Sonnet Morpheus D/A processor

Playlists embody who we are. We use musical affinities to understand (or at least categorize) others, not only as evidence of their aesthetic discernment but also of their emotional and political affiliations, which amount to an entire worldview. In other words, the database of favorite music that we carry around in our brains is no laughing matter. So, one of the most unexpected—and rewarding—things that can happen in music fandom is a complete and sudden inversion of one's beliefs. Which brings me to the perennially touchy subject of Steely Dan, a band that cleaves the ranks of listeners like a gold-plated katana.

Here, I'm not talking about the likable, slightly anodyne early records but about late-career (but pre-reunion) Dan, particularly Aja and Gaucho, on which Donald Fagen and Walter Becker reach an apotheosis of musical complexity and studio perfectionism. These records demand a lot, and listeners tend to either love or hate them. For most of my listening life, I was in the latter camp: To me, they exemplified the sound of the slickest, most airless kind of session playing, and they were "jazzy" in the worst way, meaning they borrowed from the formal language of jazz to create something more commercial and lighter that at times sounded uncomfortably like the sort of music that followed the words "please hold." Hearing even a few bars from these albums made me shudder. I recall now with real shame that when I happened to meet Fagen while doing research for my first book, I made a show of being unimpressed, even though he turned out to be approachable, funny, and kind.

Then, several years ago, my partner became obsessed with Steely Dan. He tends to acclimate himself to recordings by listening to them dozens of times in a row, and for a long while I found myself coming home every night to the sounds of "Deacon Blues" or "Third World Man." This irritated me, but there wasn't much I could do: We lived in a loft. What happened next surprised and embarrassed me—the songs began to open up to me.


First, I began to notice the weirdly literary lyrics: the detective with a facial scar and a hearing aid in "My Rival"; the louche narrator of "Babylon Sisters" drinking "kirschwasser from a shell"; the squabbling gay couple in "Gaucho" who live in a luxury high-rise named the Custerdome.

And then there was the music, haunted by restless imagination and quixotic perfectionism. Fagen and Becker brought in bands of first-call studio musicians and made them record hours of takes, then layered the most apposite parts like pieces of a mosaic. For the chorus of "Peg," Fagen and Becker asked Michael McDonald to harmonize with himself and sing parts so close to one another that he kept going out of tune and recalled spending the session terrified.

After a while, even drumming by the exalted likes of Hal Blaine and Bernard Purdie was no longer quite good enough for the duo, and they used $150,000 from Gaucho's recording budget to commission their engineer to create a percussion sequencer they named Wendell—at the time it was the most sophisticated drum machine in existence—which required 20 minutes of programming to emit a single, perfect beat.

This was intensely interesting, and before long I found myself adoring Steely Dan with as much vehemence as I'd once hated them. Stranger still was this: I could no longer identify the things I'd previously loathed, because I could no longer hear the records the same way. The music had changed me. Something in my brain had shifted.


The Morpheus
I've been thinking about this after listening to Gaucho on the Sonnet Morpheus ($3399), a digital-to-analog converter that has forced me to reexamine my assumptions about how digital sources work and the sound of certain technologies, reminding me that in audio—as in music and in life—received wisdom and easy rules of thumb are, at best, unreliable.

The Morpheus is the brainchild of Cees Ruijtenberg, who designed a series of well-liked digital components for Metrum Acoustics, a company located in the Netherlands. (Ruijtenberg credits his partner Lion Kwaaijtaal with playing an important role in the creation of his products.) Sonnet Digital Audio (which is also Netherlands-based) is his latest venture; it embodies the technical approach of his previous designs while updating them in several important ways.

The Morpheus is an R-2R ladder DAC, meaning that it relies on networks of high-precision resistors to decode the signal (as opposed to the more common approach of using integrated DAC chips that perform delta-sigma conversion; those chips make it much more practical to oversample, to decode ultrahigh sampling rates, to employ sophisticated reconstruction filters, and to handle DSD files).

To be precise, the Morpheus is a different kind of R-2R DAC. While conventional R-2R designs top out at 20 bits, the Morpheus can process 24 by splitting the bits between two sets of resistor networks and then using an algorithm to sum the output.


The Morpheus employs two SDA-2 modules per channel, each containing four resistor networks and a FPGA running proprietary code. As with Ruijtenberg's earlier designs, the user can swap the existing modules for upgraded ones should they become available.

The Morpheus turns out to be full of other thoughtful, original decisions. Consider the volume control: While most DACs rely on analog buffers or digital potentiometers, the Morpheus adjusts volume by changing its reference voltage; this approach places demands on the gain of the matching power amplifier, but it facilitates a short signal path and a lossless signal (footnote 1).


To me, the Morpheus looks quietly elegant—no larger or more attention grabbing than it needs to be, and as understated and purposeful as a vintage Olivetti typewriter. On the front there's a volume control, an LCD screen, a source selector, and a power switch. The rear offers four digital inputs—AES3, coaxial and TosLink S/PDIF, and the user's choice of USB or I2S, the latter via an RJ45 (Ethernet) cable—as well as balanced and single-ended analog outputs, mini-XLR jacks for a wired remote control, and an IEC receptacle for your power cable of choice. A rudimentary (wireless) metal remote control is included.


One more noteworthy thing: the Morpheus doesn't play DSD. Given the sparseness of DSD tracks in my collection, this didn't particularly concern me, especially since Roon and other software players are able to convert DSD to PCM on the fly. It may, however, pose an issue for listeners with large DSD libraries.

An odd convention of writing about digital sources is the continuing need to address the phenomenon of "digital sound." It has become a cliché, yet nearly everyone who's listened to a CD player or a DAC knows what it refers to: musicians reduced to flat, ghostly cutouts; the music's timing subtly smeared; instrumental timbres homogenized; certain high frequencies that sound as though they're stamped out of foil. It's tempting to suggest that "digital sound" is a figment of a bygone era, like the sound of those early, terribly mastered CDs, but some digital components at various price levels still exhibit this tendency, prioritizing needless features and dubious "innovations" over engaging musicality. The enduring popularity of vinyl records is, I think, in part a result of this situation—as is the proliferation of R-2R DACs and other alternatives to digital audio's delta-sigma chip-in-a-box mainstream (an approach that's even more prevalent among the ADCs used in studios to encode digital files).

Footnote 1: This approach apparently caused some issues in systems with high-gain amps or high-sensitivity speakers when the volume control was used. By the time this review is published, the Morpheus will have added the ability for users to reduce the output by 10dB via two switches on the Morpheus's main board. According to Ruijtenberg, this new "Mk.II" design is otherwise identical; there have been no changes that would affect the sonics.—Jim Austin
Sonnet Digital Audio Bv
Daviottenweg 9, 5222 BH

windansea's picture

I keep on hearing about musicality of R2R DACs, but of the various components in the signal chain, I say the DAC ranks with cables as least-detectable element, with speakers then amp as most detectable. I sure wish Stereophile would include a little bit of ABX DBT analysis to tease out the significance of any differences. For example, if a delta-sigma DAC has oversampling turned off, does it sound indistinguishable from an R2R DAC? Is it actually the oversampling that lessens "musicality"?

That said, I've yet to listen to an R2R DAC yet, so I'll confess my ignorance.

Axiom05's picture

A Delta-Sigma DAC requires oversampling since the DAC is only working with a "few" bits at a time. For me, the main interest of a NOS DAC is so one can use something like HQPlayer and explore oversampling and digital filtering in the software. You can use a powerful computer to do this part and with a NOS DAC you don't have an additional digital filter to "stack" on top of.

Archimago's picture

While an SDM DAC will still convert the PCM input to typically multi-bit SDM, that doesn't mean it can't turn off the oversampling applied.

You can still get a "stair-stepped" NOS 44.1kHz playback (for example) with various DACs like the RME ADI-2 series or even the old TEAC UD-501.

Demonstrated here:
TEAC UD-501 - TI/BB PCM1795 "Advanced Segment" DAC:

RME ADI-2 Pro FS R Black Edition - AKM AK4493 DAC:

georgehifi's picture

Seeing this has an output stage (100ohms and over 2v) that can drive any poweramp, it's a real shame it was not used direct using the the two preset switches to match for the loudest it can do into an amp. As this way to me it would be even better, as "the best preamp is no preamp"

Cheers George

Jack L's picture


Bingo !

Why add more harmonic & phase distortion of any premp to the music signals when a DAC with low impedance & 2V+ O/P can drive direct any power amps ???????

That's exactly what I've been doing with my 24bit/192KHz DAC - hookup to my design/built linestage with PASSIVE bypass switch ON, for a couple years now !!

YES, "the best preamp is NO preamp" !!!!!!!!

So my CD/DVD & streaming music go DIRECT to my all-triode SET via my DAC + passive linestage. The music sounds soooo transparent, fast, detailed with livelike performance environment. No problem of lacking power at all.

I never want to switch the linestage back to active mode again. It simply loses the sonic beauty & powerfullness of the above passive mode.

Listening is believing

Jack L

PS: That said above, I am still an vinyl addict !

Jack L's picture


"Great minds think alike" quoted d Belchien 1618.

Fully agreed to yr above statement. Why let harmonic & phase distortions add to the music signals passing through an active linestage preamp ???

Be a smart audio consumers by listening to the music performance in stead of the audio store salespersons' sales pitch.

I heard enough 'myths' rumouring any power amps can't deliver full powers without a preamp. Technically it is bullshit. Any CD/DVD players/DAC do deliver more than enough output voltage (2Vrms++) to drive any power amps (commercial made & home-brews like mine) to full output power. Period.

I've been using true passive line-amp since day one many many years back & then phono-preamp with its active linstage switchable to passive bypass. All are my DIYed design/built.

In passive mode, the music improvement over active mode of the same amp is sooo obvious: wide OPEN, airy, crystalline transparent, detail & FAST transient !! FYI, it is the fast transient response (shortest time the music signals swing from zero to their peak levels) gives our ears/brain the perception of the powerfulness (strength & latten energy) of the music performance that active mode come short !!

Playing vinyl does make such sonic difference even more pronounced. I know as I've compared the music by switching back & forth the passive bypass switch so often.

Listening is believing

Jack L

Panos.G's picture

Hi Alex,

Great article and insight on the Sonnet DAC.

I see you used a 3rd party ethernet (RJ45) I2S cable (Phasure ET^2) to connect the Denafrips Iris DDC to the Morpheus. My question here is, do you think that would also work for Singxer SU-6 or for Denafrips Hermes ?
Cause as it seems the I2S connection is the way to go, to get the full benefit of this DAC.

Many thanks

Nez7's picture

Hi, I am thinking about buying the Sonnet Morpheus as well s getting a Denafrips Hermes DDC to output the i2s signal. Can anyone point me to the specific i2s cable that is compatible with these components?

My understanding is the Sonnet uses an unconventional i2s input so an off the shelve generic i2s cable won't work.