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).
First let’s identify which lugs are connected in which switch positions.
The switch of a push/pull has two rows of 3 lugs, oriented vertically. I’ve labeled them in this picture A,B,C on the left and D,E,F on the right. ABC and DEF are two totally independent switching circuits, but controlled by the same push/pull actuator. I also labeled the pot lugs X,Y,Z for the wiring example below.
As with any dual-throw switch, the actuator toggles what the middle lug (B and E in this dual-pole switch) is connected to. When you push the switch down, B is connected to C, and E is connected to F (while A and D are disconnected from everything). When you pull the switch up, B is connected to A, and E is connected to D (while C and F are disconnected from everything).
This should be pretty obvious once you look at it, but you can always confirm by using a multimeter in continuity mode – touch one multimeter lead to one lug, and then touch the other lead to each of the other lugs, looking for a connection by listening for the beep, or watching for zero resistance. Each lug will only be connected to one other lug, in each switch position.
There are many useful applications for push/pulls. Let’s describe a simple one: making a pickup volume pot which cuts out the pickup signal when pulled. Kill switch!
We’ll only need one of the switch circuits here (so a SPDT switch would suffice, but they don’t make SPDT push/pulls as far as I know). Wire the pickup signal to switch lug C, and then wire switch lug B up to the center of the volume pot (lug Y). The other two volume pot lugs are the usual arrangement- one side (lug Z) to ground, and the other side (lug X) over to the tone pot or output jack.
NOTE: connecting the pickup signal to the center lug gives you independent volume wiring which is useful for 3-pickup guitars with a 3-way selector, or for 2-pickup guitars where you want to avoid interaction between the 2 volume controls. The downside is significant treble-loss when turning down the volume pot. You can instead wire the pickup signal B to the side lug X, and the output to the center lug Y. This will give you non-independent volume controls, which will eliminate treble loss when turning down- perfect for guitars with a single master volume and typical on 2-pickup Les Paul style guitars. Note that on a two-pickup guitars with a 3-way selector in the middle position- turning down one volume all the way will also kill the other (hence the term non-independent). The kill switch is the perfect solution to that problem!
Now when you pull the knob up, B gets switched to connect to A (which is connected to nothing), so your pickup goes silent. When you push down, B gets switched to connect to C and you hear your pickup through the volume pot.
Note, you can reverse the behavior so that the pickup is only active when pulled, and killed when pushed, by wiring the pickup signal to switch lug A instead of C.
For other examples of push/pull pots in guitar circuits, see the comprehensive list of wiring diagrams at the guitarelectronics website.
Filed under: Guitar