Recently I was reading old "Practical Wireless" magazines available on the World Radio H(istory) site. A design for LF used a small audio transformer to couple a loop antenna.
This was a common feature of the Ralph Burhans loop preamp designs, one of which has been updated a bit in the following article:
lwca.net/library/articles/k3siw/rcvloops/index.htm
If Ray ever decides to try a pre-amp with his, this should work well with it, especially if he's inclined to use fewer secondary turns. Just one note, though...I would not make all the grounds common as shown in the schematic. I'd keep the input transformer center tap separate and run it to a local ground connection at the antenna site (if I used it at all), possibly also the transformer core ground, but reference all the other grounds to the coax shield and not tie it to ground except at the shack end of the run.