The Mantle — Premium Bass Preamp & DI
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 proprietary, custom-wound Sapphire Transformers, engineered to deliver 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 realized form.
Signal Path Overview
Input → JFET Buffer → LPF/HPF or Dry Path → Input Transformer (−6 dB to +23 dB) → Boost EQ → Output Transformer
The Mantle’s architecture is meticulously voiced to maintain clarity, deliver musical transformer coloration, and give you control over both the front end and final output of your tone.
Transformers
The Mantle features proprietary custom-wound Sapphire Transformers. With more than a year of research, listening, and refinement, the Walrus engineering team set a new benchmark for transformer design, reflecting a 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 pristine performance across the full frequency spectrum.
The output transformer is based on the output stage of an API 312. It balances the signal quietly and effectively while also providing rich harmonic content. Like the input transformer, the core style and customized winding method result in a strong signal capable of long cable runs without signal loss.
Connections
1/4" TS unbalanced Hi-Z input optimized for electric bass, buffered by a high-quality JFET stage 1/4" TS unbalanced output for amps or additional pedals Male XLR transformer-balanced output for premium DI tones Powered by 9V DC (500 mA, center-negative), internally boosted to +24V for massive headroom
Controls
Bass & Treble — Boost/Cut Filter System
The Mantle’s EQ is a sophisticated dual-behavior design, far more expressive than standard shelving EQs. Both Bass and Treble controls feature eleven-position rotary switches for a tactile studio feel, repeatable 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 gain increases Each step adds +3 dB, up to +15 dB, without muddiness or harshness
Cutting (positions 5–1)
Bass control introduces a steep −18 dB/oct high-pass filter at selectable points: 30 Hz, 50 Hz, 80 Hz, 100 Hz, 120 Hz Treble control introduces a steep −18 dB/oct low-pass filter at selectable points: 8 kHz, 6 kHz, 4 kHz, 2 kHz, 1 kHz
This design allows precise mix shaping or broad musical coloration without sacrificing elegance or fidelity.
Gain Control
The Gain control adjusts the amount of transformer-based gain applied to the signal. The circuit derives directly from the input transformer, delivering magnetic manipulation at its finest. Gain ranges from −6 dB to +23 dB.
Combined with the JFET buffer, the result is a tone that feels alive, dimensional, and deeply expressive.
Switches
Active / Passive (−10 dB Pad) Engaged: Introduces a −10 dB input pad for active basses or high-output instruments Disengaged: Full-strength passive bass signal with maximum sensitivity Ground Lift Engaged: Separates XLR output ground from circuit ground Eliminates hum and ground-loop noise in complex live or studio setups
FAQ
Can I run this as my always-on tone solution?
Yes. The Mantle is designed to function as your primary front-end, studio-quality, always-on preamp. Can I use both 1/4" and XLR outputs at once?
Yes. Send 1/4" to an amp and XLR to FOH simultaneously. Does it take other pedals well?
Yes. The high-headroom JFET front end and transformer-driven architecture preserve clarity with compressors, drives, and modulation.
Specifications
Power Requirements: 9V DC, 500 mA, center-negative, 2.1 mm (power supply not included) Internally boosted to +24V for increased headroom Isolated power supply recommended; daisy chaining not advised Input Impedance: 1 MΩ Output Impedance: 150 Ω balanced, 150 Ω unbalanced Noise Floor: −101 dBV balanced, −94 dBV unbalanced THD @ 1 kHz, 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 mm × 119.35 mm × 57.98 mm
