PS Audio PMG M800 Monoblock Signature Power Amplifier

PMG M800

The flagship of the PMG Signature Series. The best power amplifier PS Audio has ever built — period.

PS Audio has been designing and building amplifiers for half a century. Every one has been a step toward sonic perfection — each teaching us something the last could not: about power supplies, about feedback, about the quiet ways an amplifier can color the music it carries. The M800 is where that road arrives.
Eight hundred watts into 4 ohms, doubling cleanly down from 400 into 8 — decisive, effortless, never strained.
But power was never the hard part. Speed, evenness, and restraint were. The M800 is the first amplifier we've built to hold all three at once.
Its slew rate exceeds 200 volts per microsecond. Hand it a 10 kHz square wave — the cruelest signal in audio — and it returns vertical edges and flat tops, no overshoot, no ringing. In fifty years we have never seen one this perfect. Distortion stays flat and low across the entire audible band, never trading one frequency for another. And it does all of this with strikingly low overall feedback — no heavy correction, just the music. Remarkable.
Designed by Darren Myers. Engineered by Bob Stadtherr. Hand-built in Boulder, Colorado.

Features

• 400 watts into 8Ω, doubling to 800 watts into 4Ω
• 50W Class A bias — 99% of typical listening in pure Class A
• Slew Rate >200V/uS
• Bandwidth exceeding 500 kHz
• Flat distortion across the audible band with strikingly low overall feedback
• State-of-the-art active power supply
• Balanced (XLR) and single-ended (RCA) inputs
• Available in Silver or Black
• Hand built in Boulder, Colorado

Design

The M800's character begins with its power supply. Where a conventional amplifier leans on a heavy passive transformer, the M800 is built around a state-of-the-art active power supply — a design that delivers current with a speed and stability no transformer-based supply can match. Around it sits Darren Myers' low-feedback current-based topology, chosen deliberately: the less an amplifier has to correct itself, the more honestly it passes the signal through. Every M800 is assembled and tested by hand in Boulder, Colorado, and brought into production by Bob Stadtherr — whose work ensures the amplifier you receive measures and sounds exactly like the one Darren designed.

Application

Each M800 is a monoblock — one chassis, one channel — sold as a pair for stereo. With 800 watts into 4 ohms and the current to double down without strain, a pair will drive virtually any loudspeaker made, from sensitive horns and electrostatics to the most demanding low-impedance reference designs. There is no speaker too difficult and no room too large. If you own loudspeakers that have humbled other amplifiers, the M800 is the pairing that ends the search.

Class A purity

Class A is the most linear way an amplifier can operate — and the most expensive. In a Class A output stage, every transistor conducts through the entire musical waveform and never switches off. There is no crossover point, no moment where one device hands off to another, no discontinuity for the music to stumble across. It is, simply, the purest mode of amplification known.
It is also brutally inefficient. A Class A stage runs hot and draws power continuously, even in silence, because its transistors are always fully active. That cost is why true Class A is so rare. It is rare for a high-end amplifier to deliver even a single watt of genuine, pure Class A — most designs that advertise the term operate in it for only a fraction of a watt before sliding into Class AB.
The M800 carries 50 watts of pure Class A bias. Fifty. Not a fraction of a watt, but fifty full watts before the output stage ever leaves its most linear region. For 99% of normal listening — and nearly all music lives well within that window — the M800 never crosses a notch, never sees a discontinuity, never asks its circuitry to correct an artifact it should not have created. What you hear is the natural texture of the recording: the body of a cello, the air around a voice, the decay of a struck cymbal, all intact. This is what Class A was always supposed to sound like. The M800 simply commits to it.

Power is The Key

A power amplifier is, fundamentally, an interface between a reservoir of energy and the loudspeaker. The character of that reservoir — how cleanly it stores energy, how instantly it can deliver it, how silent it is at rest — determines more about how an amplifier sounds than any other single design choice. For half a century, the high-end audio industry has approached this with passive supplies: large linear transformers feeding banks of electrolytic capacitors. The approach works. It also imposes real limitations. The transformer is the slowest element in the amplifier's signal path. The capacitors store charge but cannot return it without ripple. The rectifier introduces switching noise every time it transitions. And the entire arrangement is sized for a peak demand it will almost never actually see.
The M800 is built on a state-of-the-art active power supply that delivers performance benefits no traditional transformer-based passive supply can match. Instant transient response with no rectifier-induced noise. A vanishingly low residual noise floor. Total grip on the speaker at any output level. Full continuous output without sag. The active supply is the M800's foundation — silent, fast, and capable of delivering everything the output stage asks for the moment it asks for it.

The PMG disappears into the Music

Negative feedback is the most powerful tool an amplifier designer has — and the most easily abused. Applied in large amounts, it can drive measured distortion on a steady-state test tone almost to zero. It looks spectacular on a spec sheet. But feedback works by continuously comparing the output to the input and correcting the difference, and that correction is never quite instantaneous. With music — which is nothing but transients, never a steady tone — heavy feedback always arrives a fraction late. The amplifier spends its life chasing the signal rather than following it. Transients lose their edge. Immediacy fades. The performance begins to feel like a recording of a performance.
The M800 is built on the opposite philosophy: strikingly low overall feedback. Because its output stage is already extraordinarily linear on its own — running deep in pure Class A, where correction is barely needed — the M800 does not have to lean on a heavy feedback loop to clean up after itself. Distortion stays uniformly low across the entire audible band not by aggressive correction, but because there was little to correct in the first place.
What this produces is the M800's defining quality, and the hardest to put into words: it disappears. The electronics stop announcing themselves. The speakers and the source seem to dissolve, and what remains is the performance — present, immediate, and whole. Eight hundred watts of authority, delivered with the openness of a far smaller amplifier. The M800 gives you both.

Distortion vs. Frequency

Distortion vs. Frequency — This measurement tracks total harmonic distortion across the entire audio band, from 20 Hz to 20 kHz, under four conditions: no load, 8 ohms, 4 ohms, and a punishing 2 ohms. The traces do vary — distortion climbs gently with frequency, and the hardest 2-ohm load runs highest — but the takeaway is simple. Even at its worst, the PMG's distortion stays a tiny fraction of one percent, far below the level of audability. Linearity held this tight, across every load, and achieved without adding negative feedback, is something perhaps one amplifier in a hundred can claim — which means distortion simply stops being part of the conversation.

Twin tone Intermodulation results

Twin tone Intermodulation results — Here the amplifier is fed two tones at once — 19 kHz and 20 kHz — and we look for everything it adds that shouldn't be there. An amplifier that isn't perfectly linear lets those two tones beat against each other and spawn entirely new frequencies that have no musical relationship to the original signal. Those added tones are precisely what the ear registers as harshness, grain, and listening fatigue. The PMG produces almost none — the spectrum is essentially just the two original tones and silence. That is the measurable fingerprint of sound that stays clean and natural no matter how dense or demanding the music becomes.

10kHz square wave response

10kHz square wave response — A square wave is the cruelest signal you can hand an amplifier; it demands instantaneous swings in output voltage. Reproducing one cleanly takes tremendous speed — measured as slew rate — and the PMG Signature series exceeds 200 volts per microsecond. You can see the result here: vertical edges, flat tops, no overshoot, no ringing. Real music is full of fast transients — the leading edge of a cymbal, the snap of a plucked string — and an amplifier too slow to follow them rounds those transients off and smears the detail. The PMG follows all of it. In fifty years of designing amplifiers, we have never measured a square wave this perfect.

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