Who engineered Led Zeppelin IV, and what unconventional techniques did he use?

Andy Johns engineered Led Zeppelin IV (with Jimmy Page producing). He used unconventional techniques like recording Bonham’s drums in Headley Grange’s stone hallway for natural reverb, running tracks through a dying Altec 436C compressor, and placing a single ribbon mic far down the hall for room sound. It was all about capturing the room’s energy, not removing it.