To successfully install replacement pickups in a guitar, you need to understand this essential parameter.
A typical pickup description includes a laundry list of specs. If you want to be a savvy shopper, you'll need to wrap your head around these terms, but that can be tricky because manufacturers don't always use technical terms in a consistent way. So to make sense of pickups, we're on an ongoing mission to learn how to interpret key specs and understand why they're important. We began this exploration with the DCR value (“Demystifying DCR"). Now let's examine another important pickup spec—polarity.
We can define a pickup's polarity as the direction of its magnetic field—either south or north—as measured facing upward toward the strings. Taken together with the pickup's phase, which is the direction current travels through it, polarity is a critical parameter whenever you use two or more pickups in a wiring.
Here's why: If you want to combine pickups from different manufacturers in your favorite axe, you must take each pickup's phase and polarity into account. If you don't, you may wind up with an out-of-phase issue when you select multiple pickups with your 3-way or 5-way switch.
Another important thing to consider is the hum-cancelling feature that's available when two single-coil pickups have opposite phase and opposite polarity. Chances are good you've seen RWRP (“reverse wind, reverse polarity") in a pickup description, especially when used to describe Strat middle pickups. We'll devote another column to discussing phase—it's a big subject. But regarding polarity, here's what you need to know: To cancel hum when running two single-coils in tandem, one pickup needs to have north polarity and the other south polarity.
This principle also applies to all humbucking pickups. In a humbucker, the two coils have opposite phase and opposite polarity, so when you combine them either in series (which is the standard configuration) or parallel, the pickup will cancel hum. Many advanced wirings include a switch for splitting a humbucker's coils. Engaging only one coil in a humbucker leaves you with a single-coil pickup that's susceptible to hum. The fun really starts when you want to combine two or more humbuckers and have the option to split them. Split humbucker coils now act as two single-coils, so it can be tricky to maintain hum-free operation in this configuration.
So what happens if you combine mismatched pickups? You'll hear hum or out-of-phase tones. In the worst scenario, you'll get both at once. I think we all know the typical out-of-phase sound—a shrill, hollow tone. Although this can be cool to cut through the mix when used with a lot of distortion (think Brian May), it's generally not what you want as your guitar's default tone.
In a nutshell: If you want two pickups to be in phase, both the magnet polarity and the wind direction have to be either 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. Sounds complicated, right?
Photos courtesy of singlecoil.com
No worries. Once we explore phase as a pickup parameter in a future column, you'll discover that it isn't rocket science after all. We'll end up with a nice table of different combinations of phase and polarity, and that will make it simple for you to match pickups without any issues.
But back to polarity. Most manufacturers don't mention polarity in their pickup descriptions, but there are ways to determine a pickup's polarity, assuming you have it at hand. If you need to establish polarity before ordering a new pickup, your only option is to contact the manufacturer for that info.
There are several devices on the market specifically made for testing a pickup's polarity, and every guitar tinkerer should have one. My favorite is the Schatten Magnetic Polarity Tester ($11 at stewmac.com). It's a see-through tube with a magnet inside, and you simply place it above the pickup you want to test to receive a clear reading of north or south polarity (Photo 1).
In these days of GPS and iPhones, you may not have an old-school compass, but if you do, you can use it to test pickup polarity. Simply place your compass on the pickup (Photo 2). The pickup's magnetic pole pieces will attract the opposite magnetic polarity end of the compass needle, which means the end that's pointing up away from the pickup indicates its polarity. In this photo, the compass needle shows the polarity of the Strat pickup's pole pieces is oriented north up.
So that's it. Next month we'll tackle another guitar project. Until then ... keep on modding!