This Homemade Headphone Amplifier Is A Work Of Art
Very nice, but seeing that made me wonder whether this can be improved as follows: instead of soldering, drill holes in the copper wire that are slightly smaller than the thickness of the component wires you want to attach. Then, heat or cool both enough for the component wires to fit through the hole (thermal expansion factors will hopefully be different enough for this to work), put them in and let the device go back to room temperature.