2. analog
  3. 1065076526

Help with cartridge loading. . .

Hello,

I recently purchased a Pass X-Ono phono pre-amp, and both to my joy and horror I learned at once that there are over 500 different possible resistances I can choose to load my low output MC cartridge with. The manual gives the very helpful: "start with 100 ohms, then move up one setting; if it sounds better, then move up two. . .", which means of course I will be obsessing around in a circle forever.

Are there any rules of thumb that might help me zero in on an optimal loading more quickly? Better, is there a theory behind the settings, such that I could calculate the load given the output of the cartridge, etc.?

My analog front end: Orbe SE/SME IV/Ortofon MC3000.II. Any help would be much appreciated. Sad to say, I am a "fixed price" kind of guy.

Regards,
David Meriwether
meriweth
twl
3,251 posts
 
This is a cartridge with a very low internal impedance, and the specs recommend a load of greater than 10 ohms. This means that you'll probably be using the lowest setting on your Pass phono stage, whatever that lowest setting is. Don't go below 10 ohms, if there is such a setting. If 100 ohms is the lowest, then use that. Anything higher than that, and you'll be putting a "zing" into the high end.

Generally, the "rule of thumb" for MC cartridge loading, is to start at a load that is twice the internal cartridge impedance. In this case, the MC3000 II has an internal impedance of 5 ohms. The specs recommend greater than 10 ohms load, which is the correct starting point. Some may like it a little higher. I personally would use about 20 ohms on that cartridge, but if your phono stage goes only go as low as 100, that will do fine.
dougdeacon
3,338 posts
 
Hi Tom,

My Shelter 901 has a recommended load of 100 ohms, but the specs also seem to suggest a lower load if running through stepup transformers, which I am. It's very easy to change the load at the output of my transformers, and I'll experiment at some point, but I'm puzzled. Why would a cartridge want to see a different load depending on the presence or absence of a tranny. I can't get my head around that one and John Chapman couldn't either. Any ideas?

TIA,
Doug
twl
3,251 posts
 
Hi Doug, I was going to mention the transformer loading thing, but I didn't want to confuse him, since he's not using one.

Since you ask, and I'm not an electronics engineer, I'll offer my opinion as to why the transformer loading is less than the direct-input loading.

I think that the transformer presents a different set of characteristics to the cartridge, than the phono stage does. The transformer has a reflected impedance which is not only determined by the loading resistor, but also by the windings themselves, and the turns-ratio corresponding to the amount of gain in the step-up of the transformer secondary, and also the load that is connected to the secondary(usually 47k ohm). Thus, I conclude(whether incorrectly or correctly) that the actual loading(that the cartridge "sees") is not different, but the loading resistor that you select(to achieve that load) is different, due to the other factors that are present in the transformer's impedance characteristics. So you wind up with a similar load, but use a lower value resistor to do it.

That's my best shot at it.

BTW, I use the 40 ohm load on my Cotter Mk2 with my Shelter 501, and it kicks butt.
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