PS Audio has expanded its PMG Signature line with the PS Audio PMG S400, a stereo power amplifier that packs the full Signature topology – the same one found in the brand’s M400 monoblocks – into a single, more accessible chassis. Designed by Darren Myers and engineered by Bob Stadtherr, the S400 is hand-built at PS Audio’s own facility in Boulder, Colorado, and is priced at $9,999. It sits below the flagship M400 monoblocks in the range, aimed squarely at listeners who want the same sonic signature without dedicating a rack shelf to two separate chassis.
One Box, Two Channels of Genuine Reference Amplification
Not every system has room, or a use, for a pair of monoblocks – two boxes, two power cords and two sets of cables is one requirement too many for a lot of listeners. The PS Audio PMG S400 exists for exactly that situation: 200 watts per channel into 8 ohms, doubling cleanly to 400 watts into 4 ohms, drawn from the same state-of-the-art active power supply architecture that drives the M400 monoblock. PS Audio says the bandwidth extends beyond 500 kHz and slew rate beyond 200 volts per microsecond, delivering a clean 10 kHz square wave with no overshoot or ringing.
5 Watts of Class A Bias, Per Channel
The PS Audio PMG S400 dedicates 5 watts of pure Class A bias to each of its two channels – a serious commitment for a stereo chassis where two channels share one thermal budget. PS Audio says those 5 watts per channel cover the quiet, low-level passages where the ear is most revealing, keeping crossover artifacts out of exactly the material where they would otherwise be most audible: the decay of a note, the texture of a voice held softly. It is precisely in that low-level material that crossover distortion is most fatiguing to the ear over a long listening session, which is why PS Audio treats Class A bias as a non-negotiable part of the PMG Signature identity rather than a marketing footnote.
Closing the Gap With Monoblocks
Building a stereo amplifier that rivals a genuine pair of monoblocks comes down to one shared resource: the power supply. When one channel demands a sudden current surge, that draw can pull on the supply the other channel is using too, narrowing the soundstage under complex material.
PS Audio addresses that at the source, with an active power supply that holds its output stiff under load, combined with a layout – grounding, board topology, mechanical structure – engineered so the two channels’ currents never intermingle. The result, PS Audio says, is 200 watts per channel from a single chassis that comes remarkably close to true monoblock separation.
Strikingly Low Feedback
Like every PMG Signature amplifier, the S400 keeps overall negative feedback deliberately low, relying on an output stage that is linear by design rather than corrected after the fact. PS Audio says distortion stays flat and low across the audible band as a result, with transients arriving intact rather than smeared by a feedback loop reacting a step behind the music.
Pricing and availability
The PS Audio PMG S400 is available now, priced at $9,999 in silver or black finish, direct from PS Audio and through authorized dealers. PS Audio is also offering trade-in credit of up to $3,000 against an existing PS Audio amplifier for buyers upgrading to the S400.
Key specifications
- Power output: 200W/ch into 8Ω, 400W/ch into 4Ω (1kHz, <1% THD)
- Class A bias: 5W per channel into 8Ω
- Bandwidth: >500 kHz
- Slew rate: >200V/µS
- THD: <0.002% typical (20Hz-20kHz, 1W/8Ω)
- Damping factor: >240 at 8Ω (20Hz-1kHz)
- Inputs: 1 pair RCA (single-ended), 1 pair XLR (balanced)
- Weight: 57.2 lbs / 25.9 kg
- Price: $9,999 (silver or black finish)
Full specifications and bench measurements are available on the official PS Audio product page. The PMG S400 joins the flagship PMG Signature Series monoblocks in PS Audio’s current amplifier lineup.
