Emo Trombone Wow-Wow Alu

When used as a wah-wah with the tube inserted, everything is fine. but when the tube is taken out to get that sound of a bumble bee (which is why I bought it), it can't lock in to low A, Bb, B, C, or Db. Very annoying, because the sound is very good. Everyone comments on it. I gave it 3 stars for the manufacturing because it looks good and seems to have made with care, but there's the problem of the response....