Audio Research Corporation
Audio Research Corporation (ARC) releases a new product, expectations are high. Now, after
more than 30 years of building robust, reference-quality tube and solid-state electronics,
ARC is taking aim at digital amplification, and currently offers three class-T models: the
300Wpc 300.2, the 150Wpc 150.2, and the subject of this review, the five-channel, 150Wpc
150M.5. Each employs, according to ARC, a more advanced version of the Tripath Digital
Power Processor used in competing brands. And, like every ARC product, the 150M.5 is
hand-built by ARCs skilled craftsmen in Plymouth, Minnesota.
150M.5 multichannel power amplifier
Price: $7495 USD
Dimensions: 19"W x 7"H x 19.5"D
Weight: 64 pounds
Warranty: Three years parts and labor
- Class-T digital-switching amplifier based on Tripath chip
- Modular design
- Configurable from one to seven channels
- Two modules can be bridged for up to 600Wpc into 8 ohms
- 12V remote trigger
- XLR balanced and RCA single-ended inputs
- Black or natural faceplate
- Rack-mount handles optional
Its all about bandwidth
According to ARC, digital amplifiers offer a more efficient
means of delivering voltage and current to a loudspeaker. One of the first digital
designs, termed class-D, never found its way into wide-bandwidth applications due to
inherent distortion issues caused by the transistors "imperfect" switching
properties. Class-D amplification is largely used in subwoofers, where frequency response
is restricted. Tripath Technologies, founded in 1995, developed class-T Digital Power
Processing (DPP), which, they claim, combines class-D efficiency with more linear,
wider-bandwidth frequency response.
Both class-D and class-T
amplification track the incoming music signal and create a high-frequency analog of its
audio waveform. This parallel signal is then used to switch an amplifiers output
transistors on and off. In more conventional class-A and class-AB designs, the output
transistors are constantly on, and electrical current passes through them regardless of
the audio waveforms input level. The result is wasted energy, in the form of heat
dissipated by the transistors. Digital-switching amplifiers turn transistors on only when
the audio waveform requires it. Tripaths DPP improves on class-D by "learning
the behavior of the output transistor" and "switching [the output transistors]
with exactly the right timing to eliminate class-D distortion issues."
ARC hasnt just taken a Tripath chip, thrown it onto a
printed circuit board, and christened it the 150M.5. According to David Gordon, ARCs
manager of North American sales, it took more than a year of refinement to get the
150M.5s sound right. The chief challenge was to retain the fundamental sonic
signature of classic ARC products in a class-T design. As in any high-quality audio
device, the circuit topology and the power supply feeding it are crucial to the
150M.5s sonic integrity. The most critical aspect of the design is the low-pass
filtering, which removes high-frequency noise produced by the switching transistors.
Introducing the ARC 150M.5
The 150M.5s impeccably assembled chassis is made of
nonmagnetic aluminum and supported by five footers that look as if made of Sorbothane but
are instead an "energy-absorbing elastomer that we [ARC] prefer sonically in this
application." Customers can order a 150M with one to seven channels. Pairs of
channels can also be bridged at the factory in a fully balanced differential configuration
capable of producing 600Wpc into 8 ohms. All ARC products are available with a black or
natural aluminum faceplate. Rack-mountable faceplates and the companys trademark
handles are optional. My black, five-channel 150M.5 ($7495 USD) came without handles.
ARCs reputation for long-lasting, conservatively
built products is apparent in the 150M.5s solid but unadorned frame. Audiophiles
used to mirror-finished 2" faceplates might wonder what theyre paying for, but
once they take a look inside, the answer will be clear. Each amplifier module is
beautifully assembled and stuffed with top-quality parts from such companies as Wonder and
Nichicon. The modules slide into individual slots and securely dock into heavy-gauge,
gas-tight, multiple-pin connections. ARC chooses these connections for their "sound
[quality] and reliability under high-current conditions."
Multichannel class-AB amplifiers Ive auditioned have
gotten by with 100,000 to 200,000 microfarads (uF) of capacitance. So with a more
efficient class-T design, it might seem admissible, even logical, to save money with a
less robust power supply. ARC doesnt think so. The 150M.5s massive power
supply has a large EI power transformer with 312,000uF of capacitance -- enough,
ARC states, to drive virtually any loudspeaker load and deliver rated power simultaneously
into all installed channels. The company strongly recommends that the 150M.5 be plugged
into a dedicated 20A line, and supplies a very-high-quality, 20A power cord to ensure that
its circuits are never starved for power.
The 150M.5s high-quality parts
allow for easy, dependable connections. The sturdy, well-spaced, all-metal, five-way
binding posts were a joy to use. Each 7/16" hex head allowed me to use a socket
wrench to comfortably secure large Analysis Plus T1 spade lugs.
I used the 150M.5s high-quality, single-ended RCA
inputs. Balanced XLR connections are also supported, selectable via a small toggle switch.
I didnt use the standard 12V remote turn-on -- for optimal performance, ARC
recommends keeping the 150M.5 powered up continuously. For those fearing their electric
bill, the 150M.5s power consumption at idle is specified at a reasonable 100W.
After listening to the 150M.5 connected to my Shunyata
Hydra power conditioner, I concluded that it sounded more dynamic and open plugged
directly into my dedicated 20A wall outlet. And it didnt matter where I plugged in
the ARC -- hum was never a problem.
Letting it all through
It didnt take long for me to figure out why ARC
products are so successful. The 150M.5 was the most transparent, most musically satisfying
multichannel amplifier I have ever heard. It did exactly what an audio component should:
it let the sound through.
I watched at least a dozen films and listened to numerous
CDs with the 150M.5, and was compelled to sit and listen without thinking about the hour
or the quality of a recording. While flaws within recordings were revealed, they
didnt ruin the experience. There was no fatigue from artificially extended highs,
bloated lows, or forward mids. Nor was I bored by rolled-off highs, anemic lows, or a
recessed midrange. The words that came frequently to mind were natural, graceful,
I was riveted during the opening chapter of the underrated Titan
A.E. This dynamic soundtrack sounded delightfully open and pure. The 150M.5 perfectly
reproduced the crisp feel of the desert, the emptiness of space, and the sweet intensity
of Graeme Revells score. The immense size and weight of the Titan spaceship
was palpable as Cale Tucker and his father, Professor Sam Tucker, narrowly escape the
alien Drej (chapter 2). The 150M.5 did not embellish the sound -- whatever sweetness there
was resided in the recording, while bass response wasnt just "rumble and
thump." Low frequencies were full yet athletic and tight, and naturally extended to
the mid frequencies without abnormal bloom.
Films I have watched many times sounded remixed. Se7ens
stellar sound design can sound harsh if playback is too aggressive, detached if the
electronics are too laid-back. The 150M.5 was just right. New details within Ren
Klyces brilliant sonic collage of New York City were carried to the foreground.
Voices had marvelous vibrancy and intelligibility. Plosives and sibilants, which reveal
subtleties in dialogue, were not truncated or synthetically enhanced. Many amplifiers can
barely reproduce California whispering "You got what you deserved" to the
semiconscious Sloth (chapter 17) without adding edginess or dropping syllables. The 150M.5
separated John C. McGinleys subtle taunts from the noise floor and revealed the
slithery contempt in the S.W.A.T. commanders voice. Se7en always gives me the
chills. The 150M.5s outstanding resolution made the shivers reach even deeper.
Some amplifiers reproduce frequencies rigidly and
mechanically, as if the sound is being created by the electronics rather than merely
passing through them. I found nothing mechanical or clinical about the
150M.5s presentation. It possessed an effortless, bracingly dynamic disposition that
sneaked up on me. The massive groan of the Titanics splintering hull (Titanic,
chapter 27), and the Arizona succumbing to the concussive explosion of a Japanese
bomb (Pearl Harbor, chapter 22), seemed to appear from nowhere. At one moment the
150M.5 was calmly reproducing ambience and dialogue; within the next millisecond, it was
ripping the roof off.
Although multichannel amplifiers have shown notable recent
improvement in terms of reproducing music, the 150M.5s formidable muscle and
refinement were in a different league. The amps sincerity, wide dynamics, and
beautifully balanced soundstage made listening to classical orchestral music an absolute
joy. The blazing horns of Saint-SaŽnss Symphony 3 [Telarc CD-80274]
can sound thin and strained; the 150M.5 kept its composure and managed to disclose this
inclination while still conveying the soul of the music in all its authentic,
Leonard Bernsteins Candide Suite, from the
Minnesota Orchestras Showcase [CD, Reference Recordings RR-907CD], scared me
with its awesome dynamic swings. This is the way I expect to hear an orchestra: a
room-filling soundstage delivered with wince-inducing yet silky-smooth transients. The
150M.5s command of detail captured the sweetness of string overtones, and bass
harmonics rippled long after the initial stroke on a drum.
Listening to several cuts from Seals newest DVD-A, Seal
IV [Warner Bros. 47947], I heard a pitch-perfect presentation accompanied by splendid
decay. This fabulous recording is rich in ambience, a touch of euphoria, and wonderfully
supple vocals. All of these qualities were delivered through the ARC perfectly.
High frequencies were often so stunning that I
couldnt help but smile. Percussion on Kodos "Daraijin," from the
multichannel SACD Mondo Head [Red Ink/Sony 56111], made its way around my room with
seamless transparency. The sound was snappy, with no overhang or smearing of transients.
Lightning-quick reflexes furnished the 150M.5 with superb rhythmic timing.
Older pop recordings, such as Erasures classic
"A Little Respect," from The Innocents [Sire 25730], never sounded so
good. This track was nimble and intoxicatingly melodic. Andy Bells distinct falsetto
was full and textured, while Vince Clarkes layered synthesizers cast a solid,
Prior to the ARC, I lived with the Conrad-Johnson MF5600
($4000, discontinued) and the Pass Labs X5 ($4500) -- capable amplifiers with vastly
different sonic characters. Although the X5 has excellent dynamics and very wide frequency
response, its solid-state sound is a bit too cool, and less natural than the ARCs.
Such stark transparency can be unkind to recordings of less than reference quality, making
thin recordings sound harsh and inducing listening fatigue; the ARC, on the other hand,
encouraged me to revisit average recordings that Id left on the shelf for years.
Conrad-Johnsons MF5600 pulls me into music without
much regard for its flaws, its powerful presentation combined with an optimistic,
rose-colored view of recordings. A warm upper bass and a very euphoric midrange support
high frequencies that are a tad rolled-off. And while lower bass is well controlled, the
MF5600s overripe personality does tend to overload my medium-sized room.
By comparison, the ARCs character was defined by its
utter lack of coloration and unrivaled ability to communicate the spirit of the music.
Listening to it, I forgot about classifications and just got lost in the performance.
The build and parts qualities of the
C-J and Pass are very good to excellent. In terms of overall fitnfinish, the
C-J is bit rough around the edges, while the Pass is a model of exacting industrial
design. Although the C-J uses excellent parts, its point-to-point soldering is less tidy
and well-finished. The X5s fastidious precision seems born of robots. The
150M.5s casework is exacting and very well finished, while its hand-assembled
circuit layout is faultlessly symmetrical and skillfully constructed.
A tweak and a curtain call
Toward the end of my evaluation, ARC applied a hardware
update to the 150M.5. David Gordon offered no details other than that it was a production
change available on all class-T amplifiers and that it had to do with sonic quality. A
skeptic, I figured it would be nearly impossible for my human ears to notice a change.
I underestimated myself -- the difference I heard in my
setup was subtle yet readily apparent. The 150M.5s already excellent transient
response felt snappier, and its presentation tightened up. Its wide, deep soundstage
benefited from more well-defined outlines and a more palpable texture.
The Audio Research Corporations 150M.5 is a superb
multichannel amplifier. Its also the best one that Ive heard in my system.
Consider my expectations greatly exceeded.
|Speakers - Canton Ergo RC-A
(mains), Ergo CM 500 DC (center), Ergo F (surrounds); Thiel CS2.4 (mains), MCS1 (center),
Power Point (surrounds), SW1 (subwoofer)
- McCormack MAP 1
|Source - Esoteric DV-50
universal audio/video player
- Analysis Plus
|Monitor - Mitsubishi
WT-46809 rear-projection widescreen monitor (with Duvetyne modification and full ISF
Conditioning - Panamax, Shunyata Research