Well, pickups have a default sound but, this sound can change in determinate circumstances. We are going to see the different ways that common pickups are working and which alternate sounds can give.
Single Coil Pickups
We saw that a wire is wrapped around a magnet (or magnets) in a long run of about 7500 turns. One of the extremes of this wire is the Start wire and, the other extreme is the Finish wire.
Usually, the start is considered negative and it's being grounded, while the finish is considered positive and it's linked to the signal output. This will deliver the sound as it was designed, with the right magnetic and electrical phase.
Every coil has an start and finish wire and, every pickup has a plate ground wire.
So, we can have three wires in a single coil pickup: the start, the finish and the plate ground. On single coils, usually the plate ground is being soldered together to the start wire.
If the pickup has a metallic cover, that metallic cover is soldered to the plate ground. That helps to create a Faraday's cage around the pickup, with a good rejection of EMI and RF interferences.
The drawback is that, if you do an out-of-phase mod, and you aren't separating the plate ground wire from the start wire, you are positivizing the cover and creating some kind of antenna that it's potentially noisy.
So, if you ever had to work with an out-of-phase mod for a single coil with cover (as some P90, by example), you should separate the plate ground wire (that would be grounded, always) from the start (negative) wire (that can go to hot or ground, on demand).
See this picture, where it is shown the two ways to wire a single coil pickup.
The upper case corresponds to the regular way to wire a single coil pickup. This is being (wrongly) called in-phase.
The lower case corresponds to the alternate way to wire a single coil pickup and it's being (wrongly) called out-of-phase.
What in and out of phase really mean is that you reversed the electrical polarity of the signal but, signal phase has nothing to see with all that. But, because this is the wide spread name, we will use it to describe this kind of arrangement in our wiring.
Remember that, the plate ground and start wires can be soldered together (this is the usual stock way of delivering single coil pickups). You will notice that some Telecaster's pickups have 3 conductors, instead of the typical 2. This is because they are separating the plate ground from the start wire, to allow you to perform some mods that include an out-of-phased pickup (as seen in the Fender Tele Baja Player, by example).
Any pickup out-of-phase alone, has no noticeable change on its sound (well, some people can hear very discrete and negligible differences). When it makes the real difference is when it's being selected together (in series or parallel) with other pickup then, the sound becomes hollow, thin, nasal and twangy. The depth of the effect depends on the two pickups being combining and, how their respective frequencies are being cancelled or reinforced.
Tapered single coil pickups
A tapered coil has two finish wires. The first one corresponds to the number of turns that provide a vintage-like tone while, the second one adds some additional turns to make the coil hotter. This is a very wise way to use same coil to deliver two very different flavours, one vintage and, one more modern, with more attitude. Imagine that you connect a wire to the turn number 7500 but that, you continue wounding the coil up to 15000 turns, where you have the real end of your coil's wire.
To choose one or the other finish wire can be done with the help of a SPDT on/on switch.
Look at this diagram:
There are two ways as you can considered the tap wire. If the tap wire is closer in turns to the finish wire, you can use the diagram above, this will consider all the turns between the coil start and the tap wire and, the whole coil for the finish wire.
In the case that the tap is closer in turns to the start, you can ground the tap to achieve less turns, instead.
In any case, if you route to hot the tap wire, you will consider the number of turns between the start wire and the tap wire. If you ground the tap, you will consider the number of turns between the tap wire and the finish wire.
Therefore you can have up to three different sounds in a tapped coil: start-to-tap, tap-to-finish and start-to-finish. Three different number of turns, lead to three different sounds.
Sometimes, the number of turns between the tap wire and the finish wire are so small that we cannot achieve an useful sound for tap-to-finish combination but, if the pickup is hot enough, we can do this:
On this diagram, the different status of the DPDT switch are shown with that purple lines connecting the lugs of each pole for each of the three positions of this DPDT on/on/on type 2 switch.
The Upper case, will give us a tap-to-finish coil' sound.
The Middle case, will give us a start-to-finish coil' sound.
The Lower case, will give us a start-to-tap coil' sound.
So, imagine that we have the coil wound as vintage from start-to-tap and, vintage-hot from tap-to-finish. We can achieve very three different sounds: up = vintage-hot, middle = modern-hot, down = vintage.
But, this is only possible depending on how the pickup was tapped.
We will continue describing the 6 different sounds of a humbucker, in next Part 07.