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Running LOMC with MM (47K) loading

This is the way I run my Zyx 4D and my Benz Ebony L before it. I have a JLTi phono preamp which allows me to do this. I have been satisfied with this pre since buying it new. Yet I may be in the market for a new (Different) one. However some I have seen may not offer this ability. One that has great reviews also  has the loading and gain all tied together. Not sure about Herron but it may be out of production. Not sure about others. 
 
The question comes  with @Atma-sphere comments on loading and circuit stability. He contends that the loading  damps (stops) the cartridge cantilever from moving as freely as it was designed (my words) And it is better IF you can run with no loading. But that requires a stable circuit which not all have. Apparently my JLTi has a stable circuit because I have been running LOMC's this way for a 10-15 yrs. 

That said, should I require this attribute to my next phono preamp? And might I be better off to send the JLTi to Joe Rasmussen  (Allen Wright's partner) for upgrade to Pre and new Power supply?. That will be the cheapest and that is likely to be the step I take. However the question still exists. If the damping is as per Ralph's assessment, it would seem that the stability of the  circuit is of greater importance than the ability to have a lot of loading options with unstable circuitry. Another question, Is loading a band aid for a  circuit which is not at an optimum? I am not an electronic tech so I am not  looking to stir the pot but  for my own  understanding  Thanks
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larryi
3,997 posts
 
Rothwell, a company that supplies step up transformers said this somewhere, perhaps in their "white paper" on their site.  Vandenhul says that in their FAQ section of their site.  I think Jonathan Carr (Lyra) has also said this, but, I cannot recall where.

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.  I don't see any kind of feedback mechanism for an induced current in the coils causing a magnetic field that interacts with the magnets in the cartridge.
pindac's avatar
pindac
2,864 posts
 
I have used a LMOC on a Valve Input/Output MM Phonostage.
From a Audible Perspective, the marriage of the Two Devices delivers a prentation that is Rich and Voluminous.

As for a Presentation it suits 'IMV' non complex music combined with female volcals.
It also worked quite nicely with a Male Harmony with Harmonica and Acoustic Guitar.
With ECC81 Valves as a Input, it was Volume Control Hungry to achieve the Listening Levels I prefer, and on a few tracks, the Volume was not enough and the replay was a little wanting for extra Volume.

Put the SUT in place and the same Cartridge becomes a very airy detailed device, that lends itself to all Music Types.
The Volume Control is happiest when set at at approximately half rotation and this leaves ample more for when required.

I have not got a Problem with the MM Stage minus SUT.
I have got a Cartridge that can wear two costumes.
One version is a MM only Cob Horse with a Cart in Tow, and the other version a SUT enhanced performance Flat Race Horse released from the Stalls.     
lewm
13,071 posts
 
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.
intactaudio
301 posts
 
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.
larryi
3,997 posts
 
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.
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