He didn't test it correctly, should have had a vacuum pump and N2 purge going so that the cutting was done in an Oxygen Free atmosphere.
Also none of that equipment is as sensitive as a human ear, especially a golden ear that is accustomed to listening to the very best (most expensive) audio gear. Makes perfect sense that he could not hear the obvious improvements, this is what happens when troglodytes try to enter the exclusive world of true audiophiles........