What's a good step-up transformer?

M.A. Cotter is a very good one. Also RWD, and Verion. Jensen are commonly used as built-in to many higher end preamps. Bent Audio sells the Stephens and Billington kits and assembled units. Ortofon, Denon, Shelter, all have outboard units. Lundahl is a common brand of raw transformer for DIY use.

Not "everyone" says that moving coils are necessarily superior. An alternative solution toward the goal of a low moving mass MC cartridge, while combining the benefit of high MM output voltages (no transformer or gainstage required) is the Grado cartridge line. These are hybrids, a variable reluctance design. Very low moving mass + higher output are available in certain Grado models. I favor the woodbody designs, but they also offer some economy models.

I'd seriously suggest giving John Chapman at Bent Audio a jingle and ask about the TX-103 unit, based on the Stevens and Billington product that Twl mentions.

I have one of his TX-102 passive volume control units(preamp). It is EXCELLENT.

There is also one available from ZYX.
A very interesting design.

You might want to try K+K audio's kit. It only requires a couple of solder joints and you can set it up for 5/10/20 times the gain. It only 199.00 and it uses lundal transformers. It sounds great.

Regards Tom