The Cover and Base Plate of Guitar Pickups
In addition to the bobbin, a guitar pickup’s cover and base plate are ingredients that are mainly there to help hold it all together and protect the delicate internal wires, yet they can have a slight effect on the sound, too. You can take a look at the cover and base plate in the figure.
Both of these parts are somewhat self-descriptive. The cover is the outer shell, usually seen from the top of the pickup, which protects the coil and is often somewhat decorative; it can be made from metal or some type of plastic.
The base plate is generally screwed to the bottom of the coil and often helps to hold any magnets in place. It’s frequently made from some form of metal but occasionally a paper-fiber or plastic material.
Pickups are electromagnetic devices, so even though covers and base plates are mainly decorative and/or protective, any metal cover or base plate that has shielding, conductive, or magnetic properties can also act as an active part of the pickup, enhancing or attenuating the way other components within the structure perform. A couple of famous examples of these that actually influence a pickup’s performance include
The cover on a traditional Gibson-style humbucking pickup: Made from nickel-silver (also called German silver, a nickel alloy that’s not really silver at all), this cover can attenuate the pickup’s high-end response slightly, which is why some players remove them from their pickups. Many good contemporary pickup makers design their covered humbuckers with this in mind, so removing the covers may actually make them too shrill.
The tin base plate on a Telecaster bridge pickup: This plate increases the inductance of the pickup, thereby fattening its midrange and low-end girth just slightly.