Solid State Power Amp Reviews

In the May 2015 issue, I fairly raved about Simaudio's Moon Evolution 740P line-stage preamplifier, and now here I am confronting its Moon Evolution 860A power amp. The two are companion models of sorts, with prices of $9500 for the 740P, $15,000 for the 860A—and for much of the time I spent listening to the 740P it was hooked up to the 860A, so some of the descriptions of sound in this review will seem familiar. The two components are both products of the same design shop—Simaudio, Ltd., of Quebec, which has been a prominent brand in high-end audio for 35 years—and are often marketed as a pair, so it should be no surprise if they have a common sound. However, I did try the 740P with other power amps and the 860A with other preamps, to the point where I could make some distinctions between the two, parsing which component contributed what to their sound together. It turned out there were differences in shade and emphasis, if not so much in color or character.

The Description and Design
The Moon Evolution 860A is a solid-state amplifier with a dual-mono design and balanced differential circuitry. It pumps 200Wpc into 8 ohms or 400Wpc into 4 ohms, running in class-A up to 5W, then in class-A/B for the rest. The output stages are powered by 12 bipolar transistors per channel, each matched to extremely high standards, resulting in a wide bandwidth, minuscule distortion, and a low noise floor (or so claims the owner's manual). Circuits are DC-coupled, reducing phase shift and deepening the bass response. Two custom-built, 500VA toroidal transformers, made of high-quality, slow-rolled Japanese steel, are tightly regulated so that, as the demand for current swells, the supply of voltage dips by no more than 3%, allowing—again, according to the owner's manual—"effortless" dynamic peaks through the most complex musical passages. The output section's high damping factor (specified as 800 for frequencies below 400Hz) "ensures an excellent 'grip' on woofer cone motions." Signal paths are shortened and impedance lowered through use of a four-layer circuit board—two layers for each audio signal, one for the ground, one for the power supply—etched with copper tracings.

Simaudio's Zero Global Feedback, a standard feature in all of its amps since 1998, is claimed to lead to "more accurate" musical tones, "elimination" of phase errors, and improved dynamic range. The 860A also uses Simaudio's proprietary Lynx Circuitry (introduced in 2005), which efficiently distributes power to each active device in the amplification circuit, resulting in greater speed and dynamics.

Finally, the 860A physically resembles other Moon Evolution products, with a sleek, ultrarigid aluminum chassis with curved edges, and thumbscrew cones protruding from its four pillar feet to minimize spurious vibrations.

The Setup
The owner's manual says that the Moon Evolution 860A needs 300 hours of break-in before it sounds as good as it's going to get, and my experience supports that claim. Simaudio also suggests leaving the amp on all the time; I found that any time I turned it off for a few days or longer, it took a few days (but no longer) to warm back up.

I did all of my listening through Revel's Ultima Studio2 loudspeakers. For line-stage preamplification, I used the Moon Evolution 740P most of the time, though I occasionally swapped it out for the preamp section of the Moon Evolution 700i integrated amp and the Pass Laboratories XP-30 line-stage preamp.

To compare the 860A with other power amps, I briefly hooked up the 740P to the Pass Labs XA60.5 monoblock amps and to the amplifier section of the 700i, reconfiguring the latter's software to bypass its preamp section and volume knob. I've had the 700i in my system, off and on, for almost five years. I borrowed the Pass electronics from Stereophile's editor, John Atkinson. And I was so smitten with the sound of the Moon Evolution 740P preamp that, soon after writing up my appraisal, I bought the review sample.

The Sound
In my review of the Simaudio 740P preamplifier, I waxed about its get-out-of-the-way transparency, and the way all the music in a recording was "breathing forth at the same time." That might have struck me as a banal observation until I heard the way it reproduced the wholeness of a piano—the percussiveness of the hammers, the dynamic contrasts in the pressure and release of the pedals, the bouquet of overtones wafting in the air, the resonant vibrations of the piano itself—all of these sounds mingling at once in the same place. Ditto for the coherence of drums, and the synchronicity of a band's interplay—all were testimony to the 740P's low-level detail and distortion-free linearity.

I heard this same seamlessness with the 860A power amp; that is, the 860A amplified these details without adding colorations of its own. But I also heard other things that hadn't quite been picked up by the other amps I'd hooked up to the 740P—and that I hadn't heard, to such a degree, with other Simaudio amps. Most noticeable was the bass: subterranean, articulate, complex—and musical, not just a mush of bass tones. From Dave Douglas's Charms of the Night Sky (CD, Winter & Winter 910 015-2) I could clearly hear not just which notes but which strings of his double bass Greg Cohen was plucking: the tautness of the high strings, the thickness of the low ones, and how loosely or tightly he was clamping them on the neck. This wasn't mere "audiophile" detail for its own sake; it was the sort of detail that enriched the rhythm and flow, and that fleshed out the presence of a human musician.

The second big improvement was in the percussive edge of instruments' sounds: the strum of a guitar, the whack of a bass drum, the sss of a sibilant. Another example from that Dave Douglas album: In the March 2011 issue, when I compared the Simaudio 700i with the Krell FBI—both high-powered, high-priced integrated amps—I noted that when Douglas's trumpet and Mark Feldman's violin played in unison, both amps allowed me to distinguish the two, each in a different way. The FBI let me hear the transient attack of Douglas's mouthpiece and Feldman's bowing; the 700i let me hear their distinct harmonic overtones and the way that brass vibrations sounded different from vibrating wood and string. I didn't hear those vibrations so clearly through the FBI, nor did I hear those transient attacks so clearly through the 700i. The 860A power amp let me hear both. The overtones were still clearer than the transients, but those transients were clearly, cleanly there.

There was a similarly revealing detail in "My Funny Valentine," from Miles Davis's Cookin' (SACD/CD, Prestige/Analogue Productions LAPJ 7094 SA). When the quintet breaks into a faster tempo, the FBI revealed Philly Joe Jones letting up on the hi-hat cymbal after tapping it with his stick, an effect that adds an extra layer of rhythm and cool that I hadn't noticed with the 700i (or with many other amps I'd sampled). I could hear this extra layer with the 860A as well. Ditto for "Nuages," the first track of Chasin' the Gypsy, saxophonist James Carter's inventive tribute to Django Reinhardt (CD, Atlantic 83304-2). In the comparison with the Krell, I wrote that the 700i didn't let me hear all the subtle rhythms and counter-rhythms tapped out by the triangles, bells, woodblocks, and other percussive bric-a-brac in Carter's ensemble. Again, the 860A did show and tell all, in full flair.