Mark Levinson Nº 631 – Flagship Monaural Power Amplifier

One Amplifier. One Channel. An Entirely New Level of Ambition.

The Mark Levinson Nº 631 is the flagship power amplifier of the 600 Series, engineered for listeners building a reference audio system without compromise.

This fully discrete, fully differential monaural amplifier combines Mark Levinson's proprietary Pure Path circuitry with a high-current linear power supply, selectable high-bias operation, and a dedicated chassis for each audio channel.

Designed to drive demanding loudspeakers with control and precision, the Nº 631 brings together the brand's established amplification philosophy and its striking new Tectonic industrial design.

A sculpted aluminum-and-steel enclosure, glass detailing, signature red illumination, and a substantial floorstanding form make the Nº 631 as distinctive visually as it is technically.

For a conventional stereo system, two Nº 631 amplifiers provide independent amplification for the left and right loudspeakers.

 

Key Features

• Flagship 600 Series Amplification: Mark Levinson's dedicated monaural power amplifier.

• Pure Path Circuit Design: Proprietary analog amplification architecture.

• Fully Discrete, Fully Balanced Signal Path: Individual components arranged in a fully differential circuit.

• Class A/AB Operation: High-current amplification with a selectable high-bias mode.

• Dedicated Monaural Architecture: One amplifier chassis and power supply per audio channel.

• Ultra-Low-Noise Toroidal Power Supply: Custom transformer positioned centrally and structurally isolated.

• Low-Feedback Circuit Design: Engineered for high inherent linearity and wide bandwidth.

• Balanced and Unbalanced Inputs: XLR and RCA connectivity.

• Dual Hurricane Speaker Terminals: Two pairs of substantial loudspeaker binding posts.

• Vibration-Controlled Construction: Modular internal layout, isolated components, and mechanically decoupled feet.

• Tectonic Industrial Design: Black chassis, silver plinth, glass elements, and red accent lighting.

• Professional Integration: 12V trigger input/output and USB service connection.

• American Engineering: Designed and engineered in the USA.

   

Pure Path: The Foundation of Mark Levinson Amplification

At the heart of the Nº 631 is Mark Levinson's proprietary Pure Path analog circuit design.

Its fully discrete, fully balanced architecture uses a differential signal path engineered to maintain signal integrity throughout the amplification process.

Rather than relying on extensive corrective feedback, the circuitry is designed to achieve high inherent linearity. This allows the amplifier to operate with relatively little feedback while maintaining low distortion and wide bandwidth.

The design also employs unusually high bias current, supporting linear operation and the ability to respond rapidly to changes in the musical signal.

These engineering choices are intended to preserve the detail, spatial information, and dynamic contrasts contained in the original recording.

 

True Monaural Amplification

The Nº 631 is dedicated to a single audio channel.

In a stereo configuration, one amplifier drives the left loudspeaker while a second drives the right. Each channel benefits from its own chassis, amplification circuitry, and power supply.

This arrangement separates the electrical demands of the two channels and allows each amplifier to be positioned according to the needs of the listening room.

For large floorstanding loudspeakers and ambitious reference systems, the Nº 631 offers a purpose-built approach to amplification.

Its monaural architecture also makes it a natural partner for the Mark Levinson Nº 626 preamplifier, creating a complete separates-based 600 Series system.

Class A/AB with Selectable High-Bias Mode

The Nº 631 combines Class A/AB amplification with a selectable high-bias operating mode.

Bias current is an important part of amplifier design because it influences how the output devices operate as the audio signal changes.

The Nº 631's high-bias architecture is engineered to improve linearity while retaining the output capability of a high-current power amplifier.

The selectable mode gives owners an additional operating option for their system.

Because high-bias operation can affect heat generation and power consumption, the amplifier should be installed with the ventilation clearances specified by Mark Levinson.

 

A Power Supply Built for Demanding Loudspeakers

A reference power amplifier needs a power supply capable of responding to demanding musical passages.

The Nº 631 uses a custom-designed, ultra-low-noise toroidal transformer located centrally within the chassis.

The transformer is structurally isolated to help minimize the transfer of mechanical vibration to sensitive amplifier circuitry.

Its linear power supply is designed to support the current demands of the output stage, while the amplifier's low-feedback architecture and high-bias operation contribute to its overall performance.

The result is an amplifier engineered to maintain control during complex musical passages, from low-level acoustic recordings to large-scale orchestral performances.

 

Tectonic Design: A New Expression of Mark Levinson

The Nº 631 introduces a dramatic interpretation of Mark Levinson's industrial design.

Its floorstanding chassis combines black-anodized aluminum and steel with a contrasting silver plinth.

A glass center panel flows down the front of the amplifier, framed by red accent lighting. On the top panel, the distinctive glass Core element is surrounded by ventilation and illuminated detailing.

Custom heatsink side panels provide thermal management while contributing to the amplifier's sculptural appearance.

Inspired by geological forms, the Tectonic design makes the Nº 631 a visual centerpiece for a dedicated listening room.

It is an amplifier intended to be seen as well as heard.

 

Mechanical Isolation by Design

The Nº 631's substantial chassis is engineered to address vibration as well as electrical performance.

Its modular internal architecture separates sensitive low-level analog circuitry from the power supply.

Critical internal components are mounted using rubber isolation elements, while mechanically isolated feet help reduce the transfer of vibration between the amplifier and the supporting surface.

The transformer is also structurally isolated within the enclosure.

Together, these measures create a carefully controlled mechanical environment for the amplifier's sensitive circuitry.

 

Balanced and Unbalanced Connectivity

The Nº 631 includes one balanced XLR input and one single-ended RCA input, allowing it to connect with compatible high-performance preamplifiers.

Two pairs of Mark Levinson Hurricane binding posts provide secure loudspeaker connections and support compatible bi-wiring arrangements.

For custom installations, a 12V trigger input and output allow coordinated power operation with compatible components.

A USB-A service port is provided for maintenance functions.

The Nº 631 is a dedicated power amplifier. It requires a compatible preamplifier or another suitable source with volume control.

 

The Ultimate 600 Series Stereo Configuration

Pair two Nº 631 monaural amplifiers with the Mark Levinson Nº 626 preamplifier to create a complete reference separates system.

The Nº 626 provides analog source selection, high-resolution digital conversion, phono playback, and volume control, while the Nº 631 amplifiers handle the dedicated power amplification for each loudspeaker.

This configuration is designed for listeners who want independent amplification channels and the flexibility to choose premium loudspeakers and source components.

At The Grid HiFi, we can help evaluate loudspeaker compatibility, system layout, electrical requirements, and installation considerations for a complete 600 Series system.

Technical Specifications

Specifications are for one Nº 631 amplifier.

Specifications follow Mark Levinson's official product page and published documentation. The manufacturer's preliminary specification sheet contains a conflicting dimensions line; the table uses the dimensions consistently shown on the product page and dimension drawing. Rated output wattage and net weight have been omitted because they could not be reliably established from the published specifications reviewed.

Experience the Mark Levinson Nº 631 at The Grid HiFi

The Mark Levinson Nº 631 is designed for listeners building a reference audio system around exceptional loudspeakers, carefully selected source components, and dedicated amplification.

At The Grid HiFi, we specialize in high-performance two-channel audio, premium loudspeaker matching, reference amplification, and professional system design.

Whether you're building a complete Mark Levinson 600 Series system or integrating a pair of Nº 631 amplifiers into an existing listening room, our team can help with component selection, system configuration, and installation.

Contact The Grid HiFi to discuss the Mark Levinson Nº 631 and design your next reference listening system.