I had sort of an odd experience with my TFB550A and my TFB750-A. I owned the 550A first and loved it! After speaking to folks here and talking to Dave it seemed that the 750-A had more of a great thing going on so I had to have it. Well I sold the 550A to get the 750-A and I realized that I liked the 550A much better for my tone goals. I was sort of shocked by my experience because the 750-A was the latest and had more updates than the 550A I was playing.