Very hard since most of the amps sold on the market don't function correctly, eat tubes for breakfast or even damage the headphones. I know of at least two Blue Hawaii's that have gone up in flames and even if you can get it to work, it isn't running at 100% since the schematic isn't complete and lacks some very important bits. The Gilmore 0A2 amp would be much easier to build and just about anyone can build an Egmont (except Rudi that is).