I was upset. Everywhere I turned was an ipod. On display, in someone's hand, strapped to an arm, hidden in a pocket (the head phones are a give-away), in the train, on the bus, walking down the street. I kept thinking to myself, "What happened to that guy from the 80's with the HUGE book box on his shoulder?" Well, no more! We've been isolating each other from our musical tastes for too long, and have been acting far too respectable. Enter the Boom Bag.
Sure you can buy these. For $150.00. Which is insane. So here's how to make one. It cost me five bucks, but then I had the back pack and speaker already.
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Step 1: Materials
- A back pack (I used my fourth grade back back for that real 80's look)
- An 8 ohm speaker that will fit in an outside pocket on the back back (I used a Marshal guitar monitor)
- A battery holder (Mine's from a toy)
- Some electronics including:
-- LM386 IC
-- 100K pot
-- 10 ohm resistor
-- 0.05uf cap
-- 250uf cap
-- 10uf cap
-- 0.1uf cap
-- A headphone plug (I got mine from some crappy airplane headphones)
- Soldering iron
-1/4" MDF or plywood
- Some polyfil
- A stapler
- Some screen or mesh
Step 2: Breadboard
Test that circuit out! I'll be honest, I didn't come up with the amp myself, I used this guy's. But you'll notice my parts list is a little different. I left out c2, the cap that connects pins 1 and 8. This is the gain pot, you can increase the cap for more gain. I didn't like any gain, so I left it out. The pot controls the volume, and the last cap, c5, can be increased a bit for some bass boost. Try stuff out and see what you like.
Step 3: Circuit Board
Next, hard wire those bits up. As you can see I etched my own circuit board, I'm not going to get into how, there's many good instructables on it already. There's so few parts, you could probably solder it up without a board at all. I'd give you the image for the board, but my computer ate it.
Step 4: Cut It Up
Cut a piece of MDF to fit in the pocket of the back pack, then cut a circle out for the speaker. Speakers usually mount on the back of the board so you.ve got to leave a bit of a lip for the speaker to screw into.
Step 5: Wire It Up
Wire everything together, make sure it works.
Step 6: Mount It Up
Screw down all the pieces. Try to locate the battery pack where you'll be able to access it. Or maybe you could solarize yours! When your done here, cut a piece of screen or mesh and staple it to the front side of the mdf to protect the speaker.
Step 7: Stuff It Up
Shove your workings into your back pack pocket, and stuff the gaps with polyfil. Trace the speaker circle with chalk (you should be able to feel the MDF cut out) and carefully cut the pocket. You might want to run some seem sealer around the fresh pocket edge, or seem sew it.
Step 8: Finish It Up
Almost done, just cut a hole inside the pocket to thread the headphone jack through, or send it through the outside, what ever works for you. This old back pack had another pocket inside the main one that I could keep my phone (and mp3 player) in. Another option is to get a usb headphone connector and leave it wired in the speaker pocket. Good luck!