Walrus Audio Mantle – Premium bass preamp & DI

Walrus Audio Mantle – Premium bass preamp & DI with Sapphire transformers and massive headroom

Ian Martin Allison collaboration · Custom Sapphire input/output transformers · Neve/API-inspired voicing · 11-position Bass & Treble EQ · HPF/LPF cut modes · Gain −6 to +23 dB · Transformer-balanced XLR DI · 9V/500mA with internal +24V boost

The Walrus Audio Mantle is a premium bass preamp and DI, created in close collaboration with Ian Martin Allison, built to give your instrument an impeccable, studio-grade foundation anywhere—on stage, in the studio, or at home.

At the core are proprietary, custom-wound Sapphire Transformers. The input transformer, based on Neve design principles, is built to handle large signals cleanly while delivering authoritative low end and a musical midrange push. The output transformer draws inspiration from the output stage of an API 312, balancing the signal quietly while adding rich harmonic content and maintaining strength over long cable runs.

The Mantle is voiced for clarity and musical transformer coloration, giving you control over both the front end and the final output of your tone.

Signal path overview

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

Key features

• Premium bass preamp + DI (Ian Martin Allison collaboration)

• Custom-wound Sapphire input/output transformers

• Neve-inspired input transformer feel + API-inspired output stage harmonics

• Massive headroom: 9V power internally boosted to +24V

• Transformer-based Gain range: −6 dB to +23 dB

• Advanced EQ with 11-position rotary switches for Bass and Treble

  • True flat at noon (position 6)

  • Boost in +3 dB steps up to +15 dB

  • Cut introduces steep filters:

    • Bass cut = −18 dB/oct HPF at 30/50/80/100/120 Hz

    • Treble cut = −18 dB/oct LPF at 8k/6k/4k/2k/1k Hz

• Switches:

  • Active/Passive pad (−10 dB) for active/high-output basses

  • Ground lift to eliminate hum/ground loops on XLR

• Run 1/4″ and XLR simultaneously (amp + FOH)

Connections

• Input: 1/4″ TS unbalanced Hi-Z optimized for bass (JFET buffered)

• 1/4″ Output: TS unbalanced for amps/pedals

• XLR Output: male XLR transformer-balanced DI out

• Power: 9V DC 500mA, center-negative (2.1mm), internally boosted to +24V

Technical specifications

• Power: 9V DC, 500mA, center-negative (PSU not included)

  • Isolated supply recommended; daisy chaining not advised

  • Internally boosted to +24V

• Input impedance: 1 MΩ

• Output impedance: 150 Ω balanced, 150 Ω unbalanced

• Noise floor: −101 dBV balanced, −94 dBV unbalanced

• THD @ 1kHz, 1 Vrms: 0.04%

• Frequency response: 20 Hz – 20 kHz

• Gain range: −6 dB to +23 dB

• EQ boost range: 0 dB to +15 dB

• Enclosure dimensions (with knobs): 154.78 × 119.35 × 57.98 mm

• Country of origin: USA

• Color: Black

• Type: Bass Preamp

• Brand: Walrus Audio

Find the Walrus Audio Mantle and a carefully curated selection of boutique bass tools at onemorepedal.com, your specialist store for high-end stage and studio gear.

Studio-grade front-end for bass: transformers, headroom, and control with intent.