The next year Hammond matriculated at Yale and switched from violin to viola because, as a matter of practicality, his fingers weren't as good as his ears, and as there was a scarcity of violists, he could play in string quartets with people who were much better than he was.

Hammond played with a cellist named Artie Bernstein who had worked his way through NYU law school playing bass with pop and jazz bands in the area. Bernstein knew most of the white musicians in the area, Hammond knew most of the black, and together they knew them all. An enthusiastic evangelist, Hammond's favorite spot to take Bernstein and other white friends was Small's Paradise (an illegal speakeasy - Prohibition lasted from 1920-'33) in Harlem which featured blues and jazz performers backed by Charlie Johnson's house band.

Hammond began writing about his enthusiasm for jazz, and Yale began to seem irrelevant. A bout with hepatitis the summer before his junior year made up his mind and Hammond left school to pursue a life in music full-time. Recovered and writing for Gramaphone, Hammond went to England in late-summer-'31 because the English were more interested in jazz than white Americans, and because the bottom had fallen out of the American record market with the advent of the Depression.

In England Hammond met Spike Hughes, recording director for English Decca, who asked him to keep his eyes open for promising jazz musicians, including a white clarinetist named Benny Goodman. Hammond also came away from England as the U.S. correspondent for Melody Maker.

Full of confidence and ready to make a difference, Hammond saw a piano player named Garland Wilson and decided he should be recorded. Hammond went to Columbia's Frank Walker (because Walker had discovered Bessie Smith years before) and offered to fund and produce the Wilson session himself.

Walker quoted Hammond the price of $125 for four 12-inch sides (12-inch 78's ran about five minutes a side and were recorded with one microphone, direct to acetate), and Hammond had to buy 150 of the finished records. "St. James Infirmary" backed with "When Your Lover Has Gone" sold several thousand copies and was a substantial hit for the day. At 20, John Hammond was a successful record producer.

Hammond moved to an apartment in Greenwich Village on his 21st birthday and felt at home amongst the artists, writers and bohemian types. Though personally untouched by the Depression, Hammond's sensibilities were radicalized by it (he was a leftist but never a Marxist); and as an idealist and reformer, he was scandalized by the fact that segregation kept black jazz musicians from the more lucrative jobs on radio or in the white clubs.

To further spread the jazz word, Hammond became a DJ at radio station WEVD (named after Socialist leader Eugene V. Debs) owned by the Jewish Daily Forward newspaper. He instituted the first regular live jazz series anywhere, paying his favorite performers $10 each out of his own pocket to come in to the station to jam on Saturday nights. Unwilling to compromise his principles, Hammond took the series off the air after ten weeks when the black musicians were asked to use the freight elevator.