Some of the best measuring and worst sounding amps ever made had massive amounts of negative feedback. The Japanese amps of the 70s are the best examples of this, .0001 distortion. It is not that distortion makes an amp sound good, it is what you have to do to reduce it to tiny levels that makes it sound bad. While negative feedback may reduce measured distortion its correlation with sound quality is another matter. A good amp can have no global feedback or a moderate amount. Mine has none and has a considerably higher level of distortion than the vanishing level of distortion amps of the 70s but is a far better sound amp than they were. But intelligent design is everything; we are still searching [after all these years] for either design principals or measurements which will guarantee good sound. Peter Walker , of Quad fame, said years ago that he could build an amp that would look good on every test but that would be unable to play a recognizable tune. Neither design principals nor simple measurements is really going to tell you what an amp sounds like in a given situation. If distortion were the overriding factor then no one would ever buy a tube amp, obviously there are other factors at work.
