2 green, 2 yellow, these 2 were left over ... although any web vendor should have a set its just a basic mid sized clip, with tin coating and some cheap rubber boot
pcacesam osgeld5 years ago
thanks for replying :) I'm probably calling them the wrong thing but I was talking about the thing you were using in step 7 to hold the parts while soldering. I called them alligator clip arm just because the arms look like they have them on the end. I haven't seen one of these for years and would like to get one as I hear their awesome when building small circuits.
osgeld (author)  pcacesam5 years ago
Oh, helping hands, they can be found at radio shack or anyplace that sells electronic components Also some craft stores sell them and theres a few instructables showing how to make home made ones :)
j79jon osgeld3 years ago
I worked for a hospital and they were always throwing away old stainless steel forcips which can be made into a good helping hand.
 Or you could make some. I am planing some to look like a super-size resistor man.
are there any alternatives to the lm386?
osgeld (author)  cynical_chemical5 years ago
just about everyone makes a LM386, mine was a noname model also someone mentioned a TDA2822, which is a more power amp that's also stereo, altho its about the same size the pins are different so you would have to adapt to that chip
how would it be different for a tda2822? could someone please make a diagram of how to adapt it?.. im a beginner.. so this is all so confusing
Google tda 2822...much information.. j79jon
Since I got bored, check here.  It should work (although someone might want to double-check.  It still probably needs some work)
bmxlive osgeld4 years ago
so you show the diagram of a lm386 and build the circuit with another one?? i notice that every amp chip has a different estructure so the thing is seek the similar pins between them and make the rights conections? There are many instructubles for pocket adio amps, so choose one and buy the parts excep the amp chip. Can i use those components using a lm368? they are: 0.1 uF, 100V capacitor 100k resistor / 10k resistor & 1k resistor, and of course an OPA134 PA-ND chip that i not buy yet...
osgeld (author)  bmxlive4 years ago
no its a lm386 in this instructable, this comment thread is talking about other applications sorry if it confused you
hackman883 years ago
is it Working?
hackman883 years ago
Is it working good?
The TDA7052 http://mulyantogoblog.files.wordpress.com/2010/07/tda7052.pdf si a good alternative and the base desighn can be used and has a fair low number of components. Great ideea to squeeze it all in a 9 volt battery box.
could this power through a 63 ohm speaker?
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