Well, it really could be anything, right? Two additional impeding mechanisms have to be taken into account when talking about inductance besides the normal resistance of DC circuits: the induction of voltages in conductors self-induced by the magnetic fields of currents (inductance), and the electrostatic storage of charge induced by voltages between conductors (capacitance). The impedance caused by these two effects is collectively referred to as reactance and forms the imaginary part of complex impedance whereas resistance forms the real part.
You are dealing with transformers in your amp output circuit, right? Maybe somehow they are getting saturated?
You are dealing with transformers in your amp output circuit, right? Maybe somehow they are getting saturated?