I would like to bring up a couple of related side issues for comment . . .
First, I think that a division must be made between the use of external vs. internal transformers. Obviously, the proper loading of the transformer secondary is extremely critical, and if it is an external unit . . . than I can't see how the real-world loading can be anything but indeterminate. It also seems that external units pretty much all have very high ratios . . . for i.e. 30dB gain. This makes for an inherently compromised transformer design, and additionally puts the entire chain in a sub-optimum gain structure. An interesting comparason would be to an active MC head amp . . . an arrangement that I have found quite unsatisfactory with the few that I've used and measured.
Second, a transformer simply cannot offer anywhere near the level of flexibility in cartridge loading that an active design can . . . there are certainly a great many cartridges (including all MM types of course) for which a transformer is simply unsuitable. I must say that I am greatly impressed with the thoroughness that Raul has approached this subject, and we are quite fortunate that he freely shares it on this forum.
I'm currently in the evaluation stage of a new phono preamp design, and the main topological choice was between a direct bipolar input with four MPS-A18s in parallel, and using a low-ratio Jensen JT-346 with a 990 opamp. I chose to use the transformer/990 because it was about 5dB quieter (5 ohm source), had somewhat greater headroom, and inherently blocks the input bias current - in addition to the usual transformer strengths of ground loop isolation and RFI rejection. That's not to say that the direct bipolar approach didn't have its strengths . . . bandwidth and LF linearity were of course among them. And I did have to make a decision to make the unit incompatible with many cartridges in order to use the transformer topology.
In the end, there are pitfalls with both approaches, and I'm confident that my success or failure with this will be overwhelmingly dependent on my ability to carefully optimize all the circuit and construction parameters . . . and very little to do with my "reactive component dogma".
