Do I need a MC cartridge now? Or an attenuator?

This sounds to me like the old (Henny Youngman) joke about the tailor who made one leg of your pants too long.  So when you complain, he tells you to "limp", in order to make the pants appear to fit.

If you are only a very casual listener who is not that interested in ultimate sound quality, then sure, the Rothwell ought to work.  But it is a kludge that will compromise your sound quality no matter how good it is.  Also, I have to wonder about cartridge loading. If you are using an MM into an MC input, it not only affords far too much phono gain but also you may be loading the cartridge excessively. (High "load" here means that the input impedance of your phono stage is too low in impedance which here is another word for resistance.). There is no way to get around that, and that will really compromise the sound quality from any MM cartridge.  The standard load for an MM cartridge is 47,000 ohms (47K ohms).  Typical load for an MC cartridge is 100 to 1000 ohms.  There is no easy way to fix that with your phono stage. Furthermore, because your MM cartridge has a much higher signal voltage output than any low output MC cartridge, your cartridge is undoubtedly also overloading the phono input, which causes further distortion.  It's a mismatch any way you look at it. So you need either an MM phono stage or a new LOMC cartridge.  The Rothwell will only solve the gain problem.

I think trying to make that combination of cartridge and phono preamp work well together is going to be an exercise in kludgery that will result in you not getting the best out of either component. You’re likely to get better sound by replacing either with a properly matched component, even if it’s a budget model.

The Laiv Harmony HP2A, using their L-Ext (phono input) allows me to change the input impedance via their "selectable input impedance" at 22Ω / 47Ω / 100Ω / 470Ω / 1kΩ / 47kΩ. I am currently set up at 47kΩ (which matches the TT MM output) but the gain cannot be changed.

I have reached out to MoFi for help in determining if their MC cartridge will work with their Studiodeck+ turntable - I suspect it will. I think I then select the 100Ω input impedance, as the MoFi site tells me that their two replacement cartridges specs are "Recommended Load: ≥ 100 Ohm"

My phono experience with this TT/MM stylus into the McIntosh MA252 (into either of my speakers) has sounded superb. I cannot discern too much distortion in the new setup (though I suspect there is) - just too high a dB volume. It does not have a MC phono input however - I suppose I could go with their MA12000 which has one of each phono inputs. 

I think I could put some other form of phono pre between the TT and the L-Ext but that seems like kludgery to me as well.

I will likely get the better MoFi MC stylus. I have slacked off in overspending lately anyway, and I can't have my wife getting used to that! 

Tim

I agree with the above comments.  However, the Laiv L-Ext Phono does have a 47k setting.

Bill

Oops.  Too late.

Bill