Fig. 8 — Photo by Dan Formosa
Alnico 2, Alnico 5, and Ceramic Magnets
Alnico 2 and 5 are the most common forms of the aluminum/nickel/cobalt alloy magnet. Alnico 5 is stronger than alnico 2—as the numbers increase, so does magnetic strength. There are stronger versions, such as alnico 6 and 7, but they aren’t as useful because stronger magnets can create a harsh tone.
To that point, ceramic magnets, which are less expensive to produce and easier to shape, were commonly used in inexpensive guitars arriving in the U.S. from overseas. There was an additional price advantage: The stronger pull of ceramic magnets meant manufacturers could use less copper wire in the coil. This was truly a cost-cutting measure with little attention paid to sound quality. As a result, ceramic magnets developed a bad reputation, but this may be somewhat unfair.
In fact, ceramic magnets can be effective, if used with care. Seymour Duncan, among others, has developed pickups that employ ceramic magnets wisely, and they appear in several of his models. Curtis Novak has changed his opinion over time. “I used to turn up my nose at ceramic magnets, but I have found some really good uses for them. They can deliver a tone that is not shrill, spiky, and harsh. Using steel poles and a ceramic magnet won’t sound like a Strat, but you can make some really fine pickups by working with the coil and using different grades of ceramic.”
That said, the properties of alnico 5 seem to hit a sweet spot. Too much pull in a magnet requires a weaker coil, too little pull requires a coil with additional windings. Novak’s observation: “When guitar manufacturers embraced alnico 2, it’s because they hadn’t come up with alnico 5 yet!”
Single-coil and Humbucking Pickups
Hum in a pickup results from stray electric signals reaching the coil. To counteract this annoying sound, humbucking pickups employ equal-but-opposite coil windings that cancel the hum, or at least greatly reduce it to an acceptable level. Their invention is usually associated with Seth Lover’s design for Gibson (Fig. 8) and Ray Butts’ design of the Filter’Tron for Gretsch, which were both developed in the mid 1950s. However, origins of a hum-reducing pickup date to the mid 1930s. The pickup being developed then, patented by Armand Knoblaugh and assigned to the Baldwin Company, was intended to amplify pianos. Going even further back, in 1912 Western Electric created hum-cancelling technology for use in telephone amplification. (See Wallace Marx Jr.’s article, “The Pickup Story, Part III: The Road to the Humbucker” in the December 2009 issue of Premier Guitar.)
The 1950s hum-cancelling designs placed equal-but-opposite coils side-by-side, essentially combining two mirror-image single-coil pickups. For a long time, you could easily identify hum-cancelling pickups by their larger size. But noise-cancelling, single-coil-size pickups were eventually developed to fit into Fender-style pickup cavities.
Fig. 9 — Photo by Dan Formosa
Their coils were either stacked one on top of the other or positioned in line (with one coil wrapping around the poles for the three high strings, the other around poles for the three low strings). DiMarzio and Seymour Duncan have each been offering hum-cancelling single-coil replacements since the mid 1980s. Fig. 9 shows DiMarzio’s 1984 stacked-coil patent.
Our final topic concerns pickups that have become microphonic. In addition to the strings interrupting the magnetic field, voltages can be induced simply by vibrating the coil or the magnet. If loose pickup parts begin vibrating with resonant notes or the vibrations in the body of your guitar, the pickup will act like a microphone, ringing unwantedly. In some cases, even yelling loudly into the pickup will transmit your voice through the amp.
The solution is to “pot” the pickup by dipping it in melted wax, securing the parts to prevent them from vibrating. Many pickups have already been potted by the manufacturer. For other pickups that need potting, it’s a quick, simple procedure: Let the pickup soak briefly in a medium-hot wax bath, remove it, let it cool, and then reinstall it. As with so many guitar-related subjects, there’s plenty of debate about how potting can affect a pickup’s tone. Some guitarists prefer the liveliness of pickups that aren’t potted, but if you play really loud, potted pickups reduce the likelihood of screeching feedback.
It’s a WrapThis is an introductory article, so there are plenty of topics we didn’t get to cover. For example, the rubbery refrigerator-type magnets and low winding count used in Teisco’s “gold foil” pickups, or the inner workings of DeArmond’s relatively flat archtop-mounted Rhythm Chief, which we mentioned earlier. But all electromagnetic pickups follow the same science-class principles, and once you understand the basics, it’s easy to dissect any pickup and figure out how it works … more or less. I suspect most pickup designers would agree that pickups, like many other topics, follow a general rule: The more you learn about them, you realize the less you actually know. With that thought in mind, class dismissed.