PS Audio Stellar M1200 monoblock power amplifier

Talk about a Scarlet Letter. The term class-D amplification, which describes PS Audio’s new M1200 monoblocks, exists only because another amplifier innovation had already parked in the “C” space. Soon after appearing in high-performance audio gear, class-D became synonymous with “digital amplification” in part because, like early CDs, many listeners found the sound glary, hard, and unpleasant. Besides, class-D is related to “pulse width modulation” and requires a low-pass filter to block high-frequency pulses—that sure sounds digital. But they’re not (see sidebar).

To this day, many audio enthusiasts remain unconvinced by class-D technology. Why?

According to Bruno Putzeys, one of the format’s leading innovators, “a high-performance class-D amplifier contradicts every single item of audiophile superstition. Designing one is the ultimate test to see if you’ve got your head screwed on right.” Maybe that’s why. Judging by this powerful amplifier’s sonic performance, Stellar M1200 designer Darren Myers definitely has his head “screwed on right”!

Putzeys also said, in the same interview with Sound & Vision‘s Bob Ankosko, that “there are a few distortion mechanisms conspicuously missing in class-D, mostly those related to the input stage of a class-A(B) solid state amplifier and nonlinear capacitances” that are also “missing in valve [tube] amplifiers.” This newfangled technology, then, has much in common with old-school tubes.

Nonetheless, Myers and his team chose to implement actual tubes—a “fully vacuum tube input stage” consisting of a 12AU7 dual triode running in class-A with zero feedback, powered by its own analog power supply.

Beyond the input stage
The made-in-USA Stellar M1200, which is claimed to deliver 600W into 8 ohms and 1200 watts into 4 ohms, incorporates what Myers calls “all top-shelf components,” including PRP resistors and capacitors manufactured for PS Audio by Reliable Capacitors, which is owned by Wilson Audio Specialties.

According to Myers, the output stage is “a custom ICE-power module utilizing ICE’s latest ICEedge technology, which dramatically lowers switch-mode-amplifier–related parasitics such as high-order harmonic distortion, phase distortion and output impedance instability—especially at high frequency.” (ICE is as unfortunate a name for a class-D module as “class-D,” IMO!)

Myers told me that each MOSFET-based ICE module is “hand-modified” using an ICEpower design team–approved process intended to take full advantage of the vacuum-tube input stage; it includes removing all solid state devices in front of the ICEedge circuitry: “This creates a simple, short, and elegant signal path that conjoins the holographic and musical sound of triodes with the power, precision, and speed of top-tier switch-mode technology.”

As with his Stellar Phono preamplifier, which was just named Stereophile‘s 2020 Analog Product of the Year in the December 2020 issue, tuning was done by ear, Myers said: “Rather than simply chasing the best test bench performance, the input-stage circuit design and component selection were finalized by listening, which allowed us to optimize the tonal neutrality and musical involvement that results from proper synergy of the input and output stages.”

Myers chose a premium-grade Psvane 12AU7-TII, hand-graded and tested in PS Audio’s Boulder factory. Tube-rolling is easy thanks to rear-panel access behind a small door. I stuck with the supplied tube.

Despite the robust output, the M1200 is less than 4″ tall × 17″ wide, and it weighs 27lb, thanks to class-D efficiency. The chassis is 0.5″ taller than the tubeless, lower-powered M700 reviewed by Robert Deutsch in 2018; the other dimensions are exactly the same.

The rear panel features a main power-rocker switch, a 15A IEC jack, two pairs of five-way binding posts (for biwiring), single-ended RCA and balanced XLR inputs, trigger input and output, and the tube-access cover plate. How can something this compact and lightweight deliver 1200 watts into 4 ohms? With a superefficient power supply that doesn’t require a massive transformer. How can it cost just $5998/pair? “We just worked really hard to get the pair of M1200 monoblocks in at a price people can afford and smile at,” Paul McGowan, PS Audio’s CEO, wrote in an email. Shipping is free, and you get a 30-day in-home audition, after which you can return it and get your money back. Before deciding thumbs-up or -down, give this amp some break-in time: Leave it on overnight, every night, with something playing for at least the first week.

Your bass performance probably can’t compare
It’s no surprise that this superquiet class-D amplifier excels on bottom. Bass is what class-D was originally built for; at least that’s where it did the most good and the least musical damage.

The M1200’s ability to couple with, control, and drive the woofers of my Wilson Alexx loudspeakers matched that of any amplifier I’ve had here, including my reference darTZeel NHB-468 and Boulder’s 2150, both of which are way more costly. I’m not suggesting the bottom end produced by the M1200 is identical to those; I’ve not had the Boulder here in years, and the darTZeel’s bass, while not as grippy on bottom, has a more supple attack and a more generous sustain that works better on acoustic double bass.

But not on electric bass, where the M1200 is a monster. The 2150’s and M1200’s bottom-end performance are more similar to one another than either is to the darTZeel’s.

I returned to the direct-to-disc The Fox Touch (Crystal Clear CCS-7002), a record I referenced in my SAT XD1 turntable review in the December 2020 issue. The liner notes refer to “several visits from the local police” during the late-night recording sessions. I’m sure that if I lived in an apartment building or if my next-door neighbor wasn’t two lots away, I’d have had a visit from the locals myself. The house shook more than few times on Louis Vierne’s “Finale from the Sixth Symphony.” It did likewise through the darTZeels, but with the more expensive amplifier, the low notes were less concentrated and more bloomy. I’m not sure I preferred one over the other. One would leave a lot more money in the bank if bass was all I was after.

I pulled out the original American pressing of Manifesto (Atco SD 38-114), Roxy Music’s disco-ish 1979 album, which I’d not played in a very long time. It’s far from the band’s best effort, but the bass line on the title tune was always an attraction. (The album was mixed at Atlantic Studios in New York; the George Piros–mastered Atco pressing is better than either the UK or Japanese originals.) Two bass players are listed: Gary Tibbs and Alan Spenner; I’m not sure which of them played on the tune, but the insistent bass line was the star of the show. I’ve never before heard it shine like this.

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COMPANY INFO

PS Audio

4826 Sterling Dr.

Boulder, CO 80301

(720) 406-8946

psaudio.com

ARTICLE CONTENTS

Page 1
Page 2
Is Class-D Digital?
Specifications
Associated Equipment
Measurements

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