Cartridge loading

@antinn

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.

Indeed it's more complicated than just a mass on a spring as there comes into play the vinyl resonance (I admit I never thought about that).
But getting a mechanical resonance radiate into RF range I think is not easy. Ultrasonic yes, but RF we are talking about some 40-50kHz at least.

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.

Again: MC and MM cartridges work by the electromagnetic induction. What they generate is voltage. What I mean is if you play a cartridge unconnected what you will measure on its pins is a voltage but no current flow as the circuit is open. So cart is a voltage generator. Now, you in the electric circuit theory you can exchange current and voltage sources on the paper. You can redraw any circuit using voltage sources to current sources and vice versa. BTW the current source at teh Shures schemtics is wrongly drawn. Series resistance makes no sense with current sources. What I suspect the "current generator" thing mean is that LOMC's have a low internal resistance so for a given output voltage they will push more current. And this is of course a fact.

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 transie

Sorry, cannot understand what you mean here. Which capacitor? Can you point me to the relevant passage from your links?

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.

Dear @antinn  : There is " something " in your 4. point where you said:


"""  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. """

Medium compliance, this is what P.ledermann states about: 

"" medium to low compliance cartridges. Cartridges with a compliance between 22 and 10. Most cartridges are between 22 and 10 in compliance.  ""

I asked atmasphere that proposed the same ( almost. ) hyphotesis you posted in  point3. and 4. that he showed wich kind of electrical current must need it not to stiff the cantilever but to make the stylus tip mistrack groove modulations.
A medium compliance LOMC device say 16cu normally be a very good tracker even in very high velocities recorded in the LP grooves an even if are recorded at the most inner recording LP surface.

Now, I posted that for that medium compliance cartridge could has a mistracking problem that compliance has to goes really low, lower than 10cu and this is almost impossible that could happens with the stiffness of the cantilever.
Not science only common sense. I would like that you or other gentleman come here to shows those " numbers " that can cause the effect detailed in your 4. point. At the end it's the discussion main issue.

Ikeda designed non-cantilevered cartridges with extremely low compliance and obviouly with 1gr higher VTF that a medium compliance that normally comes with 1.5gr and up and I never read any report of such kind of problem you posted and that was what I asked to atmasphere.

Your hyphotesis probably can't be proved it can happens .

In the other side, no single audiophile in no single audio forum sites over the world never reported that phenomenon.

Seems to me that's more easy that the mistracking happens with a bad mistmatch between cartridge and the tonearm about resonance frequency in between that by the loading resistor combination with the cartridge/phonostage. Only an amateur opinion.

Regards and enjoy the MUSIC NOT DISTORTIONS,
R.

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. 😁