Solid State Power Amp Reviews

And the sound
My initial impressions were uniformly positive. More than positive. Boulder's 1151 monoblocks sounded really beautiful. I began by sampling unfamiliar recordings for possible review. Electric Fields (24/48 WAV, Download/Alpha), from Barbara Hannigan, the Labèque Sisters, and David Chalmin, struck me as a bit too Hildegard von Bingen meets new age immersive, but it was compelling and intriguing enough to warrant a review. As I continued to listen, the warm, glowing bath of sound from the 1151s kept drawing me in.

One of the first things I wrote in my notes was "I can't tell which amps I'm listening to because the sound is as beautiful as any I've heard."

After quick listens to pianist Gloria Cheng's fascinating collection of new compositions on Root Progressions (24/96 WAV, Download/Biophilia Records), which was produced and engineered by Judith Sherman, and Malakoff Kowalski's Songs with Words (24/44.1 WAV, Download/Sony), I cued up a new recording of time-tested material: Alice Sara Ott's recording of John Field • Complete Nocturnes (24/192 WAV, Download/Deutsche Grammophon). Ott's piano sounded gorgeous, warm, radiant, glowing. The sound was so enticing—like the proverbial pot of gold at the end of the rainbow—and Field's music so invitingly familiar and comfortable that I knew I had to review it.

As I listened longer and deeper into the soundscape, I found myself asking, "Do the colors of the piano sound so similar, from top to bottom, on my reference amps?" Compared to the much more expensive D'Agostino Momentum M400 MxV monoblocks, the piano's colors were a mite homogenized, the sound warmer than neutral. Nonetheless, the beauty and vibrancy of the 1151's wide-open presentation left me in critical gaga land.

The time for reference tracks had come. I began with a song that, in a demo of the dCS Varèse music system, wowed a seasoned group of audiophiles: the long version of Aretha's take on "Bridge Over Troubled Water," remastered in 2021 and issued on the compilation Aretha (24/96 FLAC, Rhino Atlantic/Qobuz; footnote 3). Bass was solid and perfectly controlled, and the sound was warm and inviting. Colors may have been a bit homogenized (again compared to my reference amplifiers), but the presentation was marvelously illumined and anything but monochromatic.

I decided to compare a recent Recording of the Month, Alec Frank-Gemmill's recording of Mozart's Horn Concertos (on B flat horn) with the Swedish Chamber Orchestra under Nicholas McGegan (24/96 WAV, Download/BIS), with Lowell Greer and McGegan's original digital recording of the concertos (on natural horn) with Philharmonia Baroque Orchestra, recorded by Peter McGrath (16/44.1 WAV, Download/Harmonia Mundi). The 1151 was no slouch at pointing out the myriad differences between the two recordings, starting with the timbres of the different horns and including color saturation.

To further test how well the 1151 could highlight differences, I compared the sound of two maximally different modern pianos captured on two different recordings from the same label: Ott's recording of Field's Nocturnes, cited above, and Murray Perahia's Beethoven Piano Sonatas (24/96 FLAC, Deutsche Grammophon/Qobuz). As much as I found myself wanting more bottom from both instruments, the difference in the basic sound of the two recordings (effusive warmth vs clanginess) stood out in sharp relief against a stunningly silent backdrop.

Round two
It sometimes helps to take a break and establish critical distance before continuing. From that vantage point, I began with two recent recordings of Schubert's song cycle, Die schöne Müllerin, that I chose for 2025's R2L4: baritone Konstantin Krimmel's account with pianist Daniel Heide (24/96 FLAC, Alpha/Qobuz) and tenor Julian Prégardien's with Kristian Bezuidenhout on fortepiano (24/48 FLAC, Harmonia Mundi/Qobuz).

If you'll pardon what may seem (at first) a digression, I heard how much more immediate, transparent, and realistic these men's voices sound when I began listening through the dCS Varèse. I regret the cliché, but it really was as if I was hearing the recordings for the first time. I have never heard digital sound so alive, human (as in pliable and emotionally available), present, and clear as I do with Varèse. The Varèse was the ultimate source, but the Boulder 1151 monoblocks enabled me to hear what it can do.

After going back and forth on five tracks, Aretha's "Bridge over Troubled Water," Ott's recording of Field's first Nocturne, Perahia's recording of Beethoven's "Hammerklavier" Sonata, the Modern Jazz Quartet's "Vendome," and Yello's "Electrified II" from Toy (24/48 FLAC, Polydor/Qobuz), the scorecard read as follows.

Costwise, comparing D'Agostino Momentum M400 MxV monoblocks ($79,950/pair) with monoblocks that cost over $32,000 less ain't fair. For the price of a helluva lot of eggs, you get more air, a more realistic sense of three-dimensional space, more definition and clarity between rapidly sounded notes, and an extra sense of color and vibrancy that on many recordings opens a portal to the magical. The D'Agostinos were also noticeably more dynamic. Downsides to the D'Agostinos? They are brighter than the 1151s. But what they reveal is musical to the core.

For an extra $1475 per monoblock, the Accuphase M-300s ($24,975 each) sing fetchingly in the comparison sweet spot. They deliver bigger bass and have a uniquely satisfying midrange that, in my memory, is equaled only by the (otherwise different sounding) Pass Labs monoblocks. They also excel at depicting air, venue, dynamics, and 3D placement. The M-300s don't dazzle with vibrant transparency the way the Boulder 1151s do, but they have other means of pulling the listener in. My memory tells me that's also true of the bridgeable Moon 861 stereo amplifier ($22,000/each), which however are no longer in-house. In this price class, these three amplifiers—the Boulder, the Accuphase, and the Moon—provide very high quality but different musical perspectives. Listen to all three if you can.

Parting thoughts
As I prepare to head to the music room and pack up the Boulder 1151 mono amplifiers for shipment to John Atkinson for measurement, I think back to my first listen: open, clear as a bell, vital, and alive. Those are the distinguishing characteristics that stood out for me then and that remain with me now. Anything but dry or sterile, these amps bring an inner warmth and freshness to music that is best described not as a breath of fresh air but as a welcome change of seasons. Think springtime. If that description and their price hit your sweet spot, I urge you to try them to see if they'll find their way into your heart. I would not be surprised to learn that they do.