Conventional magnetic pickups have been constructed based on principles known for centuries and the fundamental design has not changed since perhaps the 1930s. There are magnetic pole pieces or bars underneath metal strings, with many coils of thin wire surrounding the magnets. As the strings vibrate, they change the magnetic field and this change induces a voltage in the coils. The more coils you have, the higher the output. You can have higher output voltage, but the impedance goes up with the number of coil windings and thus will limit the cable length you can drive without significant signal and high-frequency loss. This is simple physics from Faraday’s Law which is more generalized in Maxwell’s Equations.
With the Alumitones, Lace has designed something using the same physics principles, but using a different approach. Instead of multiple, small magnetic pole pieces and a large number of turns of wire, Lace use a planar magnetic structure and a single loop of aluminum (as the coil and mechanical structure!) surrounding the magnet. The output is then inductively coupled to a secondary transformer which provides the output. The coil windings are thus shifted to the secondary transformer and this can be optimized for size. The Alumitone is smaller and lighter, provides higher output, is quieter, and has increased frequency response from a standard magnetic pickup.
The Alumitones have a flatter and higher frequency response due to its low impedance, but it also has an impedance mismatch to amplifying devices. So a secondary transformer is used to convert the signal to the correct impedance and voltage levels. This is exactly what a transformer is used for (i.e. like an output transformer interfacing a vacuum tube circuit to a speaker).
Since there are two parts to the pickup design, you can optimize them separately as opposed to a conventional design where it’s all one magnetic coil structure producing the output.
A lot of people like the Alumitones because of their flatter response, similar to active pickups like EMG. Metal players especially like this since a full frequency response can contribute to tighter, more aggressive tones. Fans of conventional blues or guitar tones may not like it, and normally use the word “sterile” to describe the sound (similar to EMG pickup sound descriptions). This might be true, but in fact the pickups are more representative of the string vibrations from the guitar — so it’s the guitar that is in fact sterile! In fact, some of the best guitar tones are because the guitar and/or pickups are subtracting and filtering out frequencies — and this contributes to the tonal character. Full response pickups do have their place in music (metal high gain, modern processed clean), so the Alumitones do have a place. I suspect also that sculpting of the magnetic structure and secondary transformer could yield less of a full-response pickup and something which blues guitarists would like.
Kudos to Lace for reinventing the magnetic pickup!