Push/Pull Pots
Let’s take a look at push/pull potentiometers. Shown here are three specimens- Bourns PDB183-GTR01-504A2, Gibson PPAT520, and AllParts EP 4286-000. These are all 500k audio taper pots with knurled split shafts. The EP4286 has a longer 3/4” shaft, while the others have the standard 3/8” or “short” shaft. This Bourns has the highest torque of the bunch– it’s the hardest to turn, while the Gibson is the easiest, and the AllParts has just a touch of mechanical graininess to the feel.
A push/pull pot is just a potentiometer sitting on top of a DPDT switch. The switch actuator is the shaft of the pot itself, which drives down right into the switch. When you pull the shaft up, you are moving the switch actuator to connect the top half of the switch, and when you push the shaft down, you are moving the switch actuator down to connect the bottom half of the switch. There’s no built-in electrical connection between the pot and the switch – if you want the switch to control the pot’s behavior, you need to connect up some wires (as in the example described at the end of this article).