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

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

Step 1: Tools and Materials

Tools:
Tweezers
Wire Cutters / Strippers
Helping Hands
Loose Clip leads (alligator clips to use as mini spring clamps)
Solder (and some way to remove it in case of mistake)
Soldering Iron
Needle Nose pliers
Small Flathead Screwdriver (jewelers style or similar)
Electric Drill and 3/16th inch drill bit
Pencil / Paper
Xacto / hobby knife
320+ grit sandpaper

Materials:
330 ohm resistor
led, I choose blue, go with a full sized bright led
10k audio pot pcb mount
1/8th inch stereo pcb mount headphone jack (female)
LM386
10uf electrolytic cap (16 + volts)
220uf electrolytic cap (16 + volts)
0.1 uf ceramic cap (with long full length leads, buy new)
dead 9 volt battery
good 9 volt battery
Electrical tape
Gel Super Glue
Low viscosity clear epoxy
heat shrink tubing (1mm and 5mm)
4* 5 inch pieces of wire, multicolored 20-24 gauge recommended
~ 1 foot of 20-14 gauge zip cord or 2 conductor speaker wire
2x alligator clips (with rubber jackets optional)
Clearcoat of some type (spray)

except for the ceramic cap, the power providing battery, and alligator clips everything was scavanged from other electronics

Comments

[hcaz-301]

What size speaker would this drive, i mean how many WATS ?

[diy_bloke]

700mW

[7r3k5t3r]

Hey,

can i also switch the two clips (the output) with a 3,5mm jack output?
(sry im german my english is bad)

[MROHM]

Deine Englisch ist sehr gut!!! Vergessen Sie das nicht.,,,Bitte! Haben Sie ein Guten Tag! Auf wiedersehen. Meine Deutsch ist schrecklich!! Ja das stimmt!!!

[diy_bloke]

Genau, Ihre Deutschkenntnisse ist sehr schlecht, aber mein Kompliment für den Versuch :-)

[jakas98]

i have problems with bass... becuose there is no bass.. what i should do?

[diy_bloke]

put a 15 k resistor between pin 1 and 5. Gives you an extra 6dB of bass

[Squishy Tank]

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.

[Squishy Tank]

and additionally, what are the watt ratings on the resistor?

[TSC]

You miss spelled building

[snowpenguin]

You misspelled misspell.

[Squishy Tank]

... grammar nazi-nazi? nice!

[art.z]

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!

[rahulhari]

Where is the audio in

[David97]

Vin (pin 3).

[thesoloman]

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......

[prabhu8885]

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).

[pcacesam]

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]

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]

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]

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]

I worked for a hospital and they were always throwing away old stainless steel forcips which can be made into a good helping hand.

[Minifig666]

 Or you could make some. I am planing some to look like a super-size resistor man.

[hackman88]

is it Working?

[hackman88]

Is it working good?

[neumanngregor]

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.

[purple people]

could this power through a 63 ohm speaker?

[qs]

If you're getting too much distortion / volume, omit the 10uF between pins 1 & 8 - leave them unconnected and that will not only will lower the overall gain but give you better frequency response as well.

[cynical_chemical]

are there any alternatives to the lm386?

[osgeld]

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

[bmxlive]

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]

no its a lm386 in this instructable, this comment thread is talking about other applications sorry if it confused you

[cynical_chemical]

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

[j79jon]

Google tda 2822...much information.. j79jon

[killersquirel11]

Since I got bored, check here.  It should work (although someone might want to double-check.  It still probably needs some work)

[bobmcbob_345]

why do you yse a 220 microfared cap at the end of the amp. it will only act as a high pass filter sou you wil get only treble. i would use somthing like a .22 uf cap

[FRABBAfrabbaFRABBA]

 electrolitics dont act as filter

[darqdean]

All capacitors act as filters since their impedance (ac resistance) is inversely proportional to frequency and capacitance value. The 220uF in the circuit schematic is correct - in conjunction with an 8ohm speaker it will give a low frequency 3dB point of 90Hz where as a 0.22uF would give a low frequency cut-off of 90KHz. (http://en.wikipedia.org/wiki/High-pass_filter)

[osgeld]

90 hz is still pretty tinny, but the brash bullhorn type cutoff helps the sound carry

[MC_Dogan]

can anybody tell me wich LM386 it has to be l, m or n?