Cartridge Impedance

Raul, I beg to differ.  Most hi-gain phono stages are "stressed" by using a high input resistance, e.g., 47K ohms, rather than using a conservative 100R with a typical LOMC.  Well designed high gain phono stages tolerate anything up to 47K without problems.  (Here and in my above post, I was referring only to MC phono stages that do NOT incorporate an SUT in order to achieve the gain needed for an LOMC.)  Probably Raul is doing the same.

The reason LOMC cartridges are relatively tolerant to capacitance (vs MM cartridges) is their very very low inductance, in the 50-100 micro-henry range, as compared to MM cartridges which exhibit inductance in the ~500 milli-henry range.  The inductance combined with capacitance introduced by the IC and by the input gain stage can cause a high frequency resonance.  With LOMCs, this occurs at very high frequencies, well beyond audibility or the capacity of any speaker to reproduce, because of the low inductance and given any reasonable amount of capacitance.  With MMs, you have to be careful about added capacitance, because the resonant peak is moved downward near to the audio frequency range due to inductance, but some benefit from just the right amount  of added capacitance which boosts treble in a desirable way.  This is the way I understand it, and I welcome any corrections.

Lewm is entirely correct. For LOMC cartridges the input impedance should be set at 10 times the internal impedance of the cartridge or a little above anywhere between 50 and 100 ohms covers most modern cartridges. It is not one of those areas where tweaking makes much difference. Play with different cartridges, move your speakers around, play with different room EQs if you can but messing around here is not productive use of your time. In this regard I always follow the manufacturers recommendation especially if you are dealing with companies like Ortofon and Clear Audio. They know a lot more than I do. 
Input capacitance does make a difference with MM cartridges because it changes frequency response in the audio part of the spectrum. Again the manufacturer will tell you what gives you the flattest response. 

Dear @terry9  : First than all I said that LOMC cartridges are not sensitive to load impedance changes in the phono stage and that's the phono stage whom is sensitive to those load impedance changes thatform a circuit internally and that " there " even capacitance has something to say.

I never told capacitance affects the LOMC items, it's obvious it did not. You, me and every one else knew about.

R.

@lewm  : ""  The inductance combined with capacitance introduced by the IC and by the input gain stage can cause a high frequency resonance. With LOMCs, this occurs at very high frequencies, well beyond audibility or the capacity of any speaker to reproduce, because of the low inductance and given any reasonable amount of capacitance.   ""

yes, that's what I mean with a very bad explanation and is something that's not totally proved: it's what in theory could happens. Now, we can hear nothing at the frequency that was affected or its frequency range.

As I said, LOMC are sensitive ( very ) to inductance and very tolerant to load capacitance changes.

R.

The loading is strictly for the preamp’s benefit and does nothing for the cartridge.

The reason it is there is because the inductance of the cartridge and the capacitance of the tone arm cable form a resonant circuit known as a tank circuit, which can be driven into excitation by the energy of the cartridge, creating ultra sonic or (more commonly with LOMC cartridges) RF noise.

If the preamp is unhappy with RFI injected into its inputs it might sound bright. The resistor detunes the tank circuit thus eliminating the RFI and calming things down. The downside as others have pointed out is that the loading forces the cantilever to do more work and makes it stiffer, less able to track higher frequencies.

If the preamp does not care about RFI then there is no need for the cartridge loading. But if its provided with a switch, its a pretty good bet that RFI is an issue. IME use the highest setting that sounds right.


You can find more at this link:http://www.hagtech.com/loading.html

IOW- I’m not making this up (I build phono sections for a living).


Now a side benefit of not having to load the cartridge is often that you also get less ticks and pops, since many of those are created by the phono section itself. Referring to the link above, we see that the peak I mentioned is a good 30 dB (1000x) higher than the signal itself! Yikes! If your phono section has poor overload margin, you tend to get ticks and pops on this account.