Help with cartridge loading. . .

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

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.

Thanks, Tom. Maybe I can get a "butt-kicking" upgrade by swapping a pair of resistors, should take about 5 seconds per tranny.

Meriweth, sorry for threadjacking. Your question just inspired my (semi-related) one.

I think Doug that your question might be more related than you give yourself credit for, simply because (I suspect) Ortofon would normally intend that their LO MC be used with their own step-up tranny (not a necessity with the Pass phonostage). I would second Tom's advice in principle, but having said that would also add that auditioning at home is free except for your time, and that David shouldn't pass up the opportunity for a bit of 'ear-education' by going ahead and listening to the results with a small variety of loading options chosen at strategically placed intervals. As a rough suggestion, I would try the lowest setting, then double that, and double that, and so on for a few to several iterations, depending on how low the lowest possible setting is. Listen not only for natural frequency response (not constricted, not overhyped), but also for good tradeoffs of image focus vs. image size, bass definition and tautness vs. bass openness and weight, and unfettered dynamics vs. transient and decay cleanliness. The 'sweet spot' of the loading range that you find will not only have much to do with the electrical properties of your cartridge and phonostage, but also your total system and room response and set-up, not to mention personal preferences. Try it, it's fun! :-)

Again, the two ubiquitous schools of thought in present day audio rear their head. I would say that you should go with what the manufacturer of the cartridge suggests, which, I guess, tips my hand. From your question it certainly appears to me that you are of the aesthetics first credo. If my assumption is right, you will have to wait for like-minded people to reply to your question, but, in the final analysis, you will not be able to avoid experimentation. Think about it another way, if preamps still had tone controls, and if you had the type of tone controls providing various curves in the response, how many different settings do you think you could conjure up? How many would you, intuitively, reject out of hand? The situation is somewhat analogous. Don't freak yourself out with the theoretical possibilities. Good luck.