Filter-Based Preamp for Bass

Having owned several Alembic basses, I've always found their electronics to be truly special. Unlike most other basses using passive tone controls or conventional 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 access a very 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 found some opportunities for improvement. Power optimizations tripled the battery life. Additionally, I made a few modifications to ensure compatibility with virtually any bass or stomp box. This was necessary because the Alembic filter utilizes an uncommon grounding scheme that is not compatible with the way most  basses and pedals are wired.

Version history

First edition
-introduced in December 2020

Second revision
-adds Alembic-compatible Molex headers, enabling drop-in replacement of the original filter
-adds an output summing resistor, making it possible to combine two or more Distillers by simply paralleling their outputs, as if they were passive pickups.

Third revision
-supports two different potentiometer types on the same board. The original grey pot is extremely hard to source, so I switched to a smaller, green potentiometer from the same top manufacturer. When fitted with the small pot, the filter is now called Distiller SE (Special Edition).

4th revision  (current as of March 2024)
-Molex headers replaced with a ubiquitous inline pin header
-the Q switch gets its own little circuit board
-noise floor further reduced compared to Rev3 (-103dBu vs -99dBu).

Specifications (revision 4)

Input impedance: 1 MΩ
Output impedance: 2.7
Supply voltage: 9V or 18V
Idle current draw: 0.3mA
Battery life (alkaline): 1500 hours
Noise floor: -103dBu
Max unclipped output: +12dBu
Dynamic range: 115dB
Cutoff frequency range: 250Hz - 8kHz
Filter slope: 12dB/octave
Resonant peak (Q switch): 0 / +5 / +10dB
Gain adjustment range: +3 to +16dB
Board size: 33x23mm
Potentiometer: sealed, long life (100,000 cycles), conductive plastic. Ø6mm shaft, M7x0.75 bushing

Official Distiller Demo

Combinator / Sean Fairchild having fun with his new Distiller SE 

(Check out his other videos too, he's incredible!)