Those T-Shirts with Equalisers on them are absolutely amazing, but the microphones tend to be underpowered, and there's no way to connect your iPod to them. This mod solves both of those problems for a few dollars - it allows you to use either:
1. The built-in low powered mic
2. A lapel mic (one attached to your collar, to better pick up your voice)
3. An iPod (or any mp3 player, phone, computer etc)
Step 1: What You Need:
An equalizer T-Shirt (obviously). Mine came from here: http://www.thinkgeek.com/tshirts-apparel/interactive/8a5b/?cpg=ab
A 2-way switch (must have six connections on its underside)
A mono headphone socket
A bit of wire (I only used about 20cm/8in, but get a metre or a yard so you have plenty of spare)
Small phillips head screwdriver
Hot glue gun (or super-glue, or anything good for plastic).
Step 2: Opening the Case
Firstly, turn on your soldering iron. Let it heat up, while you finish this step.
Disconnect the magic yellow box from the shirt.
Remove the battery cover, and take out the batteries. This isn't really crucial, but it makes it lighter so it's easier to handle.
Turn the magic yellow box over, and remove the three screws. Remove the plastic panel.
Now, see the circuit board? Without damaging the wires, try and turn it over a bit so you can see its back.
Step 3: Removing and Replacing the Mic
On the back of the circuit board, find the two little bits of solder I've marked in the image below. Grab the mic (attached to the front of these bits), and pull gently on it.
While you do this hold your soldering iron on one until the solder melts. Keep it there for another couple of seconds, and then move the soldering iron to the other bit of solder. Keep alternating between the two - you should feel the mic gradually coming free.
Once the mic is free, take a length of wire and strip a tiny tiny amount from the end with your wire strippers. You'll want to try and make it just a little more than the vertical height of the circuit board.
Hold it against on one of the bits of solder (i.e. exactly where the mic was, on the same side of the circuit board). There's a little hole there that the mic was once in, but it's covered by solid solder. So while lightly trying to push the wire into this hole, hold your soldering iron on the other side to melt the solder.
Once it's in, you may need to add some more solder to stop it coming out. Just make sure the solder doesn't get close to touching the other little bit of solder where the mic was.
Then do all that again with another bit of wire. Once you're done, the mic's metal contacts should be replaced by two wires.
Step 4: Attach the Switch
Okay, now it's easy. Close up the case, letting the wires hand up through the old mic-hole.
Strip about 1/4 to 1/2 a cm (1/10 to 1/5 of an inch) off the end of each wire. Now look at the bottom of the switch. There should be six connections, like this:
Solder one wire (it doesn't matter which) to the middle-left contact, and the other wire to the middle-right one.
Step 5: Add the Mic and the Headphone Port
Solder the mic's two contacts to the top-left and top-right contact on the switch.
Get two 5cm (or 2 in) lengths of wire, and strip a small amount off both ends of both wires. Open up the mono headphone port, and solder one wire to the big tall contact, and the other wire to one of the little tiny contacts. If you have a cover for the port, put it back on now. If not - no big deal.
Solder the other ends of the wires to the two remaining contacts on the switch. Again, it doesn't matter which is which.
Great, it should work now. With the switch in the top position (closest to the mic), turn on the unit and check it works when you speak into it. Then flip the switch and plug in an mp3 player or computer, and check that it works. Start with the player's volume very low, and gradually turn it up.
Step 6: Finishing Up
Use the hot glue gun to glue the switch somewhere nice. I put mine on the belt holder, so the mic can always be pointing upwards and outwards.
If you want to, you can also glue the headphone port as well, but I prefer to leave mine hanging. (For those of you who think that might be a metaphor - trust me, it's not).
I also glued up the old mic-hole, so if the wires get caught on anything, they won't be tugged off the circuit.
Now connect it back to the shirt, and watch your kinky music. If you have a lapel mic lying around, plug it into the headphone port, and wire it up. Make sure the switch is set on the side the headphone port is connected to.
If you're going to use an mp3 player with this, I recommend a cheap headphone-port splitter (one of those "now-you're-friends-can-hear-your-music-at-the-same-time things") so you can actually hear the music your shirt is displaying.
Finally, here's a nice trick for all you're sexy geek-parties:
Buy a cheap wireless lapel mic. Disconnect the mic from the transmitter, and using your headphone-port splitter, connect it between you're computer/stereo and speakers. Then attach the receiver to your shirt. Now your shirt will light up to the music that's playing, even if there are people talking, shouting, or loudly throwing up.