Moving Magnet Vs Moving Coil

[Guermantes]

Thanks @SIY My preamp is rated (in specs) as 120 pF for MM 47 kΩ input. I will need to measure the cable capacitance and see how much it adds.

 

[DonH56]

Typical cables are in the 20~30 pF/ft range if that helps. RG-6 is around 20 pF/ft while smaller cables may be a bit higher (thin phono cables closer to 30 pF/ft but also higher inductance so hard to predict). I used some high-impedance cable to create custom phono interconnects back in the day; still have them, someplace, but do not remember what they were. I remember the capacitance was around 10 pF/ft. They may have been 93-ohm which was (maybe still is) in use for some systems.

 

[SIY]

Thanks @SIY My preamp is rated (in specs) as 120 pF for MM 47 kΩ input. I will need to measure the cable capacitance and see how much it adds.

I never ever ever believe the manufacturer's rating- they are incorrect amazingly often. I always measure it with the circuit powered.

The best way to measure is with a scope, square wave, and large resistor (like 1M), since a lot of C meters put out voltage pulses that will overload the phono stage. Basically, you put the large resistor in series with the square wave generator output, connect the other end to the phono stage input, connect the scope (using a 10x probe!) across the phono stage input, then measure the risetime. You can then calculate C from T = RC.

 

[Pio2001]

Excessive, even moderate, Ant-Skate compensation damages carts, sonically and physically. AS is required, but it should always be set at minimum. Again, especially important during the break-in period, as the cart settles-in for life.

As the stylus pulls inwards, the AS mechanism pulls in the opposing direction, but not directly on the stylus, rather at the pivot, meaning the entire tonearm. That "compensation" (and it does not take much over a period of time) can easily offset cantilever / stylus alignment, especially with higher compliance models. It also offsets the internal generator, the magnets/coils no longer align optimally. Long term use of excessive AS skate, or even moderate AS, will often permanent offset the cantilever ... I've witnessed far too many carts/stylus with permanently offset cantilevers and excessive wear on only one side of the stylus, well before they hit 500hrs.

Hi Tbone,
This is a urban legend that I have already seen in french forums. The emphasized part is the mistake that started it all.
I've read the original article, and the idea that anti-skating puts a strain on the stylus comes from a wrong analysis of the forces applied on the stylus.

Here is how anti-skating really works. The diagrams are mine. I translate the text at the bottom.

Here is a drawing that represents a turntable viewed from above.

Arm, Record, Movement of the cartridge, Turntable.

In black, the record and the turntable. In blue, the arm and the cartridge. The arm is free to rotate along the direction shown by the arrows.
Let's zoom in in order to see the tip in the groove :

Groove, Tip, Freedom given to the tip by the arm's rotation, Running direction of the groove

As the record is spinning, the groove runs towards the bottom, beneath the tip. Meanwhile, the arm provides the tip with a degree of freedom that we can draw on the picture with the help of the previous diagram.
We can thus understand where the "skating" comes from : the tip, drawn towards the bottom of the diagram by the movement of the groove, is slightly crushed on the left hand side of the groove.

Let's list the forces applied on the tip in the horizontal plane, without anti-skating.

Force applied by the arm, Forces applied by the record, Forces applied on the tip without anti-skating.

The force applied by the arm is easy to find : since it can rotate freely, it can only apply a force directed towards its axis. The tip being stationary, it follows that the record applies on it a force that is equal in strength, and opposite in direction, here decomposed into two parts : the force of the running groove towards the bottom, and the reaction to the skating force, towards the right side.

What happens when we apply the anti-skating ? An extra force is added to these, in a direction parallel to the freedom of movement of the arm, towards the outside. If the anti-skating is properly setup, the sum of the forces applied by the arm must be parallel to the groove :

Total from the arm, Reaction of the axis of the arm, Anti-skating, Total from the record.

Since the tip is stationary, the forces applied by the groove are, again, equal in strength and opposite in direction.

We come to the conclusion that, without anti-skating, the groove is asymetrically crushed by the tip, while, with anti-skating, the pressure is the same on both sides of the groove.

We can note that if we just apply some anti-skating with a pre-defined setting, the left side of the groove won't bear an inferior pressure. It is the other side that will end up as crushed as the left side.
But the total pressure is directly controlled by the tracking force. Adding anti-skating while decreasing the tracking force allows to diminish the pressure applied on the left side of the groove without increasing the pressure applied on the right side.
In conclusion, the tracking force allows to control the pressure applied by the tip on the sides of the groove, while anti-skating allows to control the distribution of the pressure between the left side and the right side of the groove.

Now, let's have a look at what happens at the stylus base with and without anti-skating. The list of the forces, including the various torques, is more difficult to do. Therefore, let's consider a simple diagram :

Groove (stopped), Cartridge, Arm, Stylus, Position at rest.

Here, the record is stopped. The stylus is parallel to the groove. I didn't represent the tracking error (the stylus not being actually parallel to the groove).
We can understand what's going on when the groove starts running, keeping in mind that the block drawn in blue colour is completely rigid, and can rotate around the blue disc. The stylus (in red) might slant itself since it is designed to do so when it follows the signal engraved into the groove.
We can thus imagine that we are grabbing the stylus by the tip, and that we are pulling it in the direction of the groove. Without anti-skating, here is what happens :

Groove, Position at rest = position with anti-skating, Action of the anti-skating, Arm, Cartridge, Stylus, Position without anti-skating, Movement of the groove.

The arm rotates towards the bottom of the diagram and the stylus is slanted towards the top, while the tip advances a tiny bit in the groove. We can see clearly on this diagram the crushing on the inner side of the groove, shown by the slanting of the stylus.
If we now set the anti-skating on, the cartridge is going to go back and return to the position greyed out. And the stylus will be aligned again. It will bear a slightly bigger pulling force, but in a straight direction relative to the cartridge (save for the tracking error).

In conclusion, the anti-skating allows to distribute the pressure of the tip on both sides of the groove, and thus prevents the stylus from being crushed sideways.

 

[TBone]

AS offset is easy to view in real world conditions, and I've seen it occur with so many turntables and arms ... the anti-skate mechanism pulling near the pivot visually offsets the cantilever's ideal alignment with the groove, not just in a static position, but also as it runs. Cantilever compliance also plays a role, some carts are more prone to offset than others depending on setting. It should be noted that I've viewed many old, and even some relatively young stylus (micro) that had obvious uneven wear patterns based on improper use of anti-skate, mostly as a cause of too much applied force. Not to mention I've ripped many test records, often using various test tracks with varying degrees of lateral and vertical modulation, applying various anti-skate settings - in order to view any resulting change in distortions. Depending on the modulation & settings, distortions can become quite apparent with too much applied force. Therefore, no amount of graphics is going to lure me away from changing the way I view or set my AS mechanism, nor my advice to people to use minimal force. I'll stay the course, thank you very much, though I appreciate your effort with the above ...

 

[Pio2001]

I can easily believe that tips are asymetrically worn, and that stylii are crushed sideways in many circumstances.

My demonstrations only shows that the idea that a stylus would be safe without anti-skating and crushed with anti-skating is wrong.
I must also admit that the right anti-skating setting, as defined by a perfect distribution of the forces on the groove sides might very well be quite different from the setting advised by the manufacturer with numbers on the dial, or the setting that some of us get using a blank record.

The problem is that in reality, a perfect anti-skating doesn't, and can't exist.

A first reason is that the force applied by the groove on the tip, that is the source of skating, varies with the speed of the groove, which means that it is different at 45 rpm and 33 rpm. And it is also very different at the beginning of a record, where the linear speed of the groove is fast, and at the end of a record, where it is much slower.

But the worse thing is that it also depends on the signal engraved into the groove. It is minimal in the silence between the tracks, and maximal when the sound is at its loudest.
My diagrams represent a linear groove. But such a groove would be silent. A real groove with music permanently oscillates sideways. It means that the force pulling the tip changes all the time.

If we could measure in real time the skating force applied on the tip while the record is played, it would more or less look like a level meter monitoring the output level of the music !

The only real solutions to eliminate skating are radial tonearms, or very long tonearms.
The anti-skating setting on a standard arm is mostly useful to avoid the tip ripping sideways when it is put on the record.

 

[TBone]

My demonstrations only shows that the idea that a stylus would be safe without anti-skating and crushed with anti-skating is wrong. I must also admit that the right anti-skating setting, as defined by a perfect distribution of the forces on the groove sides might very well be quite different from the setting advised by the manufacturer with numbers on the dial, or the setting that some of us get using a blank record.

The problem is that in reality, a perfect anti-skating doesn't, and can't exist.

Exactly, however applied >AS forces which potentially can offset the cantilever - is really a bigger issue.

The only real solutions to eliminate skating are radial tonearms, or very long tonearms.

Yeah, but these "fixes" introduce other issues to the mix.