Note: for the full suite of measurements from the SoundStage! Audio-Electronics Lab, click here.

Serious question for you: what do you think of when you hear the term “class D”? Does it conjure associations of a sense of cleanliness, of meticulously delineated detail, of an impersonal coldness, or of a true-to-life representation of a musical event? The wise audiophile knows by now that becoming embroiled in a debate about cables or tube amplification is a potential threat to one’s sanity, but the subject of class-D versus class-A or class-AB operation remains a worthwhile discussion, by my reckoning. The reason is that we’re at kind of a watershed moment for class-D technology, though many haven’t realized it yet—and there are significant implications for the future of audio.

Most readers will likely know what class-D amplifiers are: with exceptions from the too-cheap-for-their-own-good lot, they typically produce gobs of power from very small, lightweight packages, and with low distortion and noise numbers. These advantages mean that class-D amps are everywhere now, especially in lifestyle-oriented products like active speakers. They’re not without their detractors, though: class-D designs, especially from early days in the technology’s history, have been criticized for imparting an overly dry or impersonal sound signature. Like it or not, class D is probably the future of sound reproduction. What does that future look like?

Better listening through chemistry

To answer that question, first you need to know how the tech works. In short, most class-D amps make power by switching MOSFET (metal-oxide semiconductor field-effect transistor) devices really, really quickly. By toggling between “fully off” and “fully on” states, the MOSFETs reconstruct the input signal using pulse width modulation (PWM) or pulse density modulation (PDM), in which the width and density of the on/off pulses represent the shape of the incoming waveform. (Orchard Audio’s amplifiers use PDM.) The output is run through a low-pass filter, which removes the high-frequency components of the on/off switching, resulting in a smooth representation of the input signal, but with much greater current ability and at a much higher voltage. It can therefore drive a load such as a loudspeaker.

This techno-babble is all to say that high-frequency switching is crucial to a class-D amp’s operation.

The Orchard Audio Starkrimson Mono Premium amp, which retails for $1249.95 (all prices in USD), tweaks this formula by its use of GaN FETs. GaN FETs are similar to MOSFETs, but use gallium nitride (GaN) as their semiconductor material. Orchard Audio founder Leo Ayzenshtat told me that the amplifier module used in the Starkrimson Mono Premium—and indeed, those in all of Orchard Audio’s amps—is a proprietary design he created to make use of GaN technology.

GaN FETs can switch much faster than MOSFETs, meaning that the switching frequency can be much higher. Consequently, there’s less interaction with audible frequencies. It also allows the output filter to be greatly simplified, resulting in a higher bandwidth and virtually no phase shift in the audioband. Ayzenshtat says these are the keys to the amp’s sonic merits. The Starkrimson Mono Premium’s output devices switch at 800kHz, meaning that any potentially audible intermodulation with the audio signal is a non-issue. The amp’s low-pass filter, which uses oxygen-free copper inductors and high-quality film capacitors, renders phase shift below 30kHz moot as well.

The Starkrimson Mono Premium is DC-coupled and fully balanced from input to output, meaning it accepts an input via XLR. If your preamp or source component only has a single-ended RCA output, Orchard Audio offers an RCA to XLR converter for $299.95.

The “Premium” moniker signifies that this amp replaces the outgoing Starkrimson Mono amp, boasting a handful of upgrades. The amplification module is the same, but whereas the previous model came with an external 250W power supply, the new model uses a slightly upgraded 350W internal power supply. The new power supply has a more direct, lower-impedance connection with the amplifier module, Ayzenshtat states, adding that these improvements firm up the bass and dynamics slightly over the outgoing model. Additionally, the Starkrimson Mono Premium uses heavy-duty WBT binding posts.

But the most obvious upgrade is the sleek new enclosure, which has a slanted front face, rounded top edges, and a handsomely debossed Orchard Audio logo on the top. The only miss I can find with the design is that there’s no way to know at a glance whether the amp is on, since there’s no power indicator and the switch is on the back—though because it runs cool and consumes minimal power, it’s intended to be left on all the time anyway.

The Starkrimson Mono Premium measures a shoebox-sized 3.1″H × 6.1″W × 11″D, including its feet and binding posts. The amp claims a power rating of 150W into either an 8- or a 4-ohm load, is stable into 2 ohms, and has a THD figure of less than 0.002% at 1W at 1kHz. One last noteworthy spec is its damping factor of greater than 550. Orchard Audio’s full specs, including charts, can be found here, but as usual, our own independent lab report is linked at the beginning of this review.

Setting up the Starkrimsons

Naturally, for this review I got a stereo pair of Starkrimson Mono Premiums to test. Due to the amp’s diminutive size and weight, one is granted considerable leeway with regard to placement. Orchard Audio recommends using as short a speaker cable as possible to take full advantage of the amp’s high damping factor—with an output impedance as low as the Starkrimson’s, the DC resistance of the cable becomes the dominant factor. So, I cut comically short lengths of 14AWG OFC AmazonBasics speaker cable, each about a foot long, and put the Starkrimson Mono Premiums on the floor, each right next to its respective speaker. The loudspeakers in question were a pair of DIY Amiga speakers. I used the XLR outputs of an Oppo BDP-105 Blu-ray player, which functioned as both a source and preamp. I also used Orchard Audio’s PecanPi+ Premium streamer with the Starkrimson amps, but I’m reserving my thoughts on that combo for the streamer’s forthcoming review. My LG C1 OLED television served as a streaming endpoint for Spotify and Netflix, connected to the Oppo via a Blue Jeans Cable Belden Series-FE HDMI cable. A pair of Blue Jeans Canare DA202 XLR cables carried the signal to the mono amps. The power cables used were the stock cables included with the amps.

Gallium nitride in my ears

I started by spinning a couple of CDs. First up was Used Guitars by Marti Jones (A&M Records CD 5208). The song “Back of the Line” is one that I know well, and I was impressed with the Starkrimsons’ rendering of it. As you’d expect from a pair of amplifiers with an “is it even on?” noise spec like the Orchard’s, the sound emerged from an utterly black background. This meant that sonic images of Jones’s voice, the drum kit behind and around her, and the chugga-chugga acoustic guitar off to the left edge of the soundstage all were precisely defined and had a realistic sense of body and dimension. The Starkrimson Mono Premium amps seemed to have a tight grip on the loudspeaker drivers’ movements, so the bass guitar line on this track thudded with perfect control. The midrange and treble lacked just a bit of the texture and shading you might get from the best class-A or class-AB amps out there, but the Starkrimsons’ ability to portray space and dimensionality through the mids and highs made for a worthwhile tradeoff. The high frequencies had just a tiny bit of zip, of electricity, without straying from neutrality. As I listened to the twinkle of the triangles dropping into the right side of the soundstage, I couldn’t help but think that just because a piece of gear has a very precise kind of sound doesn’t mean it can’t be musical, too.

I switched to “Thanks to You” from Boz Scaggs’s Dig (Virgin Records 7243 8 10635 2 1) as a test of just how well these mono amps could serve up some real bass. And, oh, could they! You could use these things to trick your buddies into thinking you’d hidden a subwoofer somewhere. I was surprised at how much bass these tiny amps could wring out of this audiophile cliché of a track, but the rest of it sounded, well, like an audiophile cliché. The Starkrimson Mono Premiums lent a pleasing emphasis to percussive “thwaks” and treble details, but the song itself is kind of a hi-fi snoozer. I wanted to feed these amps something with real grit. I wanted to see if they could take apart a messier track and put it all back together again.

I turned to Spotify and played Spoon’s Girls Can Tell (256kbps AAC, Matador Records / Spotify). On the opener, “Everything Hits at Once,” the Starkrimson amps’ ability to tease out the decisions made during recording and mixing let me hear the track in a new light. The artists and engineers fused many different tonal and textural elements to create the mood of the song, and the Orchard Audio amps communicated all of it with aplomb. Sonic images had reach-out-and-touch-it definition and seemed to exist in 3D space in front of me, but the separation of those sonic elements led to the soundstage seeming a bit spare compared to the beefier sound of tubes or big class-AB transistor amps.

Does that really matter, though? The Starkrimson Mono Premiums conveyed exceptional vibrancy on Britt Daniel’s vocals, with clear separation between the vox and instrumental parts on “Take the Fifth,” from the same album. And on “Car Radio,” from the band’s earlier album A Series of Sneaks (256kbps AAC, Matador Records / Spotify), the soundstage was rendered with not just incredible width and depth, but also height. The noisy, garage-style electric guitar that kicks off the song seemed to hang three feet above the edge of the console that houses my CDs and hi-fi gear. On these songs, I just didn’t care if a class-A or -AB amp could’ve fattened things up a bit.

In audio, opposites attract

Speaking of class-A amps, I compared the pair of Starkrimson Mono Premiums directly against my First Watt F5 stereo power amp (discontinued; $3000 when new), which is roughly their polar opposite. Both amps post near-cutting-edge distortion and noise specs, but the First Watt gets there from a different direction.

The F5 is a big, heavy, class-A push-pull transistor amp, with output MOSFETs bolted to chunky heatsinks, a hefty linear power supply fat with capacitors, and not much else—designer Nelson Pass favors designs that put as few parts in the way of the signal as possible. With these two amps coming from competing philosophies, I knew this would be a fun comparison.

At first, I was struck by how similar they sounded. Both amps circled closely around neutrality, but each offered its own distinct flavor. Replaying “Car Radio” with the F5, I heard the class-A amp thicken things up a touch, in the expected way. It provided more density and tonal color than the Starkrimsons, albeit at the expense of the micron-precise separation of the GaN amps. The flawless tonal presentation of the First Watt F5 gave the amp more verve and groove-factor, though it gave up some grip at the frequency extremes compared to the Starkrimson Mono Premiums. The Orchard amps let me hear everything in the music more clearly, however, and surprised me with their imaging prowess.

The Starkrimsons might’ve had a slight edge with complex or noisy rock music, but were outshone by the F5 on simpler acoustic music. “Michigan,” from the Milk Carton Kids’ debut Prologue (256kbps AAC, Milk Carton Records / Spotify), has become a reference track for me. Here, the Orchard Audio amps seemed to be missing some of the natural decay that followed each of the plucked guitar notes, which the F5 conveyed beautifully. To be clear, the Starkrimsons sounded completely competent, but the point stands—if cost were no object and one were willing to put up with the realities of a bigger, heavier, hotter amp, the class-D monos might not be the choice for someone who prefers smaller-scale music. Then again, in a system that also has to do home-theater duty, the inverse may be true.

To compare against more direct competition, the also arboreally named Peachtree Audio offers the GaN 1 stereo amp, which uses similar technology to the Orchard Audio amps. The GaN 1 makes 200Wpc and costs less than a pair of Starkrimson Mono Premiums, at $1799. The trade-off is that the Peachtree GaN 1 only has a single digital coaxial input, so it requires a digital source with a variable output. Peachtree’s Carina GaN, which starts at $2999, uses the same GaN FET tech, but as a 200Wpc integrated amp it’s not very comparable with the Orchard Audio GaN mono amps. With both Peachtree products, you’ll need just one power outlet, but you’ll miss out on the flexibility of placement the Starkrimson Mono Premium amps allow.

Hi-fi’s future is safe

I’ve always been a bit wary of class-D amplification. High-frequency switching, heavy filtering that limits bandwidth, and benefits that seem to evaporate when you subject the amp to real strain have all made the technology kind of a non-starter for me. This pair of Orchard Audio Starkrimson Mono Premium amps has turned me around, though. With more than enough power to drive virtually any speaker and without many of the drawbacks of more conventional class-D amplification, the Starkrimson Mono Premium amp is a worthy entry into the field of class-D hi-fi. There is still heaps of value to be had both in more traditional class-A or class-AB topologies, and the Starkrimson monoblocks face stiff competition from within their GaN FET niche, too. But if this is the future of audio amplification, maybe I shouldn’t be so scared of what’s to come. The kids are alright.

. . . Matt Bonaccio
mattb@soundstage.com

Note: for the full suite of measurements from the SoundStage! Audio-Electronics Lab, click here.

Associated Equipment

• Speakers: DIY Paul Carmody Amiga, built from a Parts Express kit.
• Integrated amplifier: McIntosh Laboratory MA6850.
• Power amplifier: First Watt F5.
• Digital source: Oppo BDP-105.
• Digital cables: Blue Jeans Cable Belden Series-FE HDMI cable.
• Analog interconnects: Blue Jeans Cable Canare DA202 XLR cables.
• Speaker cables: AmazonBasics 14AWG OFC speaker cables.
• Television: LG C1 OLED display, 55″, directly wired via Cat 6e cable to router.
• Internet router: Netgear R6080; Jameco 170245 Linear Regulated DC supply.

Orchard Audio Starkrimson Mono Premium Power Amplifier
Price: $1249.95.
Warranty: One year, parts and labor.

Orchard Audio
176 Franklin Ave.
Rockaway, NJ 07866
Phone: (504) 233 3444

Website: www.orchardaudio.com
Email: leo@orchardaudio.com