Best type of transformer for a preamp.

ampmade said:

The two sort of transformer are good.
In this two case, you must filter the rectifier with slow capacitor value (10 nF to 220nF) to filter HF switch off noise.
The greater HF noise come from the rectifier and not from the transformer, the transformer filtering a part of main supply and a residual noise can stay but not as high as the rectifier noise.
You must compare the builder datasheet of the components you want to buy, to see the difference between us.
I have build a lot of power supply with toroidal transformer and they are working pretty good.
I think it's a question of design.
A good transformer with a poor designed filter make a poor power supply.
I think (but i'm not sure) that predominantly the EI core transformers have a better weight/power ratio and the magnetic field loss are different from the toroidal form.
The price is a little bigger for EI core transformer too.