Because the 2 knobs on BF/SF Fender amps are designed to be flat by keeping them at 0. No MIDDLE knob means that MIDDLE is always 0. So if you set the 2 knobs (BASS and TREBLE) more than o, you hear the scooped sound. FYI, a line graph of BF Champ drawn by a Japanese amp builder. http://cream.lolipop.jp/grid/pgamp/amp/amp4/img/ftone.jpg A) Both tone knobs (BASS and TREBLE) are 0. B) BASS 10, TREBLE 0. C) BASS 0, TREBLE 10. D) BASS 10, TREBLE 10.