Found this site with good info on winding output transformers:
http://www.geofex.com/Article_Folders/xformer_des/xformer.htm
Noticed one error in a formula they have for computing turns:
N=(E*10**8)/(kfbA) A (area) should be in sq. cm not sq. inches.
Site doesn't mention toroidal xfrmr winding techniques though. But the key to high performing toroids is just using back and forth dithering of the core while winding so as to make winding layers chevron shaped and cover near 360 degrees in one sweep around core per winding. (don't overlap ends) (use good insulation between layers and core too) This essentially amounts to micro-sectioning a winding. Interleaving does not benefit in toroid case (since leakage inductance is already minimal) and only makes distributed capacitance worse. I have some cheap (surplus) Avel-Lindberg power xfmrs that appear to have been wound this way. They have a flat frequency response to 150KHz and resonance at 450KHz!!! This is far better than most "Audio" output transformers! I measured a Hammond 1650T (a low turns ratio model) trannie to compare and it is flat to 30KHz and resonant at 50KHz. Main drawback of toroid outputs is that the DC current balance must be strictly maintained to prevent saturation problems.
See my earlier posting on how to extend any transformer's phase linear bandwidth up to Mhz range.
http://www.geofex.com/Article_Folders/xformer_des/xformer.htm
Noticed one error in a formula they have for computing turns:
N=(E*10**8)/(kfbA) A (area) should be in sq. cm not sq. inches.
Site doesn't mention toroidal xfrmr winding techniques though. But the key to high performing toroids is just using back and forth dithering of the core while winding so as to make winding layers chevron shaped and cover near 360 degrees in one sweep around core per winding. (don't overlap ends) (use good insulation between layers and core too) This essentially amounts to micro-sectioning a winding. Interleaving does not benefit in toroid case (since leakage inductance is already minimal) and only makes distributed capacitance worse. I have some cheap (surplus) Avel-Lindberg power xfmrs that appear to have been wound this way. They have a flat frequency response to 150KHz and resonance at 450KHz!!! This is far better than most "Audio" output transformers! I measured a Hammond 1650T (a low turns ratio model) trannie to compare and it is flat to 30KHz and resonant at 50KHz. Main drawback of toroid outputs is that the DC current balance must be strictly maintained to prevent saturation problems.
See my earlier posting on how to extend any transformer's phase linear bandwidth up to Mhz range.