Apple's Cable includes an isolator and attenuator. If you don't have the official Apple puppy, see the next section. Radio Shack numbers are given, simply because their stores are in every shopping mall in the known universe. Of course, you can replace the phono plug with anything that'll fit your hifi. If you hear hum when recording from a stereo, try the circuit with a battery-operated radio or tape or CD player.
Power lines can introduce noise.
The circuit follows standard engineering practice and works. But Apple and other companies can mess with specifications, anybody can burn themselves with a soldering iron, and actual mileage may vary. So the author makes no guarantees.