Convert a speaker to a battery-powered amplifying party box

[Matt the Gamer] loved his pair of Minimus 7 bookshelf speakers. That is until a tragic hacking accident burned out the driver and left him with a speaker-shaped paper weight. But the defunct audio hardware has been given new life as a single portable powered speaker. Now he can grab it and go, knowing that it contains everything he needs to play back audio from a phone or iPod.

The most surprising part of the build is the battery. [Matt] went with a sealed lead-acid battery. It just barely fits through the hole for the larger speaker, and provides 12V with 1.2 mAh of capacity. He uses an 18V laptop power supply when charging the battery. The PSU is just the source, his own circuit board handles the charging via an LM317 voltage regulator. Also on the board is an amplifier built around a TDA2003A chip. He added a back panel which hosts connections for the charger and the audio input. Two switches allow the speaker to be turned on and off, and select between battery mode and charging mode. As a final touch he added a power indicator LED to the front, and a drawer pull as a carrying handle.

Comments

  1. flynblender says:

    I certainly hope that a SLA battery of that size sources more than 1.2mAh. The source states it was a 1.3Ah.
    Cool build though, it’s giving me some ideas.

  2. DjKiDD says:

    Great idea! I’m building one!

  3. Jarel says:

    I did this in a backpack once with a full on car stereo and car speakers.

    Alas, it destroyed itself eventually from the acid because the battery wasn’t the sealed kind like this one. I was a 12 year old kid at the time and had no parental supervision…

    Those were the days.

  4. Glen Hinckley says:

    Oh the humanity to ruin a pair of Minius 7w’s
    there are not many of the wood ones.

    why not the crappy silver ones.

    • Glen Hinckley says:

      As both an audiophile snob and a hacker that hurts on so many levels.

    • cachelogic says:

      I can’t imagine that the box volume taken up by the battery wouldn’t produce a noticeable peak in the bass as well. One would of course fix that by stuffing the box with damping material which would then cause the amplifier to overheat.

      Love my Minimus 77’s although they were recently rebuilt with new foam surrounds and a better tuned crossover network. The mids sound better than they did but they weren’t exactly bad to begin with.

  5. jordan says:

    I like it. My biggest suggestions would be to have incorporated a lithium battery & charger IC on the PCB. The lithium equivalents for the SLA are a lot lighter which is a definite plus for portables, and they can be had for relatively cheap from china.

    • Sven says:

      I would like to add a class D to that, i have built several speakers like these using a cheap Chinese MP3 player, 5V Class D amp, cheap 1A 5V boost converter meant to be a USB charger and a bunch of old laptop lithium cells. All stuffed into an old computer speaker or similar.

      I get something like 3-6 hours of annoyance out of a single 18650 cell.

  6. mrhaineux says:

    So, it turns out that if you reduce the volume of the speaker enclosure, you’re pretty much guaranteed to make the frequency response of the speaker worse.

    For a while, the fancy speakers that audio engineers use for monitors were switching from “passive” to “active” — ie. they were adding an amp and a power supply. The way they did this was to design a “pancake” to fit on the back of the speaker cabinet, outside the enclosure.

    If I were going to do this, I would probably use 18650 Li-Ion cells with the built-in charge protectors, because you can cover the “bottom” of the speaker with them, one cell thick, and get plenty of power. It’s more expensive than a sealed lead acid battery, but much lighter and almost as easy to charge. The amp circuit (T-amp chip) would be so small I’d probably build it into the speaker terminal opening.

  7. Galane says:

    Mono sound is becoming popular again. So much for that newfangled “stereophonic” baloney! ;)

    Just look at the wide assortment of single speakers made to plug into phones and other music playing gizmos.

    My old LG ENV2 cellphone had stereo speakers. My current Samsung Epic 4G? Just one! And it’s on the back of the phone instead of a pair of them flanking the screen like the LG had.

    Backward, turn backward…

    • Sven says:

      You mean that someone finally figured out that stereo speakers 5cm apart don’t do crap?

      Stereo will still sound better, but you need at least a couple of meters of separation or you might as well go mono, and a 2 meter wide portable sound system isn’t very portable :P

      (i do realize you could go with directional speakers to get stereo sound, but those either need a well specified surrounding, or you need to sit in exactly the right spot, neither of which is desirable in a portable system)

  8. neirolf says:

    dear hackaday it is 1.2Ah not 1.2mAh

  9. Glen Hinckley says:

    Still the humanity of destroying a 7w.

    Well at least it is a great little speaker.
    Love the 7w have several pairs of them.

  10. steve says:

    exactly what I needed for the lab. Thx.

  11. anonymoose says:

    He uses an 18V laptop power supply when charging the battery.

    Let that sink in for a moment.

  12. Steven says:

    I’ve got some M7’s and M7W’s that date back to ’86… I replaced a few woofers over the years but they’re still working, and still sounding good.

    Probably the best product and value that the shack ever put out.

  13. Frogz says:

    been there, done that, used lithium ion batteries from a laptop(upgraded rom nicads) to drive 10 watts rms per channel stereo
    original design was in a 2 way shelf speaker like this driving 1 channel per driver
    riding around pumping 80+ db from my backpack

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