Insight - How Preset works

Preset is a small variable resistor generally used to provide a variable resistance in a circuit in order to tune the circuit. They are directly mounted on the PCBs. A screwdriver or similar tool is required to adjust them.

Fig. 1: Image Showing A Standard 20K-Ohm Preset

A 20K-ohm metal preset is shown in the image above i.e. the maximum value of resistance that we can give in a circuit by using this preset is 20k ohm.

Fig. 2: A Close View of Preset Cover

The rectangular space between the cover of the preset is used to rotate it on the track. Upper side of the cover has a slight curved dent which connects the resistive strip with third leg (upper leg) of the potentiometer.

Resistance Track

Fig. 3: Resistance Track of Preset

The black arc seen in the picture is a resistance track.

Fig. 4: Image Showing Various Parts of Preset

Above images shows the components of preset that are used to structure it.

Working of presets is quite simple. It works by having a resistive track and a small plate having dents to short the track. This small plate can be rotated using a screw driver or some similar tool. Position of the dents on the track determines the amount of resistance that is to be used in the circuit.