Mark Levinson No. 631 Mono-Power Amplifier

The Mark Levinson No. 631 is the most powerful amplifier in the 600 Series and represents the pinnacle of audiophile amplification technology. As a fully balanced, completely discrete mono power amplifier, it delivers an impressive combination of power, precision, and control. Designed for music lovers who demand absolute sonic neutrality and dynamic supremacy, the No. 631 is ideal for use with sophisticated high-end speaker systems.

With its monolithic architecture, the No. 631 isn't just an amplifier—it's a statement of audiophile consistency. It ensures that every musical nuance, every impulse, every spatial information is reproduced with unsurpassed precision and stability.

Fully symmetrical circuit design in its purest form

The entire signal processing in the No. 631 is based on Pure Path circuitry, which is based on complete symmetry, minimal negative feedback, and discrete construction. This means no ICs, no unnecessary components in the signal path, and no compromises in signal purity. Amplification is Class A/AB with high bias current, ensuring highly linear operation – even with complex loads.

This design makes the amplifier virtually insensitive to parasitic capacitances. This allows for an exceptionally fast voltage change (slew rate) and an exceptional bandwidth. The music thus appears more lively, open, and, above all, more natural—with a black background against which even the finest details are clearly audible.

Powerful power supply and internal decoupling

A key element of the No. 631 is the specially developed, ultra-low-noise toroidal transformer, which is centrally located in the cabinet and structurally isolated. This isolation prevents mechanical vibrations from being transmitted to sensitive circuitry. At the same time, the power supply provides enormous energy reserves, resulting in impressive bass control and effortless dynamics – regardless of speaker load or volume.

The internal architecture is modular. Analog signal paths and power supply are separated and mounted on vibration-damped supports. This design ensures maximum isolation of sensitive components and protects the signal from unwanted influences.

Flexible connection options for high-quality setups

As a mono power amplifier, the No. 631 is designed for single-channel use. It can be connected to balanced XLR or unbalanced RCA inputs. The speaker outputs consist of two pairs of Hurricane speaker terminals—solid, gold-plated, and rated for high currents. These allow for bi-wiring or bi-amping configurations, allowing the amplifier to be optimally adapted to various speaker systems.

The integrated high-bias function allows the user to choose between a standard and a "warm" mode. In high-bias mode, the amplifier operates in Class A over a wider range, making the sound reproduction even smoother and more fluid—ideal for critical listening at moderate volumes.

High-quality workmanship and thermal concept

The exterior appearance of the No. 631 is an expression of uncompromising manufacturing quality. The case is milled entirely from solid aluminum, anodized in matte black, with a silver base and a central glass front panel stylishly illuminated by red LED accents. The generous surface ventilation and side-mounted heat sinks enable highly efficient heat dissipation – even in high-bias operation under full load.

Integration into high-end systems

For complex systems, trigger inputs and outputs as well as an RS-232 interface are available, allowing the amplifier to be remotely controlled or integrated into smart home systems. The high build quality, finely adjustable operation, and excellent circuitry make the No. 631 the ideal solution for the most demanding stereo or home theater installations—especially when paired with a matching Mark Levinson preamplifier such as the No. 626.

Technical data

• Mono power amplifier with fully symmetrical Pure Path circuit
• Fully discrete Class A/AB amplification with high bias current
• Specially developed, centrally insulated toroidal transformer
• Input: 1x balanced (XLR), 1x unbalanced (RCA)
• Output: 2 pairs of Hurricane speaker terminals
• High-performance, low-impedance power supply
• High-bias mode selectable (more Class A range)
• Modular design with mechanical decoupling of sensitive components
• Tectonic aluminum case with glass front and red LED accents
• Side heatsinks and ventilation openings in the lid
• Trigger In/Out, RS-232 control
• Designed, manufactured and assembled in the USA