Running LOMC with MM (47K) loading

Pindac, What are you saying?  Seems you are saying that if gain is insufficient, then your cartridge doesn't sound its best.  Which is almost certainly true. Clearly, the ECC81 (also known as 12AT7) substitution produced overall phono gain that was not adequate, but it would help to know what was the tube type for which the phono stage was designed. Just because it is so commonly used in phono stages, I am going to guess it was the ECC83 (also known as 12AX7).  If you did sub a ECC81 for a ECC83, it is no wonder that didn't work well.  The ECC83 has over twice the gain of an ECC81, and also the latter tube requires more plate current than an ECC83 to sound its best.  So you loaded the dice against the ECC81.  If you then added a SUT to the input of the ECC81, perhaps that worked better, because you restored the missing gain.  (I think you are also saying you run an LOMC cartridge into an MM phono stage, implying a stage with not more than 50db of gain and probably less, even when the input tube is the one for which the circuit was designed, plus or minus a SUT.) Other things, like phono input load impedance also change when you add or subtract a SUT, and that too affects SQ.

I don't see any mechanism for the electrical loading somehow affecting the mechanical movement of the cantilever.

It is common knowledge that when you ship a speaker, you should short the terminals because it provides a "dynamic brake" which limits cone excursion from sudden impacts.  A cartridge is simply a speaker in reverse and loading a MC can have a dynamic impact on the compliance.

A speaker voice coil moving in the magnetic field induces a current (if the speaker terminal is shorted) that creates a magnetic field that resists the movement (back EMF).  In the case of the cartridge, where is the back emf or back emf increase by adding a loading resistor to the circuit?  If there is any sort of back emf induced in the moving coil, it would be so negligible compared to the forces acting on the cantilever.  The cantilever is being moved by the tremendous force of the stylus tracking the groove, which in turn is being resisted by the cartridge suspension and the inertial mass of the tonearm and the cartridge.  Any theoretical counterforce from back emf would hardly matter.

@chakster 

I talked to Joe Rasmussen about a month ago about having the upgrade done. He says that the Mark 5 is a Big improvement over the 4. Quoting Joe,

 " JLTi Phono was never meant to compete
with our more expensive VSE FVP and SVP full Phono/Line Pre-amps, but to be a much cheaper stand-alone phono stage and great value.
That has changed...  For a fraction of the cost, this is on a different level entirely ...In a way our JLTi Phono is also a "current mode"
phono stage, also known as transconductance circuit, but again, we do it in a different way."

I just got an estimate from USPS for shipping to Aus. which was quite a bit  cheaper than the others. Since its small, It should be OK.
Now the problem will be not having a phono preamp for 3-4 weeks. Guess I'd better look for a temp replacement. Alnic 1202 looks interesting but loading is preset with the gain you choose. Interesting concept I wonder how they came to those figures.
The question for me is still this. 

@lewm  I'm hoping Ralph (Atma_Sphere) will chime in.

@larryi  I believe Ralph indicated that the electrical signal is what actually stiffened the suspension. But I am not elec tech minded. So my descriptions may be off as far as terminology. Hopefully he will chime in

47 kohms is for moving magnets. I would use what is recommended by the cartridge manufacturer. My hana el calls for >400 ohms, I use 430. Not certain why you would exceed the value by 10's of thousands.

47K is the industry standard for all cartridges, MM or LOMC.

damping is not required for most MC cartridges (because their resonant peaks are now well outside of the audible range) except if those peaks result in overloading of the phono stage. 

^^ This. Overload of the input section of the phono stage can result in ticks and pops. That is a very real argument for looking for that phono section that does not require a load!

I don't see any mechanism for the electrical loading somehow affecting the mechanical movement of the cantilever. The loading acts as a voltage divider with some fraction of the signal diverted through the resistor to be dissipated as heat. 

Its not a feedback mechanism. You are working with a misconception. The loading is not a voltage divider; its directly across the output of the cartridge and in the input of the phono section.

When a magnetic motor or transducer is loaded, it has to do more work. That work comes at a price: its harder to make the transducer move. You can prove this easily to yourself because a loudspeaker is a moving coil device not unlike a cartridge (and can be used as a microphone in a pinch). Remove the speaker cable from the speaker and remove the grill cloth. Push on the woofer and see how easy it is to move. Now put a quarter across the speaker terminals so as to short them out. Try to move the woofer again. You'll see its less compliant. The same thing happens when you load a cartridge. Its simple physics. This was put more succinctly:

It is common knowledge that when you ship a speaker, you should short the terminals because it provides a "dynamic brake" which limits cone excursion from sudden impacts. A cartridge is simply a speaker in reverse and loading a MC can have a dynamic impact on the compliance.

In the case of the cartridge, where is the back emf or back emf increase by adding a loading resistor to the circuit? If there is any sort of back emf induced in the moving coil, it would be so negligible compared to the forces acting on the cantilever.

Because the cartridge is a transducer producing voltage from physical movement, there is no back EMF like there is in a speaker which is doing the exact opposite! The 'EMF' in this case isn't 'back', its 'forward' which is to say it **IS** the signal :)

When a cartridge manufacturer specifies a load less than 47K, its because they either don't realize that the load is really affecting how their reference preamp works, or more commonly, they know they can't predict which tonearm cable and phono preamp you are using. Because most phono preamps have stability problems, its wise for them to make some recommendation. They are probably assuming that the tonearm cable is only a meter in length, which in turn tells them that the capacitance of the cable probably does not exceed 100pF, since getting over 30pF/foot is unwise in a phono cable.