If you are really into guitar modding, there is no way around learning how switches work.

If you are really into guitar modding, there is no way around learning how switches work. So this month let's explore the basics.

Two types of switches are commonly used for guitar mods. One is a potentiometer with a switch—a push/pull, push/ push, or the Fender S-1—and the other is a common toggle, which is available in different sizes, shapes, and configurations. When adding a switch to a passive circuit, you don't have to worry about voltage and power ratings—all that matters is that switch will fit your guitar!

Though switches come in various configurations, they all have a single purpose—to turn a signal on or off. Many variations are available, but we'll concentrate on the four most common guitar switches: SPST on/off, SPDT on/on, DPDT on/on, and DPDT on/on/on.

The first two letters of these names indicate the number of poles, while the last two letters are the number of throws. So a SPST (aka 1PST or 1P1T) means single-pole/single-throw, a SPDT (1PDT or 1P2T) means single-pole/double-throw, and DPDT (2PDT or 2P2T) means double-pole/double-throw. There are many more configurations, including 3PDT devices used for true-bypass switching in effects, and Fender's 4PDT S-1 switch. Found on push/pull or push/push pots, the DPDT on/on switch is by far the most common, and mini toggles are available in an endless number of variations.

Let's take a closer look at what's known as the switching matrix. A switch's poles are like separate channels that aren't connected until you add a jumper wire between them. A SPST or SPDT switch has only one of these channels, while a DPDT switch has two. Likewise, 3PDT and 4PDT switches have three and four channels, respectively. A switch's throws are simply the different sides of a switch. For example, a DPDT on/on switch has two channels (poles) with three lugs on each channel. Engaging the switch turns on one side or the other. When one signal is turned on, the other is turned off.

An SPST switch has only one channel (pole) with two lugs. It's the archetypal on/off switch for simple projects like replacing a 5-way switch with three on/off switches. In one switching position, the two lugs are connected, while in the other they're disconnected. Below is a visual representation of the SPST switch.


In one position, lug A and

lug B are not connected (that is,

the circuit is open). In the other,

both lugs are connected (the circuit

is closed). To use our seven-sound

mod as an example: In

one switching position, both lugs

are not connected, so the neck

pickup connected to the switch

is not engaged. In the other position,

both lugs are connected and

the neck pickup is engaged.



This is a great opportunity to

start working with a digital multimeter

(DMM). Track down an

inexpensive DMM and make sure

it has a continuity function, preferably

with an audible connection

indicator. You can then trace how

switches work by connecting the

individual lugs to your DMM

and seeing which are connected,

and then switching to the other

position and taking the same

measurement again. The beep that

sounds when you've made a connection

is a great help when you're

taking these measurements.



A SPDT (1PDT or 1P2T)

on/on switch also has only one

channel (pole), but offers three

lugs instead of two. This switch

also works for the seven-sound

mod (if you leave one lug unconnected)

or for the cap-switching

mod. Below you'll see what's

going on in this type of switch.




In one position, lugs A and

B are connected (this is throw

1), while in the other position

lugs B and C are connected

(throw 2). So lug B is the common

output of this switch,

while lugs A and C are inputs.



A DPDT (2PDT or 2P2T)

on/on switch has two channels

(poles), each having three lugs.

This is like having two SPDT

switches in one. It's the standard

configuration for most push/

pull or push/push pots, and you

can use it for almost all mods,

including the seven-sound mod

(if you leave one pole unconnected),

coil-splitting a humbucker,

out-of-phase mods (by adding

some jumper wires from pole 1

to pole 2), a direct-through mod,

and countless others. Let's see

what's going on here.




In one switching position,

lugs B and C of pole 1 and lugs

E and F of pole 2 are connected

(throw 1). In the other position,

lugs A and B of pole 1 and D

and E of pole 2 are connected

(throw 2). It's exactly like a

SPDT switch, but with two

poles instead of one.



Finally, we come to a very

special but important type of

switch: the DPDT (2PDT

or 2P2T) on/on/on. Larry

DiMarzio made this switch

famous in the '80s, and this is

the device to use when you have

a four-conductor humbucker

and want to take full advantage

of all its wiring possibilities.



It's still a 2PDT switch with

two channels (poles) sporting

three lugs each, but in

comparison to a DPDT on/on

switch with only two switching

positions, the DPDT on/on/

on switch has three positions.

This is often called a “centeron"

switch, because it has a

third position in the middle

between the common left and

right positions.



Although the DPDT on/

on/on switch has the same

number of poles and lugs as our

previous DPDT on/on switch

(which means the illustrations

for these switches look identical),

this version has an additional

switch position.



In switching position 1 (left

throw), lugs B and C of pole 1

and lugs E and F of pole 2 are

connected. In position 2 (center

throw), lugs A and B of pole 1

and lugs E and F of pole 2 are

connected. Finally, in position

3 (right throw), lugs A and B of

pole 1 and lugs D and E of pole

2 are connected.



This switch facilitates three

sounds from a four-conductor

humbucker: both coils in series

(standard humbucking mode),

both coils in parallel (sounds

similar to a single-coil, but in a

hum-cancelling configuration),

and a true single-coil mode.



All right—that's it. I know

this is very dry, but it's worth

investing some hours to understand

switching basics.



See you next month—and

keep on modding!




Dirk Wacker lives in

Germany and is fascinated

by anything related to old

Fender guitars and amps.

He plays country, rockabilly,

and surf music in two

bands, works regularly as a

session musician for a local studio, and writes

for several guitar mags. He's also a hardcore

guitar and amp DIY-er who runs an extensive

website—singlecoil.com—on the subject.

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