some kick ass music to impress everyone who said this couldn't be done
What to do:
The audio amplifier should have certain external connections, such as the left and right inputs, left and right outputs, voltage A, voltage B, and ground. These will all be printed on the circuit. I'm sorry, but I can't tell you how to build the circuit from scratch.
First, take the audio amplifier. If it hasn't been put together, put it together. Next, take the old headphones and rip the wires out of the ear peices. One side will be the right side, the other will be the left. In each side, separate the two strands. One will be the input, the other will be ground. Solder these to the left and right inputs and ground. You really only need either left or right, but the extra wires make it more impressive.
Inputs are done. Now to the output. Get some wire and connect it to the left or right output and ground. If you only have one input, make sure your output is on the same side. Solder one wire to ground and the the other to the output on the board. This will be your speaker wire.
You need power to make this all work. Take your transformer. It should be able to handle AC current and transform it to 6-12V at 3A. One side of the transformer will have two pins. Cut an old extension cord in half and solder a wire to each pin. The other side of the transformer will have three pins. The center pin is ground. Solder that pin to the ground of the circuit board. Pick one of the other pins to connect to an input voltage on the board. That'll set up your power.
Speakers. Now, you could just attach some regular speakers to this circuit and it should work fine. However, you did all this work of soldering and buying parts, you want to make this look good. Take the old hard drives. You will remove almost everything from this. What you need to save are the actual hard disks, the heads (the little metallic peices that rest and move on the disk), the servo that moves the heads, and the wires that are attached to the servo. Basically, the cover of the hard drive and all the circuitry should go.
Everything is ready, now it's time to test. Plug in the transformer. The output leads from the board should be connected to the wires coming out of the servo. The testing part comes in finding the right connections. You will find that some connections yield no sound, good sound, a lot of head movement, etc. Touch the leads to the servo in different combinations to find what you are looking for. When you are satisfied with the sound part, solder those connections together. To add more speakers, or hard drives, connect them in parallel to the other speakers. In other words, the speaker leads should all be branching off of a common output, the output from the board.
Next, invite all your friends over who think the idea of a hard drive speaker system is very retarded or something for geeks. Show them all your hard work. Show them the heads dancing around to the beat of the music.
Parts I purchased:
