We need an opamp chip, 2 transistors, a diode, 2 preset potentiometers, various resistors and capacitors, battery clip, 2 jack sockets, box, wire solder, soldering iron and some hand tools. Plus a PCB or perfboard to hold the parts.

F Pena's PCB makes life a lot easier, it guarantees that the parts fit together correctly, with good soldering.

The other parts are easily availible, except the 2N5457 transistor, but I do have the J201 transistor in quantity, so I thought I would see if I got it working.