I design and manufacture audio transformers for all Music Reference amplifiers. I also make OTL amplifiers with and without autotransformers which actually extend the frequency response in the high end.
Here are a few things to note. An autotranformer is not like a standard output transformer in that there is no need for HV insulation and the winding scheme is totally different. Where we interleave sections in an output transformer we can mulitfilar wind in a autoformer which reduces the leakage reactance markedly..
Also, in a 2 to 1 (4 to 1 impedance ratio) autoformer half the current is direct and half is transformed. So they are smaller and lower loss.
As to McIntosh, their use is very clever and wise. If you note they drive the autoformer typically at the 2 ohm tap. This allows them to use lower rail voltages and stay out of the second breakdown region that all bipolar transistors suffer from.
This is just a glance, if you want more just ask. As many of you know I have been doing this since 1980 and I find the art of transformers facsinating. Every design brings new challenges.
Here are a few things to note. An autotranformer is not like a standard output transformer in that there is no need for HV insulation and the winding scheme is totally different. Where we interleave sections in an output transformer we can mulitfilar wind in a autoformer which reduces the leakage reactance markedly..
Also, in a 2 to 1 (4 to 1 impedance ratio) autoformer half the current is direct and half is transformed. So they are smaller and lower loss.
As to McIntosh, their use is very clever and wise. If you note they drive the autoformer typically at the 2 ohm tap. This allows them to use lower rail voltages and stay out of the second breakdown region that all bipolar transistors suffer from.
This is just a glance, if you want more just ask. As many of you know I have been doing this since 1980 and I find the art of transformers facsinating. Every design brings new challenges.