The EV55ST is equipped with an Overall Negative Feedback (NFB) switch. This is a process where a percentage of the output of an amplifier is fed back to the input in reverse (negative) phase. This lowers the output impedance and reduces distortion to improve overall frequency response.
As NFB at high frequencies can cause instability at high frequencies with awkward loudspeakers we recommend with horn loudspeakers that triode operation with low NFB is the way to go, however with conventional, low sensitivity loudspeakers Ultra linear mode with high NFB would be a suitable choice. Either way, we’ve made the EV55ST as flexible as possible to cater for different speakers, sound sources and tastes.