Make music controlled Christmas lights for very cheap. This uses very basic parts. This idea was not originated by me. It is a derivative of Rybitski's design located herehere.

Step 1: Parts List

-Old Speakers
-Solid State Relay (buy at DigiKey.com)buy at DigiKey.com)
-Excess power cord taken from some old device.
-Outlet adapter
-Soldering Iron and equipment
-Christmas Lights

Step 2: Speaker Setup

Take apart the main speaker (the one that has the power going to it). You will see that the amplifier has two wires going to it. It should also have labeled which one is positive and which one is negative (image 1). Using the soldering iron, melt the solder that connects these two wires so that you can disconnect them from the amplifier (image 2).

Step 3: Connecting the Speaker to the SSR

Now you'll need to connect the SSR (Solid State Relay) to the speaker. Solder the two wires that we removed from the amplifier to the two left hand leads (with the words on the SSR facing up) on the SSR. Make sure the positive wire is connected to the lead furthest left.

Step 4: Attach the Power Cord

Take the excess cord that you have take from some old electronic device and cut the cord so that the two (or three if it's ground) wires are displayed. Cut a hole in the back of the speaker casing so that you can insert this cord into the hole (refer to above video for visual). Bypassing any grounding wire, solder either of the two wires directly to the third lead from the left on the SSR.

Step 5: Adding Outlet Adapter

Cut two notches in the top of the speaker casing so that you can fit the outlet adapter into it (refer to the above video for visual). Solder the remaining wire (excluding the grounding wire) from the power cord to one prong of the adapter. Solder the other prong of the adapter to the last lead of the SSR.

Step 6: Final Steps

If the amplifier is still screwed into the front of the speaker casing, then remove it. Then put the speaker casing back together with all the wires and SSR tucked inside. Now all you have to do is plug in the speakers, plug in the excess power cord (which is now connected to the SSR inside the speaker casing), and then plug the audio input into any computer or mp3 player and enjoy!