Keeley Super Phat Mod Full Range Overdrive

The Keeley Super Phat Mod Full Range Overdrive is an overdrive pedal that takes Robert Keeley's best-known modification of the Boss BD-2 Blues Driver and builds it into its own pedal. Gearnews described it plainly when it launched in 2016: "basically a refined and redesigned Boss BD-2"¹. Instead of sending your BD-2 off to be modded, you get all of Keeley's upgrades to that circuit in one hand-built USA box.

The pedal uses specially selected JFETs, which MusicRadar reported "deliver natural break-up and dynamic tones"². Keeley himself described the design as "our famous mod now perfected with amazing sounding JFETs that emulate old tube amps"³. Gearnews noted it was designed to be very good at picking up the subtle nuances of your playing style¹.

A Boss BD-2 with the upgrades built in

Robert Keeley started out in the effects business modifying existing circuits, and one of those mods was the Super Phat mod for the Boss BD-2². The Phat mod upgraded a number of the Boss components, added asymmetrical clipping and adjusted the tonal profile significantly⁶. The bass response was also beefed up, selectable on most modded pedals via a small toggle switch⁷.

The Super Phat Mod Full Range Overdrive combines all of those upgrades in a single pedal¹. For a player, that means the character of a modded BD-2 without hunting down a modified unit: by 2015, reviewers noted Keeley was no longer doing these mods and modded units were getting harder to find⁷.

What the Phat mod did to a BD-2, according to reviewers:

• Added asymmetrical clipping⁶
• Beefed up the bass response, switchable on most modded pedals⁷
• Brought a whole new level of output volume on tap, usable as a clean boost or to push a tube amp into almost-breakup territory⁷
• Fattened the lows while taking away a little high end, for a cleaner signal all around⁷

Guitar Pedal X's Stefan Karlsson called the Keeley-modded BD-2 his favorite all-time overdrive, citing "the way it cleans up on the volume dial and its richly textured crunch"⁶.

The mod also has a documented player behind it: Andy Timmons used a Boss Blues Driver BD-2 that had received Keeley's signature Phat Mod⁸.

Controls and the Flat/Phat switch

Guitar.com's review lists the control set as "Level, tone, drive; flat/phat switch"⁴. The three knobs mirror the Boss BD-2 layout, so a player coming from that pedal will feel at home immediately.

The Flat/Phat switch is the pedal's signature control. In Flat mode the EQ stays as the standard circuit voicing; in Phat mode it engages the beefed-up bass response that came from the original BD-2 modification⁷. Reviewers of the modded BD-2 found the Phat setting "really fattens up the lows" while taking away a little of the high end, making for a cleaner signal all around⁷. The same Flat/Phat toggle carried over to later Keeley pedals built on this circuit, including the Germanium versions⁵. ===

JFETs, not germanium

The Super Phat Mod was designed, as Keeley's own product description put it, to be "very good at picking up all the subtle nuances of your playing style"¹². In the UK it carried a list price of £149 RRP¹.

Germanium transistors belong to a different pedal in the family, covered below.

Where the Super Phat Mod came from

The pedal started out life many years ago as an upgrade for a standard Boss overdrive pedal¹. Guitar.com's review traced the lineage: "an overdrive based on his old 'Phat' modification of the Boss BD-2", allowing Keeley to design a new overdrive with the same amp-like dynamics⁴. The BD-2 itself delivers warm distortion and overdrive⁹, and the Phat mod pushed that base circuit toward a fatter, more amp-like voice.

The Germanium and Retro versions

Keeley has issued several variants on the Super Phat Mod, and the differences matter if you are comparing used or new listings.

The Germanium Super Phat Mod was described by Gearnews as essentially a limited run of the modification Keeley started selling 16 years earlier, "a souped-up version of the Boss BD-2 Blues Driver circuit", this time using a Tungsram AC125 germanium transistor to improve the tone further⁵. Its control layout is the same idea: Volume, Tone and Gain knobs plus a switch for Flat or Phat modes⁵. Gearnews found it a decent sounding overdrive pedal giving a more "amp-like" guitar tone⁵.

Delicious Audio, quoting Keeley, described the Germanium Anniversary Edition as "a more aggressively voiced overdrive with a spongy compression and fuzz that only germanium transistors give", which Keeley calls a dynamic overdrive¹⁰. The Retro Super Germanium Phat Mod, a Custom Shop limited edition, is at heart the same Germanium pedal with a mini toggle choosing between Flat and Phat¹¹, and it is now considered rare¹¹.

What reviewers said

Early coverage was positive. Gearnews concluded of the launch: "This could be one to check out if you want a versatile overdrive with an already proven heritage"¹. Guitar.com's review positioned it as an overdrive pedal made in USA by Keeley Engineering, with the same amp-like dynamics as the original mod⁴. The longer view from Guitar Pedal X is harder to top: the Keeley-modded BD-2 remained Stefan Karlsson's favorite overdrive in 2023 and 2024 coverage, ahead of the stock BD-2, BD-2W and JB-2 Angry Driver⁶¹²¹³.

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