Mad Professor Little Green Wonder

The Mad Professor Little Green Wonder is a high-headroom overdrive and booster pedal made in Finland by Mad Professor. First released in 2007 under license from BJFe¹, it is now back in the maker's Handwired series, twenty years after its debut²³. Its gain range runs from light breakup to a relatively driven overdrive, but with more headroom than a classic Tube Screamer-type pedal, and its Body control is what sets it apart from that family⁴.

Mad Professor positions it as more than an overdrive. The company also suggests using it as a booster pedal, or to calm down an overly bright amplifier or a raspy sounding fuzz⁵. Reviewers have echoed that flexibility: Guitar World called it "another very versatile little drive pedal - with the unique Body control being the crux of its versatility"⁶.

What it does to your sound

Most players will, fairly, assume the Little Green Wonder is a take on a Tube Screamer, as Guitar World's reviewer put it⁴. The gain range is similar, going from light breakup to a relatively driven overdrive, but the increased headroom and the Body control are where it differs drastically from a classic TS-type pedal⁴. The high input impedance presents only a light load to the pickups, so the volume control on the guitar can be used to control the gain⁷.

The pedal is optimized to pair with any guitar or amp setup. Retailer listings describe a specially tuned EQ curve and focused drive²³, and the Body control is what lets one pedal cover both single coils and humbuckers²³.

The controls: Volume, Drive and Body

The original Little Green Wonder carries three knobs: Volume, Gain and Body⁴. Volume sets the overall output level, and Gain adds more drive⁴. The Body control is the unusual one:

That single knob is why the pedal works across pickup types: wind it one way for humbuckers that need the low mids lifted, the other way to add bite to single coils⁵³.

The 2022 successor, The Green Wonder, replaced Body with separate Bass and Treble knobs, giving four controls in total: Volume, Drive, Bass and Treble⁴⁸. Its Bass control ranges from a slight low-frequency cut to a significant boost, and Treble runs from warm and smooth to bright and cutting⁷. In Mad Professor's own demo video, Marko Karhu showed off that significant bass boost, the treble control, and the drive range, playing a Fender CS '64, a Danocaster and a Gibson CS 1958 reissue through a clean Fender Deluxe Reverb set to three⁹.

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Power and connections

The handwired Little Green Wonder runs on a 7.5 to 18V supply, drawing approximately 4mA at 9V, through a 2.1mm center negative DC plug³. Guitar World's review of the handwired original lists 9V center negative at 4mA⁴. The Green Wonder shares the same supply range of 7.5 to 18V DC and the same 4mA maximum draw at 9V⁷³. Input impedance is 500kOhm and output impedance is listed as 10kOhm for The Green Wonder⁷, while the handwired Little Green Wonder listing gives 500 K in and 50 K out³.

History and versions

The Little Green Wonder began as a BJFe design. In 2007, Mad Professor Amplification of Finland released it under license from BJFe, the first of many licensed designs that would follow¹. The Mad Professor version was based on the final BJFe version, the one that Bjorn was most happy with, and the IC has always remained socketed, including in the Mad Professor version, for those who know what they are doing¹.

The timeline of the pedal family:

• 2007: Mad Professor releases the Little Green Wonder under license from BJFe¹
• PCB era: Mad Professor offers a number of its stompboxes in a PCB format, with pots, switch and jack sockets mounted on the board, at more affordable prices than the hand-wired versions⁵
• August 2022: The Green Wonder is announced as an updated version, with release set for October 2022⁷⁹¹⁰
• 2026: The original layout returns in the Handwired series, twenty years after its debut²⁴

The handwired reissue is faithful to the original circuit, with the same updates as previous Handwired pedals: high-quality through-hole components, Alpha pots and switches, and Switchcraft jacks, all in a rugged sheet-metal enclosure with top-mounted jacks². Guitar World's reviewer found the artwork more intricate than the less expensive factory version, with an art deco approach that "just looks better and, yes, more premium as a result"⁴.

Little Green Wonder versus The Green Wonder

The Green Wonder is a revised version of the popular Little Green Wonder⁸⁷. The core difference is the EQ: the original's Body control was replaced by Treble and Bass controls on the second iteration⁴. Those expanded knobs allow the player to dial in low and high frequencies, from gentle cuts to a hefty boost⁸. Mad Professor described the new pedal as including everything loved about the classic Little Green Wonder, with added versatility drawn from customer wishes¹⁰, and Guitar.com reported it as "the ultimate high-headroom overdrive/booster pedal," with an EQ colored to offer a slight boost in the midrange¹⁰.

Both pedals are true bypass⁴⁷, and both are designed to work with single coil and humbucking pickups through clean, overdriven or distorted amps⁷⁸. The Little Green Wonder also appeared in Guitar.com's Thomann Tube Screamer shootout, alongside pedals including the Electro-Harmonix East River Drive, MXR GT-OD, J Rockett Blue Note and Keeley Red Dirt¹¹.

What reviewers said

Guitar World's 2026 review of the handwired Little Green Wonder gave build quality a full five stars, noting that being a hand-wired pedal means a hand-wired price, and that the metal chassis boasts a near-indestructible feel for the money⁴. MusicRadar's review noted the pedal's day job as an overdrive, with booster and amp-taming duties as bonuses⁵, and observed that Mad Professor will still make you a hand-wired version of all its pedals if you wish⁵. On price, MusicRadar found the PCB-era pedals more affordable than the hand-wired originals, whose price tags started from figures that made reviewers choke, though still a little pricey for some⁵.

For players comparing green overdrives, the Little Green Wonder's combination of high headroom, a socketed IC and the Body control places it a step away from the standard Tube Screamer formula, while The Green Wonder moves it closer to a conventional two-band EQ layout⁴¹.

Videos

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Questions