With parts you already have around your workshop, you can probably build this cable for using your iPhone as a guitar amp, as one Instructables user did:
If you own an iPhone or an iPod Touch and happen to be a guitar player chances are you have already heard of either GuitarBud by PRS or of iRig by Amplitube.
Both products allow you to connect your guitar to your iPhone or iPod Touch and use it as a practice amplifier via their own apps or any others that can do the same. Isn’t technology fun and useful? It’s also expensive and hard to find especially in Portugal.
Inspired by these products I decided to do my own version, only much cheaper and not as nice looking. On the next steps I will try to explain how to make your own cable.