Unfortunately, the above post displays a lot of confusion and incomplete understanding of the nature of transformers in general, and of toroidal transfomers in particular. Toroidal transformers are indeed lighter and more compact than frame style or square-core transformers, but they cost considerably more, VA-forVA-rating due to the amount of copper used and necessarily slower winding speeds. There is no tendency for toroidal transformers to 'let a lot of noise through'; quite the contrary, in fact. With correct design parameters, they can be highly effective at blocking noise transfer.
Toroidal transformers, again depending on design parameters can show very low distortion. In fact, if some of the the incoming power-line distortion is higher-order and the transformer is designed for narrow bandwidth, it can actually eliminate distortion in the incoming waveform. And a toroidal transformer can very easily REDUCE the source impedance of the power-line. It's not uncommon for the power-line in the house to show a source impedance of half an Ohm or more. Torus Power Conditioners, which use toroidal transformers, have a source impedance as low as 40 milliOhms, at least a factor of 10 lower than the wall plug.
The larger Bryston amplifiers do use Torus-type transformers in their power-supplies, for all the above reasons. Beyond that, of course they use 'additional filtering', at least part of which is up to 200,000 microFarads of filter capacitors per channel! We would not use them if they were not the best way to arrive at the best performance.
