The new Bartolini b-axis pickups series is based on the very foundations of Bill Bartolini's initial pickup designs back in the early '70s. The main design principle was to provide a highly asymmetric magnetic field in order to preferentially sense string vibrations normal (perpendicular) to the string plane. This high asymmetry provides tonal characteristics similar to acoustic instruments, which have a naturally asymmetric response due to the bridge structure and increasing and decreasing biased tension.
Initially, Bartolini pickups were branded as 'Hi-A' as shorthand for high asymmetry, but the brand was later changed to Bartolini for the same pickups designs. Some of the first Hi-A pickups were multi-coil such that they had a coil for each string and some were split coil such that each coil would sense multiple strings. From those first designs forward, Bartolini has been focused on asymmetric response. Most of our designs to this day feature magnetic structures to create asymmetry. Therefore, the magnetic structures are much more complicated than what is found in what we call Simple Flat-work Pickups (SFPs) where a magnet is pressed into flat flanges to create a bobbin for winding the coil. Due to this complexity, our pickup structures (or skeletons as we call them) are often not physically self-supporting, so we encapsulate our pickups in epoxy. This of course has additional benefits of keeping out moisture and sweat while also eliminating microphonics.
For decades, customers have been asking us for pickups with exposed pole pieces. Many design iterations and prototypes have been produced. Without creating an SFP, we had two primary challenges: 1. How do we have holes in the shell for pole pieces but still encapsulate the structure in epoxy? 2. How do we create an appropriate asymmetric field relative to the coil without modifying the top of the magnets? The solution comes down to precision. We now have the capability to control positioning of the skeleton in the shell with accuracy of 5 thousandths of an inch. This allows us to stage the encapsulation process with a milling process to create the holes for the magnets after the skeleton is already assembled. We create a precise magnetic structure along with the Alnico V magnets, below the surface of the pickup shell so that we can control the magnetic coupling to the coil on each side variably with the traverse of the string. The optimal magnetic structure offset to the coil was calculated to be contained in a 26 degree angle with a separation of 0.053" between pole magnets. And we have the technology to create very precise full bobbins to position the coil wire relative to the magnetic structure for control of the relative level of asymmetric response.
The result is a fully encapsulated pickup with exposed poles and asymmetric response that provides a huge punchy tone.