Here's a moving coil phono step up transformer box using a pair of german made Haufe T 5860/1. These transformers have split primary coils, each with a 1:30 ratio, so they can be used at either 1:30 with the coils in parallel or 1:15 in series. You can see there's a switch to select between these ratios. Assuming your preamp has a standard 47,000 ohm input resistance, these two settings will load the cart with approx. 200 ohms on 1:15 or 50 ohms on 1:30.The 1:15 ratio and 200 ohm load work really nicely for the standard Denon DL-103. They'll also work with lots of other cartridges with similar voltage output. The 1:30 ratio can work with lower impedance cartridges below 10 ohms or so.These are miniature transformers, and their small size is very well suited to the small power output from MC cartridges. The frequency response and sound are excellent. The main disadvantage of transformers this size compared to larger ones is the use of finer copper, higher DC coil resistance, making them a little bit less efficient than larger transformers. Even though the actual turns ratio is 1:15, with the secondary loaded at 47k the actual voltage gain will be in the neighborhood of 12-14 times.