Audio Research • Reference 150 Stereo Amplifier

by Dennis Davis | March 1, 2012

Audio Research has seen some dramatic changes over the past few years. In 2008, Quadrivio SGR, a private-equity firm that already owned Sonus Faber through its subsidiary Fine Sounds SPA, acquired the venerable electronics company. Fine Sounds then purchased Wadia Digital in late 2010, combining under one virtual roof the speaker company, the digital manufacturer and the venerable maker of tubed electronics. Then, in December 2011, company founder William Zane Johnson passed away.

Audio Research is one of the oldest high-end audio companies to survive into the 21st century. Founded in 1970, the company’s tube equipment was already iconic before Dave Wilson built his first speaker, when Harry Weisfeld was best known for the VPI Brick, and when the name Krell referred only to an extinct race of advanced beings from the planet Altair IV. Yet, through all these years, Audio Research has continued to grow and thrive, maintaining a core set of employees and never resting on its laurels. If anything, the acquisition of the company by Fine Sounds seems to have enabled the process of innovation to continue at a faster pace. Like any company that continues to grow, Audio Research must deal with the tension between delivering products that a consumer can be satisfied with over the long haul while at the same time striving to look for ways of constantly improving its brand.

Audio Research’s current wave of new offerings (and it is a veritable tidal wave) is largely inspired by the innovations developed for its ultra-expensive Reference Anniversary preamplifier, a limited-edition two-chassis design that celebrated the company’s 40th anniversary. The company has extracted those elements from its super high-end preamplifier that could be incorporated into the rest of its Reference line without breaking new price barriers for those products. As a result, Audio Research is replacing all of its Reference models, except the CD8, with new models, all incorporating a similar set of upgrades. The Reference 110 stereo amp was replaced with the Reference 150, the Reference 210 monoblocks with the Reference 250s, and the Reference 610Ts with the Reference 750s. Both the Reference Phono 2 and the Reference 5 have been replaced with new models designated "SE" for "Special Edition." While not all of the Reference Anniversary’s innovations could be packed into each of these products, it’s clear that a consistent theme is increasing the power-supply sections of each new unit and upgrading critical components.

The new Reference 150 has exactly the same external dimensions as the Reference 110. Aesthetically, the only real change is the default shift to a uniform color. The classic Audio Research look included a silver front panel with a black frame and black handles. The new models have front plate, frame and handles all in silver or all in black (although the customer retains the option to mix and match colors to achieve a more retro look if that’s what he seeks). No matter how you mix colors, however, Audio Research is sticking to its classic "rack-mount with handles" look, which, given the weight of the package, is probably a good thing. The Reference 150 weighs in at 75 pounds, about 8 more than the Reference 110.

What would a designer like Deiter Rams (responsible for museum-grade industrial designs for Braun electronics, which later inspired Steve Jobs at Apple) have wrapped around a 75-pound hunk of metal filled with hot, glowing tubes? Rams and Jobs were dealing with relatively small and lightweight devices that required little heat dissipation, allowing the use of plastics and fluid casement lines. While some modern designers (mostly Italian) have tried to bring this aesthetic to (usually much lighter weight) tube designs, to me these designs feel forced and instantly dated. Sleek Pininfarina lines and blocks of carved aluminum are the territory of solid-state designs.

With large tube amplifiers, the need for a sturdy frame really leaves two choices: a fully enclosed box design (like the Audio Research) or a lower-profile box with protruding tubes and transformers. I’m happy with the clunky classic industrial design, softened by a bit of rounding and beveling, used by Audio Research. I also approve of the move away from black handles and cases, which always reminded me of rack-mounted supercomputers from the 1960s.

While outwardly the Reference 150 appears little different from its predecessor, several changes are immediately obvious once you look inside. With my own Reference 110 on hand, side-by-side comparison was possible. The already large transformers used in the Reference 110 have swollen in size, accounting for much of the new amplifier's increased weight. The number of electrolytic storage capacitors in the power supply has doubled, with two banks of a dozen each in the Reference 150. The added bank is mounted to a vertical circuit board at the front of the unit. Audio Research claims that the total storage is now 1040 joules. The new interstage coupling capacitors appear to have been injected with steroids compared to those in the Reference 110. The resistor complement has also been modified with what appears to be the largest-value resistors replaced with two smaller resistors in parallel.

But what is probably most obvious is the switch from 6550C power tubes over to KT120s. Audio Research had already begun the switch to KT120s with late-production Reference 110s, and has incorporated this change into the next generation of its amplifiers. The published specifications claim a significant increase in power bandwidth from the Reference 110’s 12Hz-60kHz to the Reference 150’s 5Hz-80kHz.

Like its predecessor, the Reference 150 is fan cooled using a pair of fans, which are now chassis-mounted on rubber grommets. The new fans are noticeably quieter than those in the Reference 110, in part because they literally stick out the back of the amp. I opened up both units to make sure that I had the fans set to the highest of the three available speeds. While the Reference 110's noise level was not obtrusive, it was clearly audible. The new low-noise fan arrangement for the Reference 150 is much quieter. I had to put my ear close to the amp to hear any noise, even with the fans set to the highest speed.

Why choose a stereo amp rather than a pair of mono amplifiers? I suppose if space and financial considerations were not involved, audiophiles would always gravitate to mono amps. Audio Research’s next step up in the Reference series is a pair of Reference 250s. While I’ve not yet heard them outside show conditions, I have little doubt that they will deliver even more of what the Reference 150 provides -- but at a significant cost premium. And with two boxes demanding twice the real estate, not everyone can take this route. In any event, a 150Wpc amp is powerful enough to comfortably drive most speakers that can be moved into most homes that lack a loading dock.

When the Reference 150 landed on my doorstep, it was nicely burned for about 475 hours, allowing for immediate testing. The first thing I listened to was a Townes Van Zandt song, "Waitin’ ‘Round To Die" from Heartworn Highway [Hacktone VJCD167], a collection of vintage recordings from a 1975 documentary that was first released on CD in the UK in 2006. I was tipped off to this release by my UK connection, fellow TAB contributor Roy Gregory, and quickly ordered a copy from the UK (it’s now available on CD and vinyl from the usual suspects in the US). I’ve heard this cut on various iterations of my own home system, on friends’ rigs and on innumerable systems at every CES and Rocky Mountain Audio Fest over the last half-decade. There’s nothing showy about it, just Townes in his kitchen with his guitar, a female guest humming in the background, and a dog. The recording has atmosphere to spare, and if the equipment is up to it, it's one of the most realistic-sounding recordings around. I've listened to it on well-set-up systems employing components far more costly than most audiophiles get a chance to audition, let alone own, so I know what gold lies buried in those digital pits. The Reference 110 always fell a bit short of capturing the subtle acoustic nuances I knew to be there, no matter the speakers it was paired with. The Reference 150 created a more detailed soundstage and captured aural cues that added up to exquisite resolution.

Audio Research equipment has always been known for creating a large and well-defined soundstage. The Reference 150 took this to a new level. Think of the soundfield as a cube made up of an infinite number of bits, like the scan lines on a video screen, only in three dimensions. More bits of information in that space give greater weight and texture to everything in the soundfield. The 150 just seemed to have more bits in each of the three dimensions. As a result, the stage depth of the 110 was slightly collapsed compared to that of the 150, especially with recordings like Heartworn Highway that offer realistic stage depth. Not only does this allow you to better place a particular event within the soundstage, but also the image within that special context has more texture and therefore less grain. Van Zandt’s voice, scarred by years of substance abuse, health problems and, in this instance, a premium-grade hangover is not something I would usually call delicate, yet the Reference 150 brought out the subtle nuances of each and every insult endured by those ravaged vocal cords, making the reproduction feel far more lifelike than I hear from most amplifiers. To put it another way, this amplifier filled in the space around the notes with all the extraneous information that should be there -- the scraping of a chair on stage or a previously unnoticed cough in the audience. This kind of detail adds substance and form, life and context, to what is all too often an almost synthetic, solely musical event. It puts the people back into recordings.

Lest all this talk of bits and scan lines suggests that the Reference 150’s attributes shine more brightly on digital than analog, fear not. I pulled out Diabolus in Musica, Accordo Interprets Paganini on DGG [Deutsche Grammophon 0289 477 6492], a 1996 LP compilation on two records and a set that equals anything in my collection for music and sound. The Reference 150 brought out the holographic soundstage of this recording better than I’ve ever heard. The sound of these LPs is excellent on any decent system, but as the quality of the front-end and electronics increases, the records continue to serve up an endless supply of delights. After swapping in the Reference 150 for the 110, the London Philharmonic created a deeper and more three-dimensional soundstage, and the dynamic range increased. For the first time, my attention focused on the orchestral accompaniment rather than being captivated by Accardo’s pyrotechnics.

The changes to the amplifier were also felt with records that have significant bass energy. The Reference 150 won’t make the two 7" woofers of an Avalon Transcendent sound like the 11" woofers of the Time, nor supply the bass kick of more expensive monoblocks, but the difference is there to hear. Even with speakers that have moderate bass extension, the Reference 150’s extended low frequencies make themselves known with greater shape and control. One of my favorite cuts for this purpose is Gol’s "Angelica in Delirium" from Trance Planet Volume Two [Triloka 7210-2], long out of print but a disc I’ve been listening to since the mid-1990s. It produces bass well below the threshold of any speakers I’ve had in my listening room. I made a direct comparison between the 110 and 150, and at first I thought I was hearing less bass energy with the 150, but after hearing a few more bass-rich recordings, I realized that the 150 simply tightened up the bass, displaying much faster, cleaner decay. I confirmed this with some of my favorite headbanger rock music, including Who’s Next [Track 2408 102] and Led Zeppelin II (UK Plum label [Atlantic 588198]). These records are at their best on a much larger system. With more modestly sized speakers and a stereo amplifier, it’s easy for the loudest passages to distort. The Reference 150 held the bass in check in places where even the 110 would lose a bit of control and become muddy. And at the other end of the spectrum, it added a bit of extension. The upper reaches of piano and violin, the shimmer of high-hat percussion and the sparkle of piccolo, all well treated by the Reference 110, confirmed the published claim that the frequency extremes of the 150 trump those of the 110.

For me, the Reference 150 is the sweet spot in the Audio Research Reference amplifier range. The Reference 110 had been in production since mid-2006. It started off priced at $9995 and later increased to $10,995. The Reference 150, priced at $12,995, while expensive, can hold its own with exotic amplifiers costing a lot more. I’ve used or owned many Audio Research amps over the last 25 years, and I can’t remember an improvement between generations to compare with the advances built into the Reference 150. I approached the amplifier with modest expectations. After all, the Reference 110 was an extremely accomplished performer -- my reference. How much could it be improved upon? The answer is "a lot." I’ve not had so much fun with a new product in a long time.

Price: $12,995
Warranty: Three years parts and labor.

Audio Research Corporation
3900 Annapolis Lane North
Plymouth, Minnesota 55447
(763) 577-9700

Associated Equipment

Analog: VPI TNT-6 turntable with rim drive and SDS speed controller, VPI 12.7 tonearm, Lyra Skala and Titan Mono cartridges, Koetsu Coral cartridge, Audio Research Reference Phono 2 phono stage.

Digital: Audio Research Reference CD7 CD player.

Preamplifier: Audio Research Reference 5.

Power amplifier: Audio Research Reference 110.

Loudspeakers: Avalon Acoustics Transcendent.

Interconnects: Nordost Valhalla.

Speaker cables: Nordost Frey.

Power conditioners: Quantum QBase 8 and QX4.

Power cords: Nordost Valhalla.

Equipment rack, platforms and accessories: Billy Bags equipment rack modified with a 4" maple platform, Stillpoints Ultra isolators, Stillpoints Component Stands, Furutec GTX D-Rhodium AC outlet.