Integrated Amplifiers

HFN Apr ’18 featured Perreaux’s 255i, the self-proclaimed ‘World’s Most Powerful Integrated Amplifier’ which, on test, delivered 2x435W/8ohm and 2x630W/4ohm. While this still bests McIntosh’s 2x420W by the skin of its transistors, the MA9000 has its own claim to fame – the ‘Audio Autoformer’. While transformers are typically used to match the high output impedance of a tube circuit, and deliver useful power, to the low (8, 4ohm, etc) impedance of a loudspeaker, McIntosh is using its own multifilar-wound transformers here to manage the power of its solid-state amp into different speaker loads without fear of overload or overheating. Thus it can rate the MA9000 as offering a consistent 300W into 8, 4 and 2ohm loads when measured via the 8, 4 and 2ohm secondary windings of its autoformer. (There are two secondary windings – one 8ohm and another for 4ohm with a 2ohm tap.) Moreover, with the secondaries and primaries interleaved for improved frequency response and forming part of the MA9000’s feedback network, it suffers neither the high output impedance nor the distortion (at low frequencies) of the archetypal valve amp. PM