Ever wanted to have a little practice amp that you could take anywhere? What about one where you could plug in your headphones?
You may already have all the parts you need to make this simple little practice amp, in which case it would be free!
Step 1: What You Need
Powered (old school) computer speakers and a 1/4" phono jack.
Make sure you get the ones that plug into the wall with an adapter. Also, get ones that have a headphone jack built in and have the cable with the plug that connects to the computer (usually green). BTW, USB powered computer speakers won't work.
I already had a set lying around but you can get a similar pair for less than $5. Go to your thrift store or swap meet, don't pay more than a few bucks for a set.
You'll also need a soldering iron, wire cutters and phillips screwdriver
If you're lucky, you can find a set that works off a 9V adapter, in which case you can mod it with a 9V battery for complete portability. If you are even luckier, you'll find a set that already is made to work off batteries.
Step 2: Open the Case and Prepare to Modify
Use a phillips screwdriver to take apart the speaker with the amp circuitry. You won't need the second one (unless you want to have a double speaker amp).
I wanted mine to look like a miniature guitar amp so I threw away the 2nd speaker.
Clip the wires and leave a few inches of the input wire (the one with the green plug)
Step 3: Solder and Drill
Solder the input wires to the phono jack as shown. Make sure you don't get the ground and input wires mixed up.
Drill a hole for the 1/4" jack. Don't make it too big or the jack won't tighten. Remember, start small - you can always make the hole bigger - it is really tough to make the hole smaller later.
Also, the guitar cable needs to go into the jack, so watch out where you drill the hole. I made it on the opposite side of the headphone jack and a bit towards the rear to make sure the cable plug didn't hit the speaker when I plugged it in.
If you are going to add a 9V battery connection, do so now.
Step 4: Done!
I've made a couple of these out of speakers I had laying around the house. Obviously, the bigger the speaker, the louder it will get.
Step 5: Play!
OK, don't make fun of my guitar playing or my vertical iPhone videography, this was a quickie.
The amp is not going to be super loud but it is enough to make some noise and if you plug in your headphones, it is plenty loud.