AnalogMagik Tutorial No. 8:
How to set Vertical Tracking Force (VTF)
Vertical Tracking Force
Most cartridge manufacturer will specify a number which the Tracking Force should be set at. More often than not, this number is a range instead of a fixed number (eg. 1.8g to 2.2g on most cartridges). AnalogMagik have spoken with a number of cartridge manufacturers, and none was able to provide them with a firm answer on how to how to determine an exact number except to "go by ear". As far as we know, AnalogMagik is the first to attempt to propose a theory and methodology on calibrating tracking force scientifically.
AnalogMagik have discovered that changing the VTF will affect the Total Harmonic Distortion differently at different frequencies. For example, if you increase the VTF, the THD% on high frequencies will go up while the THD% on low frequencies will go down. But after a certain level, both sets of numbers will go up again.
AnalogMagik believe one way to optimize VTF is to find a setting which yields the lowest possible Total Harmonic Distortion across both high frequencies and low frequencies.
The Analog Magik test LP contains two test tracks for VTF calibration, one with a high-frequency test signal, and one with a low frequency. Repeat the measurement by using different tracking force levels. You may discover that different VTA settings will cause the THD% to go up or down between the two frequencies. If an observable correlation can be found, then adjust tracking force to a level in which both the THD% is at their lowest, on both the High Frequency and Low-Frequency Test tones.
Within our labs, AnalogMagik have experimented with a countless number of different distortion tests on different VTF, and they can certainly produce an entire LP with 10 different test signals and perform 10 different sets of test on VTF alone. But if it is too complicated, none one will understand it and very few will spend money on the product. At the end, they have decided to include one test which is easy to use and understand and will likely yield meaningful results. Perhaps if there is enough market demand, AnalogMagik will release a product focused on VTF alone.
Lastly, we do not want to discredit anyone who decides to choose a setting most suited for their ears too. We do that too, but that is not a scientifically repeatable method.