Colorsound Overdriver

The Colorsound Overdriver is a British boost and overdrive pedal made by Sola Sound around 1971, designed by Gary Stewart, who later founded Colorsound¹. It began life as a revision of the earlier Power Boost circuit, and its place in the family tree of early British fuzz and boost boxes is unusual: the same three-transistor circuit gives you a Power Boost at 18V and an Overdriver at 9V². Guitar.com calls it "a forgotten giant of early British fuzz"³.

For a player, what it does depends on your pickups. TONEHOME describes it as an overdrive pedal with a distinctive bass and treble boost: with single coils it gives a very transparent, super clean boost that sounds dynamic and open, while humbuckers will always result in a slightly overdriven signal⁴. Tru-Fi adds that it was known both for its powerful overdrive and its incredible boost factor, usable for pushing fuzz pedals or simply boosting the signal⁵.

A boost that tips into overdrive

The Overdriver's core idea is that it bridges the gap between a clean boost and an overdrive. GuitarPCB, whose ColorTone board recreates the circuit, describes it as "bridged the gap between Boost & Overdrive recreating many of those popular, but hard to get tones of the 70's"⁶. The bass and treble controls allow a wide range of tonal options, including a full-on treble boost⁴.

The original units had no master volume control, and that was the pedal's defining quirk. Because of the remarkable volume jump when the pedal was engaged, very few vintage Overdrivers are left unmodded: many owners added a master volume pot themselves, and the reissue pedals carry one as well⁴. Analog Man's version of the pedal lists four knobs: Treble, Bass, Overdrive, and Master Volume, with the master volume added "to allow overdrive at useable volumes"⁷. Analog Man's unit came in a thin stamped gray metal case, narrower than a typical pedal, with a list price of $259 in 2015⁷.

The circuit itself is a three-transistor design with Drive, Volume, Treble and Bass controls, documented in vero (stripboard) and tagboard layouts by the Guitar FX Layouts community². The original transistors were BC169C in the Q1 and Q2 positions and a BC184C in Q3; the layout notes specify the pinout orientation for each, BCE for the BC169Cs and EBC for the BC184C². GuitarPCB's ColorTone Overdrive v3 build document instead lists BC109 transistors for Q1, Q2 and Q3, a common substitution for builders⁸.

One builder who made the vero layout reported a split verdict on the circuit's character²:

Guitar FX Layouts commenter, on the Overdriver vero layout²

Versions and the 1996 reissue's minimum volume

The Overdriver's history is a story of small revisions. Aion FX traces it as an updated version of the Power Boost circuit, a third revision from 1972, and notes the name change came after Sola Sound took the Power Boost to a trade show in the United States and drew a lot of interest⁹. Tru-Fi dates the change more simply: in 1971, Colorsound changed the Power Boost into the 9V Overdriver, dropping the power requirement down to a single battery¹⁰⁹. Over the years there have been different variations and reissues, some with slight modifications to the circuit or enclosure design¹.

The relationship between the two circuits is direct enough that builders treat them as one layout with two settings: run the layout at 18V and you get the Power Boost; omit the level pot and you get the Overdriver².

The 1996 reissue is the version most players will encounter today, and it has one well-known catch. It incorporated a volume pot on the output, finally answering the original's no-volume-control problem, but it also included a minimum volume resistor that prevents the output from going to zero¹¹. The practical result is that the reissue cannot reach unity gain at higher gain settings, so the pedal is always adding some level. Aion FX reports that, as far as they know, this minimum volume resistor is still in current reissues¹¹. Guitar.com's review of the Tru-Fi Mini '71 Colordriver, a modern tribute pedal, notes both the Power Boost and Overdriver tributes come with master volume, courtesy of legendary London dealer Macari's¹².

Who played it

The Overdriver gained popularity in the 1970s and was used by various guitarists of that era¹. Tru-Fi names David Gilmour of Pink Floyd, Jeff Beck, and T. Rex's Marc Bolan as users of the 9V version⁵, and GuitarPCB calls it "a favorite of Mr. Gilmour and Jan Akkerman of Focus among many"⁶. Vintage units are now sought after by guitar enthusiasts and collectors¹.

Building one today

The circuit is well served in the DIY world. GuitarPCB sells the ColorTone Overdriver v3, a PCB for building a similar circuit to the classic Overdriver⁶, with a build document listing the BC109 transistor option⁸. Aion FX offers the circuit as a project called the Plasma, a vintage drive build⁹. The Guitar FX Layouts vero and tagboard layouts remain the reference for stripboard builders, with the transistor pinouts and the 18V Power Boost variant both documented².

The Overdriver's influence also shows up in the DIY community. Tagboard Effects publishes vero (stripboard) and tagboard layouts for the three-transistor circuit, with Drive, Volume, Treble and Bass controls, and notes the original transistors were BC169C in the Q1 and Q2 positions and BC184C at Q3². The lineage runs both ways: running the layout at 18V gives the Power Boost, and omitting the level pot gives the Overdriver². One builder who made the layout reported it "works as a beautiful clean boost but the overdrive seems too harsh"².

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