I was trying to track down a noisy inductor (I like to call them a squealer) in the back of a monitor so I thought I would design a electronic stethoscope - then I remembered I had one from something I built from Robert Penfolds article in a practical electronics (silicon chip magazine for people in other countries) magazine in my youth. so I checked my box o'junk and found that I had salvaged parts from it.
So I made myself a new stripboard layout and built a new one. I had to change the odd part cause the original called for stuff that costs stupid money by opportunist eBayers.
But it works a lot better than the old one ever did - so hurray for opportunists I guess.
I use this to drive a pair of in-ear headphones and it really does work really dam well. so if you need something to track down the source of noise or spy on people through the wall or something - this is for you.
NB: if it's a bit too hissy for you - you can remedy that by putting a 1n capacitor in parallel with R6