This topic can be one of the most contentious ones you'll find in this forum. There are people I respect greatly, but with whom I disagree on this topic.
The relevant question (as far as colorations are concerned) is to compare an MC step-up against an active gain stage.
I fear that those who report bad results with step-ups are wrongly accusing the architecture when it is the implementation that is at fault. Anytime you're given freedom to choose (a transformer, interconnect, line stage, etc.), you have an opportunity to screw up.
Matching a trannie to a cartridge (assuming we're talking about a quality trannie) involves knowing the DC Resistance (DCR) of the coils in your cartridge. You're typically looking to match the cartridge's DCR with that of the transformer's primary ... with the trannie being as much as double the cartridge's DCR, but not much more than that.
Secondly, there is the issue of the reflected impedance that the cartridge sees. In it's native mode (without additional loading resistors), a cartridge will "see" a 470 ohm load through a 1:10 step-up, when connected to a phono stage with a 47K input impedance.
You can run into problems if for example you have a cartridge that wants to be loaded at 1K or 5K and you're using a 1:10 step-up. You will have excessive high frequency roll-off. This is not normally an issue, because the numbers tend to work in your favor. For example, almost all .2mv to .5mv cartridges can use a 1:10 step-up from a gain perspective, as well as from the perspective of the impedance they like to see, which is typically well under 470 ohms. You can always add resistors in parallel to drop the load, but you can't easily raise it.
For some excellent discussions on transformers, go to the Jensen transformer website (http://www.jensen-transformers.com/mc.html). On my support page, I
have some links to excellent articles on step-ups - written by Jim Hagerman (Hagerman Technology) and John Chapman (Bent Audio).
Trannies are yet one more instance of the old adage - it's not so much the chosen architecture, but how well you implement it. I happen to like them because it allows you to tailor a phono stage to a particular cartridge. Other people are baffled by such choices. Others have fallen in love with the colorations of their favorite MC active gain stage.
Knowledge is power.
Cheers,
Thom @ Galibier
