A humbucker has two coils, therefore, we can have the sound of each coil separately, or the sound of both coils together arranged in several ways. That gives us the following 6 possibilities:
- Coil A
- Coil B
- Coil A in series and in-phase with Coil B
- Coil A in series and out-of-phase with Coil B
- Coil A in parallel and in-phase with Coil B
- Coil A in parallel and out-of-phase with Coil B.
Independently that this particular pickup can be put out-of-phase respect any other pickup (single or humbucker), its own coils can be put out-of-phase respect the other.
The standard way of wiring a humbucker is with their two coils in series and in-phase. This is the typical humbucker sound, powerful, warm, a tad dark, with good sustain and less bite and definition than single coils. Original humbucker had the wires of both coils soldered together and, what we had was just the starting wire soldered together to the plate wire and those, soldered to the metallic cover of a braided cable. The finish wire was soldered to the inner conductor of that braided cable.
In some cases we had this humbucker coming with a separate wire for the plate ground, but this is really rare.
Those kind of humbuckers have a single sound, both coils in series and in-phase (pure humbucker sound). They doesn't allow any other combination. Even that we could put that pickup out-of-phase with other, this is a bad thing, since we are positivizing the cover of the pickup and the braid of the braided cable, removing the Faraday's cage that covered both, the pickup itself and the inner signal conductor, potentially making the guitar very prone to catch noises of any kind.
To be able to put a humbucker out-of-phase, without risks, we need the plate ground in a separate wire (usually a bare wire) and two not-braided conductors, that can be twisted together.
If you are thinking on doing some mod to your humbucker loaded guitars, be sure to get a humbucker with 4 conductors + plate ground wire, instead of the classic single braided conductor ones. In that way, you will be always able to select any of the 6 combinations we already mentioned above and, even to safely put out-of-phase this humbucker respect any other pickup in your axe.
Look at this picture:
We are using here Seymour Duncan's color code. The coil with adjustable poles is often named screw-coil and, the coil without adjustable poles is often named slug-coil.
The start wire of the slug coil is the black wire and, its finish is the white one (represented here in light blue).
The start of the screw coil is the green wire and, its finish is the red one.
The first picture is the standard humbucker mode, that is, both coils in series and in-phase.
The second picture is coils in series but out-of-phase (OOP from now). Note that the wires of the slug coil were inverted on connections.
The third picture is coils in parallel and in-phase (from now, if we omit it, it means in-phase).
The forth picture is coils in parallel and OOP.
The five picture is really two pictures. The first one corresponds to the selection of the slug coil, where the white wire goes to hot and the black to ground. The second one corresponds to the selection of the screw coil, where the green goes to ground and the red to hot.
When one of the coils is selected, instead of both coils, it's being named coil-split. So we can coil-split to slug or to screw coils. For sure, every humbucker is not made the same and, while the most have one slug coil and one screw coil, there are other designs were both coils have adjustable poles, or even blades or, the cover doesn't shows the poles below.
We will use this convention to name the two coils of a humbucker, just for our convenience and, will represent any humbucker in that way, independently of the real aspect because, at the end, the only important thing is to understand how to get the 6 different sounds and which one to choose for each application.
When we need to put this pickup OOP with another one, we will just need to swap the black and green wires in those pictures above.
The most wanted mod, respect of humbuckers is just the ability to choose humbucker or split mode with the help of a switch. Look at this picture:
The first corresponds to a way to select humbucker/split to slug. It needs just a SPDT on/on but, you can use any bigger switch but, just use one pole.
The second corresponds to a way to select humbucker/split to screw. It also needs just a SPDT on/on but, this is a bad way to do it. The issue here is that white and red are put together with black in the hot path. This shortcuts slug coil but, there is something the risk of some bleeding from that coil.
The third picture corresponds to a way to select split to slug/humbucker/split to screw. It needs a SPDT on/off/on (center off) switch but, it presents same potential issue than the previous one.
A better way to do this two last mods is to use a DPDT and a 3PDT switch instead, to completely remove the slug pickup from the hot path. See the following picture:
The first case corresponds to humbucker/split-screw, with the help of a DPDT on/on switch and, removing any possible bleeding from the slug pickup (as happened before).
The second case corresponds to screw/humbucker/slug, with the help of a 3PDT on/on/on switch (type 2).
If you don't understand how it works, just print out this picture 3 times and, put in each printing, the status of the switches so you can get the picture what is being connected for each case.
The exit of both pictures is the orange wire (HOT) and, the ground is being represented by this inverted triangle.
The two first schemes of the first picture and the first schema of the second picture can be implemented by using a pull/push or push/push pot and, therefore, the mods will not alter the external aspect of the guitar.
The last schema of each picture need some toggle or rotary switch, instead.
That's why, we will usually see a humbucker/split switch that will split to just one of the coils; which one will depend on how are we wiring the switch but, the usual is to split to slug coil.
To be able to select the 6 different sounds of a humbucker, we will need a 4 poles 6 throws switch and, this is usually only possible with a double-wafer rotary switch.
In the above picture, the positions correspond to the following:
- Humbucker (in series)
- Coils in Parallel
- Split to Slug
- Split to Screw
- Series OOP
- Parallel OOP
If your guitar has 2 humbuckers and you put a 4P6T rotary switch for each humbucker (to select its own 6 sounds) and you place one more 4P6T switch to combine both pickups, you have all the possible sounds that 2 humbuckers can generate. That means 6 * 6 * 4 = 144 different combos for the central position, when both humbuckers are selected together, that, combined with the 6 sounds of each pickup alone, makes a total of 156 unique combos with 2 humbuckers.
It can sound very exciting but, to be honest to test more than 20 combos it's really difficult, first because of the time it requires and, second because when you are trying the 21 you already forgot the previous 20.
This is a good exercise to make to a lab guitar, to help you to exactly determine which combos make any sense for your needs and then, design the right wiring diagram that includes those must-have combos.
You will see with the time that not everything is useful for you. Many people doesn't like OOP, since it makes the sound weaker, thinner, nasal, hollow and tiny but, Peter Green's middle position has the Neck OOP respect of Bridge and, it sounds damn good.
You will discover that there is not so much difference between the slug or the screw coil and, this is specially true if the humbucker has twin coils. In some cases, the difference is so notable that you will prefer to just get one of the two and not the other.
Don't be worry if you don't fully understand the schemes above. You can come back to this page one you are more schooled in wiring diagrams.
On next part, we are going to discuss the modular approach to design your own diagrams.