Why use a transformer?
Step-Up Transformers (SUT) are a serious option for anyone who owns a Moving Coil (MC) cartridge, one that can significantly improve both the sound quality and sonic character. Quite simply, a good transformer is the best way to audition an MC cartridge with the highest performance possible.
Since the output of MC cartridges is lower than that of a Moving Magnet (MM), higher gain is required to utilize them, such as that provided by SUTs or MC phono preamplifiers. Although both devices provide this requirement, both are fundamentally different in function and in sonic character. This is where SUTs are frequently seen as superior; they are completely passive and offer exceptional noise performance and sound quality.
This is due to the fact that the structure of harmonic and intermodulation distortion is fundamentally different between MC-preamps and SUTs. While an MC pre-amplifier has a constant resistive input impedance, an SUT has an input impedance that is frequency dependent. The harmonic distortion produced by SUTs is highest at the lowest frequencies and drops as the frequency rises, whereas in most MC preamps the distortion increases as the frequency rises. Combined with significantly lower Intermodulation Distortion (IMD), the sound produced with an SUT will be much more open, dynamic, spacious, and natural.