Rethinking the Onboard Preamp: How McGrath Guitars Re-Engineered a Studio Cult Classic for Bass

For decades, bassists hunting for tonal flexibility faced a familiar dilemma, carve out room on their instrument for a wall of knobs and stacked pots, or settle for a standard 3-band EQ. Yet, in practice, many players end up running multi-band active EQs totally flat or worse, the dreaded “all-maxed” boost.

High-end custom builder McGrath Guitars is challenging that multi-knob paradigm with an intuitive solution inspired by one of the recording world’s most famous utility secrets.

From Keith Duffy’s Brainstorm to Max Martin’s Hit Factory

The spark for bringing this circuit onboard didn’t come from a workshop whiteboard, it came directly from touring bassistKeith Duffy (The Corrs, Ronan Keating). Duffy approached McGrath Guitars with the concept of embedding an active tilt EQ circuit straight into the bass control cavity allowing for an instant “sweet-spot” tone shaper at his fingertips on stage.

Duffy’s vision drew heavily on the legacy of the DOD FX10 Bi-FET Preamp. Originally released in 1982 as an active preamp for acoustic piezo pickups, the FX10 circuit quickly became a secret weapon across recording studios. Legendary pop producer Max Martin famously relied on the FX10 circuit in the late ’90s shaping iconic, punchy tracks like Britney Spears’ “…Baby One More Time” to push signals hard into mixing desks with pristine clarity.

Before long, low-end tone connoisseurs like Juan Alderete (The Mars Volta, Marilyn Manson) and Jonathan Hischke (Hella, Broken Bells) adopted the FX10 as an essential utility pedal to restore low-end fundamentals and top-end snap through complex signal chains.

Why Put the Buffer Onboard?

While running an FX10 at the start of a pedalboard works wonders, placing that active circuit directly inside the instrument provides a massive technical edge:

• Signal Protection at the Source: High-impedance passive pickup signals suffer from cable capacitance loss over long cable runs, stealing high-end clarity and dulling low-end punch before the signal ever hits an amp or audio interface.

• Low-Impedance Drive: By buffering the signal right at the pickup output, the McGrath Tilt EQ converts the signal into a low-impedance line. Your tone remains completely immune to cable length and high-capacitance setups.

• The “Always-On” Tone Enhancer: Even set at the zero center detent, the active circuit acts as an onboard tone enhancer. It injects dynamic feel, preserves harmonic detail, and keeps the fundamental tight across the entire fingerboard without altering your natural passive tone.

Technical Breakdown: The McGrath Tilt EQ

McGrath Guitars adapted this classic Bi-FET concept into a sleek, single-pot onboard workspace.

Technical Specifications

McGrath Tilt EQ Onboard Preamp

Circuit Architecture

Active Tilt EQ with high-grade, audio-grade components

Primary Control

Single tone pot with center-detent (Flat/Neutral baseline)

Master Gain Control

Internal PCB-mounted trimpot (set-and-forget output level matching)

Power & Powering

Native 9V or 18V operation

Installation

Solderless/Easy-connect terminal blocks

Bypass Options

Pairs seamlessly with push-pull active/passive switching

How It Shifts Tone

• Treble Tilt: Rotating clockwise shifts focus to upper-mid clarity and finger attack without cutting or thinning out low-end tightness.
• Bass Tilt: Rolling counterclockwise dials in immediate vintage warmth and low-end weight. Pushed to its limit, it turns the instrument into a true sub-bass machine.

The Upcoming Studio & Live Machine: Streamlined P-Style Basses

While McGrath first introduced the Tilt EQ on complex builds, like their medium-scale, 5-string J-style Thunderhorse featuring the McGrath Switch, the builder is teasing an ultra-focused bass model aimed directly at gigging and session musicians.

“I totally get that the Thunderhorse, with its three pickups and 14 tonal combinations, can be a bit intimidating,” says luthier Cormac McGrath. “While that level of versatility is amazing for tone-chasers, we wanted to build something stripped-down and foolproof for players who just want to plug in and get a world-class recorded tone in seconds.”

Coming soon, McGrath Guitars is launching a series of streamlined P-Style basses built around a minimal 3-control control plate:

1. Master Volume

2. Passive Tone

3. McGrath Tilt EQ

By combining a split-coil P pickup with Keith Duffy’s requested Tilt EQ buffer concept, players get the organic dynamic punch of a classic P-bass paired with the cable-driving power, silent noise floor, and instant sweet-spot tone shaping required for modern studio work and live performances.

Beyond refining the frequency response, the updated circuit has been substantially miniaturized to drop effortlessly into tight control cavities without requiring routing modifications. The board now integrates quick-connect terminal blocks for fast, solderless drops, while the master gain stage has been moved to a PCB-mounted trimpot for set-and-forget level matching. Power delivery is fully adaptable, operating natively on either 9V or 18V supplies to give players their choice of standard operation or maximum clean headroom. Crucially, the control features a center-detent neutral position, and the treble tilt profile has been redesigned so that rolling clockwise boosts high-end attack and clarity without cutting or thinning out the essential low-end foundation. 

For players looking to get their hands on this circuit, note that McGrath Guitars does not currently offer the Tilt EQ preamp as an individual aftermarket component. Instead, the proprietary active buffer is built exclusively into McGrath instruments, meaning the only way to experience its signal-boosting clarity and tone-shaping power is by snagging one of their available in-stock builds or configuring a custom model through their interactive online Bass Builder.

For more visit: McGrath Guitars