Cartridge impedance loading question


Hi folks. I have a Shelter 501 Mk 11 cartridge going into a Lehmann Black Cube phono pre. The Shelter's impedance is 12 ohms. The recommended load impedance in the Shelter specs is ambiguous…

Other than a user retrofittable option the Lehmann moving coil options are 80, 100, 470 & 47k ohms. What would you be using?

Thanks!
houseofhits

Showing 10 responses by lewm

Apropos of Atma's last two posts, last night I auditioned for the first time a newly acquired Ortofon MC2000 cartridge, one of the lowest of the "LO" MCs ever made. The MC2000 is said to have an internal resistance of 3 ohms, so a 100R load would seem to be quite appropriate. However, I inadvertently loaded it at 47K, as I began my listening session. This is using the phono section of Atma-sphere's own MP1 full function preamplifier. My MP1 has more than ample gain to accept the output of the MC2000 directly. In any case, I was blown away by my initial results. The MC2000 is one great cartridge, certainly one of the best sounding LOMCs I ever have heard in my system. After about 30 minutes of bliss, I noticed that I was running it at 47K, instead of 100R, which would have been my first choice. So I switched it over to 100R. With that load, it's still very good, but I think the sound lost some magic. The bass response was a little sloppy at 47K compared to 100R, but every other facet of reproduction was at least a little if not a lot superior at 47K. Pending further evaluation, I am a convert to 47K for LOMC, or certainly for the MC2000. I may try 1000R just to see if that tames the bass a bit, compared to 47K.
Don, I did not (yet) say I prefer 47K. I did say I tried it by serendipitous accident and was surprised at how good it sounded with the MC2000, with the one exception that bass was a bit flabby. When I then switched to the gospel 100R load, I don't believe it sounded as open, free, undamped, dynamic, etc. Whatever adjective you choose, I thought the 47K load made the music sound more like real live music sounds. This was essentially on one Ella Fitzgerald original Verve album, the Berlin Songbook. Obviously, I need several hours more of listening to a wider variety of LPs before I would draw any conclusions. On the other hand, I am very familiar with this album on several different systems in my home.

Most people need an SUT with the MC2000, due to its very low output. If you are using an SUT, then the choice of a net 47K load is not really there for you. Let's say the SUT has 1:10 gain; you'd need a 4.7M load resistor on the secondaries in order to make the cartridge see 47K. Thus I don't wonder that most folks are loading down the MC2000 to around 100R, which in fact ought to be just fine, in theory, based on its 3-ohm internal resistance.
Don, The phono cables are the OEM cables supplied with the Kenwood L07D and L07J tonearm. These are very low in capacitance Litz type. I re-terminated them with male XLRs, for use with the Atma MP1.
Atmasphere is of course correct re the ease with which the load R can be changed on the MP1. I, however, never happy unless I am messing around, have installed a 4-pole, DT switch on the rear panel, such that I can choose among 3 load resistances without having to gain access to the rear of the preamplifier to change resistors, as is needed with the OEM set-up. With my switch in neutral position, the load is the basic 47K. With the switch in either of the other two (up or down) positions, the load is 100R or 1000R, respectively. Of course, both those values are in parallel with 47K, so the actual R is slightly lower than either 100R or 1000R. Should I feel the need, it is no problem to modify this arrangement. Truthfully, I am not at all sure that the flabby extreme low bass response I hear with the 47K load is per se due to effects of that load. It could be a tonearm/cartridge resonance thing. Anyway, it's really not objectionable compared to the other benefits.
Thanks, Fleib. Which is why I next intend to try the third alternative readily available to me, the way I have set up my MP1… 1000R, in hopes that it will provide the best tonal balance. But 47K is soooo good!

Of course, now I want to re-visit all my other LOMC cartridges to see what if anything I've been missing, to include Koetsu Urushi and Ortofon MC7500. Ironically, I purchased the MC7500 from Raul early on in the course of his MM thread. Then Raul always said his fave LOMC was the MC2000.
John, Please see my post above and Atmasphere's post above that. The numbers say that what you say is happening in the audible band is happening at way way higher frequencies than that. Can you offer the math? Aside from that argument, if you listened to an MC cartridge loaded at 47K, and if it sounded better in most ways at 47K than it did at some significantly lower value (higher load), would you then conclude that you had to change the load resistor to conform better to the theory, or would you say f*** it and just enjoy the music?

Then too, we have the arguments from Jonathan Carr, Allen Wright, and Ralph Karsten, not to mention other authorities we do not know about, all to the contrary of your position. I concede that all of those guys, as well as you, know more about the physics of the situation than I do, but there is an argument opposite yours, apparently.

These analogies between cartridge loading and automobile technology have their limitations.
And a cool cat, too.
Interesting: The URL offered by Atmasphere gives access to calculators for both RC and RL type filters. Using the RC calculator, I cranked in 150pF as an approximation of capacitance of my tonearm wire plus that of the phono input stage (which is a cascode and thus not sensitive to Miller capacitance, anyway). The equation itself tells you right away that fc is inversely related to both R and C; thus it is no surprise that when R = 100 ohms, fc is >10,000,000Hz. When R = 47K, fc comes down to ~22,000Hz. So if you look at it as an RC circuit, 47K would not make for a bright sound, compared to 100R. I then cranked the same values into the RL formula, were fc is directly proportional to R. I used 50 microHenries as an approximation of the inductance of the MC2000 (a typical value for a LOMC cartridge). Not surprisingly, in this case, when R = 47K, fc is much higher than when R = 100 ohms, but even with 100 ohms, fc is >300,000Hz. So again, 47K is not going to make for a brighter sound that we could possibly hear. In the actual situation, fc is a function of R, L, and C. Comments of Atma and Fleib, or anyone else, appreciated.
Pkoegz, When you mess around with very low output cartridges, there are many sources of noise besides RFI. If you hear noise, a careful investigation is in order to try to reduce it or eliminate it, but in some cases, especially with an all-tube phono stage, you may just have to live with a faint background hiss. I find this not to be annoying, since it is really only apparent when the stylus is up off the LP or during silent passages between cuts on an LP. In the situation you describe, I would advise leave well enough alone. There is no reason at all to fuss with the cartridge loading, and moreover, the loading will have only an incidental effect if any on "noise".
John, I won't make a "religion" out of it, if you won't say I was making a religion out of it. The hostility in your response is inappropriate. I only relayed my preliminary and to me surprising observations; I did not say anywhere that I had found a new God or even that everyone in the world should use 47K as an MC load. A priori, I thought the same as you, and I probably don't even disagree with you now. I thought it was an interesting topic for discussion and that this thread was proper for discussing it.