U.S. Patent No. 1,822,758 - 09/08/1931 - Pierre Marie Gabriel Toulon
Comments Concerning the Patent Gerald Stanley 03/03/2003: "Negative feedback amplifier, speaker, cutter. In 1931 P.M.G. Toulon (an audio guy) was able to get his patent on negative feedback issued six years before Black despite having filed later. Toulon shows negative feedback applied to the movement of a loudspeaker and a record cutter as well as an amplifier. He had no math to tame his invention, but had the right philosophy."