The Ashdown ABM-RPM-JE is a rack-mounting bass preamp from Ashdown Engineering. Ashdown describes it as a way of putting "all the ABM facilities in a convenient rack-mounting package", meaning the tone-shaping features of the company's ABM amplifiers in a unit that can live in a rack rather than an amp head. For a player, it serves as the front end of a bass rig: you plug your bass in, shape the tone with its EQ and sub-harmonic controls, and send the signal on to a power amp, a DI out for the front of house, or both1.
Inputs and outputs
The front end is built around a single input that Ashdown says is switchable for passive and active instruments, so both kinds of bass can be matched to the preamp. Behind that sit two instrument input paths: a high instrument input specified at 3.9M Ohms impedance with an input range of 150mV to 20mV p-p, and a low instrument input at 10k Ohms with an input range of 300mV to 40V p-p1.
On the output side, the unit carries a set of connections that cover the usual live and studio needs1:
| Connection | Specification |
|---|---|
| DI Output | 600 Ohms balanced, level 0dBu nominal, with pre or post EQ switching1 |
| Sub Output | Impedance 1k Ohms, level 0dBu nominal1 |
| Tuner Output | Impedance 22k Ohms, level 0dBu nominal1 |
| FX Loop | Effects return at 22k Ohms, input level 0dBu nominal1 |
| Line Input | Included alongside the FX loop1 |
| Speaker Outputs | Minimum impedance 4 Ohms1 |
The balanced DI out with pre or post EQ switching is the connection most players will use at a gig: pre-EQ sends the desk a clean signal before your tone controls, post-EQ sends what your preamp settings have shaped. The sub-bass output is there for rigs that add a dedicated subwoofer, and the tuner output lets you tune silently without interrupting your signal path1.
Tone controls
The ABM facilities Ashdown refers to are largely about EQ. The preamp has three rotary tone controls that Ashdown says "provide 20dB of cut and boost at 60Hz, 660Hz and 5kHz", covering low, low-mid and high frequencies. These are supplemented, in Ashdown's words, by "two pairs of additional sliders giving 15dB cut and boost at 180Hz, 340Hz, 1.3kHz and 2.6kHz", which fill in the midrange in finer steps1.
Ashdown specifies the EQ bands as follows1:
| Band | Center frequency | Cut/boost |
|---|---|---|
| Bass | 45Hz | +/- 15dB |
| Middle | 660Hz | +/- 15dB |
| Treble | 7kHz | +/- 15dB |
The EQ can be switched in and out, and switched between flat and shaped settings, by footswitch, which lets a player move between a flat sound and an EQ'd sound mid-set without touching the panel. Alongside the EQ sits a sub-harmonic level control: Ashdown describes this as enabling "the player to add just the right amount of low-end reinforcement", generating low-end content below what the bass itself plays1.
Power, size and weight
The ABM-RPM-JE requires 115/230V mains power, so it runs from the wall rather than a pedalboard supply. It occupies 2U of rack space, with Ashdown listing its dimensions as 90 x 483 x 267 mm (H x W x D) and its weight as 6 kg1. The 90 mm height corresponds to the standard 2U rack format, so it fits a standard rack alongside other rack gear.
Because the ABM-RPM-JE runs on 115/230V mains, it is rack gear rather than pedalboard gear: it needs an AC outlet, not a pedal supply.
Where it sits in Ashdown's range
Ashdown Engineering was founded by Mark Gooday in 1997, and the ABM series is the company's professional bass amplification line, which the company later extended with UK-made UK-ABM-EVO IV heads and cabinets. Players who want ABM-style tone in pedal form rather than a rack unit can look at Ashdown's pedal range, including the Ashdown Pro-DI for direct recording and the company's bass effects pedals such as the Ashdown Triple Shot overdrive or the Ashdown Lomenzo Mega Drive distortion. For a broader view of the category, see Preamp Pedals and Bass Pedals.
Questions
How many rack spaces does the Ashdown ABM-RPM-JE take?
It takes two rack spaces. Ashdown lists the unit's height as 90 mm, with a width of 483 mm and a depth of 267 mm, which is the standard 2U rack format. That makes it a straightforward fit in a standard rack or rack bag alongside other rack gear.
Does the Ashdown ABM-RPM-JE have a DI output?
Yes. The ABM RPM-JE features a balanced DI output with pre or post EQ switching, so you can send a signal to the mixing desk either before or after the preamp's tone controls. Ashdown specifies the DI output at 600 Ohms balanced with a nominal level of 0dBu.
Can the ABM-RPM-JE be used with active and passive basses?
Yes. Ashdown describes a single input that is switchable for passive and active instruments. The unit also offers high and low instrument input paths, with the high input specified at 3.9M Ohms impedance and the low input at 10k Ohms, so a range of basses can be matched to the preamp.
Does the ABM-RPM-JE have an effects loop?
Yes. The preamp includes an FX loop, and Ashdown specifies the effects return at 22k Ohms impedance with a nominal input level of 0dBu. The unit's other outputs include a sub-bass output, a tuner output and a line input alongside the balanced DI out.
How much does the ABM-RPM-JE weigh?
Ashdown lists the weight as 6 kg. Combined with its 2U, 90 mm height and 267 mm depth, that makes it a manageable unit to carry in a rack to gigs or sessions.
Sources (1)
- ABM-RPM-JE, Ashdown Engineering
