On the primary side, I have a low-impedance AC supply that can be adjusted to a minimum of 100V, with a frequency variable from 5 to 800Hz (and I need to operate over this whole range). I need to somehow transform this down to 2.5V or lower, naturally as efficiently as possible, with the secondary side drawing up to 12A.
I considered just buying a transformer of roughly the right ratio and maybe a bit higher power rating than I need, but there's rarely any detailed information with regards to resistance, loop counts, wire gauge and/or inductance that I'd need to properly calculate the losses caused by running a 50Hz transformer at 5Hz. I have no idea if it would just get a little hot, or melt through the casing; and even if the losses were acceptable I wouldn't know if it would even transfer enough power to the secondary.
I have looked at audio transformers, as they are designed to operate at a wide frequency range, but even they seem to only go down to 20Hz.
What would a more experienced engineer than I do in this situation? Are there certain specs I can look for in pre-made components, or will I need to look at having one custom-made?