Avantgarde themselves only make solid state amps for their speakers. From a review by Roy Gregory in Audiobeat:
"But in the end, buyers of ambitious horn-based speaker systems want more than a slim-line integrated to do the driving. And there’s the rub, the continuing conundrum that has confronted Avantgarde from day one. Their speakers place very specific demands on the partnering amplifier. With sensitivities across the range that get comfortably into three figures, low noise is a critical consideration, but so too are dynamic range and speed of response. After all, there’s no point in building those qualities into the speaker if you crush them out of the signal before it even gets that far. Then throw in the fact that the spherical horns are used in a hybrid array, underpinned by active subwoofers, and it becomes apparent that the matching amplification needs more than just dynamics and speed -- it needs authority too. It’s no accident that all Avantgarde’s amplifier designs have been solid state, nor that every time I’ve heard the speakers sounding glorious it has been with solid-state amps -- and most of the times they’ve disappointed it has been with tubes."
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