Vox amPlug works great!
This is a neat little tool. I purchased this because my hearing is getting quite bad in noisy areas such as jams. Being a bluegrass player I play a lot of jams and find it very hard to hear my guitar breaks but with the amPlug that eliminates the problem. Just plug it in (if you have a jack in your instrument of which I do) and put in an earphone and problem solved. Would also work good as a personal monitor on stage. I love it!