Dan D’Agostino MOMENTUM S250 MxV STEREO AMPLIFIER

Scaling New Heights

Delivering the extraordinary sound quality of the Momentum M400 MxV Monoblock, the Momentum S250 MxV Stereo Amplifier features techniques and topologies developed and implemented in the Relentless Series. This fullest expression of the Momentum circuitry is reflected in the model’s name, MxV. Those with a physics background will recognize that MxV, or Mass times Velocity, is the equation for Momentum.

Advancements in Every Area

Every major section of the amplifier—power supply, input, driver, and output stages—has been enhanced. An improved transformer winding provides over 50% more current output from the same transformer footprint, offering greater headroom during dynamic passages. The input stage combines revised circuit topology with advanced components feeding the driver and output stages. Crucial to the new circuit are bipolar transistors powering the front end that deliver ten times the current and power of the originals. These wider bandwidth, higher-power components extend low- and high-frequency performance with reduced distortion at both frequency extremes. 

Energizing the driver stage is a bias stability circuit providing a nearly 50% increase in operating bias. Increasing Class A operation directly correlates to better sound quality. However, there is a limit to bias level in any amplifier. With this new circuit topology and our unique copper heatsinks, thermal issues are not a practical concern, preventing excessive temperatures even under the greatest demand. Additional power transistors in the output stage reduce workload foreach device, so the entire output section works more efficiently. The result is a richer, more dynamic, and intimate presentation of the music. 

The final output stage features 28 new high-output transistors originally sourced for the flagship Relentless Series amplifiers. Among the fastest available, these run at a blistering 69 MHz and permit the amplifier to achieve incredible bandwidth. Each transistor mounts with two stainless steel fasteners—a rarity among flat-package transistors—for maximum thermal transfer to the copper heatsinks. A capacitor/resistor network connected to the base of each transistor ensures stability even at high frequencies and with low-impedance speakers. Additionally, every output transistor is measured, and only devices that match the required performance specifications are used. As with all D’Agostino models, the Momentum S250 MxV Stereo Amplifier features discrete, direct-coupled balanced circuitry, the most accurate circuit platform possible.

Defying its compact size, the Momentum S250 MxV is a powerhouse amplifier. The backbone is an ultra-quiet 2,200 VA linear transformer. An improved winding scheme reduces the hysteresis effect by 90%, minimizing power and thermal loss. This combination provides 50% improvement in output. This engine drives a nearly 100,000 μF capacitor bank resulting in 250 watts per channel of power output into 8 ohms. Output doubles to 500 watts per channel into 4 ohms and 1,000 watts per channel into 2 ohms. The Momentum M250 MxV Stereo Amplifier is capable of driving any loudspeaker to its fullest potential. 

A critical element of any amplifier output stage is circuitry known as the driver section. In the Momentum S250 MxV, this stage is a fully complementary design. Individual transistors are employed for the positive and negative halves of the musical signal. This nearly doubles the current drive necessary to maximize the enhanced output stage that follows. The new output stage takes this increased drive to boost the open loop gain by the same factor of two. The result is a sound that is more authoritative, richer, and more expansive.

Upgrading to MxV Performance

Because the Momentum S250 MxV Stereo Amplifier employs the same chassis as previous generations, all Momentum stereo amplifiers can be upgraded to the Momentum S250 MxV performance level. All electrical enhancements are included in the upgrade while the original metalwork is retained. Original Momentum amplifiers receive a new 250-Watt meter plate reflecting the power output increase included in the upgrade. Momentum S250 units already have this power increase and meter.