Lehle RMI Basswitch Classic Boost

The Lehle RMI Basswitch Classic Boost is a high-end bass preamp and booster from Ruppert Musical Instruments (RMI), a company based in Luxembourg, with the hardware manufactured, assembled and tested in Germany¹. Its main job is what the name says: boosting your bass signal with an adjustable EQ, up to a maximum gain of plus or minus 15 dB¹. The maker describes it as a preamp "gently voiced for passive P, JJ and PJ type basses," and the input accepts both active and passive instruments¹.

Instead of a conventional true bypass switch, the pedal uses what Lehle calls True Sound Technology: switching handled exclusively by gold-plated contact relays and gold-plated switches¹. One footswitch toggles between the booster and a straight-through mode, with a status LED that turns blue when the boost is on and white when the pedal is bypassed¹.

Power and connections

The Classic Boost runs on an external power supply delivering between 9 and 15 volts, either AC or DC, through a standard 5.5 x 2.1 mm connector, with a power consumption of max 60 mA¹². Polarity does not matter: the manual states that "either alternating (AC) or direct current (DC) sources can be used and the polarity is not relevant"¹. Whatever you feed it, the voltage is internally rectified, filtered, stabilized and brought to 18 volts, which is how the pedal reaches its specified maximum level of 15 dBu with a 12 volt supply¹.

Connections are simple. The input is designed for your first instrument, active or passive, and the output feeds a bass amp, a power amplifier or an active monitor¹.

Controls and EQ

The control surface is minimal: one GAIN knob and one footswitch. GAIN adjusts the volume of the Classic Boost, boosting or cutting the signal, with a neutral position at 12 o'clock¹. Pressing the footswitch turns the Classic Boost on or into straight-through mode¹.

The EQ section is a two-band design, and the manual gives the ranges for each band¹:

Both bands are peaking filters, so they boost or cut around a center frequency rather than shelving. With a maximum gain of plus or minus 15 dB overall, the pedal can push an amp harder or pull a hot active signal back¹.

Sound quality and measurements

The specifications the maker publishes point to a clean, transparent signal path rather than a character piece¹:

• Frequency range: 30 Hz to 150 kHz (+1/-3 dB)¹
• Distortion: 0.002 %¹
• Signal-to-noise ratio: -96 dB at 1 kHz, 0 dBu¹

A frequency range that extends far past the audible band, very low distortion and a high signal-to-noise ratio are the numbers of a hi-fi buffer and line driver, which fits the pedal's role as a boost and preamp rather than an overdrive. The 2 MOhm input impedance means passive basses see a light load, preserving top end in long cable runs¹.

Where it comes from

Ruppert Musical Instruments is based at 20a, rue de Bascharage, L-4995 Schouweiler, Luxembourg¹. The RMI Basswitch line is built by Lehle in Germany on RMI's behalf; Lehle's own product page for the discontinued Basswitch IQ DI states that "the BASSWITCH IQ DI is manufactured by LEHLE in Germany on behalf of RMI"³. The Classic Boost itself is manufactured, assembled and tested in Germany, according to its manual¹.

The Basswitch family extends beyond this booster. The RMI Basswitch Dual Band Compressor, a compressor for bass, can be switched between buffered and true bypass when not engaged, a choice Gearnews welcomed in its coverage⁴. The RMI Basswitch Enhanced Overdrive, an overdrive pedal reviewed by Premier Guitar in 2021, is also completely manufactured in Germany⁵. The Classic Boost shares its power architecture with both: 9 to 15 V AC or DC, internally rectified, filtered, stabilized and brought to 18 V⁴¹⁵.

How it differs from other boosters

Two things set the Classic Boost apart from a typical boost pedal. First, the switching: rather than true bypass, Lehle True Sound Technology routes the signal through gold-plated contact relays and gold-plated switches, an approach Lehle uses across its products¹. Second, the power section: the internal conversion to 18 volts from any 9 to 15 V supply gives the headroom figure of 15 dBu, and the indifference to polarity means the pedal works with supplies that would rule out polarity-sensitive pedals¹.

For bass players comparing options, the pedal sits in the bass pedals and preamp categories, and its controls reflect its bass-focused design: a single footswitch turns the Classic Boost on or into 'straight through' mode, and its 2 MOhm input impedance and 150 Ohm output impedance suit it to instrument-level signals¹.

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