How to make a powered speaker for your MP3 player

Boing Boing reader Ross "rossindetroit" Hershberger created the Monobox, a nice speaker with a built in amp based on the venerable LM386 IC. MAKE produced a nice how-to video about it for its Weekend Projects program. This is a great project for parents and older kids (I'm guessing 9 and up).

MonoBox is a small, inexpensive powered speaker that amplifies the output of your headphone music player. It's little but it's loud! All the circuit parts are available from RadioShack. The speaker and cabinet are left to your preference.



You're probably thinking, "Sure, but it's so small. Does it rock?" Fair question. The prototype has been exhaustively tested and it does indeed rock. Maximum volume output is 90dB, and with the added bass boost your socks will be rocked clean off!

Complete step-by-step instructions for making a MonoBox



  1. i thought they stopped production of the “venerable LM386″  (no doubt there are adequate replacements?)

  2. If I had some spare electronics lying around, including an old Mac or three, a printer, some other stuff, what parts might I be able to scavenge? Would it be possible to find everything but the LM386, or even to find the chip in an old machine? Perhaps this question belongs on the Make page…

    1. This is a cheap project to build.  If you can scrounge a quality speaker from a dead radio or TV, and some kind of box that can be sealed up, you’re about halfway there.  The rest is Radio Shack parts.

  3. That LM386 is just a OpAmp with fixed gain.

    Sounds like a project for hipsters! That thing is rocks out 1 watt max, how much of it is even available from a 9v battery? Those Makezine video could sound a bit less like infomercial… I remember the time when I was a child, borrowed loads of books all with fantastical illustrations, saying you could program awesome games in Basic, after typing in lines of code only to face palm with syntax errors.  

    1. I tested the prototypes extensively for sound quality.  I was dissatisfied with the feeble tones and low volume of typical powered ‘computer’ speakers.  Just never satisfying.   The prototype shown will reach 90db peaks running off of a fresh 9v battery, though that runs the batt down pretty quickly.  90dbs is loud.  Loudness wasn’t the only goal, though. The frequency balance is pretty decent, though I didn’t put a calibrated mic and an RTA on it.  Because who cares how it measures when you can play Rockpile’s “Play that Fast Thing One More Time” cranked up and it makes you want to dance.  That’s a metric I can support.

      1. Now, just to play devil’s advocate, you could play Rockpile through a Fisher-Price phonograph speaker and it’d make you want to dance. 

        Nick Lowe is bloody awesome. 

        1. Nick Lowe is indeed awesome and very danceworthy.  But Dave Edmunds, too!  I find that the boogie factor, the characteristic that makes you want to get up and move, is correlated to frequencies between about 400 and 100 hz.  Yes, I tested this with parametric DSP equalization.  Because I’m a nerd.  A friend who repairs juke boxes tipped me off to this as well.  Small speakers rarely have much power in this range unless you sacrifice overall sensitivity and broadband gain/volume.  But it was a good compromise to get overall musical listenability.  Bottom line, no matter how good something measures, if I don’t feel like playing tunes on it it’s a failure.

  4. I have wanted to build an I phone charger and alarm clock for a while.  this looks like it could be part of the design of such a project.

    Is there an easy way to add volume?

    1. All you need is a potentiometer.  Cut the wire from the output to the speaker, and connect the speaker to the center pin, the output to one side, and the other side to ground.

      If the volume control is ‘wrong’ (i.e. left turns it down rather than up), swap the connections to the two side pins.

      EDIT – fair enough, ignore me.

      1.  I hope dragonfrog does not dispense advice about which end of a soldering iron to hold, or someone will get burned.

        The correct location for a volume control potentiometer in this case is, of course, at the *input*.  If placed out the output, the potentiometer must be rated for full output power of the amplifier, plus will need to match the few-ohm output impedance.  You’d also prefer an audio taper on it, which you very likely won’t find on a low-ohm potentiometer.

        So connect your sound source to the pot high terminal (maximum clockwise one), the input to the amplifier to the pot center terminal, and both in & out ground to the low side (ccw terminal) of the pot.

  5. Thanks for ‘promoting’ this post, Mark. It’s always great fun to create things for MAKE Magazine. I have to disclose that the video was all the magazine’s doing. I think it’s outstanding and it greatly clarifies the device and its construction.
    So why is this speaker and amp in a cigar box? Two reasons. 1) my last project for MAKE, the Squelette hifi chip amp, was designed with a cool looking but complex aluminum and plexiglas cabinet. That was a ton of work and I didn’t have the time or the budget for this one. 2) I want people to think for themselves what kind of enclosure they’d like THEIR speaker to have. I like cigar boxes. Lunch boxes, tool boxes, plastic tubs and tons of other containers will work as well. That makes it personal.
    I hope this inspires people to do cool stuff with inexpensive speakers and simple amps. You can get ideas for modifications by looking up the datasheet for the LM386 chip.

    1. This can be plugged into anything with a headphone jack.  To plug it into a ‘line’ audio source such as the output of a home CD player with fixed level, in place of the 100 Ohm input resistor you put a 10K Ohm potentiometer as a volume control and don’t install the 100 Ohm resistor.

    1. Thank you!!1!  I love the cane material.  I think it goes well with the distressed wood of the cigar box.  Cane material was my first choice for the speaker grille of the prototype but I had other options.  I made mockups with grilles of copper screen, cane and vintage speaker grille cloth and posted pix on Facebook for approval.  There was a clear preference for the vintage cloth so I used that for the final model.  I’m glad to see that the MAKE staffers like the cane and used it for one of their builds in the video.  Mark states it above, but I want to be sure that MAKE gets the credit for the video.  This is an excellent explanation of the project.

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