Integrated Amplifiers

The MA9500's multifilar-wound transformer-coupled output has been a staple of McIntosh's high-power amplifiers for decades [MC510, HFN Jun '08; MC601, HFN May '11 and MA9000, HFN Sep '18]. Once again, this 'Audio Autoformer' ensures the MA9500 overwhelms its basic 300W specification with a 400W+ output. In practice, while transformers are more commonly 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 transformers here to manage the MA9500's power into different speaker loads without fear of overload or overheating. Hence the consistent 300W rating 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 MA9500's feedback network, it suffers neither the high output impedance nor the distortion (at low frequencies) of the archetypal valve amp. PM