For over thirty years, ATC Loudspeaker Technology has built a sterling reputation for engineering self-amplified or active speaker systems for professional applications—from recording studios and mastering facilities to ritzy music venues like Disney Hall. ATC consumer gear, though less well known, places the same sharp emphasis on tonal realism, dynamic freedom, and bulletproof reliability. Over the years I have owned a couple of ATC passive two-ways, including my current reference SCM20-2, and I can vouch for these attributes. The SIA2-150 is the first integrated amplifier I’ve reviewed from ATC. In all candor, I have to admit that I was especially interested to see how this amp would mate with my SCM20-2s—a passive version of the bi-amplified studio monitor.
The SIA2-150 is a Class AB solid-state design with a considerable amount of toasty Class A bias. It outputs 150Wpc into 8 ohms. The SIA2-150 uses the same gain-reduction and protection circuits ATC packs into its bi- and tri-amped active speakers to prevent amplifier clipping at high output levels—which can damage loudspeaker drivers. It’s also a proudly minimalist amp with only basic input and volume wheels and a “Standby” button bedecking its titanium-anodized aluminum front panel. There are no glowing front-panel displays, tone and balance controls, or—perish the thought—re-namable inputs or iPod accommodations. It’s just the facts, mum. ATC products are like that; they’ve got a job to do. In a concession to contemporary realities however, a basic remote control is standard. I spoke with founder/designer Billy Woodman about the provocative retro-look and he commented, “The visuals were inspired by my fondness for Art Deco industrial design as expressed in the interior design of automobile dashboards of the 30s and the visual appeal of professional electronic gear of the 50s and 60s. I have tried to give the SIA2 a modern interpretation whilst retaining some of that style.”
As an advocate for the revitalized integrated amplifier, I’d been looking forward to taking on the ATC. One thing is certain: There’s nothing passive or Old School about its performance. It’s a paradigm of balance. Across all the conventional sonic criteria that reviewers take into account, from dynamics and speed to tonality and transparency, the SIA2-150 performs without fanfare and is never caught napping. Its sonic signature is an unwavering midrange forthrightness and fluidity. Its neutral to warmer tonal balance allows for the most critical listening, yet doesn’t cross the threshold into the starkly clinical. Musical fundamentals and overtones are expressed like continuous liquid waves of energy. When Shelby Lynne sings “How Can I Be Sure?” [Lost Highway], the energy of her voice is forceful—you can hear it pressurizing the microphone. Upper-mid and lower-treble information is smooth, and biased to the sweeter side of the spectrum. Listening to solo piano I found that treble transparency does reveal a little shading and doesn’t seem as unfettered or open as it could be, but this is far from an attention-grabber.
Bass response is excellent with precise pitch and plenty of slam, although its style is a more diffuse one—with a larger degree of romantic bloom and warmth. This character was revealed most often with soundboard instruments like acoustic bass or piano or the explosive close-miked guitar of Laurence Juber [LJ Plays the Beatles, Solid Air]. Warren Bernhart’s piano [So Real, DMP] sounded fuller and less contained in the upper bass, even if it doesn’t seem as firecracker-quick off the line. Similarly Edgar Meyer’s stand-up bass [Appalachian Journey, Sony] conveys a more primal mood rather than a purely calculated one, throwing generous resonances onto the soundstage—a presentation that suggested to me more of what a real bass does in a live performance. There’s plenty of headroom macro-dynamically but the SIA2-150 was equally dogged expressing the low-level micro-dynamics and harmonics of the lead acoustic guitar and rhythm section during Elton John’s “Madman Across the Water.” (This is the raw, “original” version that only made it onto the recent SACD reissue of Tumbleweed Connection [Island/Rocket].)
Perhaps the most impressive aspect of this amp was the wide net it cast in resolving soundstaging and imaging. An all-acoustic a cappella recording like Laurel Massé’s Feather & Bone [Nonesuch] exemplified this, as the amp elegantly charted the vast boundaries of the legendary Troy Savings Bank in New York. Similarly when I cued up Judy Collins’ “Amazing Grace” [Elektra], which was recorded in St. Paul’s Chapel at Columbia University, I could hear the moment when the analog tape began rolling—the chapel’s acoustic came alive, the density of air seemed to increase and engulf the performers and, without the aide of artificial reverb, Collins’ voice seemed to echo into eternity. Like only the best amps I’ve heard the ATC clings tenaciously to a decaying reverberant field, permitting the ear insights into the recording process that few other integrated amps can match.
In a significant way—and I don’t think this is a coincidence—the SIA2-150 has a “voice” that emulates its loudspeakers. These are midrange values, allowing vocals and piano to emerge from a deep wellspring of authority. Voices seem to enlarge in scale, with greater musical weight and color and a “you are there” physicality. As with ATC’s speakers it’s easy to come to the quick conclusion that the overall perspective is a bit softer and perhaps less articulate on top. Perhaps. But in my view the presentation is simply cleaner and lacking the auditory “backlighting” of distortions and colorations that laser-etch harmonics and transients—wow factors that the ear ultimately tires of over extended listening.
Let me put the ATC in perspective with a few of the presumptive leaders in this range. The Pass Labs INT-150, Plinius 9200, and the MBL 7008 differ in sonic personality but in only the subtlest ways from the ATC. The 7008 gets highest marks for its silky, transparent treble, the best in this group (and well it needs to be, driving MBL’s own low-distortion omnis). Its overall signature is a darker one, however, than either the Plinius, ATC, or the Pass Labs. The INT-150, on the other hand, has exemplary low-level resolution, a tube-like warmth, and all the low-end control of the best solid-state—a true renaissance amplifier. Like the ATC, the Plinius throws its weight and balance where it’s most appreciated—in the midrange. The key differences are the slightly drier character and tighter lower end of the 9200.
For all its retro-stylistic flourishes the SIA2-150 is a thoroughly modern instrument that quickly gets down to the business of making music. In my view, fidelity to the source is built on balance—the way sonic criteria interlock like fingers to form a powerful fist—and so goes the SIA2-150. Powerful, dynamic, and virtually colorless, it’s major league all the way. In case you haven’t already guessed, the SIA2-150 is my kind of amp.
Output Power into 8 ohms: 150W
Input Sensitivity: 350mV
Input Impedance: 22k ohms
Frequency Response: 5Hz – 200KHz ±0.1dB
Signal / Noise Ratio: >100dB
Dimensions (HxWxD): 135x435x325
Weight (HxWxD): 20kg / 44lbs