Cartridge loading

I am probably crazy for jumping into this conversation, but boldly going in; there is a lot conversation with a lot of experience on this subject, but from a engineering perspective, actual analysis can be pretty light, and the accuracy of vendor data often a best guess.  

For the mechanical resonance issue, this article that you can download is a good detailed explanation:  "On The Mechanics of Tone Arms" Dick Pierce Professional Audio Development, Jan-05. But, it also begs the question - how does each vendor measure and report mechanical compliances.   Recently I was reviewing test data for some cartridges, and a noted vendor reported a cartridge compliance of 16, but when tested, it measured 23; that can be a big difference.  And, depending on your particular setup, the tonearm compliance can be different from the vendor data.  If, you are 9-10Hz calculated, then you have a pretty good margin for error.  But, if you are at the margins, maybe not; so a test record to verify is recommended.  Unfortunately, electrical can be a bit more complicated.

For the electrical resonance/loading issue, this article on TNT http://www.tnt-audio.com/sorgenti/load_the_magnets_e.html; does a closed loop electrical analysis, but then shows by testing that the actual measured results do not follow the simple electrical closed loop model.  However, this article "NEW FACTORS IN PHONOGRAPH PREAMPLIFIER DESIGN" TOMLINSON HOLMAN, 1975, clearly addresses multiple pre-amp design factors that can effect the overall cartridge-preamp performance; so the skill of the pre-amp designer and the pre-amp has a lot bearing.  Add to this, that the vendor reported cartridge data may not be correct.  When I was reviewing test data for some cartridges, a noted vendor reports a cartridge output voltage of 5.5mV, but it measured 10mV; that is a big difference.  

In summary, and somewhat amusingly, here we are in the 21st century, all full of metrics and big-data, and we are still trying to predict with accuracy how an over half-century technology will perform.  So, with the data we have, we take our best guess as to what will work.  But,  in the absence of actual integrated data - cartridge-tonearm-cable-preamp, which is surprisingly limited, we are still left just listening to the music; and making adjustments and decisions based on what sounds best.  An imperfect system that with patience can produce near perfect sound, one of those "freakin" miracles :).

All,

This artcle http://www.gammaelectronics.xyz/s_1987-8_cartridge-tweak.html, makes the following statement "The importance of the resistive load across the output of cartridges was reported by J. Peter Moncrieff in 1980.[2] He found that a lower shunt (parallel) resistance reduced distortion levels: he postulated that the reduction in distortion was due to electromechanical damping being applied to motion of the stylus assembly (though others were unable to replicate his findings to anything like the same degree)" which would support the premise that electrical loading can affect the mechanical function of the stylus.  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.

Atmasphere,

No arguments of the electrical-mechanical fundamentals, but the aspect is not well doucumented for cartridges, and therefore, the nay-sayer(s) will debate.  However, that being said, this document shows how the phono-preamp design can affect the performance. And, lets not even begin to discuss how Impedance is often incorrectly used for resistance, with Impedance = Resistance + Reactance and is frequency dependent, whereas resistance is fixed.
 http://www.pmillett.com/file_downloads/LR%20Phono%20Preamps.pdf

atmasphere,

The article I referenced was only to address the affect of inductors.  When you say, RFI, are you talking radio frequency interference, or in general, electro-magnetic interference (EMI)?  EMI encompasses conducted emissions (CE) , conducted susceptibility (CS), radiative emissions (RE), and radiative susceptibility (RS). My background includes testing equipment to EMI requirements, so I am just trying make sure we are on the same page when communicating.  However, Peter at Soundsmith addresses the concept of stylus jitter https://www.sound-smith.com/articles/fixed-coil-vs-moving-coil-why-make-jump-different-technology. 

I also have experience with vibration testing.  So when I read all this, my analogy is that stylus is tracking the record such that you want the transmissibility (essentially the ratio of the record grove to the stylus-cantilever movement) to be unity, that way the stylus-cantilever reads exactly the groove.  If the transmissibility drops below unity, then the stylus-cantilever-suspension is absorbing energy and there will be loss of data.  It may read the frequency correctly, but the signal output will be lower than normal, and this could be frequency dependent, so an oscilliscope trace may show some 'suck-out' at the affected frequencies.  The list of items that can cause transmissibility less than unity can be of mechanical origin (such as too much VTF) or electrical (such as circuit speed).

If the stylus-cantilever-suspension transmissibility is greater than unity, but not resonating then it will output more data than what is on the record, i.e. it may read the frequency, but the signal output may be high than normal, but again this may be frequency dependent.  So, an oscilliscope trace may show some peaking at the affected frequencies.  The list of items that can cause transmissibility greater than unity can be of mechanical origin (such as VTA) or electrical (such as cartridge loading and maybe an electrical circuit causing a weird impedance).

However, if the stylus-cantilever-suspension resonates, the transmissibility increases many times causing the stylus-cantilever assembly to move far greater than what is in the groove, thee output signal to increase proportionally, and depending on whether the stylus maintains groove contact, and depending on the pre-amp overload margin can lead to massive harmonic distortion (smearing of the output signal, i.e. conducted emissions) with distorted sound, and/or pops.  

Ergo, anything that effects the stylus-cantilever-suspension stiffness, be it of mechanical or electrical origins can affect its ability to properly read the groove.  And, since low, mid and high frequency information can simultaneously exist, there can be shall we say over 20,000 opportunities for this unravel.   Yes, its a mircale that this works, but as Corey Greenberg said many years ago, a 1000 years from now, good luck trying to find a CD player, but you could play a vinyl record with a pine needle.

All,
Re-reading my response above, I failed to address the actual question.  So, did some more research and came upon the site,  http://pspatialaudio.com/index_help.htm which has a wealth of historical data, with detailed info, lots of calculations, and this article  http://pspatialaudio.com/analogy.htm presents an interesting model of the equivalent circuit of the dynamic system of a phono cartridge.  While it does not clearly show that harmonic distortion can mimic unloading, the mechanical resonances are not so simple".  Depending on the design of electrical circuit, harmonic distortion can saturate capacitors and inductors thus shifting the electrical resonance frequencies, and if they coincide with the mechanical resonances, there should be no reason that the circuit in the presence of the high harmonic current behaves as if the cartridge is unloaded. 

Bydlo,

That article was modeling the mechanical resonances as an equivalent electrical circuit.  I was trying to show that the mechanical resonances were more complex than I originally thought, and if the cartridge goes into physical resonance (which is more likely at high frequency), then there will be a high harmonic distortion (EMI/RFI) produced.  Its my understanding that LOMC, are poor voltage generators, but good current generators which is why the new generation of LOMC preamps are current sensing.  If a capacitor saturates because of the high harmonic current, and there is no dampening resistor, the only thing that is left is the capacitor equivalent series resistance (ESR). If the circuit current suddenly increases, this will by the back emf, dampen the motion of the cartridge armature (stylus-cantilever-suspension), and may depending on where on the record this is occuring (i.e. radial velocity), cause miss tracking.  So long as the current was not outrageous and the capacitor is not damaged, and most will self-heal, once the current drops, the capacitor returns to function.  So the event can be very transient.  

bydlo,

First, the sequence of events is dependent on the cartridge and the pre-amp.  One of the premises of this entire thread has been the limits of 'some' pre-amps.

This article is an extension of the first Shure article I referenced, and it goes deeper into the cantilever stiffness, with the risk of mistracking at high velocity.   http://pspatialaudio.com/analogy.htm#cantilever.  This mechanically induced instability will lead to harmonic distortion.

From this article https://www.analogplanet.com/content/current-affair-intriguing-mr-labs-vera-20-mc-phono-preamplifier, the statement is made that LOMC  "Moving coil cartridges output very low voltages but relatively high current on the order of tens of micro-amperes".  Dynamic microphones that operate on the same principle, state current output. https://www.audio-technica.com/cms/site/b0d226992d31e25d/index.html/

Depending on the pre-amp, using this as an example, https://sound-au.com/project06.htm, if there is a line to line capacitor with no dampening resistor, and IF the capacitor saturates from the harmonic distortion, then the events should be setup for a high current to occur.  So, it may be that the mechanical instability begins the event, but the consequence is that a small mistracking event can cause harmonic distortion that because of the poor preamp design leads to an even larger mistracking event.

bydlo,

After further thought, here is my best hypothesis, and it really is just a 'perfect storm', for all the variables to come together.

1.  Many LOMC cartridges have very wide bandwidth, out to 47kHz and maybe even beyond.  So, the harmonic distortion that starts the event may begin at a very high inaudible frequency.  

2.  For capacitors used in audio such as Elna, Nichion, etc, a 25V, 4.7uF capacitor may only be rated 25mA, but this rating is at 120Hz.  There is a Coefficient of Frequency for Rated Ripple Current that for higher frequencies, you can add 20% or more to the rating.   But, the capacitance can drop with higher frequency, so this all adds uncertainty.  And. as I addressed in my very first post, per this very old article www.aes.org/tmpFiles/elib/20200131/2623.pdf; the preamp design has a lot of influence on the entire circuit.

3.  If the event first starts at very high inaudible frequencies, and the preamp circuit saturates, overloads, oscillates or otherwise becomes unstable, and if a current surge occurs, then the LOMC cartridge may now try to function as a moving coil instrument https://www.yourelectricalguide.com/2017/01/permanent-magnet-moving-coil.html; "When the moving coil instrument is connected in the circuit, the operating current flows through the coil which is mounted on the spindle. Since the coil is placed in the strong field of permanent magnets, a force is exerted on the current carrying conductors of the coil which produces deflecting torque.".  

4.  If item 3 above occurs, the cantilever will stiffen.  The stiffening of the cantilever assembly will cause the cartridge effective compliance to decrease.  If the LOMC cartridge is a medium compliance with low VTF, then it stands to reason that the cartridge will likely miss-track at audible frequencies.  If the LOMC cartridge is a very low compliance (i.e. Denon DT103R) with high VTF, it may not miss-track.  However, when the cartridge cantilever assembly stiffens and the effective compliance decreases, the cartridge-arm resonant frequency will increase, and this 'may' depending on the cartridge-arm combination increase the cartridge-arm mechanical resonant frequency into the audible range.

rauliruegas,

As I said it was a hypothesis, and as a hypothesis, there is no empircal data to support, but for me only deductive reasoning from a multitude of sources that I have addressed in a number of posts. But, your statement that the compliance cannot stiffen beyound some point because of the stiffness of the cantilever without any data does not make sense either.  The compliance is more than than the cantilever stiffness; it includes the suspension, and this is addressed in many of the articles here http://pspatialaudio.com/index_help.htm.   If current in the circuit from the harmonic distortion exists, it can by the back-emf torque the coil to 'effectively' stiffen the the cantilever assembly causing the cartridge compliance to decrease, the stiffer the cantilever, the worse it should be.  As far as an Ikeda non-cantilever cartridge which I have no knowledge of and found no data on the web, but assume is similar to a London-Decca design, the unique design with very low compliance may be immune to this event.  As I implied with the Denon example, for a very low compliance cartridge, the design is so stiff to begin with that there is not much margin/room left to futher stiffen. But, there are medium compliance cartridges with very stiff boron cantilevers. If a medium compliance 22 cartridge with only 1.4-gm VTF was to decrease to 10, but, if at 10 requires 1.8-gm VTF, that is a difference of almost 30%, and in my mind it stands to reason it could mistrack.  It becomes very dependent on the individual cartridge design. I never said, it was for it was for every cartridge. But, the cartridge and tonearm form a mechanical resonance, which is very different from the loading resistor that forms an electrical resonance, but that does not mean that one cannot manifest itself as the other, especially for LOMC.   There is an old saying, We do not what we do not know.   Otherwise, we agree to disagree.  In the meantime, I use only Soundmith moving iron cartridges (Paua & Carmen on two different arms). And, to be honest, after all my reading on LOMC, I highly doubt I will ever dip my toe into those churning waters. 😁

Dear rauliruegas,

The amount of current is just one of the many questions left to answer.  And, I agree with your other statements.  A basic challenge with vinyl is the difficulty in measuring it, and this is very consistent with electro-mechanical systems.  In oil lubricated turbo machinery there is a bearing known as the Kinsbury Tilt thrust bearing that is widely used, and has been for over 50 yrs.  But, Professors have been  studying it for over 50 yrs trying to unlock all of its secrets.  However, my last turbo machinery project was having nothing to do with that; we used magnetic bearings that could generate almost 1 MB of data every minute; we had no trouble measuring everything.

But to me, and I suspect you by your last sentence,  one of endearing qualities of vinyl is the challenge, which pushes it into a different category other than just listening.  It is not plug and play.   Vinyl takes some skill (and tools) and perseverance (devil often in the details) to get it to sound good and that can be very rewarding/satisfying.  However the 'vinyl-challenge' obviously can frustrate some (if not many 😁).  And, there are the unknowns which stimulates the never ending conversation (frustrating some, engaging others, all good as long as we stay civil), and a lot is still an art-form (of course that defies the IOT - Internet of Things🤔).  This site is doing some measurements of cartridges though-
  https://www.lowbeats.de/tonabnehmer-messungen-bei-lowbeats-tests/.  Its in German, but Android devices will translate.  It is surprising that Stereophile has not taken a lead in this area, but JA who for sure leans to digital, is probably less than enthusiastic.  

I am not a luddite as you can see from the 1st paragraph above, but, the true irony may be that this 2015 report "ARSC Guide to Audio Preservation", commissioned by the Library of Congress states:  "Vinyl discs are the most stable physical sound recording format developed to date; they can last 100 years in a controlled environment.", and the Voyager probe carries a gold record that will last for centuries and beyound with simple details on how to play back.  

Best Regards, 
N.