|Posted by "AudioAficionado" on July 8, 2017 at 11:30 AM|
Turntable calibration by itself can be an art form. The fact that one can alter the sound to taste by making tiny adjustments to different parameters is physics magic. But the Anti-Skate mechanism in many turntables is so full of mysticism, that most people don’t understand what it actually does. In these article I’ll do my best to explain how it works, keeping in mind that this problem has hunted audiophiles for decades and no perfect solution exist.
Anti-skate, as defined in our turntable set-up guide, is an effort to counteract the skating force that tends to draw the tonearm/cartridge towards the center of the record when the cartridge is mounted in an offset head shell. This force can produce distortion and, uneven, and premature, wear of the walls of the record groove and stylus. But what causes this problem?
Friction between the stylus tip and the record produces tangential forces, which pushes the tip toward the inner record grove and create a tracking force imbalance. People tend to confuse this phenomenon with centrifugal force, which is not the case, because centrifugal force would pull the stylus tip to the outer record groves and not the inward.
Most tonearms provide some kind of skating force compensation mechanism. The idea is to provide a compensatory torque by means of a weight, spring or magnet. This torque counteracts the skating force, perfectly balancing the tracking weight between the record groves. Makes sense right?
Not so easy, the geometry of the arm and record will affect the amount of skating force. Such factors as; tonearm length, pivot to spindle distance and the stylus distance to the center of the record, will all have an effect in skating force. Thankfully, the first two factors will always be fixed. Unfortunately, the last one will not. Meaning, the skating force magnitude will vary as the stylus rides across the record.
Sorry, did I forget to mention that modulations velocity in the record also affect the skating force. By now, it would seem impossible to compensate for all this variables; it may seem easier to have the stars line up in the sky.
The reality is that to be practical we are only expected to counterbalance the effects of skating force at an average modulation level across the record surface. Skating force variations while playing the record will have negligible effect on sound performance, as long as the counterbalance is well set up.
As mentioned before, there is no magic formula to solve the skating problem. Each tonearm and cartridge combination will have different setting and there will always be a compromise. So how do I know I have the correct setting?
If something is clear, is that some sort of anti-skating force needs to be apply to obtain a respectable tracking force balance. Some turntable manufactures believe that anti-skate is not that important and simply bypass it all together from their design. This may be a tactic to simplify their product for the end user, but it doesn’t mean is correct.
A basic recommendation is to set anti-skate equal to the cartridge vertical tracking force (VTF), then adjust to taste. Studies have shown there is a linear relation between skating force and VTF. Although, this relation can change depending by stylus profile and vinyl quality, it still is a good starting point. As example if you VTF is 1.5 grams you will set your anti skate accordingly.
Other option is using a test record like The Ultimate Analogue Test LP (Analogue Productions - AAPT 1). Good result can be obtain by adjusting the amount of anti-skate until the Bias Setting tracks produce a clean, undistorted signal in both channels. Buzzing in the right channel indicates that more anti-skating force is required, whereas buzzing in the left channel indicates that less anti-skating force is required.
Although, is true that due to the fact that most test record use a modulation velocity set to high, like big crescendo music passages, the anti-skate may end up being set to high for the habitual music genre. This can be easily fixed by lowering down the setting until good results are obtained with a variety of music.
I have heard of a lot of different methods to set up anti-skate and all of them require some kind of tuning by ear. Just remember, there will be compromises, set it were it sound good and forget it. Enjoy the music!
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Categories: Analog 101