Cartridge loading

Dear @lewm : """ is not perfectly damped... "" almost nothing in audio is perfect. Where do you read what you posted not only that but about that sporious motion that stiffens the cantilever?

Everything in a cartridge quality performance is important in its design and building quality but the cartridge suspension is CRITICAL and you can ask Ortofon about and you will know what they have to say in that issue.

The problem is that for years atmasphere posted here and in other net sites the same with out shows any single foundation ( numbers/charts, white papers, etc. ) that can attest that the cartridge lost high frequency tracking abilities ( " it can also affect the compliance of the cantilever of the cartridge. " """ will limit the ability of the cartridge to trace higher frequencies .."""   These are statements he posted.) and till we have true facts about by his side what he said on the subject is just false and with no true sense of that lost high frequency tracking ability by the cartridge. Maybe makes sense to you, not to me.

R.

"[Lowering the R_load]... of course will limit the ability of the cartridge to trace higher frequencies. "
I fail to see it either, unless the below reasoning is wrong. I think of a simple cart model as a damped harmonic oscillator, excited by an external force of freq. f (the movement of the diamond induced by tracing the groove with a tone of freq. f). Loading the coils creates a current flow in them, which results in a damping force, opposing the movement of the coils in the magnetic field of the pole pieces. This is just a well known electromagnetic breaking force, proportional to the velocity of the movement (in turn proportional to the frequency) and inversely proportional to the R. It is just plainly ~f/R, like any other linear damping force. It adds to the total damping force, acting on the cantilever (the rest comes e.g. for the mechanical damping in the suspension). Lowering the R, just lowers the output across the entire spectrum but the nature of the output (its functional dependence on f) does not change at all. No additional damping of higher frequencies beyond the normal behavior of a damped oscillator. Just the damping coefficient increases.

I’m much more intrigued by @intactaudio dave’s observations of lowering the IMD. Have you tried plotting the IMD vs. R dependence?
Cheers

i have a Kiseki Purpleheart mounted on an SME 312S feeding a Pass XP 17. I don’t know the capacitance of the included tonearm cable, though I may try to find that out. I’m pretty sure that when I did the tonearm/cartridge resonance calculation, the value was in range, something like 10cu. I had been playing around with all manner of load settings, mainly in the range of 100 to 452 ohms, and had settled for the most part on 452, though I sensed something was off, not a lack of high frequencies per se but a sense of harshness. When I increased the loading value to 1000 ohms, the sound became smoother and had better spectral balance. FWIW, 1000 ohms is in the 800 to 1000 ohm range recommended adamantly in Bob Levi’s Purpleheart review, as opposed to the Kiseki recommenced 400 ohms. His equipment is different than mine however. Still, it sounds like stereo5 made the same conclusion as me with a totally different setup. I don’t want to generalize here, but it’s tempting to think that these lower load recommendations are not optimal in many situations.

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

I for one would love to see documentation of the ability of a cartridge to generate a 1MHz signal to excite this resonance.

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.

Dear @atmasphere and friends: "" and as I mentioned earlier, when you load the cartridge it stiffens the cantilever. ..""

"" It will be stiffer, less compliant. """

both statement from you failed for something very simple: no explanation about, no explanation why that: less/limited ability to trace high frequencies by the cartridge.

I would have thought that the reason for the reduced compliance (stiffer cantilever) would have been obvious! A cartridge is a simple magnetic motor/generator, just like a dynamic microphone or loudspeaker, in that a coil has an audio signal transduced into it by a magnetic means- either by moving the magnet with relation to the coil (MM) or moving the coil in relation to the magnet (LOMC). It is easy to demonstrate this principle with a woofer of a loudspeaker with the grill removed (dynamic speakers operate on the moving coil principle of course). With nothing connected to the loudspeaker, simply depress the woofer cone and see how easy it is to move. Now short out the speaker terminals and do it again. You’ll find that the woofer has become much stiffer! This is exactly what happens with a cartridge as the modus operandi is identical.


As I mentioned earlier, if this were not to happen, a new branch of physics would thus come into existence :) because it would violate Kirchhoff’s Laws. The operating principle is similar to how motors and generators work so you can study them as well. In short, its impossible for a cartridge to drive a lower resistance load and *not* have a stiffer cantilever!

This is just a well known electromagnetic breaking force, proportional to the velocity of the movement (in turn proportional to the frequency) and inversely proportional to the R. It is just plainly ~f/R, like any other linear damping force. It adds to the total damping force, acting on the cantilever (the rest comes e.g. for the mechanical damping in the suspension). Lowering the R, just lowers the output across the entire spectrum but the nature of the output (its functional dependence on f) does not change at all. No additional damping of higher frequencies beyond the normal behavior of a damped oscillator. Just the damping coefficient increases.

I think you might be over-thinking this.

You got most of this right, right up until your conclusion. Think about a generator, one with no load and one with a load, which will be harder to turn? By your logic above (if I’m reading it right) somehow the loaded generator is easier to turn, which certainly isn’t going to happen. I think where you’re getting into trouble is the idea that the output goes down with reduced R load, which it does. The problem is: a certain amount of energy is used to make the stylus move. Where does that energy go? It is of course applied to the input load of the preamp in the form of a voltage. Now if you decrease the voltage by reducing the R load value, where is that same energy going? The Law of energy conservation says it has to go somewhere! It does not just ’vanish’. It is dissipated in the load and also by the cartridge coils themselves, both in the form of heat. But I think you will find if you do some measurements that the output does not go down as fast as it appears you are thinking. This is because the stock 47K load is easy to drive and the output of the cartridge will stay pretty constant until the load is decreased to some point below 10x the impedance of the cartridge; IOW probably less than 100 ohms.