input impedance load on a cartridge.

lew...Ralph states above:

If however, the preamp is properly designed and is stable with RFI, then the loading resistor will be found to have no effect.

and

Our preamps are stable so no loading is needed.

but you are saying it does have an effect?  So what's going on?

I have found that 47K is optimal with LOMCs, using my Atma-sphere MP1, of course. The sound seems a bit more open and extended, compared to using loads of 1000 ohms or 100 ohms.  (I have set my MP1 up so I can quickly switch among 47K, 1K, and 100R load resistances, which makes it easy to compare.)  However, even 100R does sound fine, just a bit more closed in.  LOMC cartridges I've tried:  Ortofon MC7500, Ortofon MC2000, Koetsu Urushi, ZYX UNIverse.

The 47K load is kind of an antithesis of "current-drive", for LOMCs.

That explains why I almost always like 47K since I have a herron. If I had a chance to try an mp1 I wouldn't turn it down. 

^^ Yes- loading of higher output cartridges is a different matter!

Keith Herron is a proponent of "infinite" loading of mc cartridges. Gauging by atmasphere’s excellent post above, one can conclude Herron pre’s are also stable designs. Loading of mm and mi cartridges is a different matter.

@atmasphere 

Yes, thank you. That sums it up very nicely.

If however, the preamp is properly designed and is stable with RFI, then the loading resistor will be found to have no effect.

Ralph...thank you!  I have always considered myself pretty much an expert on vinyl disk systems, but I never knew that.

Always appreciate continued education...

Many of the above posts are incorrect.

The reason why loading has an effect has nothing to do with the cartridge directly. It has to do with the stability of the preamp.

The inductance of the winding of the cartridge is in parallel with the capacitance of the tone arm cable. This forms a Radio Frequency tuned circuit (also known as a tank circuit). The tank circuit is set into oscillation by the energy produced by the cartridge. It often resonates at several MHz and thus produces RFI (Radio Frequency Interference). Some preamps don't like that and don't sound right as a result.

The loading resistor detunes the tank circuit enough that it will no longer resonate. Then the preamp sounds fine.

If however, the preamp is properly designed and is stable with RFI, then the loading resistor will be found to have no effect.

IOW, if you need the loading resistor to make your cartridge sound right, it points to a stability problem in the preamp.

You can find this topic discussed elsewhere on this site and others. Jonathan Carr of Lyra and Jim Hagerman have discussed it at length as well as myself. Jim has a good article online:
http://www.hagtech.com/loading.html

-which goes into the math of it.

Our preamps are stable so no loading is needed. We provide a loading strip, but it is mostly for high output MM cartridges where loading is critical and affects the cartridge directly at audio frequencies.

One additional point- when loading the cartridge, you are making it do work. This stiffens up the cantilever, changing its tracking characteristic- it will be less compliant; that's not a good thing. You are better off with a stable phono preamp.

The "rule of thumb" is 10X the mc cartridge's internal impedance: Denon 103 impedance is 30 ohms, so 30 X 10 = 300 ohms for best (flattest) response.

To add to which it’s not just the cartridge and phono stage but also how the downstream pre deals with HF resonances. Some setups actually like the extra boost you get from a high loading while others are insensitive so you have to try it and see

Generally, if you're loading at X ohms and its sounds a bit dull/lifeless/bass heavy that way, try higher loading to get it to even out a bit. Alternatively, if you're loading at Y ohms and its sounds a bit too sparkly/tinny/HF heavy, then try lower loading. to get it to even out a bit.

That's correct.  Most cartridge loading pertaining to sonics will be very subtle.  The more resolving the system, the more you will hear it, but it will not change the overall sound aspect of the cartridge.

There are some that prefer loading a MC cart at 47K ohms, just like a MM cart.  I have owned a few MC carts that do indeed sound better up that high.

The end game is:  do whatever sounds the best to you.  Again, you can NOT hurt anything doing this.

Generally, if you're loading at X ohms and its sounds a bit dull/lifeless/bass heavy that way, try higher loading to get it to even out a bit.  Alternatively, if you're loading at Y ohms and its sounds a bit too sparkly/tinny/HF heavy, then try lower loading. to get it to even out a bit.

That's a preferable option =)

But just to fill my understanding of what is happening here - why match the recommended load if you have the ability and if you don't, what if anything is missing?

Negligable or... important?

No.  I'd leave it as is and see how it sounds.  Absolutely will not hurt anything.

This is great advice.

The cart is a Hana EL which has a manufacturer suggested load impedance of >400ohm. My MCP-1 would be giving it 110 ohm.

Negligable or... important?

What would this actually do?

Only reason I’m fussing is because buying and returning carts is not as easy as say a cable or other such things.

Outside of doing harm to the components, would there be any detrimental effect on the sound if I were to go outside of the manufacturers recommended specs?

No.  Just as analogluvr stated above, sometimes you just need to try it and listen.

Also, the load difference between 100 and 400 ohms is pretty small and you might not even hear a difference.  Depends on the cart and all the associated gear.

I always try to get close to the recommended load, but you never know.

I have owned the same exact unit you have and many, many more that you can replace the resistors in.  You can drive yourself crazy, if you get to concerned about it.

 In my experience  Often times the best sound is not anywhere's near the manufactures recommended load.  I have a herron phono stage and have preferred almost all cartridges on it with no additional low just their "infinite loading"
 These are cartridges that are calling for 200 ohm load in some cases that I am running at almost 47K 
no hard and fast rules just experiment

Thank you.

Outside of doing harm to the components, would there be any detrimental effect on the sound if I were to go outside of the manufacturers recommended specs?

This an Audio Research MCP-1 head amp that I am thinking about modifying.

http://www.audioresearch.com/ContentsFiles/MCP1_Manual_Schem.pdf

See page 3.

In theory I should be able to change the resistors to alter the load but I am worried that going beyond the recommended value would harm the pre amp/head amp.

I've never heard of this kind of change ever harming a preamp or head amp.  All you are doing is changing the value of the resistor.  All associated electronic parts in this chain should have more than enough capacity.