There is an interesting article in IAR #5 by Peter Moncrief titled "Audio Fallacies Exposed Low Impedance Loads for MC Cartridges" about loading and he proposes that loading down a cartridge helps it keep better contact with the grove.
Moncrief attacks the general held belief that 'loading a MC cartridge damps a HF ringing and the "dull sound" from too great of a load is simply an overdamped response' He then goes on to show swept frequency responses of MC cartridges under varying loads showing minimal change in the frequency response.
He then goes on to point out that loading down a cartridge has a sincere effect on the side bands created from 400hz + 4Khz intermod test track. He shows plots of different load situations and it can clearly be seen that the more the MC cartridge is loaded the more the side bands that are created are reduced. Being the Skeptic that I am I repeated his tests and confirmed his results.
dave |
I did repeat the experiment with a completely different setup and my results paralleled Moncrief's. I would expect different absolute results with different tonearm / cartridge combos. I did see a pattern of behavior that was consistent with both low and high compliance cartridges.
I do believe that the effect of the load is showing up as an adjustment of the compliance and would expect this to be a dynamic behavior.
dave |
I agree that the load effecting the compliance is a plausible explanation for part of what is happening with loading but when it comes to "work" and tracing high frequencies the water becomes a bit more muddled. It seems that moncrief pretty clearly illustrates and I have confirmed that loading a cartridge reduces the sidebands created from a 400hz + 4Khz test track. This suggests to me that the stylus must be tracing the groove better if a more accurate representation of the original is seen. Now you mention with respect to a cartridge doing more "work"
That of course will limit the ability of the cartridge to trace higher frequencies.
I think the above is in relation to the idea posed that a lightly loaded cartridge will trace high frequencies better than a heavily loaded one because it is doing less work. This seems at odds with the intermod findings WRT loading and I wouldn't be surprised if there is a point where a cartridge will become so loaded down that it does indeed mistrack high frequencies. What I am interested in is the underlying explanation why a cartridge doing more work will necessarily have this "limited ability to trace higher frequencies" dave |
Syntax, you mention cartridges sound purest into 47K and dull into larger loads and if your phono stage isn't up to it you are in trouble. Mocrief suggests (and then supports with data) that the "dull" sound reported from loading a cartridge is simply the removal of high frequency distortions mistakenly perceived as detail. He goes on to suggest that many accept added information not in the original to compensate for deficiencies elsewhere in the system. These are two very different takes on the same topic and currently Moncrief's viewpoint is somewhat more plausible to me. Marketing can replace knowledge [and does of course and when it is repeated
countless times, it becomes ---> A Fact :-)] I 100% agree with the above. Facts are objective, repeatable, and provable. Attaching facts to a purely subjective experience can only sullen their beauty. dave |
Mijostyn,
The Hagerman site gives loading examples for what appear to be a typical MM cartridge where the resonances being damped are just outside the audio band. This discussion has been about MC cartridges where the resonance in question is typically above 1 megahertz which is a very different situation. The typical MC cartridge has around 1/1000th the inductance of an MM so enter 0.005 into the mH field of the calculator to see what we are discussing.
I for one would love to see documentation of the ability of a cartridge to generate a 1MHz signal to excite this resonance.
dave |
I’m much more intrigued by @intactaudio dave’s observations of lowering the IMD. Have you tried plotting the IMD vs. R dependence? not yet. coming up with a concept for a test methodology to do this is not an easy task and then bringing that concept to fruition is equally as difficult. Collecting the information in a meaningful way is one thing and presenting it is an easy to understand fashion another. Moncrief shows the results fo both a JVC cart and an EMT and simply showing graphs give a quick visual result of the pattern but having a better understanding of that pattern would be nice. I'm thinking that the source tone is a 4K + 400hz signal and normalizing the 4K fundamental for various loads and plotting the following frequencies (7200, 7600, 8000, 8400, 8800) against load should be informative. dave |
Hey Ralph, this is where we got last time we had this discussion. Quite simply it does not need to! Audio energy can cause the excitation. A resonant circuit can be driven into excitation with a single pulse; it should be no surprise that on-going audio signals can do this as well.
I would like to see some documented proof of this or point me to a way to measure it. I have no doubt that an unstable phono will have problems with spurious HF info but I do not see the cartridge ever generating anything in the megahertz realm to excite this. I do not see anyone debating that a loaded MC cartridge will stiffen its suspension, what I think is up for debate here is that this stiffening of the suspension will lower the cartridges ability to accurately trace high frequency info. The 800 pound primate hiding in the corner here is the trend for some to insist that a cartridge is inherently a current generator and should feed a current amplifier for optimal performance. This necessitates the cartridge driving a near dead short which by your reasoning would have a sever impact on the HF tracking ability. dave |
Ok, so if by tracking problems at HF you mean attenuated HF then I agree. But this behavior applies to any damping, also purely mechanical, not only to electromagnetic. The first thing Moncrief does in his article is to do a frequency plot of the cartridge with the two different loads he did the IM sweeps of. This was to show that the frequency response did not appreciably change to rule out the "old wives' tale" of loading damping a rising response inherent to MC carts. |
Alas this article is not available online but if you go to the IAR website it states Issue #5 can be purchased. I got my copies off of Ebay when I was pointed to the topic. I said in proper design it is obviously possible to reach a neutral balance and this is what we all do adjusting the load I think most of us agree that adjusting the load of an MC cart does have some effect on the sound. It is the cause of what we are hearing is that is up for debate. As it stands now I think the quoted text above sums it up pretty nicely and I find it interesting that outside of Moncrief, historically I have yet to see mention of this. dave |
who is this "palmer" and can someone point me to the relevant posts of his regarding this subject?
dave |
To add to what I mentioned above, The big wrinkle that got me interested in all of this is the trend for current amplification that pops up every half a decade or so. The story goes something like this....
A MC cartridge is inherently a current generator and the best way to get the ultimate performance out of it is to treat it as such and feed it into a current amplifier.
By definition a true current amplifier would load a cartridge with a dead short which is about as far away from 47K as you can get. With all of the discussions of how loading a cartridge has negative effects, one has to wonder how these current stages could possibly work. There are many reports that they do indeed work, and work quite well. It wasn't until I came across Moncrief that a possible reconciliation of the opposing viewpoints was possible for me.
dave |
I think much of the issue here is confusing / lumping together the electrical and mechanical aspects of loading. Tracing high frequencies is a mechanical thing and while electrical loading will have an effect on this mechanical aspect, assuming that if follows the electrical model is flawed. Parallels can be drawn between the underdamped, critically damped and overdamped in both the mechanical and electrical realm but the net results are quite different. In the electrical realm you get variations in output level and in the mechanical realm you get mistracking which creates new information that is not on the original. Ultimately the choice of what load is best is a subjective one based on the best choice of compromise between often conflicting objective details. |
As I have mentioned many times, the input impedance cannot be zero. If it were, you would have no output at all because the signal would be connected directly to ground. While it is true that no voltage can develop across 0Ω that doesn’t mean that the current that is generated cannot be amplified and then converted back to voltage. While I agree that in reality 0Ω is an impossibility, I am also not convinced it is a good target to shoot for from anything other than an academic perspective. Like everything else in audio, the truth rarely lies at the extremes and lives in the subtleties of the middle. |
Hey Lew. It appears as if this guy has a good take on what is going on with the 0Ω http://phonoclone.com/diy-pho4.html I quickly simmed the circuit and it appears as if the input Z is frequency dependent and around 0.001Ω @ 10hz and increases by a factor of 10 for every decade which puts it at 1Ω @ 10khz and 10Ω @ 100khz. how you translate this into an easy to understand input impedance for the masses is not an easy task. Is 0Ω 100% accurate? no... but for the majority of the audio band it is close. Just try to explain a frequency dependent variable to a group used to values being ruler flat form 20-20K. In the end I do not think there is anything disingenuous with the claims but once taken out of the context of being an audio generalization for the masses it does become problematic. dave |
A MC cartridge is inherently a current generator I want to be clear that I was not stating this as my belief but to point out it is an argument made for using a current amplifier rather than a voltage amplifier. My personal take on it is that the coil generates what you tell it to. Leave it open it generates voltage, Load it down it generates current. dave |
I don't agree. Coil moving in a magnetic field can generate only one thing - voltage. This is the lesson of papa Faraday :) OK you win :-) Ralph... If I can ask you a question which might clear up a lot of things here.... IOW when the cartridge is loaded (damped) its ability to trace high frequencies is reduced because the cantilever will be stiffer. when you say "ability to trace" are you referring to the output generated by the cartridge or the physical ability for the stylus to remain in contact with the groove wall? dave |
Ralph, To be clear, a current amplifier does not significantly load the cartridge. The 'zero ohms' thing that you see talked about in reference to them refers to the virtual ground with which the cartridge plays a part. I built a spice simulation of the circuit in question and while the input Z was not 0Ω, it was low and followed the output V / R pattern that Lewm described. When I placed a 0.05mv 2Ω source it delivered 25µA of current into the phonoclone circuit. I am referring to the simple fact that a stiffer cantilever will be unable to trace higher frequencies- at some point, it won't be able to follow the groove wall impressed with higher frequencies.
I believe that if a cantilever is either too stiff or too compliant it will have issues tracking high frequencies. As for 47K being the optimal load, I see all kinds of manufacturers suggesting values other than 47K as the optimal load for their cartridges. dave |
Raoul,
Yes... I confirmed the results via measurement. I did not put forth any listening impressions.
To be clear the stage that Lew M is using is not a current amp in the true definition of the term. Its circa 20Ω input Z is multiples enough of his cartridge internal impedance that it acts as a traditional voltage amplification stage. |
Now, if someone can find International Audio Review 5, 1980 pp.31-159, the answer to the existental challenge of prove-it may be answered. Have a copy in hand.... which is why I took exception to the thought that loading a cartridge down must adversely effect the ability to trace high frequencies. I think the following text from IAR 5 sums it up pretty well Now, as the force against the groove wall lessens
momentarily, the stylus’ motion is no longer as damped
by the compliance (springiness) of the vinyl interacting
with the mechanical impedance of the stylus assembly.
The stylus assembly is, as John Curl has put it, more
on its own. And that’s when the additional damping
imposed on the stylus motion by the electromagneto-
motive effects of Lenz’ law and a low load resistor can
come into play. Stylus tip damping, from whatever
source, helps the stylus assembly to cope with groove
rattling problems (note that cantilever pivot damping
in the cartridge might not, especially at higher fre-
quencies). maybe accurately tracing high frequencies is the wrong term and loading can help prevent the creation of "non-source contained" high frequency information. dave |
