Ever heard about either Alembic or Wal bass guitars and their preamps? I bet you have. Alembic is from the USA. It’s fancy, often weird looking and extremely expensive. Wal is British. It has a somewhat more regular shape. A bit more workmanlike overall, but still very expensive. Both basses are built out of wood pieces that you can only see in high end furniture otherwise. So why are they in the same article? What’s the connection? Well, it’s the preamp.
Wal or Alembic – the secret is in the preamplifiers
In a passive (non-powered) system, the pickup, the potentiometers in the guitar, the cable and the input of the amplifier form what’s called a 2nd order low pass filter. It means that the resulting signal will have a 12dB/octave roll-off slope. Not only that, but at the corner point of the slope, it will form a nice, healthy resonant peak. That resonance is the very thing that gives character to every passive magnetic pickup. Depending on the actual pickup, it can be anywhere from about 1 to 5kHz (usually). The frequency of this resonance can then only be changed slightly with changing the capacitance of your bass/guitar cable. Which practically means, longer cable = lower resonance.
The preamps in both the Wal and the Alembic basses emulate that behavior with active, powered circuits. In the case of a regular, EQ equipped preamp, you only get bass, treble and sometimes a mid control. Even if you can boost any of these, the peak will not be strong enough to form a well audible resonance. Also, the roll of slope of a usual active system is 6dB/octave. Ever wondered about that crisp top end active basses and guitars have? That’s the reason why. The preamps in Wal’s and Alembic’s instruments have a so-called Sallen-Key low pass filter. It’s able to control where the resonant peak occurs. They just had to design the circuit so the resonance range falls in the gist of the audible spectrum. It means that you can have your very own signature sound. No wonder such diverse artists like Stanley Clarke, Mark King, Geddy Lee or Mick Karn could find their own voice on these kind of basses. Or more like they could sound even more like their natural selves. Only on steroids. Of course there are a couple tricks done to the pickups themselves in the case of both Wal and Alembic, that makes them even more unique. Just think of Wal’s separate coils per each pole piece. These are then summed in pairs with their own buffers. Just like what a Music-Man Stingray or most double coil EMG pickups do. Only in the case of the Wal, doing so will bring the natural peak of the coil pairs much higher, resulting in a flatter, more natural response. Thus giving a better base for the electronics to alter the sound.
Mod your bass to get closer
While these basses are really expensive, you can find other makers who at least make very similar preamps. These will get you in the ball park. You can also try and make your own. Good luck for that and don’t solder your fingers.