Thanks for the info, gentlemen. I prefer to keep all of the electronic components on the amplifier board so they are better protected. The loop will be just wire, nothing else.

My preamplifier design does not need a transformer. All of the common-mode rejection and impedance matching is done electronically, and for less money than what just the transformer would cost.

But since we are talking of loop sizes, it sounds like it would be a good idea to include a couple of jumper blocks at the preamplifier to match it to a range of loop sizes. That way there's no need to attach additional components to different size loops-- just select the appropriate jumper setting. I can envision the 1' x 8' size for "normal" use, and maybe a 1' x 6' size for narrow 1/12 scale tracks, and perhaps a 6" x 4' size for micro cars like Mini-Z's. Do you have any requests or suggestions?