About Needle damping with MC systems

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Correct needle damping is important

The cartridge is mass-spring system like any other. Though very tiny, the moving parts have a certain mass. The cantilever is fitted into a rubber piece, which acts as a spring and a damper at the same time. The construction must not be understood in detail, it is enough to regard it a mass-spring system. If you attach a mass on a spring, you can sure move the mass, but when you let go of it, it will keep on moving by itself. In a MC system that is not any different. Though very small size, physics are the same. There will be self-movement as well. The record groove specifies the required movement, and of course we want no other. With it's own needle movement, we should not think of somethig "swinging" but rather random small movements the needle tip can make, which do not fully correspond with the groove. This is distortion when it's a planar movement, and loss of stereo information when the unwanted movements are vertical.

The right amount of damping simply stops the self-movement. If more damping as needed, the self-movements will of course also stop, but it woll be much harder for the needle to move at higher speed. (which is at higher frequencies). So there will be loss of high frequency. For the engineers: The MC system is a generator, and with all generatores, the voltage increases with the speed of movement, which is the case with higher frequencies.

The opposite can happen too. When there is not enough damping is, the needle may skip a groove at loud music pieces, when you touch the record player, or step on the floor to hard.

How is the needle damped?

The first part of the damping is achieved mechanically, inside the cartridge. The rubber part allows movement, but has also friction. Electrical damping takes place by connecting a resistor to the cartridge. This resistor, if there is voltage across it, will pull some current, and the energy for this is taken from the needle movement. The smaller value this resistor, the harder it is, to move the needle very fast.

However when systems are aging, the composition of the rubber changes. Over the years it may get harder, or softer, either way. This is not a defect, but normal aging, and it can be nicely compensated by changing the electrical damping.

How is the cartridge load applied?

The first part is done by the phono amplifier, which has a standard impedance of 47k. This value is transformed down by the MC transformer by the square of the transfer ratio. So with a 1:10 transformer it becomes a load of 10x10 times lower, so 470 Ohms. The transformer's windings resistance adds up to this. Let's say it becomes 500 ohms. Without any additional damping, this number would be fixed. It is a matter of good luck, if this value would be just right. This is why a good MC unit has also a damping adjustment. This damping is typically done at the secondary side, because this makes use of the transfer ratio of the transformer as well, which helps a lot to reduce the range of resistors needed.

For adjustment, EE50 and EE51 have some resistors, which are connected in various ways. Other PCBs like EE20 or EE21 use fixed or variable resistors. For a quick sound compare, with EE50, EE51 and EE20, the damping can be switched on and off.

An Example of finding out the best damping

As an example, let's look at the DENON DL103 cartridge. The manufacturer specifies it as follows:

What we need first, is find out what step up ratio gives the required output voltage for the RIAA amplifier. This calculation is a bit difficult, but when you know how to do this yourself, you can do it. A faster way is use the selection table. You will see there, the Denon 103 needs a transfer ratio of 1:16 or 1:20. We choose normally the highest value. So let's see what 1:20 means for the damping. The RIAA amplifier has 47k impedance. This value is represents the cartridge load, but it appears at the cartridge side with a factor 20x20 lower. So we get 118 Ohms. This does not go below the minimum damping of 100 Ohms. So all is fine, and this is indeed the most used configuration. With EE50 and EE51, damping would be set to "very soft" which indeed means, no damping is added by the board itself. You could also try the "Soft" setting, now a resistor is added which results in a total load of 98 Ohms. Well it is just below 100, perhaps you like this, but probably not. Just try it out. Nobody can advise it on paper.

Also check the larger possibilities of the Denon 103R vs. the 103.

Too much damping gives loss of high frequency, and loss of stereo information. That is because faster needle movements (as needed for high frequency) get damped a lot more. The stereo information is coded in the vertical needle movement, which get damped just as well.

Not enough damping leads to reduced groove contact during loud sound parts, which is a form of harmonic distortion, but also a loss of stereo information. Reason is because the stereo information is coded in the VERTICAL movement of the needle! At very loud music pieces, the needle because of it's V-Shape, will see a vertical force. This pushes the needle upwards, and in bad cases even out of the groove, and it skips a groove. This upward force, is created by the planar movement of the needle (so the mono information) This is mistakenly judged sometimes as not enough weight on the cartridge. Even so, more weight will also help to some level, but this would be curing the problem not at the source.

Down to earth

We see sometimes web pages, where damping resistors are specified in huge tables, with extreme precision. WIth all respect, but this is not really needed. As you will see (or hear), changing the damping one step, for instance from soft to very soft, is audible, but the difference is not huge. So, 5 steps will cover the range nicely, and finer steps are not needed. In many cases, very soft, or soft damping is what you will need anyway. Harder damping may be needed when your house has wooden floors, or when the sound is too bright. All on all, this is difficult to predict, or to calculate. Better just try it out what sounds best.