Amplifier built inside a 9v battery

It’s pretty creative to use a 9v battery as an enclosure. That’s what [Osgeld] did when building this amplifier. There are several advantages; they’re easy to find, it keeps a bit of the dead battery out of the landfill, and this method provides a built-in connector for a 9v power source. In this case the circuit is built around a LM386 audio amplifier. It’s glued to the back of a potentiometer and wired up with the other components for a package smaller than a quarter. A stereo jack reside in the side of the battery case with a cable and alligator clips for connection with a speaker. Now the amp can be quickly connect to any 4-8 ohm speaker.

42 thoughts on “Amplifier built inside a 9v battery

  1. yea probably, the amp is running at a gain of 200 so it sounds like total ass, (in a loud bullhorn kind of way)

    anyway, its a little bit of an old article but I sent it in to get away from the lack of stuff going on the last day or so

  2. I’m getting pretty irritated by some of the comments here.

    * Please read the article/post

    I understand that you might know something but there is no reason to front here. Ashmedai, read the article, he says PART of the battery, not the whole thing.

  3. I’d really rather not have to spell out the obvious, but will often do so on request.

    The battery casing is a minor if not insignificant waste disposal issue. On the other hand, the toxic contents are a major issue and it would be very nice to keep them out of landfills. This project does not do that. As a recycling effort, this is about as useful as ripping the wire out of an old A/C then dumping the freon into the environment. The build is cute and creative, but that part of the summary is irrelevant if not flat misleading.

  4. Just to note, I make no mention of it being green or keeping anything out of a landfill

    Rest assured the AAAA’s that were in the battery were tossed in a recycling bin, but only cause we happen to have one at work

  5. The most notorious part of this project is about cheap and good case for small project. And its not about being green so shut up

  6. The only change I’d make is to use the terminals as the connectors. Then all you’d have is the switch on the end.

  7. @Darwin…
    The only problem with using the terminals as connectors is what about a power source? He would need to throw on an extra port for either power or audio.

  8. @osgeld
    Haha, the main reason instructables is terrible is because it separates out projects into parts, where most hack projects don’t have parts. Hacks just shouldn’t be in tutorial form. On the other hand, it’s simple and allows for images, so I won’t complain too much.

    That said, cool idea and I’m glad someone is keeping HAD alive. I’ve done a few projects lately, but nothing we haven’t seen a million times.

  9. When you link to an “Instructable”, please mention that it is a link to an “Instructable”. They need the publicity, and I don’t need the aggravation.

  10. I did link to the instructable and called it an instructable

    what happens here is you basically submit a link and what it is and anything else, but the hack a day staff are the ones who put the post up and we have no control over what they say (note the green argument from earlier)

  11. @osgeld.

    I do alot with the 386 and to fix your ass sounding problem, try not to go over 4 volts for the input. Also, instead of hooking up a speaker directly to the output of the amp, use a 470uf capacitor in series. It will only let the modulated current through, otherwise, your speaker is “zeroed” at more than 0 volts. usually around half of the input voltage.

    Hope this helps!

  12. this is a great use for an old 9v, you could use a variation on this for 9v powered projects as a more secure and rugged version of the two wire snap connectors as it could be secured to the housing of another enclosure easily.

    and a -serious- lol at people for all the hate, he did keep a “bit” of the battery out of the landfill and did ya know that you can hover over a link to tell where it leads (in most browsers)?

  13. well theres already a 220uf cap on the output, that does help and I would imagine larger values would help more against the low frequency oscillation

    but most of its bad sound is based on there’s next to no filtering on the input, the decoupling cap on the power was replaced with a LED (which drastically reduces oscillation but not nearly as good as a cap) and the 200 gain

    It wasn’t really intended for good audio quality, I just wanted to make the smallest and loudest amp I could out of some scavenged parts lying around :)

  14. 1. save the case of one battery from the landfill to make an amplifier.

    2. send 10 more batteries to the landfill while powering the device during it’s lifespan.

    3. Eventually send the device itself to the landfill. [and it will go to the landfill eventually, unless we're talking about a museum piece of an amplifier here....]

  15. “it keeps a bit of the dead battery out of the landfill”

    Um, who here is irresponsible enough to throw batteries in the trash? I think even Home Depot will accept your dead batteries for recycling. I’m not a tree huger and I love red meat, but this is the only “pale blue dot” that we have.

  16. I have a 386 hooked up to a fostex 7cm fullrange driver in a horn enclosure, sounds okay at moderate volumes. In fact, sounds ridiculously good for a cheap little chip. It’s powered by 4 AA, why not go over 4 volts for sound quality? And I have only a 220 uF cap in series w/the speaker, probably causing the clipping at higher volumes.

  17. @hans and Pete

    please read early comments, we covered the green aspect, I am not claiming green anything, the summery of the post is written by hack a day staff, I only submitted a link

    so go hug a tree or something, I did put the cells in a battery recycle bin at work, which is not required where I live

  18. my apologies to you Osgeld, as my comment was indeed directed towards the hackaday staff and not you. sorry if it did not come across as such.

    Mad respect for the project, despite the mis-labeling

  19. @osgled

    I made no mention of you or your ‘hack’ when I made my comment. I also never thought that you were the author of “it keeps a bit of the dead battery out of the landfill”. I was merely commenting on the general lack of awareness when it comes to recycling.

    PS “so go hug a tree or something, I did put the cells in a battery recycle bin at work, which is not required where I live”.
    Glad you recycle even though you aren’t ‘required’ to.

  20. I’m wondering what else might fit inside various different battery cases.

    By the nature of them, they’re tough and cheap, and any of the squarish styles would nestle together neatly if several each contained a modular part of something bigger – I’m thinking each stage of a radio etc… quite a few military rigs have little potted modules in them for robustness, a dozen little battery cases within an outer shell would enable a very cheap way to emulate this… better yet if each module was potted in resin inside it’s little battery-case…

  21. Those enclosures are very nice. I collect them every time before recycling contents, have perhaps 10 of them now and not sure yet how they will be used. By the way, what else are they good for?

    Some fifteen years ago I often used these 9v battery enclosures as moulds for nice-looking lead weights. Because of no recycling initiatives in my country back then, discarded car batteries were easy to find; the largest lead chunks from them consist of clean metal so almost no slag and other junk results during the process. Oh, good times. Now it’s different.

  22. I once took some used batteries to Radio Shack and asked them if they’d recycle them. They gave me a weird look and then tossed them in the trash. I don’t bother wasting gas to take my batteries to be recycled anymore.

  23. i tear up my batteries for the carbon rods.. sometimes i use the zinc too.. but i use rechargeable batteries and i only tear up dead batteries for the carbon rods when i want to experiment with electrolysis.. but i throw the acid soaked batteryguts in the trash because i dont have a lab where i burn everything and then recycle the ashes into pure elements/compounds.. although i do want to do that one day and electrolyze seawater to build lightweight hulls for my fleet of unidentified flying o-shaped thingies.
    thats also how the hulls are repaired. just crash-land into the ocean and.. why did i just post this on something about amplifiers inside batteries

  24. the best way to recycle used batteries is to throw them into a fire! don’t forget to bring a towel!
    er, wear safety goggles and back to a reasonably safe distance but don’t wear earplugs because then you don’t get to enjoy the sound of batteries going
    POP! then see what plants grow where you just burned your batteries. if none, then you just discovered the importance of recycling.

  25. @jeditalian
    “i tear up my batteries for the carbon rods”

    Regardless of whether the batteries were new or dead, it is worth to clean the rods by heating them red-hot. Flame will go funny-colored for some time, which means that the carbon was soaked in some unwelcome stuff.

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