Herman's math is correct, as is the chart on Bent Audio's page and the spreadsheet on Galibier's (Thom Mackris') site. My experience is similar to his also.
Patrick's advice is good in theory but difficult to apply in real life. As Herman says, it's normal to choose a stepup with the right amount of gain, then match impedance as needed.
I've had 5 or 6 stepups in my system. Results varied depending on the cartridge, but with my ZYX UNIverse the best results were obtained with Bent Audio Mu and the appropriate resistors on the secondary side. Other trannies were less satisfactory, whether with resistors or without.
There is a sort of cartridge/stepup synergy that transcends mere impedance, since I've also heard stepups other than the Mu sound better with other ZYX cartridges, even though their gain/impedance requirements were nominally the same as the UNIverse's. This was somewhat mysterious, thoroughly unpredictable from specs, and seems consistent with what Patrick reported.
WARNING: LOMC's playing through stepups are EXTREMELY sensitive to input impedance and resistor type. I had to pair resistors on the Mu's to fine tune the value to obtain optimum response. I then tested various brands/types of resistors to find the optimum one, and discovered that the values required changed ever so slightly compared with the cheap resistors I'd started with. In this application the tiniest changes are audible, and experimentation is the only way to find the right values for a particular cartridge in a particular system. If you're picky, it's unlikely that a single resistor will hit the optimum value on the head.
Best of all is no stepup transformer, but that's a different kettle of fish.
Doug
