Rangemaster

The Dallas Rangemaster is a germanium treble booster, a small preamplifier built in England in the mid-1960s that lifts the signal strength of the guitar going into the amplifier and boosts the high harmonics on the way¹. It was designed to solve a specific problem: British tube amplifiers such as the Vox AC30 or Marshall JTM45 tended to produce slightly dark, muddy tones when overdriven, and a treble booster in front of them restored bite². Its most famous user was Eric Clapton, who ran one with John Mayall and the Bluesbreakers, where its biting, powerful sound is clearly in evidence on the "Beano" album, and who also used the booster when playing in Cream³⁴.

The circuit itself is about as small as a guitar effect gets: a single germanium transistor and a few components, with a volume control and an on/off switch. That simplicity is why it became one of the most copied circuits in effects history, and why it is still a standard first build for DIYers and a template for commercial pedals more than sixty years after its mid-1960s release⁵⁶².

Where the Rangemaster came from

The Rangemaster Treble Booster was first made in the 1960s by London company Dallas Musical Ltd., which was incorporated in 1959¹. GuitarPCB's technical analysis dates the design to 1965, designed in London by Dallas Musical Ltd², while British Pedal Company's history describes the unit as born in the mid-1960s¹. It was designed by Ivor Arbiter, the founder of Dallas Arbiter, together with Barry Pyatt³.

The unit gained notable recognition when Eric Clapton used it with John Mayall and the Bluesbreakers³. BSM's manual for its own Range Master-based booster notes that the British unit was produced between 1965 and 1969, and that Clapton also used the booster in Cream⁴. Another documented player is Tony Iommi, who Fuzzlord Effects describes as having used a modified Rangemaster⁸. Rory Gallagher is the other name permanently attached to the unit; British Pedal Company built its relic reissue to the specification of Rory's original Number 1 Rangemaster, with the Gallagher family's authorization⁹.

How many were built is unknown, and originals are now collector items. British Pedal Company says original examples regularly fetch over £1000¹; Analog Man reports them selling for thousands of dollars, and much more with the original box¹⁰.

A tabletop unit, not a pedal

The Rangemaster was not a pedal at all. It was a tabletop unit with an on/off switch and a volume knob¹⁰, a gray metal box designed to sit on top of the amp rather than on the floor as most pedals are today². Its controls were a simple ON/OFF sliding switch and a potentiometer to adjust the volume².

The original volume pot was a UK Welwyn 10k ohm unit, sometimes 20k, with two mounting screws and a bakelite body isolated from the chassis². Among the British boosters of the era, the Rangemaster stood out for having that volume control at all: as General Guitar Gadgets notes, with the exception of the Rangemaster, none of these boosters had one⁷.

How it works: one germanium transistor and a small input capacitor

GuitarPCB's circuit analysis breaks the Rangemaster down as a typical common emitter amplifier using a bipolar junction transistor, with a voltage divider network setting a stable bias voltage at the transistor base¹¹. The original germanium transistor was the Mullard OC44, long discontinued, and the circuit was built from the parts available in the 1960s, including carbon comp resistors².

The defining component is the small input capacitor. C1 creates a high-pass filter with a corner frequency of about 2.6kHz, attenuating harmonics below that point². That is what makes it a treble booster rather than a clean boost: the lows and low mids are rolled off before the gain stage, so what comes out is a thinner, brighter, hotter signal that pushes an amp's front end without flubbing the low end.

The measured numbers from GuitarPCB's analysis:

That 38dB figure is worth context: GuitarPCB calls it a high voltage gain for a booster pedal, noting that similar pedals like the MXR MicroAmp have a lower voltage gain of 26dB². The Rangemaster is not a subtle lift.

It is also not entirely clean. When the Vol control is maxed out, the signal is boosted and driven into soft clipping, which colors the sound; the analysis describes asymmetric soft clipping with the transistor biased off the middle of its swing area². British Pedal Company's history makes the same point from the player's angle: the vintage components in the Rangemaster circuitry could add characteristic distortion and overtones that color the guitar sound, much in the way of more modern overdrive pedals¹. KMA Audio Machines, whose Strokkur is an inspired take on the design, describes the original as known for its power and exploding harmonics when pushing a tube amp on the edge of breakup¹².

Gain, bias and transistor selection

Because the circuit is one transistor, the transistor is most of the sound, and builders are picky about it. GuitarPCB's guidance is to find a germanium transistor with an HFE gain of 90, and that any value between 75 and 100 would be great².

The OC44 itself has a specific story. R2R Electric's comparison of the OC44 against the AC107 explains that OC44s typically measured in the gain range and leakage that is ideal for the Rangemaster circuit, but that the transistor was mainly designed for oscillator and mixer use, not audio¹³. That happy accident is why the OC44 became the part to have, and why NOS examples command prices today.

Biasing is the other half of the job. It is commonly agreed that the ideal bias point is a Q1 collector voltage of -7.0V, with any value between -6.9 and -7.1 being great; referred to ground on the original supply, that is Vc = +2V, ideally between 1.9 and 2.1V². General Guitar Gadgets' build document gives working voltages for its replica with a 9V supply: 9.2V at the supply, 7.2V at the Q1 collector and 0.7V at the emitter⁷.

Power and grounding: positive ground, battery only

This is the part every Rangemaster builder has to understand before wiring anything. The original circuit is PNP positive ground: it sounds fantastic, but it works only on batteries, and an external DC adapter would create a short circuit². The power supply section is simply a single 47uF capacitor, with no protection against reverse polarity connections². BSM's manuals for its Range Master-based boosters carry the same warning in one line: the positive pole of the battery is ground⁴.

There are two ways around it, and builders disagree about how well they work:

• PNP negative ground mod: a modern mod that adapts the pedal to a standard daisy chain power supply, but GuitarPCB describes it as very prone to oscillations, hissing and motorboating noise, and does not recommend it².
• Charge pump: a small converter that inverts the supply inside the pedal. General Guitar Gadgets offers this on its replica, where the addition of a charge pump on the input power gives the ability to daisy chain power to a PNP positive ground build⁷. GuitarPCB's Pump'd Up Rangemaster Plus includes a charge pump allowing a vintage PNP transistor to share power with standard negative-ground pedals¹⁴.

Pedals based on the Rangemaster

The Rangemaster's influence shows up across the whole booster market, in faithful replicas and in looser interpretations:

The Rory Gallagher reissue is the closest thing to an official continuation: a pedal, not a tabletop box, with an ON/OFF switch, authorized by the Gallagher family and built to the specification of his original unit⁹. The Fuzzbug takes the circuit somewhere else entirely, pairing the Rangemaster name with Fuzz Face-style two and three transistor fuzz circuits in a cast aluminum casing¹⁵. At the faithful end, R2R Electric's Replica Series is a part for part build of an original, using what was used to build the Rangemaster in the 1960s¹⁶.

DIY kits and builds

The Rangemaster is a standard DIY project, and available kits and PCBs show how builders have solved the circuit's power problem in different ways¹⁸⁷¹⁹:

• General Guitar Gadgets sells a replica kit and PCB project in PNP germanium, NPN germanium, and PNP with charge pump versions, running from a 9V battery or 9V power supply⁷. Their notes on transistor choice: germanium transistors have a bit more gritty sound, while silicon transistors offer a more stable, reliable sound⁷.
• GuitarPCB's Pump'd Up Rangemaster Plus (P.U.R.P.) is a DIY effects PCB based on the original treble booster, with Tonmann's modern design changes to the old circuit¹¹¹⁸, and includes the charge pump for sharing power with negative-ground pedals¹⁴.

For a builder choosing a first version, the GGG kit's three variants map directly onto the power discussion above: the straight PNP version is the original sound with the original battery-only limitation, the NPN version flips the ground, and the charge pump version keeps the PNP transistor while fitting a modern pedalboard supply⁷.

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