The Ashdown ABM-RPM-GZR is a Custom Bass Preamplifier specifically designed and made for Geezer Butler Black Sabbath’s ‘The End Tour’, billed as the band's farewell tour.

Built for 'The End'...

When designing the ABM-RPM-GZR, we took an original JE pre amp and came up with a few specific modifications. They needed to be able to split the signals to run 4 cabs for the full range signal into the 412’s so we modified the existing two-way crossover to a custom transformer derived crossover able to power 4 outputs to feed the two APM-1000’s that would drive his on stage 412’s.

This was also mimicked with an identical pre-amp and power amp configuration to power the Low pass signals for his 4 on stage 215’s. Geezer also needed a little more grit in his tone so we increased the current to the pre-amps on board JJ-12-AX7 tube to give it much more of a rich harmonic distortion to suit his legendary tone.

Three straightforward rotary tone controls provide 20dB of cut and boost at 60Hz, 660Hz and 5kHz, and are supplemented by two pairs of additional sliders giving 15dB cut and boost at 180Hz, 340Hz, 1.3kHz and 2.6kHz. The EQ can be switched in/out, and flat/shaped by footswitch, enabling players to go from a flat fretless sound to a boosted sound via a favourite EQ setting. 

Signature Ashdown Bass Tone

The ABM-RPM-GZR features a single input is switchable for passive and active instruments with a blend of solid state and dual triode tube preamps stages which can be preset and selected by footswitch, providing access to a massive range of clean, warm and overdriven tones.

Sub-Harmonic Generator

Also footswitchable is the mighty Ashdown sub-harmonic generator which precisely tracks the main signal and reproduces it an octave lower. 

A sub-harmonic level control enables the player to add just the right amount of low-end reinforcement - everything from a subtle, thickening of the sound to unbridled, bone crushing tone. The ABM RPM-GZR preamp features a balanced DI out with pre or post EQ switching, a sub-bass output, a tuner output, an FX loop and a line input for the connection of an external sampler or sound source. 

Output muting cuts the signal from the DI output but leaves the tuner output 'live', allowing the player to tune up in silence. 

The addition of a high-precision crossover with variable frequency from 35Hz to 160Hz and a level control for the low-pass output, enables the configuration of sophisticated bi-amped systems, in which the bass and mid/high frequencies are amplified separately. We took this further for Geezer with four individual outputs with the option to patch in either the Full pass signal, High Pass Signal or Low pass signal to two Ashdown Power 1000 watt Power amps. 



Power Requirement  115/230V
Frequency Response -3dB @ 17Hz and 30kHz
High Instrument Input Impedance 3.9M Ohms, input range 150mV - 20mV p-p
Low Instrument Input Impedance 10k Input range 300mV to 40V p-p
Line Input  Impedance 22k Ohms, input level 0dBu nominal 
Sub Output  Impedance 1k Ohms, level 0dBu nominal
DI Output 600 Ohms balanced, level 0dBu nominal 
Tuner Output  Impedance 22k Ohms, level 0dBu nominal
EQ  Bass +/- 15dB @ 45Hz Middle +/- 15dB @ 660Hz Treble +/- 7kHz
Effects send Impedance 22k Ohm, level 0dBu nominal 
Effects return Impedance 22k Ohm, Input level 0dBu nominal 
H x W x D (mm) 90 x 483 x 267
Weight (kg) 6

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