Solid State Power Amp Reviews

Lord Acton said, famously, that power corrupts and absolute power corrupts absolutely. If there ever were an amplifier to test that maxim's applicability to audiophiles, it is surely the Chord SPM 14000 Ultimate Monoblock. Priced no less than $75,000/pair, the SPM 14000 is rated to produce power as do very few other amplifiers on the planet: it is very conservatively rated at 1kW into an 8 ohm load, 2kW into 4 ohms, and "will easily exceed" 2800W (give or take a few watts) into 2 ohms.

Everything about the big Chord proclaims it a bespoke product. Normally, the SPM 14000 is built to order; the pair of samples sent me by Bluebird Music, Chord's North American importer, was the set that had debuted the model at the 2005 Consumer Electronics Show. They arrived, with Bluebird's Jay Rein and two moving men in tow, in gargantuan Anvil-style road cases. When released from their posh accommodations, getting them out and on to the floor of my listening room was a two-man operation. These are seriously heavy amplifiers: 165 lbs each.

The level of fit and finish is exquisite, and the styling is from the clean, minimalist, Euro-modern school. The amp's top is not the usual slab, but is a beautifully machined piece of aluminum that frames the circuitry living inside the impeccably finished casework (footnote 1). Adding to the high-tech effect are the blue lights inside the case, which illuminate the innards when the amp is powered up and can be seen through windows in the top panel. The effect is way cool and very cybertech. The front panel has a logo plate, power switch, four warning lights, and precision-machined detailing. The rear panel has AC in, in-phase and out-of-phase RCA and XLR inputs, and two massive sets of speaker binding posts.

The Chord within
Inside the SPM 14000 Ultimate is a bushel's worth of imposingly high technology. The power supply itself deserves some explanation. John Franks, Chord's founder and chief designer, first worked in the aerospace industry, where he specialized in the design of lightweight, high-powered, extremely reliable power supplies. He decided to put that technology to use in audio applications. The central principle was a "high-frequency," switching power supply that would recharge far more often than a conventional supply's 120 times per second.

Ten years of experimentation and labor later, he realized his dream. The Chord power supply was introduced to the public in 1989's Chord SPM900 stereo amplifier. These days, the Chord power-supply unit comes in four capacities: 600W, 2kW, 4kW, and 12kW. These self-contained, self-monitoring units can be used individually or in parallel, allowing great flexibility in design.

AC from the wall is filtered, then rectified to DC—some 300–350V worth—and stored in a bank of high-voltage capacitors. At this point, the current is still connected to the mains. It is then "chopped," using high-voltage MOSFETs running at 80kHz (footnote 2). From there, the resulting high-frequency waveform is sent to a custom-made ceramic-core transformer wound with multistrand Litz wire. As the size of a transformer decreases as operating frequencies increase, only a small transformer is required to re-rectify the 80kHz waveform. At the transformer's output a bank of very fast rectifiers, a small coil, and small capacitors convert the waveform back to DC for the final time, when the electricity is handed off to Chord's Dynamic Coupling system prior to being stored in a final bank of capacitors.

I e-mailed John Franks about the amplifier's unique design, and he explained Dynamic Coupling to me in terms understandable to a reviewer who was a political-science major in college:

"Specifically, Dynamic Coupling of the power-supply rails means that power delivery is always balanced and free from ground-loop modulation distortion. The power-supply rails operate at frequencies well above that which most amplifiers can accommodate. This, and other advanced techniques, enables the ultra-high-frequency, low-ESR power supply to store a great deal more energy far more efficiently."

Making use of all this heavily filtered, multiply rectified juice are 64 MOSFET output devices. These are not off-the-shelf items—the power MOSFETs were designed by Chord and are made specifically for them. Chord claims that "clipping is virtually impossible" with the SPM 14000 and states that the output signal path is totally free of the fuses or sound-degrading resistive components often used to sense overload. This is achieved by relying "on a magnetic flux being generated between the power rails." The amplifier self-monitors differences in the flux density between the rails over time and uses an algorithm to determine whether or not power should be delivered or withheld. The amplifier section is a class-AB sliding-bias design that operates in class-A during most normal use, shifting into class-B only in the most demanding situations.

Chord products are designed to be used 24/365. The company is a significant player in the world of professional audio, holding pride of place as the amplifier of choice at the Royal Opera House, Abbey Road Studios, Skywalker Sound, Toshiba/EMI Japan, and a long list of other demanding users. In my system, the SPM 14000s proved totally unflappable.

There are some clear similarities in the approaches of Chord's John Franks and Halcro's Bruce Candy. These are not the result of either man pilfering the other's ideas, but certain rules of the road apply to anyone endeavoring to use high-speed switching power supplies in audio amplification. Both Franks and Candy are highly skilled engineers who were involved with cutting-edge high-tech applications in their pre-audio careers. Both are interested in pushing the furthest limits of sound quality and technology, so it is natural that there should be some overlap in their approaches. Bruce Candy succeeded; has John Franks done the same?

Power Chord
It is hard to conjure up in words the sense of utter effortlessness the SPM 14000 Ultimates brought to my listening room through both the Legacy Audio Whisper and Wilson Audio Sophia loudspeakers. The Legacy is rated at a highly sensitive 94dB, the Wilson at a more commonplace 89.5dB, though the Sophia's 4-ohm load doubles the power available from the amplifier. With the Sophias, I managed to light three of the SPM 14000s' front-panel warning lights when playing "The Battle" and "The Might of Rome," both from The Gladiator soundtrack (CD, Decca 467 094-2), but both amplifiers and speakers remained unruffled, which is more than I could say for myself.

No matter what I pounded these amps with, their impeccably English manners were never in the least flustered. Played at disco levels, power techno-pop—Sugar's "Misty Blue" (Korean CD single, Starworld/Jeil JIDA-6616); Armin van Buuren's luscious, techno-chill "Never Wanted This" and "Burned with Desire," from 76 (CD, Ultra L1168-2); and Ron van den Beuken's stomping "Clokx" and "Timeless," from Ultra.Trance:3 (CD, Ultra ULT1180-2)—had the sweep and scope that such music needs to be most effective.

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Footnote 1: Metalworking is extremely expensive; I suspect that the Chord's casework, which is unique to the SPM 14000 and flawlessly executed, costs considerably more than do many good-sounding amplifiers.

Footnote 2: The SPM 14000 features Chord's latest-generation, 12kW-capable power supply, and the chopping MOSFETs are run asynchronously, which John Franks says results in both a steadier supply of electricity through the circuits and provides lower noise.