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Boulder 2150 Mono Power Amplifier and 2110 Preamplifier

The Boulder 2150 mono power amplifier and 2110 stereo preamplifier mark the second time in a few months that I’ve reviewed electronics that define the state of the art in sound quality, design, and luxury. I can recommend both without reservation to anyone who has the money and is looking for superb sound quality.

They do, however, present a challenge to both the reviewer and the audiophile. Here’s the issue: With equipment this good—and this neutral and transparent—almost all of the colorations you hear come from the recording, the front end, the interconnects and speaker cables, the load presented by the speaker, and the complex room interactions that shape the sound of the speaker at a given listening position.

What is Truth? Jesting Pilate Asked
There is no such thing as a truly neutral and transparent amplifier or preamplifier, but increasingly the inherent sound quality of a small number of elite units has become extremely difficult to gauge due to interactions with more-colored equipment. The question becomes: What are you really reviewing? Even if—as I did—you use a mix of other components, speakers, and listening positions, you can’t avoid the reality that any given reader is going to hear sound that is dominated by the colorations of a different mix of recordings, components, and listening rooms.

This may sound a bit hypothetical, but it was all too clear in practice on the day that the Boulder 2150 mono power amplifier arrived. It literally came in from the cold, and was then thrust immediately into a setup designed for my Pass reference amp. The end result was that the 2150 initially sounded thin and lacking in midrange warmth.

The problem, however, was not in the Boulder. The thinness and lack of warmth came from the fact I was using Transparent Audio speaker cables designed specifically for the radically different loads of Pass amps used with the Wilson Alexias.

The sonic problems that I at first thought were in the 2150 went away the moment I substituted a high-quality AudioQuest speaker cable. They did not exist when Transparent Audio sent me one of its speaker cables specifically configured for the Boulder amps. They also did not exist when I used a high-quality Kimber speaker cable.

The practical problem that did exist, however, was that each speaker cable that worked well in broad terms also changed some aspect of the upper bass and lower midrange, and presented a slightly different soundstage. They were all really good speaker cables, but they changed the sound in ways that were more audible than the colorations of the Boulder 2150.

Much of my initial listening came on a day when Peter McGrath of both Wilson Audio and recording fame was helping me adjust the position of my Alexias. Like my experience with the Pass Xs 300 power amps, the Boulder 2150 has an almost incredible amount of reserve power and an extremely high damping factor. It has an al- most unmatched ability to control speaker loads with the right cable.

What no amp can do, however, is control speaker/room interaction or be precisely designed for a given speaker load.


Once again, the low coloration in the 2150 made the colorations in other aspects of my “system” more apparent—particularly if one adds the room in as part of the “system.” The sound of the Wilsons changed slightly with only a one-inch back-and- forth movements, and shifted significantly from warm to neutral after being moved less than 3.5″ forward. We also could hear the differences between digital front ends more clearly—devices where I often find the analog audio circuits to be at least as colored as any of the digital circuitry.

A few weeks later, I was listening to four different digital front ends: The Sooloos, the EMM Labs XDS1, the PS Audio PerfectWave DAC II, and a brilliant new Swiss server called “The Beast.” I also was now using both the Boulder 2110 preamp and the Boulder 2150 mono amplifier. Once again, the sonic differences between the digital front ends dominated the sound character of the Boulders.

There were many cases, however, in which the colorations in the recordings were more dominant. For example, I listened to six different recordings of the Mozart Third Violin Concerto, spanning some forty years from the earliest to the most recent disc. The records ranged from bright and over-detailed to dull and over-warm to just right (for me). As was the case with the Pass Xs preamp and Xs 300 mono amp I had reviewed a few months earlier, these differences in recording quality were sonically more important than the differences in preamps and amplifiers, as well as the difference in digital front ends and “wires.” If I had focused on only one recording, I would have chosen a different mix of front ends and wires, and might well have thought that the Boulder 2150 and Boulder 2110 was somehow providing the coloration rather than the disc itself.

This situation became even more problematic in the deep bass. I use organ music, Telarc bass drum recordings, and synthesizer music for reviewing, but my quick tests are the somewhat exaggerated bass tones in “Rock You Gently” and “Way Down Deep” in the Jennifer Warnes recording The Hunter (vinyl and CD). Each digital front end produced a slightly different mix of bass dynamics, detail, and frequency balance. Moreover, when I compared the sound using both the Boulder 2150 and 2110 with my reference Pass XA160 and Xs preamp, it was clear that it was the digital front ends that provided the overwhelming amount of coloration and not the preamps and amp.

These are all practical examples of the extent to which Pilate’s question—“What is truth?”—clearly applies to audio reviewing, as well as to metaphysics. And this became even clearer as my listening went on. Interconnects made much less sonic difference than speaker cables, but the Boulder 2150 and later the Boulder 2110 were so low in coloration that even the relatively limited sonic impact of top-quality interconnects became easier to identify.

Understand, I am not saying that all amps and preamps sound alike, or that the Pass and Boulder electronics sound exactly alike. I am saying something very different. If you can afford gear as good as the Boulder 2150 and Boulder 2110, you will find that every other component in your system is going to present more of a problem, that you will explore the musical and sonic strengths and weakness of your recordings in new ways, and that you will almost certainly find yourself tweaking your entire sys- tem to explore its new limits.

Boulder 2150 Mono Amplifier
Let me begin my more detailed comments on the Boulder 2150 with points that may be obvious, but still seem necessary to make. You can only approach this level of sound quality in a luxury product, and the Boulder 2150s cost some $98,000 a pair. They are components that only a handful of the very lucky can afford.

If you are willing and able to search for ultimates, then the Boulder 2150s are choices you should consider. If you want to recalibrate your idea of what a solid-state reference can sound like, then find a dealer or audiophile who can demonstrate these monoblocks. If you get mad at the idea of luxury cars, homes, and art collections, you can get mad at the Boulder 2150s as well. If you are a violent neo- Luddite and oppose all reporting on technology, then pick on my esteemed editor. I’m only a humble reviewer who is tasked from above.

The Boulder 2150s, however, will strike even the Luddite as remarkably attractive pieces of equipment. Rich Maez of Boulder—another target for you violent neo-Luddites—proudly tells me that there is no sheet metal in the 2150. All casework and interior chassis parts are machined from solid stock. Moreover, the 2150s are built to order in-house, and no aspect of production other than anodizing is done outside the Boulder factory. He claims that Boulder is the last North American manufacturer which still does all of its own manufacturing, including metalwork, circuit boards, engineering, design, testing, and assembly.


If you know anything about electronics and manufacturing, and get the chance to remove the tops of these amps, you will also see that they are superbly built and that the circuit topology is remarkable straight-forward and beautifully laid out. Moreover, the 2150s will probably not be used in the power-amplifier- juggling event at the next high-end Olympics. They weigh 240 pounds each (332 pounds in the shipping box), and measure 18″ wide x 10.75″ high x 26.75″ deep with 12″ clearance in the rear for the power connector.

The 2150s are physical symbols of electronic power, but their musical power is incredible. They are nominally rated at 1000 watts per channel into 8, 4, and 2 ohms with peak power of 2000 watts into 4 ohms, and 4000 watts with minimal distortion and a 135dB signal-to-noise ratio (assuming the AC line can continue to provide enough power without sagging). They are also dead silent, with no fan noise, vibration, or any indicator they are working other than the music and a discrete LED pilot light.

Both a good technical fact sheet and the manual are available on the Boulder Web site, but I asked Rich Maez for a summary of some of the key reasons for the amp’s cost and he provided the following data: “Every circuit in the 2150 is new and many are derived from Boulder’s top-of-the-line 3050 mono amplifier. It operates in pure linear Class A. The bias current is actively monitored and adjusted in order to increase efficiency and reduce wasted radiated heat and energy. A new, high-efficiency, microprocessor-controlled standby-mode reduces power consumption when engaged.

“There are 80 output devices and 48 filter caps in each amp— necessary to attain the 1000W spec and to be able to double power into halved loads. The size of the amp and the number of components are the result of the goal of 1000W, not the other way around.

“The amp is always running in Class A mode to full rated output power. There’s a circuit that monitors voltage at the out- puts, current draw, and load to bump the bias up during transient peaks and then slowly ramp it down over a period of 28 seconds in an analog fashion unless another peak is detected. Every circuit board in the amp is surface-mount to improve board layout and optimize ground-planing, among other technical advantages. Boards are not screwed down onto plates or sheet metal. All boards are mounted in machined frames with damping material sandwiched between the board and the frame in order to minimize resonances. Gain stages are the 99H2, Boulder’s own discrete gain stage, built in-house. This is a lower-voltage derivative of the 99H, the gain stage used in the 3000 Series amps and an evolution of the 993 gain stage that was previously used in the earlier 2000 Series products. The 2150 replaces the 2050, an amp that remained in our product line for 17 years. Power up, standby, bias control, and all aspects of protection are microprocessor- controlled. The microprocessor board is isolated from the rest of the amplifier by opto-couplers. Optical coupling eliminates any noise from the microprocessor board interfering with audio reproduction.”

What really counts, however, is that this one of the least- colored, best-performing amplifiers ever made. I’ve only listened to one other amplifier that competes, and its lack of coloration does make the music in great recordings and performance far more satisfying. I spent hour after hour listening to this amp with my Wilson Alexias, the Legacy Aeries, a friend’s Quad ESL-2905s, and a pair of classic Spendor BC1s. And I’m convinced that the 2150 can get the best out of any real-world speaker on the market.

Boulder 2110 Preamp
The Boulder 2110 preamp is made in the same superb mold as the 2150 amplifier. Like the 2150, the Boulder 2110 is a luxury product that sells for $54,000. It is a four-chassis unit with a separate power supply and, like the 2150, it is “built” in every sense of the term. The main unit is 24″ wide x 16″ high x 23″ deep and weighs about 85 pounds. The power supply is 24″ wide x 12″ high x 21″ deep and weighs about 59 pounds.

The 2110 has a striking dual-mono physical layout. The audio chassis essentially houses two mono preamps stacked over a common display and switching unit. Like the 2150, it is one hell of an attractive piece of gear. The separate power-supply chassis houses four independent power supplies for left audio, right audio, logic and user interface, and standby/power on. Each individual power supply is microprocessor-monitored; output is muted in the event of fault detection, and the problem is indicated on the front-panel display.

The Boulder 2110 also has all the features an audiophile is likely to need in a linestage preamp. It is fully balanced and uses all-XLR connections. (Any device using RCA connections will need an adapter.) The 2110 has six pairs of inputs that can be labeled by name, three sets of main outputs, and programmable recording-output features. It also has master-slave and theater- mode features, polarity control, adjustable display brightness, full remote control (including the ability to remotely control an amplifier), a time-travel option, automated widefield zombie repellant, etc. etc. (Rich Maez of Boulder notes that “there are two programming options that we’re working on for the 2110 that you weren’t aware of, in addition to the zombie repellant and time travel: sponge-bath assistance and light yardwork. But they’re delayed due to the 2110 not being entirely watertight and its lawn-mowing tolerances being a tad too OCD to ever finish the lawn before it’s time to mow again. Both will be made available to original owners as a free update when completed.”)


As with the new 2150 power amp, all of the 2110’s circuitry is different from that of Boulder’s earlier preamp, the 2010. Once again, the inside is a visual work of art as well as a musical one. The core features include new ultra-low-noise, surface-mount 993S gain stages that are encased in a fully machined and potted housing for thermal stability, and a “next generation,” CMOS- actuated stepped volume control that incorporates fully balanced operation for a lower noise floor and the elimination of any step noise.

The 2110 is differentially balanced from the inputs to the out- puts for optimal common-mode noise rejection in its 993S gain stages, the design of which is explained in more detail in the 2110 technical paper on the Boulder website, along with Boulder’s unique approach to feedback. The 2110 also incorporates a fully balanced volume attenuator to eliminate step noise and increase resolution through the volume control. It has very precise volume and balance adjustments that are displayed in easy to read increments. The 2110 has a 1.0dB option for the steps in the volume control (default is 0.5dB and there’s also an option for 0.1dB).

There are new front-panel designs for both the preamplifier and power supply chassis. The preamplifier front panel features a new wraparound, custom-ground, mirrored-glass display window with a redesigned high-visibility white-LED front-panel display. The rear-panel connections are also slightly different: The 2110 has a trio of main outputs, whereas the 2010 had only a pair per channel. The 2110 also has full IP control via Ethernet for use with advanced control systems, and a 12V trigger out for remote power control of connected power amplifiers.

Rich Maez tells me that the remote control is much simpler, featuring direct access to each input instead of having to press the input button and then select an input. It is also much smaller and uses “coin batteries” that will not leak and are much easier to fit into a slim-line chassis. Remotes can hold the same batteries for years depending on how much they get used, and prevention of eventual leaking was a primary concern during the redesign. The new remote also has the IR emitters recessed to prevent damage to them if the remote is dropped.

From a listening standpoint, what counts most is that the 2110 preamp is even quieter and more neutral than the 2150, in part because the preamp, unlike the amp, doesn’t have to contend with the far more complex, demanding, and power-hungry loads of a loudspeaker. The 2110 also does not have to make the compromises inherent in DACs that try to include digital volume and bass controls, or have to compromise by adding analog controls. The Boulder did a superb job with a wide range of interconnects, digital front ends, and phono preamps, and it showed that the right equipment can be extremely revealing without compromising the quality of the music with all but the worst recordings.

Summing Up
I would love to own this equipment. Admittedly, spending a fraction of the price can get you a very good high-end system, and gains in sound quality do diminish as the price rises, but diminishing returns are a fact of life with any luxury. You can still hear the differences, and my experience is that you come to enjoy them more and more with time.

The Boulder 2150 and 2110 are also the kinds of gear that represent a lasting investment. Their sound quality is so good that that they can be the core of a great system for years to come. They are superbly built and their construction is modular enough that any future repairs should be easy.

As I said at the start of this review, it is hard to described colorations you cannot actually hear. Yet I would much rather have gear that disappears into the music, and the rest of the system, than gear that highlights some special aspect of music. The Boulder 2150 and 2110 are consistently musically involving with any music I know of, and they are revealing of every aspect of the music and recording, without emphasizing any given aspect.

As for some kind of ranking relative to other top contenders, I no longer have both the Pass Xs preamp and Pass Xs 300 amplifier—and these are the only units I’ve ever reviewed that are good enough to make a fair comparison. Nuances at this level are so much a matter of personal taste that I really question their value. I’m sure I would hear some small differences in the soundstage, in the bass and midrange, and in treble air. At the same time, I really mean it when I say that the differences in sound between electronics of this caliber have reached the point where setup, choice in recordings, room interactions, and other external factor will do more to shape the sound.

And yes, I’m sure better designs will come in time, and I recognize the fact that others may prefer more euphonic components. But I’m amazed by the extent to which this new generation of the very best amps and preamps really does outpace the other elements in a high-end system and does approach the absolute sound.


2150 Power Amplifier
Output power: 1000W into 8, 4, 2 ohms
Peak power: 2000W/4 ohms, 4000W/2 ohms
Frequency response: -3 [email protected] 0.015Hz, 200kHz
Voltage gain: 26dB
Signal-to-noise ratio: 135dB, unweighted, 20–20kHz (1000W into 8 ohms)
Input impedance: Bal, 200k ohms; unbal, 100k ohms
Dimensions: 18″ x 10.75″ x 26.75″
Weight: 240 pounds (shipping, 332 pounds)
Price: $98,000

2110 Preamplifier
Balanced inputs: Six
Main balanced outputs: Three
Record balanced outputs: One
Auxiliary outputs: One
Maximum input level: 7V RMS
Maximum output level: 28V RMS
Maximum voltage gain: 20dB
Volume range: 100dB
Volume steps: 0.1, 0.5, 1.0 dB +/-0.01 dB
Frequency response: 20 Hz–20 kHz +0.00, -0.03 dB
Frequency response: –3 dB at 0.02Hz, 300kHz
Input impedance 200k ohms, balanced (per leg)
Output impedance: 49.9 ohms, balanced (per leg)
Dimensions (main chassis): 18.0″ x 6.875″ x 16.25″
Dimensions (power supply): 18.0″ x 4.25″ x 15.5″
Price: $54,000

3235 Prairie Ave.
Boulder, CO 80301
(303) 449-8220

By Anthony Cordesman

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