Smoothtrak Pots

Have you ever wondered why standard guitar tone pots do most of their work around the last 10% of travel?

The reason is simply that the logarithmic curve of the pot is not ideal for high impedance magnetic guitar pickups. It never has been. Back in the 1930s when the first electric guitars were coming into use, only limited specification electronic components were available, and in the case of potentiometers, guitar makers simply used the available radio pots. These were fine for radios but have always left a lot to be desired on passive electric guitar circuits. The amazing thing is that, as far as I am aware, for the last 80 or so years this problem has not been addressed!

This is why I developed the Entwistle Smoothtrak pots.

So, what is the difference between a standard guitar tone pot (Log A) and an Entwistle Smoothtrak pot (Log AE)?

Your standard Log A pot is most commonly available in 500K or 250K options. If you put the pot on a digital multimeter, you will see that when rotated fully clockwise it will measure it's full value, and rotated fully anticlockwise it will measure zero. So far so good, and this is the same result you will get with an Entwistle Smoothtrak. However, if you rotate the standard pot to just 50% of it's travel you will see that it will measure around 10% of its full value. For example, a 500K pot will measure around 50K, and this is too high a value to be truly effective as a tone control, as it actually limits the effect of the tone capacitor

Like standard tone pots, the Smoothtrak comes in both 500K and 250K values, and they look and feel the same, but the difference is in the tracking. This can be demonstrated by doing the same multimeter test on the Smoothtrak. This time at the 50% rotation point the Smoothtrak only measures around 5% of the total potentiometer value. For example on a 500K Smoothtrak pot, you will measure around 25K, and this value is allowing the effect of the tone capacitor to really come through.

The overall advantage is clear. A standard guitar tone pot is only really effective for around 10% of its travel, whereas the Entwistle Smoothtrak is effective across about 70% of it's travel, and the actual curve is different allowing the effect of the tone capacitor to lift away from around 70% of it's clockwise travel into a kind of very bright bypass mode.

Alan Entwistle