2. analog
  3. 166647-2693

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
artemus_5

Showing 6 responses by larryi

larryi
4,226 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.
larryi
4,226 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.
larryi
4,226 posts
 
Quite a number of experts say that loading does NOT supply physical damping of the movement of the cantilever but it supplies electrical damping that reduces ringing of high frequencies.  Atmasphere and J. Carr of Lyra say that such 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.  

With the cartridges I have used with my phono stage (Viva Fono) I prefer no additional loading or very modest loading (meaning high value resistor) on the primary side of the step up transformer.  With the cartridge modestly loaded, the top end seems more open and airy and the decay of notes sound more natural.  
larryi
4,226 posts
 
Atmasphere,

Thank you for your explanation.  I understand that in the case of the speaker movement, that movement induces a current, which in turn, if you complete the circuit, creates a magnetic field that resists the movement of the speaker.  Could you expand further on the mechanism for resisting the motion of the cantilever?  Is it also the magnetic field generated by the coils in the cartridge?  As for conservation laws of simple physics, I can see the price being paid for the loading being paid by the electrical signal, but I don't quite understand why it has to be paid by resistance to the physical movement of the cantilever.

Jonathan Carr of Lyra, said, in a very long post in the What's Best Forum that when we load a cartridge;

"we don't affect what the cartridge does at all (unless the value of the load approaches or drops below the internal impedance of the cartridge).  What adding resistive loading at the phono stage input accomplishes is to dampen the resonant energy of the ultrasonic spike, and give the phono stage an operating environment that isn't so likely to trigger any latent non-linearity tendencies that the phono stage circuitry may have.  

For the reasons given, the phrase "cartridge load" is misleading.  "Phono stage input terminator" is a better description of what really happens."

I am wondering what aspects of his comments you agree with or disagree with.  I regard you both as experts in this field.

Thanks.

larryi
4,226 posts
 
Pindac,

I find it interesting that you experimented with lower gain tubes and use of a SUT and like that combination.  I think that there are many ways to achieve the sound one personally favors, and it is your own taste and matching to your particular system that matters (I tend to like SUT in phono setups myself).  I also agree that one can have quite different sound from two arrangements and one is not necessarily inferior to the other.  

I am curious as to why the ECC83 in the input stage did not work out sonically for you.  I've tried a few different ECC83/12AX7 tubes in my phono stage and they can sound dramatically different, so, perhaps it was the particular brand/vintage that did not work out for you.  I was lucky to have a friend who had a wide array of these tubes so I got to hear a number of vintage tubes.  I ended up getting Telefunken ECC 803S tubes (real vintage tubes, not fakes).  These tubes are certainly not for everyone's taste as they are leaner and brighter than many other vintage alternatives.
larryi
4,226 posts
 
It has been about my experience that once you have a value above 200 ohms or so, there is not that much difference; at that point, you are not applying much loading.  That is why some phono stages, like the Linn Linto, had fixed loading at some almost universally acceptable value of something like 125 or 150 ohms.  

If you want to adjust tonal quality, such as increasing the apparent bass response, you can go with more loading (to decrease the treble response) by selecting a LOWER value, but, this comes at the expense of lower gain and a more muffled sound.  If I need a "fix" for something like excess sibilance and shrill top end, I tend to look more at altering VTA/SRA than changing loading.
More to discover