When I was at university, best part of 30 years ago, I ordered a funny little homemade headphone amp from an ad in the back of a music paper.
It sort of worked, but as soon as the battery started to wear out (which didn't take very long at all) the sound would degenerate into a load of chattering noise which seemed to bear no relation to the notes you were playing.
I quite liked it. :lol: