Humbuckers, Polarity and Phase
In the last blog we looked at why you get unwanted hum from single coil pickups. Now, we are going to look at two coil pickups or ‘humbuckers’ as they are commonly known and also why magnetic polarity and wind direction are so important when installing pickups.
The reason why humbuckers effectively tackle 50 (or 60) cycle hum and electromechanical interference that if you run a signal through a coil in one direction then reverse it in relation to the magnet and wind in the next one, the waves of the AC current’s oscillating 50 cycles (i.e the hum) go unseen by the pickup. The two coils are wound in different directions; looking from the top) one is wound clockwise and the other counter-clockwise. In addition, the magnets inside the coils have opposite polarities. One coil has the north side of its magnet at the top and the other has the south side of its magnet at the top. These two factors are the ‘polarity’ and ‘phase’ of pickups. Phase and polarity are why, even though all three Stratocaster pickups may look the same, you will probably run into problems with phase and hum if you put them in a different position to the one indicated on the pickup.
If you have a Stratocaster or another guitar with two single coils you can get the humbucker effect in the switch ‘mix’ position, but only if both the polarity and wind direction are opposite in the two mixed pickups. A stock factory fender Strat's middle pickup should always be opposite in polarity and wind to the bridge and neck pickup. If the polarity and wind were the same in both pickups you will have an in-phase arrangement but you will not not get hum cancelling. But, if only one of either the polarity or the winding is different, you will get phase cancellation - what’s called an ‘out-of-phase’ signal (see the diagram above). This is where most of each coil’s signal cancels out the other coil’s signal because the waves are working in opposite directions. Because no two pickups are identical, some of the signal will get through, but it won't be a very full sound and it will be quieter. You only get both in-phase and hum cancelling if both the phase and winding are opposite in the two coils.
An out-of-phase sound is 'thin' - quieter and lacking in middle range. Some guitarists find this sound useful and some even prefer to have their pickups wired this way. Peter Green of Fleetwood Mac deliberately used out-of-phase humbuckers in his Les Paul. However, most people prefer the beefier in-phase sound and would want to avoid a permanent out-of-phase effect with their humbucker or when mixing two single coils.There was a period in the eighties where many Japanese companies' guitars came equipped with in/out phase switches and it is not a difficult mod to achieve if your humbucker has separate wires for each coil.
Using the following polarity and winding direction combinations will give you the following results:
You will note that only opposite winding and opposite magnet polarity gives you an in-phase tone and hum-cancelling properties.
Some pickup manufacturers will tell you whether their pickups are reverse polarity and wind or ‘standard’ (although what is standard in terms of polarity is not agreed by manufacturers). Seymour Duncan, for example, produce standard and ‘reverse wound, reverse polarity’ (RWRP) pickups so that if you want to replace your pickups you can do so and avoid issues with phase and hum. This is certainly something to be aware of when you are considering replacing your pickups. We have sometimes had issues with a client’s replacement bridge pickup being out-of-phase with the middle and neck single coils, producing a thin mix position. Because there is no agreed standard for coil wind direction and magnetic polarity, it’s not easy to know what the wind and polarity of your pickup is and you will need specialist equipment (a centre position microammeter) to properly test polarity.
Ideally, on a three pickup guitar the middle pickup will have reverse wind and polarity, so that when it is
mixed with either the neck or bridge pickup, hum is cancelled and the guitar is in phase. The same
should apply to a guitar with two single coils, like a Telecaster. In our experience, this often isn’t the case, especially with less expensive guitars, like the Ibanez RG pictured here, where the two single coils are identical and therefore not hum cancelling. At a guess, this is because it would cost more to produce two differently wound pickups and maybe it’s just easier and more reliable to pull out all the pickups from the same box when assembling a guitar on a production line.
One thing worth bearing in mind when coil splitting a humbucker is that, when split, it is preferable to use the coil which is RWRP to any other pickup you may want to mix it with. For example, if you have an H-S-S format strat, you need the split humbucker’s live coil to be opposite to the middle position single coil and this may not be the one which the manufacturer defauls to in their wiring recommendation. The same would apply in a guitar with two split humbuckers of differrent type. You will need some equipment to work out the polarity and wind, or you can take the experimental road and swap the wires around until it’s right!