Filter-Based Preamp for Bass

As someone who has owned several Alembic basses, I have always found their electronics to be truly special. Unlike most other basses that feature passive tone controls or simple 2- or 3-band EQs, Alembic basses come equipped with a unique 12dB-per-octave low-pass filter that features a widely adjustable cutoff frequency and a resonant peak just before the cut. With just one knob, you can easily achieve a wide range of tones, from the darkest dub and reggae sounds to the brightest slap and funk tones and everything in between. 

While synth players routinely use resonant filters, they are not common among bassists, who may only encounter them on a few high-end, boutique instruments.

Initially, I built an exact replica of the Alembic filter, which performed exceptionally well. However, I later identified areas for improvement. I optimized the operational amplifier biasing approach, increasing the battery life by over three times. Additionally, I made modifications to ensure compatibility with virtually any bass or common stomp box. This was necessary because the original Alembic design utilized an uncommon grounding scheme that was not compatible with the wiring of most basses and pedals. This process led to the first version of the Distiller:

Distiller REV1

The second revision adds Alembic-compatible 2- and 3-pin headers (Molex KK 254 series), making it very simple to integrate with Alembic pickups or basses without the need for soldering. However, for those (such as myself) who prefer to solder everything, oversized soldering pads are still available on the back of the board.

Another new feature in REV2 is the integrated output summing resistor, which allows for combining two Distillers by simply connecting their outputs in parallel through a pickup selector or blend pot.

Distiller REV2

The third revision (purple) includes the capability to support two different potentiometer sizes on the same board. This was a necessary change as the original gray potentiometer was no longer available. As an alternative, I sourced a more readily available part, from the same reputable manufacturer (TT). When equipped with the small green pot, the product is referred to as "Distiller SE" (Special Edition). If the larger gray pot becomes available again in the future, it can still be retrofitted.

Distiller REV3 (SE)

Distillers flying in formation. I think they're migrating southward to escape the Canadian cold.


Input impedance 1 MΩ
Output impedance 2.7
Supply voltage 9V or 18V
Current draw 0.3mA
Battery life (alkaline) 1200 hours
Noise floor -99dBu
Dynamic range 108dB
Cutoff freq. range 250Hz - 8kHz
Slope 12dB/octave
Resonant peak 0 / 5 / 9dB
Gain trim range +3 to +12dB
Board size 21x34mm 

Video Demo