Audio Merge KTBK-1B 'King Tubby’s Big Knob'

The Audio Merge  KTBK-1B "King Tubby’s Big Knob" is a completely passive, single-channel variable high-pass dub filter and vintage-style equaliser based on the classic Altec 9069B design, featuring a 3rd-order passive filter topology, 10 stepped cut-off frequencies from 70Hz to 7.5kHz, selectable filter modes, adjustable resonance control, 600Ω impedance architecture and a handcrafted multi-tap inductor coil to deliver authentic analogue tone with modern studio adaptability.

A Classic Dub Filter Reimagined for the Modern Studio

The King Tubby’s Big Knob KTBK-1B recreates the legendary tone of the Altec 9069B, a vintage passive program equaliser introduced during the 1960s. Audio Merge designed the unit to capture the unmistakable character of the filter that appeared on King Tubby’s MCI mixing console, widely recognised as the producer’s “Big Knob” secret weapon used to shape dub mixes.

The original circuit relied on a passive inductor-based T-network filter with toroidally wound inductances, producing an 18dB per octave slope and discrete stepped frequency selection. Audio Merge recreates this behaviour using a custom multi-tap inductor coil, validated with DSP analysis to achieve a highly accurate frequency response and consistent stereo pairing in modern production environments.

The KTBK-1B retains the signature stepped filtering behaviour while adding modern control features that expand its creative potential in contemporary music production.

Variable Passive High-Pass Filtering

The filter section provides ten discrete cut-off frequencies ranging from 70Hz to 7.5kHz. Each position introduces a defined step in the high-pass response, which allows engineers to sculpt low-frequency content while preserving musical tone.

The circuit originally targeted dialogue and broadcast processing applications where engineers needed to remove rumble, hum and other low-frequency noise. In modern production the same filtering structure shapes bass content, enhances mix clarity and introduces character when used creatively in dub and electronic music workflows.

The passive architecture requires no power supply and maintains extremely low distortion with a THD rating below 0.01 percent at 1kHz and +17dBu. The design supports a maximum input level of +38dBu and provides a flat frequency response within ±0.5dB from 10Hz to 70kHz when bypassed.

Three Distinct Filter Modes

The KTBK-1B expands the original Altec response through a selectable filter mode system that dramatically increases tonal flexibility.

The 600 mode reproduces the original Altec 9069B response and operates with a 6dB insertion loss, preserving the classic behaviour of the vintage circuit. Engineers can use this setting when they require the authentic passive high-pass filtering characteristics of the original design.

The Bell mode recreates the signature sound associated with King Tubby’s dub mixing techniques. This mode generates a resonant high-pass filter response without insertion loss, creating a pronounced resonance peak above the selected cut-off frequency. Engineers often sweep this response to produce phasing-like effects when the filtered signal blends with the dry mix.

The Notch mode introduces a unique Audio Merge design that behaves as a variable notch filter. The attenuation level and Q factor change dynamically depending on the selected cut-off frequency and resonance setting, creating an unconventional filter response that engineers can use for creative tonal shaping.

Resonance and Damping Control

A dedicated resonance level control allows engineers to adjust the damping of the filter response. Six damping levels shape the resonance behaviour in both Bell and Notch modes.

This feature enables precise tuning of the filter’s peak response, allowing subtle tonal enhancement or dramatic resonant sweeps during performance and mixing.

Passive Circuit Design

The KTBK-1B uses a completely passive signal path that requires no power consumption. The circuit relies on carefully matched impedance levels to maintain correct filter behaviour.

The design follows the original 600Ω input and output impedance specification used in the Altec circuit, while the mode selector allows compatibility with a wide range of modern studio equipment. This ensures the unit reproduces the classic high-pass response or generates a resonant filter depending on the selected configuration.

Custom Inductor and Precision Construction

Audio Merge builds every KTBK-1B unit by hand in Barcelona. The engineers designed a custom multi-tap inductor using extensive frequency response and phase analysis to achieve accurate cut-off frequencies across the stepped selector.

The rotary switch offers a smooth but controlled resistance, allowing engineers to perform frequency sweeps during live dubbing or mixing while maintaining precise step positioning.

Inspired by the Altec 9069B Legacy

Arthur Davis designed the original Altec 9069B as part of the Altec 9067B programme equaliser system. The device served broadcast, radio and cinema applications where engineers used filtering to simulate distance effects or control low-frequency noise.

Dub pioneer King Tubby later incorporated the filter into his MCI mixing console, where its stepped switching, audible clicks and phase interactions with the dry signal became part of the distinctive dub production aesthetic.

The KTBK-1B captures this sonic heritage while introducing modern flexibility for contemporary recording and mixing workflows.

Why Choose the Audio Merge King Tubby’s Big Knob KTBK-1B

• Delivers the authentic sonic character of the legendary Altec 9069B filter used in classic dub productions

• Provides powerful tone-shaping capabilities for mixing, sound design and creative filtering

• Produces distinctive resonant sweeps that recreate the iconic King Tubby dub mixing effect

• Integrates easily into modern studio setups while maintaining vintage circuit behaviour

• Offers highly musical stepped filtering that enhances analogue character in digital workflows

• Supports creative performance techniques through smooth stepped switching and resonance control

• Provides handcrafted build quality with carefully tuned passive components

• Passive 3rd order variable high-pass filter based on the Altec 9069B design
• Ten stepped cut-off frequencies from 70Hz to 7.5kHz
• Three selectable filter modes: 600, Bell and Notch
• Six resonance damping levels for Bell and Notch modes
• Custom multi-tap inductor coil for accurate frequency response
• DSP-validated filter curves for consistent stereo pairing
• Passive signal path with zero power consumption
• Maximum input level of +38dBu
• Total harmonic distortion below 0.01 percent at 1kHz +17dBu
• Frequency response within ±0.5dB from 10Hz to 70kHz in bypass
• 600Ω input and output impedance
• True bypass switching
• 6dB insertion loss in 600 mode
• Zero insertion loss in Bell and Notch modes
• Smooth stepped rotary switch for frequency selection
• Handbuilt construction in Barcelona
• 1/4-inch input and output connections
• Compact desktop chassis design

This item, like everything we supply, comes with the complete support of our expert team. Our excellent technicians have been specifying, building and supporting studios for over twenty years. If you have any problems with installation, setup or everyday use, they’re never more than a click away, and always happy to help.

You can contact them here.