The new S400 Stereo — the PMG Signature voice in a more accessible stereo chassis. Two hundred watts per channel into 8 ohms, doubling to 400 into 4, with 5 watts of pure Class A bias per channel, a state-of-the-art active power supply, and the same strikingly low-feedback topology as the Signature monoblocks. Hand-assembled in Boulder, Colorado, and perfected by Bob Stadtherr.

Design

The S400 combines two complete PMG Signature channels within a single chassis, engineered so neither channel interferes with the other. Each channel draws from the same state-of-the-art active power supply as the monoblocks, with internal layout and isolation engineered so one channel’s demands only minutely disturb the other’s signal. The low-feedback, high-slew-rate topology remains unchanged.

Application

The S400 is a single stereo chassis with one power cord — the Signature experience without two boxes on the floor. At 200 watts per channel into 8 ohms, doubling into 4, it will comfortably drive the great majority of high-quality loudspeakers in rooms of moderate to generous size. It suits listeners who want genuine reference amplification but value simplicity, space, and a clean installation.

Class A Purity

Class A operation means every transistor conducts through the entire waveform and never switches off — no crossover point, no handoff between devices, no discontinuity for the music to cross. The S400 dedicates 5 watts of pure Class A bias to each of its two channels, covering the quiet, low-level passages where the ear is at its most revealing. Both channels carry the same operating integrity as a PMG Signature monoblock.

Two Channels, One Design

When the left channel demands a sudden surge of current — a drum strike, a crescendo — that demand pulls on the supply the right channel is using too. The S400 counters this with a state-of-the-art active power supply delivering far cleaner power and far greater current on demand, combined with a layout engineered channel by channel so the two channels’ currents never intermingle — the separation of true monoblocks, from a single chassis with a single power cord.

The PMG Disappears into the Music

The S400 follows the same principle as every PMG Signature amplifier: strikingly low overall feedback. With an output stage engineered to be deeply linear on its own merits, only a light touch of feedback is required — keeping distortion flat and low across the entire audible band, not scrubbed away after the fact but largely absent to begin with. No phase smear, no recovered artifacts masquerading as detail. The amplifier disappears.

Specifications

• Power Output: 200W/ch into 8Ω, 400W/ch into 4Ω (1kHz, <1% THD)
• Class A Power Output: 5W/ch into 8Ω
• Frequency Response: <10Hz – 80kHz (±0.25dB)
• Input Impedance: 100kΩ single-ended; 200kΩ balanced
• Bandwidth: >500kHz · THD: <0.002% typical · Damping Factor: >240 at 8Ω
• Crosstalk: >90dB at 1kHz · Gain: 26.2dB · Sensitivity: 2.0V
• Inputs: RCA 1 pair, XLR 1 pair · Speaker Outputs: 4 pair binding posts
• Power: Auto 120/230VAC 50/60Hz · Idle 190W
• Weight: 57.2 lbs (25.9 kg) · Dimensions: 16″L × 17.5″W × 8″H