which is better ? MC phono stage or MM+step-up ?

Any argument that a stepup is theoretically inferior because it adds an extra device is simplistic at best, maybe specious. An active MC stage also adds an extra device. The question is, which device works best with any particular cartridge and the following (MM) gain stage?

The answer depends on the individual components.

FWIW, the active MC phono section in my $12K Doshi Alaap outplays my $800 Bent Audio Mu (copper version) stepups, despite fanatical tuning of the Mu's impedance for individual carts. What does this prove? Maybe not much, given the price difference. Still, though I haven't heard every stepup (not even the reportedly better silver Mu) no MC section of any type has ever outplayed the Alaap's IME.

One important fact: impedance matching with stepus is orders of magnitude more critical than with an active MC stage. True afficionados may use both primary side loading (for the cart) and secondary side (Ziebel) loading (to control transformer resonance). Getting all this right in a resolving system can take alot of trial and error work. Impedance setting with an active stage, while certainly audible, tends to be less critical.

Not to complicate an already very complicated matter, but if you have a good MM phono that you are happy with, you can also use one of several "head amps" or pre-preamps" that are available. These are stand alone active gain stages and would be used instead of an SUT. For a time, I used a ZYX (I think its called the CCP-1) and it was very good. There are supposedly 2 advantages of the active gain approach- the first one doug has elaborated on well. The second, actually a corollary of the first, is that an active gain stage (internal or external) is more likely to mate well with more than one LOMC, while its more likely that the SUT approach will require very elaborate tweeking and/or a different SUT for a different cart.

Question: which is better ? MC phono stage or MM+step-up ?
Answer: Yes.

Well said, Lewm!

I find that transformers tend to obscure detail and they limit bandwidth. So if you have enough gain, an MC high gain phono section might be better if properly designed.

The loading of the transformer is critical, else it can ring (distort), making things brighter and obscuring detail. All the following is assuming that the transformer is properly loaded:

If you do not have enough output from your cartridge, most phono sections will loose some bass impact. Where a transformer will normally do that too, in this case they will win you some back.

If you have too much noise, the noise will obscure low level detail. Where transformer will also loose detail, it also gets you gain without noise, and so wins you back some of that low level detail.

So- its not something that you can always state what will work in all cases. Usually the manufacturer of the phono section will know if the cartridge you have will need a transformer or not.

If there was a panacea, I would state it but as a manufacturer myself that is well-known for not liking transformers, I'll be the first to admit that they can be very beneficial in a variety of situations!