If you pay any attention to the mechanics of playing a record, you will quickly discover that some of the physics involved will induce a migraine (and I’m not even referring to the immortal Calvin and Hobbes strip discussing the different speeds on the same record). The pressure exerted by a stylus on the groove of a record is in excess of 300lbs per square inch and during dynamic passages, the lateral forces from the groove wall on the stylus are staggeringly high. What looks calm and sedate from your listening position is anything but.
One force that your turntable has to deal with is a simple function of how a record works. As the stylus tracks the groove of the record towards the centre, the force on the outer edge of the stylus increases as it is ‘steered’ toward the centre of the record. Over the lifetime of the stylus, this will produce uneven wear on the diamond. In some cases, the force being applied will cause the arm to jump and fail to follow the record correctly.
Happily, the solution to this is built into the bulk of players on sale today and it is usually referred to as the “anti-skate mechanism”. Anti-skate is a process by which a degree of “counter rotational torque” is applied to the arm to centre the stylus in the groove of the record. “Counter rotational torque” is a posh way of saying that a mechanism pulls against the arm as it moves inwards, nullifying the force as it moves towards the centre of the record. The amount of force involved is not particularly large- rarely more than two grams of weight in total- but as noted, two grams in the crazy world at the end of a stylus is a great deal of force.
Anti-skate mechanisms come in two broad categories. The first are systems that rely on a small counterweight to apply the required force. The weight is usually suspended on a line and pulley arrangement and the movement of the arm at the pivot will raise the weight up the pulley. The amount of force exerted is adjusted by moving the end of the line nearer to or further from the pivot point of the arm- the further the distance to the pivot, the more force is being exerted. The second are systems that rely on small spring system that provides a degree of resistance on the arm as it moves across the record. The amount of force can usually be adjusted via a rotary control on the side of the arm.
While completely different, both of these mechanisms have exactly the same effect. Needless to say, because this industry has managed to turn pretty much every aspect of turntable design into an argument, there are keen advocates of both systems. Counterweight anti-skate systems can look a bit crude and be almighty dust traps but they do have some advantages. The force they exert is extremely consistent from the start of the record to the end because the resistance of the weight and line is constant regardless of position. Of course, just to make life difficult, it’s worth noting that the force the record applies on the stylus isn’t constant so all consistency actually does is ensure that the force is exerted at the same level rather than create a perfect response.
By contrast a spring system will rarely exert absolutely consistent resistance because the mechanical resistance of the spring is not completely constant as it expands and contracts (and it will change as the spring ages). Equally, while counterweight systems are a little approximate, spring systems are marked and set with a degree of confidence (although, just how accurate the dial is does vary a lot from arm to arm).
Just to muddy the waters a little more, there are arms that do without either of these systems and operate almost entirely without anti-skate at all. Linear tracking arms- that move across the record on a rail arrangement in a straight line- do not use any anti-skate because the forces acting on the stylus are different. Some conventional arms also do without. US turntable manufacturer VPI makes arms that have no bearings or fixed contacts in their pivots. The only anti-skate that these arms traditionally had took the form the signal cable leaving via the top of the arm and having a twist in it that exerted a tiny amount of anti-skate force on the arm. The photo at the head of this piece shows a VPI arm with this system and the back of an SME arm that uses a counterweight anti-skate. While the two systems are completely different, both arms can track the same test record equally well.
So, having established that the force required for anti-skate can be applied in different ways, is not always the amount that is actually needed and in some cases is ignored altogether, what are the guidelines for actually using it on your own equipment? As you might appreciate, with so much variability there’s no hard and fast rules for this but there are some guidelines you can follow. The first is that if the paperwork with the turntable (or if you have an aftermarket arm, the paperwork supplied with that) says that the arm won’t work without some anti-skate being set, you can probably guarantee that this is the case. Many popular designs like the Pro-Ject Debut and Essential lines will skitter madly across to the centre of the record without anti-skate. If the manufacturer recommends some anti-skate, it would be best to apply it.
The conditions under which an arm may sound better with little or no anti-skate are fairly specific. If you have an arm that works under unipivot principles and you have selected a cartridge with good tracking abilities, you may find that the force exerted by the anti-skate is correcting an issue that isn’t there. If the manufacturer is more ambiguous about setting anti-skate, you can carefully start to experiment with the settings. The best process is to start with a known quantity of anti-skate that allows the arm to track correctly across the whole record and reduce it in small increments, using a record you are not enormously attached to.
Having done this, the tests are pretty straightforward. If there’s no improvement in sound quality, leave it as it is. If the needle leaves the groove, you (obviously), need to go back to the point where it doesn’t. What you need to be listening for carefully is any sign of distortion towards the end of a side. Distortion in the left channel would suggest that the cartridge is pushing too hard against the outer groove and anti-skate force needs to be increased. Distortion in the right channel suggests that the anti-skate force is too high and needs to be backed off.
Ultimately, anti-skate is an area where you have to accept a degree of laissez faire- it will never be the perfect amount at every part of the record and it will vary depending on the cartridge you use. Measuring it is tricky (and devices that claim to can vary wildly in their accuracy) so there will be a degree of combining the manufacturer's recommendations with your own experiments to see what works best for you. It joins the other countless forces acting on your turntable and records and in order to avoid that migraine, it’s frequently best to accept that it often works in spite of the science rather than because of it, and set and forget- there’s music waiting to be listened to.
Ed is a UK based journalist and consultant in the HiFi industry. He has an unhealthy obsession with nineties electronica and is skilled at removing plastic toys from speakers.
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