Size Does Matter with pickups …. and the coils of Mini Humbuckers & Filtertrons are too darn small. UPDATE March-2021: we have solved the problems with these types of pickups, check out our fabulous new Mini-Bucker's in the humbucker section.
Here's what we previously believed: Cramming small gauge wire into small bobbins inevitable results in a excessive Parasitic Coil Capacitance***. In these pickups Parasitic Coil Capacitance acts like an eq circuit and singles out certain harmonic frequencies most audibly on the low wound strings robbing them of important midrange frequencies which impacts severely on definition and attack.
The Gretsch Filtertron from some accounts has a twangy sound but when I played one recently I immediately heard the low E and A string sounded muffled and very indistinct.
Only the D & G strings had any kind of focus and twang, and even then it wasn’t quality twang but more the product of upper midrange spikes that are the precursors to ear piercing harshness. I wondered if the pickups I tested were somehow faulty but on every sound clip on the Internet I heard the same thing, and then I read on some forums players complaining about the very same thing. I since read an interview with Ray Butts and it seems Chet Atkins wanted that dull, thuddy wound string sound for his finger picking style where his thumb would play bass lines and his fingers played the melody lines on the other strings. Well that's fine if you play Chet Atkins style.
Players complain about the indistinct sound of the low wounds with humbuckers but Mini-buckers and Filtertrons are far worse simply because their coils are too darn small.
Compact (economy) pickups such as dimarzio Area (Strat) series suffer from the same problem.
Kinman in the past has refuses to make these types of pickups because we know there is no way to improve their sound because of the limited dimensions, in other words it’s against our religion to use flawed designs.
UPDATE 20-Oct-2017: Boss Chris is a tireless innovator always looking for solutions to problems. Kinman is very pleased to announce that we have found a solution to improve the sound of Filtertrons and Mini-humbuckers outta sight. We expect a sound with greater clarity much like a single coil and a fair degree of twang from the low wound strings. We hope to bring out a range of products late 2019.
Parasitic Coil Capacitance*** Parasitic capacitance (Cs) limits the self-resonant frequency of the coil, above which the coil will not behave as an inductor any more. In a first-order approximation, the parasitic capacitance of a planar coil usually has two major components: the capacitance between turns and the capacitance between layers. Courtesy of https://www.sciencedirect.com/topics/engineering/parasitic-capacitance