The BSM RM-Metal model is based on the British Range Master unit produced between 1965 and 1969, as used by Eric Clapton in John Mayall´s Bluesbreakers. Eric also used the booster when playing in the legendary group Cream. Its biting, powerful sound is clearly in evidence on the Bluesbreakers "Beano" album. Blues rocker Rory Gallagher, Heavy Rock pioneer Tony Iommi and Brian May from Queen were also heavy users of the orginal Range Master unit. The long yearned for new edition, now issued under the name RM from BSM, includes the same OC44 germanium transistors as the the original 1965 version. The RM Metal is a modified `69er RM model like Mr. Iommi´s unit, which he has used on his second Black Sabbath records and later. The RM Metal model is recommend for Nu-Rock, low dropped tunings and baritone guitars.
Almost all British rock guitarists using single coil pickup guitars used a germanium Treble Booster from the late 60's to the mid 70's. By the end of the seventies, the Treble Booster was replaced by a new circuit from Japan, the so called Tube Screamer and other similar overdrive circuits. These were based on the old Treble Boosters and therefore had a very similar frequency response. The germanium boosters on the other hand, sadly fell into oblivion despite their unique and inimitable sound. The RM Treble Booster has been designed for single coil and humbucking pickups with standard coil inductance, such as pickups in Fender, Gretsch, Burns or Gibson guitars. On these pickups, the RM Metal produces (with the volume control of the guitar turned up to the max) a fat, biting and penetrating lead sound, minus any shrill characteristics. By lowering the guitar's volume control, many shades of crunch can be easily dialed in. Another thing to consider is that when a guitar amp's volume is turned up (reaching saturation), the power amp normally begins to mute the highs, which results in a duller sound. At an amp's full tilt, the RM Metal Treble Booster allows a more transparent tone (covering the entire frequency range) to shine through. The presence control on the amp need only be minimally used (if at all). When vintage amps are used (such as the Fender Deluxe, Fender Bassman, Vox AC30, plexi Marshall 50 or 100 watt) it is amazing what effect the use of a good treble booster has. It is also of interest to note that Tony Iommi used a Laney stack with Black Sabbath.
The Treble Booster is inserted between guitar and amplifier, not into the FX loop. The magical tone is achieved by the interaction between guitar pickup, treble booster and amplifier. The unit is powered by a 9V battery with a current consumption of approx. 250 uA. The average output level is 10dBm, the maximum output voltage when the strings are struck really hard is 7V max. Note: The positive pole of the battery is ground.