Mad Professor SIMBLE

The Mad Professor Simble is an analog overdrive pedal from Finnish maker Mad Professor, first shown at NAMM in January 2014¹²³. It is the company's take on the classic Dumble Overdrive Special, the boutique amplifier design that a whole family of "D-style" pedals imitate⁴. Where most overdrives push one fixed voicing, the Simble follows the Dumble approach of letting you shape the signal both before and after the overdrive stage, which is where its unusual control layout comes from⁵.

RockBoard's PedalPedia describes the pedal as having "a natural organic tone, unsurpassable touch sensitivity, sweet tube-like compression and built in inspiration"². In practice it covers a wide range: RockBoard's PedalPedia says it works as a clean boost, an "on the edge" crunch, or a sweet singing overdrive². A revised version, the Simble MkII, arrived in 2025 with an improved circuit by the original designer⁶⁷.

A Dumble-style overdrive

The Simble belongs to the category of drive pedals inspired by Dumble guitar amplifiers, a trend MusicRadar notes has grown steadily, with the Simble MKII one of a growing number of such pedals (and, as MusicRadar points out, not marketed as a Dumble clone)⁷. Gearnews describes the Simble simply as "Mad Professor's take on the classic Dumble Overdrive Special"⁴. Guitar Pedal X calls it "one of the great takes / flavours of Dumble Drive / Dumble ODS"⁶.

The Dumble lineage shows up in the circuit's structure. Delicious Audio notes that the pedal, "just like a real Dumble, lets you EQ the signal before or after the overdrive"⁵. That is why the Simble has two brightness controls rather than one: Accent works on the signal going into the drive stage, and Contour works on what comes out.

MusicRadar's 2014 launch coverage said the pedal was "intended to recreate an authentic tube sound without compromising the tone of your amp and guitar"⁹. In Pete Thorn's demo video for the pedal, he described it as "meant to capture the awesome warm illustrous overdrive tones produced by a certain famous Boutique amp that starts with" the letter D¹⁰.

The pedal suits a range of instruments. RockBoard's PedalPedia says it is happy with either single coil pickups or humbuckers, and thanks to the pedal's wide bandwidth it also works with bass². Delicious Audio's reviewer went further on pickups, finding that "It can really sing with humbuckers and almost sounds better with them over single-coils"⁵.

The controls

The Simble has four knobs, and they are interactive: Pete Thorn noted in his demo that "it's all very interactive and you kind of just have to play with it to get a feel for for the tones"¹⁰. The MkII keeps the same control set, with Guitar Pedal X listing Level, Sensitivity, Contour and Accent⁶.

The split between Accent and Contour is the pedal's defining feature. As Delicious Audio puts it, "The Accent control adjusts the brightness before the drive, and Contour sets the brightness after the drive stage"⁵. Pedal of the Day's review explained the practical effect: Contour "controls the brightness level of the output signal, acting like a Tone knob, adding in or taking away the highs," while Accent "adjusts the pick attack before the drive comes on"³. On the MkII, MusicRadar describes the Accent control (which it calls the Attack dial) as shaping "the tonal response of the overdrive"⁷.

Simble vs Simble MkII

The MkII, released in 2025, is a reissued and improved version of the original, upgraded by original Simble circuit designer Lassi Ukkonen⁶⁷. The changes are about headroom and clarity rather than a new concept:

• More headroom, brightness and openness compared to the original⁵⁶
• Tweaks that improve string clarity, particularly when drive is maxed out⁷
• A redesigned enclosure: deep red with cream text and black dials, replacing the original's faux wood panelling⁶⁷

Guitar Pedal X's writer admitted some nostalgia for the old look: "I always felt that the wood-finish enclosure was very representative of its organic sound"⁶. Gearnews reported that the MkII "promises improved headroom, greater clarity, and the same transparent sound that made its predecessor" popular¹¹.

Power and connections

The Simble MkII runs on 9V DC, drawing 10 mA²⁷. The original's listed supply range is 9 to 12V, with a current draw of about 10 mA at 9V⁵. Power comes from either a 6F22 9V battery or a DC eliminator with a 2.1 mm plug, center negative and positive sleeve⁵. When the LED dims, it is time to change the battery⁵. Input impedance is 430 kohm and output impedance is 50 kohm⁵.

What reviewers said

Reviews of the original were positive about its range. Pedal of the Day found "Nice range here, from a great clean boost to a crunchy mid-gain drive-type sound, useful in so many applications"³. Delicious Audio's later write-up called the MkII "One of the most convincing D-Style compact pedals"⁵.

Guitar Pedal X's Stefan Karlsson, who had lived with the original for years, wrote: "For several years this was my favourite of that type"⁶. On the MkII he was still adding one to his collection, while admitting he "may still overall prefer the Demon Kondo-Shifuku and Tanabe Zenkudo"⁶. Gearnews's verdict on the MkII was that it "certainly builds on and improves the original, and the official price point is excellent at only €199"¹¹.

That Pedal Show covered the Simble MkII in a 2026 episode comparing four gain pedals, alongside the Crazy Tube Circuits Triptychøn, the Empress Drive and the EAE Citadel, with the Simble segment starting at 2:20¹².

Pete Thorn's demo of the original pedal walks through the controls and their interactive behavior¹⁰:

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Questions