BSM RPA Full Quarter Booster

The RPA Full Quarter Booster is a special preamp/booster pedal made by BSM, the German company behind the BSM Black Box and the RPA Special Booster. It was designed by Bernd C. Meiser, whom the company describes as its "tech-head and mastermind"¹. Its purpose is specific: to keep powerful, fat pickups from producing a muddy or dull sound through conventional amps, achieving a dynamic, transparent sound instead².

What it was designed for

The Full Quarter was developed for fat single coil pickups like the "Schecter F500" and the OBL 450XL (or similar) double blade humbuckers that Ritchie Blackmore used in the 1980s and the beginning of the 90s²³⁴. Pickups of this kind carry a lot of output, and through a conventional amp they can push an amp's input into a dull, congested response. BSM's manual says the pedal ensures no muddy or dull sound with powerful pickups, so the amp keeps a dynamic, transparent character².

The pickups the pedal was developed around:

• "Schecter F500" fat single coil²
• OBL 450XL double blade humbucker, or similar²
• The double blade humbuckers Ritchie Blackmore used in the 1980s and the beginning of the 90s³⁴

It also copes with extra inductance elsewhere in the guitar's wiring. The manual states: "It can also handle the additional inductivity (which tends to cause a dull sound as well) of a dummy coil"². That matters for players who fit dummy coils to cut hum on single coil guitars, since a dummy coil normally dulls the signal before it even reaches the amp.

Power and placement

The unit is powered by a 9V battery, and because of the external DC jack you can also power it with 9 volts from a supply. The negative pole of the battery is ground, and current consumption is approximately 400 uA, which is far below what a typical pedal draws². The maximum output voltage when the strings are struck really hard is 7V max².

Placement is fixed by design: the RPA Full Quarter Booster is inserted between guitar and amplifier, not into the FX loop². That placement lets it work on the guitar's own signal, including the inductance of its pickups and any dummy coil, before the amp sees it.

What amp to pair it with

BSM's manual says you can use any mild sounding amp with a good master control function². The idea is that the booster shapes the signal going in while the amp's master volume keeps overall level under control, which suits players running conventional, relatively clean amps rather than amps already pushed into heavy distortion. For more on where pedals like this sit, see Preamp Pedals and Boost Pedals.

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