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"The KTBK filter gives exactly what you expect from it, whether on drum tracks, brass, rhythm sections or on a effects return bus."

Reggae Dub Producer

"It's amazing that something as simple as a HPF brings so much magic to the mix. It has become an essential tool in my day to day."

Reggae Dub Producer

"What a great job on the unit - sounds amazing! So much fun for the mix. Thanks for the great unit!!!"

Electronic Music Pioneer
Audio Merge KTBK-1B

An Equalizer with Vintage Flavour for the Modern Studio

For music-quality-conscious people who enjoy the warm character of an analog filter. The King Tubby’s Big Knob (KTBK) provides the same genuine tone as an Altec 9069B, a vintage equalizer, designed in 60s, which enable a great control over the sound tone. The KTBK unit includes two additional switches, a mode selector and a resonance leveler which allows to modify the filter response for adapting it to the modern studio for different phases of the music production workflow.

The KTBK filter is a very precise replica of the Altec 9069B adapted for the modern studio with new controls for impedance matching and resonance. It was designed through Reverse Engineering techniques and validated with DSP to achieve the most accurate cutoffs utilising a customized multi-tap coil.

New Altec Replica controls

Description and Features

Let's Design the Sound

Tweak the Big Knob to get different tones, textures and an unrivalled sound effect. Allows to remove rumble noise, the parasitic frequencies and muddy sound effect in order to reducing the masking effect and achiving a clear sound. The KTBK Variable Passive High Pass Filter has stepped frequency selection with ten unequally spaced cut-offs offering a crossover type action – 70, 100, 150, 250, 500, 1k, 2k, 3k, 5k and 7.5k. A need when it is required an accurate control of the sound tone.

Multifaceted Equalizer

Passive filters are very sensitive to the impedance matching. Originally, the Altec 9069B was designed to perform with a 600Ω impedance transfer standard and currently modern audio equipments require other values. Our unit includes a mode control switch to be adapted to any equipment, allows to reproduce the original HPF response, or to generate a resonance bell over the cut-off frequency.

Sweep the Sound like
a Dub Master

Sweep and layer your sounds with the KTBK filter to get unmatched sound signature. Perfect gear to create a dynamic mix with LO-FI tones! The digitalization has changed the way to record, produce and process music. It is time to explore new ways, taking the best of analog and digital domain.

Handbuilt with Love and
a Customized Features

The assembly and subsequent validation of each unit is manually done in our workshop, sited in Barcelona. The multi-tap inductor is a custom-designed element based on various frequency response and phase distortion analyses using different cores and coil winding techniques, in order to get the most accurate cut-off frequencies. The customized stepped rotary switch offers a very smoothed rotation resistance to guarantee the creative freedom during the performance. High quality ELMA rotary switch with proven solvency in the world of professional audio equipment. 

New Controls, New Curves

Passive filters are very sensitive to the impedance matching. Originally, the Altec 9069B was designed to perform with a 600Ω impedance transfer standard but currently audio equipments require other values. Our unit includes a mode control switch to be adapted to any equipment, allows to reproduce the original HPF response, or to generate a resonance bell over the cut-off frequency or a variable notch filter, we call it VARI-NOTCH because the attenuation level increases with the frequency.

KTBK Dev Details: When the quality is a must

Announce the release of AUDIO MERGE IN DIB feat. Roberto Sánchez & Chalart58 Dubbing with KTBK filter


📣 Audio Merge presents AUDIO MERGE in DUB feat.  Roberto “Lone Ark” Sanchez and Chalart58. 10 dubs LP mixed with the KTBK passive HPF filter unit.

KTBK-1B filter in Barcelona
basics in a modern home studio




We will send you a demo
for Ableton.

How Does the KTBK Sounds?

Drums - BELL Mode

Horns - BELL Mode

Thanks to Chalart58 and La Panchita Records for providing all these amazing sounds.

The Altec 9069B, The Influencer of the Big Knob

At the 60s, Altec Lansing launched the 9069B, a variable high pass filter designed by Arthur Davis. The 9069B was a passive inductor based T-network filter, with toroidally winded inductances which provides 18 dB/oct attenuation with 10 positions for low frequency cutoff to reproduce unmatchable sound tones. Originally it was part of the Altec 9067B unit with the LPF 9068B unit.

1950 - 1965
A Program Equalizer's Creator
If we speak about vintage equalisers, Art Davis is our man. He designed Graphic and Program Equalisers like the Altec 9069B, the Langevin EQ255a and the Cinema Engineering 4031 for different brands.
1950 - 1965
Altec 9069B Passive Program Equalizer
Originally comprised the class of sound effects filters used to simulate distant sounds, radiophonic voice, and other such spatial effects in radio and cinema sound design.
The King Tubby's Sound Signature
King Tubby, a Jamaican producer is considered as the dub music inventor and remixing. Tubby achieved an outstanding sound signature experimenting with recordings at his MCI mixing desk using an Altec 9069B, recognized as his secret weapon, in combination with reverb and tape delay effects.
Since 70s to 1989
The Big Knob, a Secret Weapon
"It was a red knob, slightly bigger than the others—hence its name Big Knob—, in the right top corner of the MCI console. The strongest characteristics of the filter's sound are the discrete steps, the clicks and crunches when the frequency is switched, and the phasing effect heard when filtered signals are mixed with the unfiltered originals." Extracted from Tubby's Dub Style thesis.
Since 70s to 1989
Since 1990
Dub Around the World
Dub Music is a form of music created at 70s, that gave birth to and influenced many genres of music for years, including Rock, Punk, Pop, Hip Hop, Disco, Folk and later House Techno and other EDMs. Indeed, Dub has become a basis for genres like Drum and Bass, Jungle and Dubstep. Nowadays, dub culture continues to grow and attract new generation of fans and followers.
Since 1990
three ktbk prototypes
The New Vintage Program Equalizer
Audio Merge, a very small startup sited in Barcelona-Terrassa, builds three KTBK prototypes to get a very accurate and robust Altec 9069B replica, using a handmade customized small coil and adding two new features to the original Altec's design: resonance control and mode selector.

Big Knob's Testimonials

"The strongest characteristics of the filter's sound are the discrete steps, the clicks and crunches when the frequency is switched, and the phasing effect heard when filtered signals are mixed with the unfiltered originals."

"Often used on Charleston cymbals, snare or the microphones of the voices, it cuts off the undesired frequencies, and gives a clearer sound. You can also use it to eliminate parasitic noises during voice recording, especially during speeches."

Follow our Spotify List with some examples of songs using an Altec 9069B or a KTBK unit >>>


This KTBK adventure has brought us many funny, intense and priceless experiences. Indeed, we want to continue with this and other sonic adventures, and that’s why we want to encourage you to support us in a crowdfunding campaign that we will launch soon, aiming to produce the first KTBK series to you. Subscribe it and let us share with you the main events and details of our research, technical tips and other surprises!

The KTBK Challenge
The KTBK project started with a phone call in January 2020. Xavi, who is passionate about Dub, wanted to acquire a clone of the Altec 9069B for his productions. After speaking with Arnau, they decided to create their own Altec replica.
Our Handmade Coil
The circuit of a passive filter consists only of passive elements, namely capacitors and coils. We had no issues getting the capacitors. Nevertheless, the multitap coil is inexistent in our era. So, we realized the best choice was to build our own coils manually, turn by turn.
The First Prototype
Arnau did a handmade luthier's job building the multitap coil. After some experiments, we got our first prototype, which you probably have already seen in the videos that Xavi published in the Instagram profile of @xlaudiodesign
The Audio Merge's Birth
During this period, we thought about the possibility of creating a cooperative for music tech creators. With this idea, we contacted the office of entrepreneurs of the City of Terrassa (Barcelona) that quickly became interested in our project.
KTBK vs Altec 9069B
After developing two more prototypes, through an Hispasonic user, we found an original unit in the hands of the great reggae-dub producer, Roberto Sánchez, who immediately lent his support and helped us compare our replica with the original one. The results of the comparison were surprisingly positive, we had a precise replica.
A Big Choice
The office of entrepreneurs of the City of Terrassa selected our project to participate in the Crowdfunding Bootcamp Terrassa to receive specialized training. We thought it was a good opportunity to accelerate our project and to test our team with a very challenging goal. So, we applied and luckily we were selected.
The Crowdfunding Campaign
During the last months, we have been preparing a crowdfunding campaign, with the aim of getting funds to produce the first KTBK's series and doing what we like. No longer as a one-off project, which arises by chance, but to devote ourselves exclusively to made up new vintage audio equipments.
January 2020
March 10, 2020
May 2020
August, 2020
October, 2020
Nov, 2020
February 2021


The KTBK project is initiated by Arnau Muñoz and Xavi Lizarraga, two sound engineers and audio freaks from Barcelona-Terrassa, who decided to join their professional strengths to creating quality audio equipment and focusing on to design, ergonomics and sonic quality.

Arnau Muñoz

Electronics Engineer

Xavi Lizarraga

Audio Researcher

To know more details about the KTBK filter, the Altec 9069B, other passive filters and new Audio Merge products, please subscribe to our newsletter to get access to exclusive news, tips and blog posts.