MXR M400 Turbo Tuner

The MXR M400 Turbo Tuner combines the precision of the original Sonic Research Turbo Tuner with expanded tuning options and flexible bypass configurations. Developed around Sonic Research's true strobe tuning technology, the M400 delivers accuracy within ±0.02 cents and a zero-latency display that responds directly to changes in string pitch. Its rugged MXR enclosure, bright LED display, and straightforward controls make it a practical choice for pedalboards, studio setups, and professional touring rigs.

Unlike conventional tuners that approximate pitch using a moving needle or simulated strobe display, the Turbo Tuner uses a true strobe pattern driven by the instrument's signal. The LED pattern rotates right when a note is sharp and left when it is flat, slowing as the string approaches the correct pitch. This immediate visual feedback allows for fast, precise adjustments without waiting for a display to settle. Four selectable brightness levels keep the display readable in different lighting conditions, from dark stages to outdoor performances.

The M400 offers six tuning modes, including a chromatic mode that recognizes all twelve notes and five customizable presets. Dedicated Guitar and Bass presets recognize programmed open-string pitches and display string numbers instead of note names, while three additional presets come preloaded with standard guitar, Drop D, and six-string bass tunings. Each customizable preset can accommodate up to twelve strings, with individual pitch offsets adjustable from -50 to +50 cents in 0.1-cent increments. Custom chromatic temperaments, flat tuning down to nine semitones, and an adjustable A4 reference from 300.0 to 599.9 Hz provide further flexibility for alternate tunings and specialized setups.

An internal switch allows players to choose between true bypass and buffered bypass operation. In true bypass mode, the pedal mutes the output while tuning and removes itself from the signal path when disengaged. Buffered bypass offers three operating modes, including conventional silent tuning, continuous signal passthrough, and an always-on monitoring mode with footswitch-controlled muting. These options allow the M400 to accommodate different pedalboard layouts and performance requirements.

Additional features include USB-C connectivity for firmware updates and editor software, a 9V DC power output for passing power to another compatible device, and the option to operate from a standard 9V battery or external power supply. With a wide tuning range from C0 to C8, precision strobe tracking, and Sonic Research's heavy-duty switching design, the MXR Turbo Tuner provides accurate tuning for guitar, bass, and extended-range instruments.

Highlights

• Sonic Research true strobe technology with ±0.02-cent accuracy and zero-latency tracking

• Six tuning modes, including chromatic and five customizable presets supporting up to twelve strings

• Adjustable tuning offsets, custom temperaments, nine-semitone drop tuning, and variable A4 reference pitch

• Selectable true bypass or buffered bypass with three operating modes

• Four-level LED brightness, USB-C connectivity, and 9V DC power passthrough

Specifications

General

• Brand: MXR

• Model: M400 Turbo Tuner

• Effect Type: True Strobe Chromatic Tuner

• Technology: Sonic Research True Strobe

• Tuning Accuracy: ±0.02 Cents

• Tuning Range: C0 (16.35 Hz) to C8 (4,186 Hz)

• Display: LED True Strobe Ring with Note Display

• Display Brightness: 4 Adjustable Levels

• Tracking: Zero Latency

• Finish: Black

Tuning Features

• Total Presets: 6

• Chromatic Mode: All 12 Notes

• Customizable Presets: 5

• Factory Presets:

  • Chromatic

  • Standard Guitar

  • Standard 4-String/5-String Bass

  • Custom 1: Standard Guitar

  • Custom 2: Drop D Guitar

  • Custom 3: Standard 6-String Bass

• Custom Tuning Capacity: Up to 12 Strings per Preset

• Custom Pitch Offsets: ±50 Cents

• Offset Adjustment Resolution: 0.1 Cent

• Custom Chromatic Temperaments: Supported

• Flat Tuning Range: 0–9 Semitones Down

• Reference Pitch Range: A4 = 300.0–599.9 Hz

• Reference Pitch Adjustment: 0.1 Hz Increments

• Default Reference Pitch: A4 = 440 Hz

• Open Tuning Display: String Number

• Chromatic Display: Note Name

• True Temperament Tuning Support: Yes

Controls & Switching

• Footswitch: Heavy-Duty On/Bypass Switch

• Preset Selection: Left and Right Arrow Buttons

• Bypass Selection: Internal Toggle Switch

• Bypass Types: True Bypass or Buffered Bypass

• True Bypass Operation: Silent Tuning with Relay Switching

• Buffered Bypass Modes:

  • Mode 1: Silent Tuning

  • Mode 2: Continuous Signal Passthrough

  • Mode 3: Always-On Tuner with Footswitch-Controlled Muting

• Display Brightness Adjustment: 4 Levels

• Automatic Power-On: Configurable

Connections

• Instrument Input: 1/4"

• Instrument Output: 1/4"

• Power Input: 9V DC

• Power Output: 9V DC Passthrough

• USB Port: USB-C

• USB Function: Firmware Updates and Editor Software

Power

• Power Requirements: 9V DC

• Battery Operation: One 9V Battery

• External Power Supply: Compatible 9V DC Supply

• Typical Current Draw: 48 mA at Minimum Brightness

• Typical Maximum Current Draw: 73 mA at Maximum Brightness

Dimensions & Weight

• Height: 4.4" (11.2 cm)

• Width: 2.4" (6.1 cm)

• Depth: 1.9" (4.8 cm)

• Weight: 6.8 oz (192 g), Without Battery

Miscellaneous

• Model Number: M400

• Manufacturer: MXR / Dunlop Manufacturing

• Tuning Engine: Sonic Research

• Firmware Updates: Supported via USB-C

• Editor Software: Supported

• Applications: Electric Guitar, Bass Guitar, Extended-Range Instruments, and Custom Tuning Systems

Why Buy from Tone Shop Guitars?

Tone Shop Guitars is an independent MXR dealer with locations in Addison, Southlake and Fort Worth, Texas. We offer free nationwide shipping on new gear and multiple financing options.