Wiring DIY - Part 03

Resistors

Despite of the potentiometers, that are variable resistors at the end and that we already discussed above, the use of resistors is very uncommon in guitar wiring but, for some specific applications they are being used.

In principle, a resistor should transform part of the electrical power that receives into heat and, therefore, dismisses the overall energy (decreasing the voltage). But, a capacitor together with a resistor are the basic bricks to build a passive filter and, resistors change the Q of an iinductance and, our coils are inductances, at the end.

Fender TBX tone control works with some resistors. A resistor can be seen in Treble Bleed mods, also. And, there are some other wiring that include resistors just to modify the sound of a pickup for a certain switch position.

We can say that the higher the total resistance is in our circuit, the lowest the output level and the sharper the resonant peak of our pickups will be.
We will discuss those cases later, when they appear. By now, forget resistors (except pots).


Switches

Switches are mechanical devices that allow us to choose between different alternative connections for a certain wire. Switches are usually described by their number of poles (wires that we can switch at same time) and throws (number of alternative ways for each pole).

The simplest switch is of type SPDT (Single Pole Double Throw), that is, a switch where we can attach a wire to the Pole lug or pin and then choose two different connections or paths depending on the position of the switch. This can be compared to the switch you use to light on and off any lamp at home. The lamp is wired to the pole and there are two alternate paths: one disconnects the lamp (so the wire deads there) and the other connects the lamp.

Even that the number of poles and throws basically define a switch, they are being designed in different ways and, sometimes they have more positions (handles) than throws.  By example, a SPDT switch can have just two handles (positions of its actuating lever or button) but, each position can be implemented in different ways. You will read following additional info together with a switch:

• ON: Permanent on. This links the pole to the throw until the lever is being moved to a new position.
• OFF: Permanent off. This leaves the pole linked to no throw (disconnected).
• [ON]: Temporary on. This links the pole to the throw while we manually maintain the force on the lever or we remain pushing the button.
• [OFF]: Temporary off. This disconnects the pole while we manually maintain the force on the lever or we remain pushing the button.

So, we could have SPDT on/on or SPDT on/off  or SPDT [on]/[on] switches, by example.
Usually, toggle switches (actuated with the help of a lever that has several positions) use an additional handle or position, when the lever is centered. This center position can be implemented as center ON or center OFF.
Switches with center ON will connect the pole to both throws at same time if the lever is centered.
Switches with center OFF will disconnect the pole from both throws at same time, if the lever is centered.

So, we can have SPDT on/on/on and SPDT on/off/on switches, by example.

Look at the following picture, that describes which contacts are being actually linked when changing the position of the lever.

The pole is the center hole in this pictures, that correspond to the center pin or lug in a typical switch, the throws are the upper and lower ones. The blue lines determine which lugs are connected together at a certain lever position. Lever is simplified here with that black dot-ended line.

See that the way as the center position is being implemented in a center on or center off switch is completely different and, correspond to different logical decisions.

An on/on switch responds to alternative decisions: or path1 or path 2.

An on/on/on switch responds to alternative decisions: or path1, or both, or path 2.

An on/off/on switch responds to alternative decisions: or path1, or none, or path 2.

When we put two SPDT switches together, under the same case and, we actuate both at same time with a single lever or button, we are having a DPDT (double pole double throw switch).

A DPDT can have a tricky central position. There are several ways to implement the centered position.

Look at the following chart:

A Pull/Push or Push/Push Pot, has a switch under its pot that can be actuated by pushing down or pulling up the pots rod (case of pull/push pot) or the switch toggles when pressing down the rod (push/push).

Usually, pull/push and push/push pots seen in guitar wiring are DPDT on/on types but, they can be implemented in two ways: connecting the upper throws when the rod is down or connecting the lower throws when the rod is down so, be careful when getting a pull/push or push/push pot.

Usually, when the rod is down, the lower pins are being connected with the pole and, when the rod is up, the upper pins are being connected, instead.

Mini Toggle Switches that are usually found for guitar circuits have their centered on position usually implemented as i the type 2 shown above but, you should always identify how the centered position is being implemented in any on/on/on switch you are buying because, the diagram design can change or, if you are trying a diagram designed with type 2 in mind and you  are using type 1 or 3, your project will fail (and you will wonder why?).

You cannot order type 1, type 2 or type 3, this is how I named them to distinguish them in our context. They have no special name on stores, you need to look to the switch's technical specifications or directly ask to your seller.

Toggle switches, usually have just two throws (two alternative paths by pole) and up to 4 poles.

So, if we combine a DPDT switch together with an SPDT Switch, we have a 3PDT (3 poles, double throw) switch, that allows us to decide two alternative paths for three wires at same time.

You see that center on position of a DPDT can be implemented in three different ways. Since a 3DPT is a SPDT + a DPDT, we can have same issues with a 3PDT switch.

Look at the following chart:

As in the case of DPDTs, the usually found one is type 2 in this chart. There are still more possibilities to implement that intermediate position. Think on the different permutations you can do with those three poles, leaving one or two down or up but, since the design of a 3PDT is based on coupling together a SPDT and a DPDT, those three types should be just enough. Anyway, always get the information about how the centered on position is working in your 3PDT switch!.

Finally, the biggest toggle switch you would see in a guitar is a 4PDT switch. A 4DPT switch is (yes, you guessed it!) two DPDT put together. So same types seen in DPDTs will be seen in 4DPTs.

As in the rest of cases, the more usual center on implementation will be type 2.

We will continue describing more switches on next part.