Walrus Audio Mantle Analogue Bass Preamp/DI Pedal

The Mantle is a premium preamp and DI for electric bass, created in close collaboration with Ian Martin Allison. Designed to give your instrument an impeccable sonic foundation, the Mantle brings studio-grade refinement to any environment - whether you’re stepping onstage, tracking in the studio, or shaping your tone at home.

At the heart of the circuit are our proprietary, custom-wound Sapphire Transformers, engineered to deliver the authoritative low-end and midrange push reminiscent of a classic Neve circuit, paired with an airy, articulate top end inspired by revered API preamp architecture. Together, they provide a harmonically rich canvas that elevates your playing while preserving every nuance of your instrument.

The Mantle empowers you to sculpt your signal with intention, offering musical gain, smartly tuned EQ, tremendous headroom, and transformer-balanced outputs. Every component and stage of the signal path is built to ensure whatever comes next - amp, interface, or mixer - receives your bass in its most confident, fully realised form.

Signal Path Overview

Input → JFET Buffer → LPF/HPF or Dry Path → Input Transformer (-6dB to +23dB) → Boost EQ → Output Transformer

The Mantle’s architecture is meticulously voiced to maintain clarity, delivering musical transformer colouration, and giving you control over both the front end and final output of your tone.

Transformers

The Mantle features our proprietary custom-wound “Sapphire Transformers”. With more than a year of research, listening, and refinement, the Walrus engineering team has set a new benchmark for their designs with new input and output transformers reflecting our commitment to providing creators with cutting-edge tools that inspire innovation and creativity.

Based on Neve designs, the input transformer is capable of handling large signals without added distortion while maintaining a clean, strong, and quiet signal. High-quality core material and copper windings were used to achieve the gain needed for pristine performance across the frequency spectrum.

The output transformer is based on the output stage of an API 312. This serves two functions: It balances the signal quietly and effectively while also providing rich harmonic content to the amplified signal. Like the input transformer, the style of core and customised winding method result in a strong signal that can be transmitted over long cable runs without signal loss.

Connections

The Mantle features a 1/4" TS unbalanced Hi-Z input optimised for electric bass, buffered by a high-quality JFET stage to maintain proper impedance, detail, and instrument integrity. A 1/4" TS unbalanced output allows you to send your shaped signal to an amp or additional pedals, while the male XLR output is transformer-balanced for elevated DI tones that feel at home in high-end studio and live environments. The Mantle is powered by 9V DC (500 mA, centre-negative) and internally boosted to +24V, delivering massive headroom and a clean, authoritative bass response.

Controls

Bass & Treble (Boost/Cut Filter System)

The Mantle’s EQ is a sophisticated dual-behaviour design, far more expressive than standard shelves. Both Bass and Treble controls feature eleven-position rotary switches for a satisfying studio feel, easily reproducible settings, and a true flat response at noon (position 6).

Boosting (positions 7–11):

• Begins as a shelf, gradually transitioning into a broad, musical bell as you increase gain.
• Each increment adds +3dB, up to +15dB, without drifting into muddiness or harshness.

Cutting (positions 5–1):

• Introduces a steep -18dB/oct HPF on the Bass control at selectable points: 30Hz, 50Hz, 80Hz, 100Hz, 120Hz
• Introduces a steep -18dB/oct LPF on the Treble control at selectable points: 8kHz, 6kHz, 4kHz, 2kHz, 1kHz

This design allows precision mix shaping or broad musical colouration, without sacrificing elegance or fidelity.

Gain Control

The Gain control adjusts the amount of transformer-based gain applied to the signal. The gain circuit comes directly from the input transformer, creating magnetic manipulation at its finest. This control offers a gain range from -6dB to +23dB across the control range. With the combination of the JFET buffer and transformer gain, the result is a tone that feels alive, dimensional, and deeply expressive.

Switches

Active / Passive (-10dB Pad)

• Engaged: Introduces a -10dB input pad, ideal for active basses or instruments with high-output preamps. Prevents overloading the input stage.
• Disengaged: Bypasses the pad for full-strength passive bass output and maximum sensitivity.

Ground Lift

• Engaged: Separates the XLR output ground from circuit ground.
• Purpose: Eliminates hum and ground-loop noise when connecting to unfamiliar or complex live/studio setups.

• Studio Grade - Premium preamp and DI for electric bass, created in close collaboration with Ian Martin Allison — delivering a studio-grade bass foundation for live and studio use.
• Premium Components - The Mantle is built around custom-wound Sapphire transformers — combining Neve-inspired low-end and midrange push with an airy, articulate top end drawn from classic API preamp designs.
• Easy to Dial In - Musical, intentional tone shaping with musical gain, smartly tuned EQ, tremendous headroom, and transformer-balanced outputs for a confident, fully realised bass tone.
• Custom EQ - Custom Bass and Treble EQ, featuring a sophisticated dual-behaviour design with eleven-position rotary switches for a satisfying studio feel and easily reproducible settings — co-designed with Ian and utilising a blend of shelving, bandpass, and selectable LPF/HPF behaviours.
• Built for Home, Stage or Studio - Rig-ready flexibility, with transformer-balanced XLR output for elevated DI tones that feel at home in high-end studio and live environments — including a -10 dB pad for active basses and a Ground Lift for eliminating hum and ground-loop noise.

• Power Requirements: 9VDC, 500mA, Centre-Negative, 2.1mm. Power supply not included.
• Internally boosted to +24V for higher headroom.
• The use of an isolated power supply is recommended for powering all Walrus Audio pedals. Daisy chain power supplies are not recommended.
• Input Impedance: 1MΩ
• Output Impedance: 150 Balanced, 150 Unbalanced
• Noise floor: Balanced -101dBV, Unbalanced -94dBV
• THD @ 1kHz 1Vrms: 0.04%
• Frequency Response: 20Hz - 20kHz
• Gain Range: -6dB → +23dB
• EQ Boost Range: 0dB → +15dB
• Exact Size of the die-cast enclosure (with knobs) is 154.78 mm x 119.35 mm x 57.98 mm