a lack of negative feedback as far as i can tell. negative feedback keeps all the frequencies in check..it's sort of a loop that prevents anything from getting to far out of spec, but without, the poweramp is free to breathe as your fingers decide.
this may or may not have anything to do with dynawatt, as i've been known to use logic rather than fact.
hope somone here has a real answer, as i've always been rather curious myself.
andy