Help with cartridge loading. . .


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.

David Meriwether
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.
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.
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?

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! :-)
In theory, I agree with both Zaikesman and Pbb! :)

Start with the manufacturer's recommended setting and listen long enough to get a good understanding of how it sounds. Then experiment, listening critically to decide if the differences you hear are actually improvements. It's easy to get fooled into thinking something is better just because it's different. Having a second listener to give independent feedback reduces errors and is more fun.

Zaikesman's protocol is much better than the step-by-step chinese water torture method in Meriweth's owner's manual. Make a big move down from the starting point and get a handle on the sound there. Then make a big move up. This will help you hear and understand the differences quickly and easily. Make big enough moves so that you surround the sweet spot. Homing in on your one preferred setting can be done with more confidence if you've established your upper and lower tolerance limits first.
Pbb: cartridge loading has WAY more going on than just tonal balance. One of the most obvious changes in cartridge performance when varying terminating impedances are those of transient response and noise characteristics. While it is true that tonal balance can be altered to suit one's personal preferences, careful attention paid while experimenting will typically show that a cartridge will have a "sweet spot" where it works best at. This "best" is typically a compromise between tonal balance, transient response and noise floor. In my experience, most cartridges do NOT work best where the manufacturer recommends they be adjusted for. I don't know if this is because of production tolerances differing from unit to unit or if they had specific design objectives ( specific tonal / noise / transient characteristics ) that they thought were more important than how the cartridge performed on the whole.

Moncrieff touched on this in IAR a long time ago and gave some very specific recommendations with plenty of graphs to interpret. Even he comments that samples from the same batch of cartridges sent him by the manufacturer typically had measurable variances in them. In some instances, he even comments that three cartridges sent him measured much quite different from one another, so he typically gave the manufacturer the benefit of doubt and posted the test results and his observations for the "best of the bunch".

Like anything else, there is a certain amount of "science" involved in getting the best performance out of a component or system. One can strive to obtain that OR simply go for something that they think sounds "good" to their ears. Hopefully, the best performance and what sounds "good" to that person are one and the same : ) Sean
I don't know, but it was refreshing to read the manual (if you can call it that) that comes with the Rega P9. It seems the designer takes a simpler view of things as they pertain to playing a black disc. I guess everybody is right! My feelings are that unit to unit variability obviously exists, but is probably over hyped. I guess I just don't have that tweaker fibre! I like the notion that vinyl records don't require cleaning since the stylus will simply shove away the dirt in its path. I will soon see how much shovelling of dirt the P9 can actually accomplish. As for me, I will set it to whatever the cart manufacturer recommends and pray for a mild winter.
And, when you have driven yourself half-crazy diddling with the load resistance, you can go the rest of the way to fully crazy by playing with capacitance.

My old Tandberg 3008 preamp has three resistance settings (100K, 47K, and 33K) and three capacitance settings (20, 120, 350 pF). Don't forget the turntable interconnect capacitance.

What with this pickup loading issue and all the arm setup angles and forces, it's enough to drive you digital!
Sean, good post. According to my in-house scientist, raising the electrical impedance to a cartridge not only requires the cantilever to move more forcefully to generate a signal, it also makes the cartridge more resistant to such movement. Almost like you had the ability to stiffen the suspension. Reducing impedance has the opposite effect of course. Clearly this will effect transient response as well as tracking accuracy at different frequencies. Next time I have a vacation week to spare I'll look up that article by Moncrieff. He's good, but this whole forum combined couldn't outwrite him. :)

Pbb, near the end of an unwashed record the other day I noticed my cantilever had a big pile of fluff on top. Watching more closely, I saw the stylus shovelling stuff out of the groove at a prodigious rate. Most of it ended up on top of the cantilever somehow. When the pile got big enough some of it would actually topple off, only to be replaced by more junk being dug out by the stylus. Who needs TV? I can watch this for hours!

Happily for your "damn the washing, full speed ahead" philosopy, I couldn't hear any degradation of sound, even after I knew the grooves were full of junk. (My old cartridge would have sounded very scratchy in such circumstances, so YMMV. I'm sure stylus geometry controls how well it deals with dirt.)

Of course playing dirty vinyl will shorten the life of both stylus and record. That's just common sense. In my case, while I can apparently play through mounds of loose fluff, the slightest layer of anything is quite audible (mold release agents, inadequate rinse, smog from NJ, whatever). So I wash. That's also the only way to remove anything so stuck in the groove that the stylus won't dislodge it. That stuff causes those annoying pops and clicks, and can do real damage to a stylus.

OTOH, maybe you really should just enjoy the new table. The rest of us are pretty wacko anyway, as you well know!
Doug, I believe the loading resistance value vs. damping question works in reverse fashion to the way you seem to have described it, i.e., the lower the terminating resistance presented to a MC cart, the more damped it's resonance becomes.
If someone prefers to hunt around for their preferred impedance, I have no strong objection. Just don't go below your cartridge's internal impedance. IME some cartridges (eg OC9) are very sensitive to impedance loading. Some (eg Lydian Beta) are not very sensitive to loading.

A lower load impedance loads up the cartridge with higher current, making it harder for the cantilever to move. So the manufacturers spec may also take this into account, to provide optimum damping.

I always use the manufacturer's recommended spec for MC loading. I set VTF and antiskate using the manufacturer's spec and a test record, because I find that minimizing the number of variables allows me to concentrate on finding an ideal VTA. If everything's changing, it gets very confusing, and you can get way off base. This is compounded by the fact that impedance loading and VTA have very similar effects on the sound.

Just a few thoughts on the posts above:
MC cartridges react very little to capacitance. Less is best, because capacitance causes phase shift. MM's require the manufacturer's exact specified capacitance to provide proper frequency response.

Transformers and preamps sometimes carry different impedance specs (eg OC9 says 20R for tx, 100R for a gain stage) because a transformer works optimally with current, while an amplifier prefers voltage. Current is maximized at a point slightly above the cartridge's internal impedance, and that will be the specified load for a transformer. The impedance for a gain stage is spec'ed for a reasonable voltage and current, but maximum efficiency.

Dan Bonhomme
Dan: Using a terminating impedance that is very near or lower than that of the cartridge itself will "load down" the cartridge. This typically results in muddy bass and severe high frequency sag. If one has a cartridge that has noticeable high frequency rise and very light bass, this can be put to use to some extent. Obviously, it is a matter of juggling the variables to arrive at something that you think is enjoyable and works well.

El: I agree that vinyl can be as simple or complex as you want to make it. Then again, it is not called "analog" for nothing. Some think you have to be "anal" to enjoy vinyl while others think it is "the shit" ( aka "log" ) compared to what other formats have to offer. Sorry for the bad pun, but i just hadta do it. If this type of stuff upsets some of you, send an audiophile woman over my way to "reprimand me" for "being bad" : )

Once you get things set up correctly though, it is relatively hassle free other than performing basic maintenance on the records and the stylus. That is, so long as you have good quality gear and your house isn't built over a fault line and gets shaken on a regular basis. I do have to admit that having test equipment and knowing how to use it can make things both simpler and "more accurate" rather than just twiddling, listening and guessing. Just having a scope, reference material and doing some experimentation can teach one GOBS in a very short period of time.

Doug: Since the phono cartridge is basically an "electrical generator" that interprets analogue data and spits out its' interpretation, it is sensitive to both the material that is fed into it AND the demands placed upon it by the load. Changing any of these variables ( quality and cleanliness of data presented to it, tracking angle, sidewall thrust, ability to transfer both electrical and mechanical energy, etc... ) may offer very different presentations.

As far as Moncrieff goes and phono cartridges, IAR Journal 5 ( the big thick one, NOT the "flyer sized" Hotline 5 ) covers quite a bit of info about phono cartridges. Most of it covers older products ( obviously ), but much of the knowledge learned then still applies today to much newer products. Sean
Zaikesman, thanks for the dope slap. My own ears tell me that I wrote it backwards.

Dan, thanks for the clear explanation of loading for tranny vs. phono stage. Brilliantly simple and helpful. Even an english major should understand that a tranny needs maximum current input while a phono stage needs maximum voltage input. The cart needs to be loaded to provide whichever is appropriate. TGIF!

Sean, you stated clearly what I was fumbling toward. A cartridge mediates between kinetic and electrical energy. Changing either side affects the result.

Can I go home now?
To all who responded to my question, thanks.

David Meriwether