Last Year I did this because I needed speakers for a project that consisted of a NES Clone. It ended up working and I thought it would be good to make an Instructable for because its not a huge task to take and it builds upon knowledge.
Keep in mind this Instructable will not be very detailed, it will basically just point you in the right direction.
Q: Why Reengineer a USB speaker to the 'universal' 3.5mm Jack?
A: To build knowledge & experience or you might just need a speaker for something that uses 3.5mm etc....................
In my opinion USB speakers are the cheapest speakers but maybe I'm not looking in the right places.
The speaker I used for this Instructable has a 3.5mm jack but its for plugging in headphones not to input audio
Step 1: TOOLS + PARTS
SOLDERING IRON ( with a sponge to clean it of course ) + SOLDER
WIRE + WIRE CUTTERS + WIRE STRIPPERS
USB SPEAKER ( make sure it doesn't have 3.5mm if your doing this for experience )
3.5MM JACK ( Desolder one off of something or buy one online )
# If your not confident with your soldering skills then I recommend flux because you can bridge the tiny pins on Chips REALLY FAST if your not extremely careful and flux makes it a bit easier in my opinion #
Step 2: Taking Apart the Speaker
1. Grab your screwdriver
2. Take apart the Speaker in till you have access to its Circuit Board
Step 3: Chip Identification
1. Look for any Chips on the Circuit Board
2. Try to find they're Datasheets online and learn how they work
Step 4: 3.5mm Jack
1. From the Knowledge you gained from the Chip's Datasheet, Solder one of It's pins and wire it to the 3.5mm Jack.
2. Plug some Audio into the Jack ( 3.5mm cord ) and see if it works !
If its working but the audio is really bad check and see if the audio going to that pin goes through a Capacitor or Resistor first.