Reference-class monoblock power. The M400 carries the M800’s design DNA, scaled for the systems most reference listeners actually live with. Two hundred watts into 8 ohms, doubling to 400 into 4, with 30 watts of pure Class A bias, the same state-of-the-art active power supply as the flagship, and strikingly low overall feedback. Sold as a pair. Hand-assembled in Boulder, Colorado, and perfected by Bob Stadtherr.

Design

The M400 inherits the M800’s engineering philosophy intact. At its heart is the same state-of-the-art active power supply — active pure power in place of a passive transformer — paired with Darren Myers’s strikingly low-feedback topology. The difference between the M400 and the flagship is not one of design integrity but of scale: the M400 delivers reference-grade performance into the power envelope a real-world system actually uses.

Application

The M400 is a monoblock, sold as a pair for stereo. Two hundred watts into 8 ohms — doubling to 400 into 4 — is enough authority for the overwhelming majority of high-performance loudspeakers, from efficient floorstanders to demanding modern transducers. For most rooms and most speakers, the M400 will never be the limiting factor in the system.

Class A Purity

Class A is the most linear mode an amplifier can operate in — every transistor conducting through the whole waveform, no crossover point, no handoff, no discontinuity. The M400 carries 30 watts of pure Class A bias. At the modest power levels where real music actually lives, that 30-watt window covers roughly 60% of normal listening. Within it, the amplifier never leaves its purest operating mode: no crossover distortion, no class-switching artifacts, no subtle shift in character as the volume rises and falls.

Power Scaled

Every quality an amplifier is praised for traces back to one place: the power supply. The M400 is built on the same state-of-the-art active power supply that powers the M800, scaled precisely to its 200-watt-into-8-ohm output. Nothing about the supply’s behavior was compromised, only its size. It still delivers current the instant the output stage calls for it, with no rectifier noise and no sag under sustained load — which is why the M400 doubles its power cleanly into 4 ohms, on demand, without strain.

The PMG Disappears into the Music

The M400 reaches its low distortion not through large amounts of negative feedback, but because Darren Myers’s topology is engineered to be highly linear before any feedback is applied at all — so only a small, gentle amount is needed. Bandwidth extends well beyond 500 kHz, so transients pass through unhurried and uncolored. There is no phase smear, no faint haze of correction artifacts to surface later as listening fatigue. The M400 simply gets out of the way.

Specifications

• Power Output (per monoblock): 200W into 8Ω, 400W into 4Ω (1kHz, <1% THD)
• Class A Power Output: 30W into 8Ω
• Frequency Response: <10Hz – 80kHz (±0.25dB)
• Input Impedance: 100kΩ SE; 200kΩ balanced
• Bandwidth: >500kHz · THD: <0.002% typical · Damping Factor: >300 at 8Ω
• Inputs: RCA 1 pair, XLR 1 pair · Speaker Outputs: 2 pair · Gain 26.2dB · Sensitivity 2.0V
• Power: Auto 120/230VAC 50/60Hz · Idle 220W
• Weight: 55.8 lbs (25.3 kg) each · Dimensions: 16″L × 17.5″W × 8″H