Tuesday, 31 March 2015

Pickups: Pole Polarity and Phase

Every pickup coil has two properties that affect how they will sound when they are combined with others. These properties are called phase and polarity. Phase is the direction current travels through the pickup. Polarity is the direction of the magnetic field in the polepiece magnets. With both properties, there are only two options:

Phase: can either be "top coming" or "top going", where "going" in this sense refers to the direction of the current traveling towards ground.

Polarity: can either be south or north, and refers to the magnetic polarity of the polepiece magnets closest to the strings.

The phase of each coil is indicated by connections to "output" and "ground"
when the direction of wind is constant. The polarity is indicated by the magnetic
pole indicators on the top of the polepieces.

A typical application of these principles is with single coil pickups. One interesting property of single coils is that depending on their phase and polarity, it may be possible for them to be hum cancelling when combined. The key to a strong, full tone with hum cancelling is to combine single coil pickups that have both opposite phase and opposite polarity. If one pickup is north polarity, top going, the other must be south polarity, top coming. That is to say, the secobd pickup must be what is known as reverse wind - reverse polarity, or RWRP for short.

Humbuckers all operate on this same principle. The two coils have opposite wind and opposite polarity. When combined, the hum is cancelled out. Splitting a humbucker will, of course, bring the hum back!

For two single coil pickups to be in phase, both the magnet polarity and the wind direction have to either be identical, or opposite. In other words, two pickups with the same wind and polarity will be in phase, and so will two pickups that have opposite polarity and wind. If the two pickups have the same wind but different polarity, or the same polarity but different wind, they will be out of phase with each other.

The most common reason for two single coils to be out of phase is that one of them is wired backwards. The lead that was supposed to be connected to ground is connected to the output, and vise versa. This wiring error effectively changes a top coming pickup into a top going.