Sonnet Digital Audio Morpheus DAC
Modern versions of R-2R 'ladder’ DACs (R for resistor) have been flourishing in the last several years as an alternative to Delta-Sigma DACs. Fans of R-2R DACs commonly describe them as sounding ‘more musical and natural; less smoothed out’ than their Delta-Sigma counterparts (which by far dominate the market). R-2R actually is an older technology than the modern Delta-Sigma approach, going back to the early 1950s; it is a variation of a so-called binary-weighted DAC. For many years now, R-2R has been largely left aside in favor of modern tiny Delta-Sigma chips that can easily process at very high resolutions, handle native DSD at mind boggling rates, and offer many filtering options and over-sampling. (Examples include the outstanding 32 bit ESS Technology 9038PRO SABRE chip used in many high-end DACS today.)
However, not all R-2R DACs are true R-2R.
By true, I mean using traditional R-2R ladder chip sets (such as the AD1862, or PCM63, both vintage—decades old—and no longer manufactured). True R-2R can only process 20 bit files, cannot not process DSD, is non-over-sampling (NOS), and also does not resort to any kind of filtering. (And they generally have no interest in dealing with MQA.)
An exemplary example of pure R-2R is the Mojo Audio Mystique EVO Pro DAC ($12,000); it is currently my reference.
The vast majority of R-2R DACs on the market today are not pure; I will refer to them here as hybrid R-2R: For a helping hand they incorporate other technologies in addition to R-2R ladders to obtain, for example, 24 bit processing (as opposed to only 20), resistance matching, DSD processing, oversampling and filtering.
This requires algorithms and computing capabilities on board and thus Field Programmable Gate Arrays (FPGA) are often used within. (Note: This use of an FPGA is not to be confused with the novel PS Audio DSD DAC which is not an R-2R DAC but (remarkably) uses an FPGA with sophisticated in-house programming to do all the processing via upsampling any digital input into a DSD type format.)
Advantages of hybrid include lower cost and more options than a pure R-2R. They also have the potential to bridge the gap in sound quality between a pure R-2R and the finest of the Delta-Sigma. In short, they should be taken seriously when designed well.
Enter: Morpheus
I am all ears, so I am pleased to be able to present here for review a very interesting hybrid R-2R DAC: The Sonnet Digital Audio Morpheus DAC, manufactured in the Netherlands. Many thanks to Rob Fritz of Audio Art Cable for bringing this unit to my attention, getting me in touch with Cees Ruijtenberg (Sonnet CEO and one of its Co-Founders) and for sending me a review unit.
The Morpheus is Roon Ready and retails for $3399, but my review unit (with a silver face plate, black is also available) also came with an optional pre-installed MQA decoder bringing the cost up slightly to $3598. A free of charge I2S module can be installed in lieu of USB for digital in, but that option is mainly dedicated for the Sonnet Hermes Streamer which I did not use in this review; I used USB with my own reference music server (Mojo Audio Deja Vu).
The Morpheus is small (290 x 250 x 60 mm) and light (only 3.2kg), can process 24 bit PCM files up to 384 Khz, is NOS, does not use filtering and does not play DSD. It also has a built-in digital volume control for direct-to-amps usage, but, of course, can be bypassed to work with your own preamp. It comes with a very solidly built black aluminum and simple to use remote control; but one can also control the unit from the front panel of the DAC.
What kind of hybrid is the Morpheus?
The Morpheus processes 24 bit input via what is called (using current lingo) a segmented R-2R approach: it uses one R-2R ladder for the most significant bits (out of the 24 handed it) and a second one for the least significant bits. Then, it uses an algorithm to combine the summed outputs from both R-2R ladders to get the original 24 bits in analog. Ruijtenberg explained his version of this approach to me as follows:
Compared to a pure R-2R ladder DAC, our approach is completely different as we split a desired 24 bit range over two 16 bit R-2R ladder modules. For splitting this digital format we use a very fast FPGA which is part of each module. Like every single R-2R ladder it is hard to get linearity in the lower ranges, so by sending just 12 bits to the most significant part (MSB) of the R-2R ladder we can ensure that high linearity holds. We also do this trick for the least significant part (LSB) of the 24 bit stream. So, as a result the very low signals that normally come out as the LSB part will come out very loud as it is sent to the MSB part of the second R-2R ladder. In fact the LSB part of the lower 12 bits are far too loud ( +64dB) and will not match with the upper R-2R ladder. So, in the analog domain we have two very loud signals. One of them (in fact the real LSB part of this 24 bit stream) should be attenuated and glued to the upper analog part. This last process is probably the most difficult aspect of the job to accomplish.
By using this approach we have more than one advantage here:
1) The amplitude of the switching noise is always far below that of the analog signal. This is especially so for the LSB part as we have to create a 64 dB attenuation for that part so that switching noise is far below noise levels and not measurable.
2) Linearity is a straight line down to -140 dB
As verified by Ruijtenberg, the Morpheus uses two SDA-2 (R-2R) DAC modules per channel (L/R), for a total of four in which each module has four 16-bit ladders, and one FPGA.
Note: There are other ways of accomplishing segmenting to get 24 bit, there is even an off the shelf segmented R-2R chip that does it all for you and is becoming more popular: versions of the PCM1704 chip set.
Further specifications
Balanced Non oversampling DAC
Two SDA-2 DAC modules per channel in differential mode
Power supply 15VA 110/115V AC 220/230V AC 60/50Hz. Power required max 8 Watts
Input 1x optical, 1x coaxial and 1x AES/EBU and USB
Output 1x stereo pair single ended 2 Volts RMS
Output 1x stereo pair XLR balanced 4 Volts RMS
Recommended gain of used power amp in variable gain mode 22 - 26dB
Frequency Response 44.1 kHz sampling 1Hz – 20 khz -2.5 dB
Frequency Response 192 kHz sampling 1Hz – 65 kHz – 3dB and 384kHz (USB)
Distortion 0.004% THD
Channel separation 120dB
Noise Floor -155 dB related to 2 Volt RMS
Output impedance RCA 100 Ohm, XLR 100 Ohm
Sampling rate Optical 44.1 – 96 kHz
Sampling rate Coax and AES/EBU: 44.1 -192 kHz
Sampling rate USB 44.1 – 384kHz
Setup and Use
The simple and tasteful front panel with Sonnet written near the top and Morpheus near the bottom has a small centered blue monitor, a power button, source button and a large volume knob. In addition to the volume (0db down to -40s), the monitor lets you know that you are using (say) USB, what the volume is, and displays ‘MQA Studio’ if an MQA file is playing.
It does not show what the resolution is of a playing file; but since it is Roon Ready, you can see such things on your Roon Remote if you use Roon, which is what I did: After connecting a USB cable from my music server to the Morpheus, Roon immediately recognized `Morpheus’ as a device and I set up a zone for it right away without any problem.
When re-powering the Morpheus, it resets the volume to -46db to ensure protection of your speakers if you are going direct-to amps, but you can enable it to stay at a specific volume of your choice instead. I almost exclusively used my own preamp during this review (PS Audio BHK) hence kept the Morpheus volume set at 0 (full blast) and used my preamp’s own remote for volume. For burn in: Ruijtenberg told me to merely keep the unit powered on for about two days (no music even needs to play) before reviewing. Isn’t that nice. I kept it on always anyhow, so, that was easy.
A note about using MQA: If your unit has the MQA option, then just be sure to set your player software to defer all of the MQA unfolding processing to the Morpheus. Roon Labs for example, allows one to choose from among only allowing Roon to do the first unfolding (which is all it can do) while allowing the DAC to do the rest, or to defer all the unfolding to the DAC, or to not handling MQA at all.
If you choose Roon to do only the first unfolding, you will get some strange outcomes (even with non-MQA files) as I found out by at first employing that by mistake.
The back of the unit allows for balanced or single-ended analog out; optical, USB, coaxial or AES/EBU digital in; and a power cord connector that can handle your own high-end cables.
There is no separate power switch on the back; only the front panel power button.
General sound impressions
The Morpheus clearly had that musical and natural less smoothed out type of sound that I treasure from my reference Mystique DAC; however, the Mystique digs deeper and widens what it can do both in the sound stage size, picking up subtleties and nuances, and handling higher volumes with aplomb. To be fair, the Morpheus gets about 80% of the way with ease; at about 1/3rd the price of my reference—that is very impressive. And I have to take my hat off to the Morpheus for the fact that it does not try to do too much (DSD, and oversampling for example). I next offer five examples of how well it performed and impressed me.
Music
‘Holy Mother’, Eric Clapton and Luciano Pavarotti (yes, odd bed fellows!) from Pavarotti-The Duets, 16/44.1 Qobuz. A highly unusual live performance with the two stars on front center stage with the East London Gospel Choir, the Torino Philharmonic Orchestra and Clapton’s backup musicians. From 1996, this to me is Clapton at his peak; his singing is pitch perfect and he even performs an amazing/classic uniquely Clapton electric guitar solo while Pavarotti sways back and forth to keep time like a human metronome while beaming with happiness (check out the video on Youtube; a must see). They sing back and forth and when they sing together, Pavarotti’s powerful tenor voice drowns out Clapton. Fascinating.
Written by Clapton and Steven Bishop, ‘Holy Mother’ was originally recorded on Clapton’s 1986 August album (the somber/serious/needy tone might fool one into thinking that this song has something to do with the tragedy of losing his son; but that loss occurred much later); but this 1996 performance with Pavarotti is special, and the Morpheus does more than its duty to present it naturally and get you hooked.
Patricia Barber’s new album Clique! Coming out in August 2021. I was lucky to be given an advance HiRes file by her PR people. The tracks `This town’, and my favorite track 6, ‘The In Crowd’ in particular impressed me.
‘This Town’ was written by Lee Hazlewood and made famous when sung by Frank Sinatra years ago, but Barber does a unique (her own style) job ending (as did Frank Sinatra, although his voice is very faint and possibly missed by many listeners) with `Bye Bye, bye bye,....’, a lovely touch.
I mainly paid attention to Barber on piano and voice (her voice does not age!), Patrick Mulcahy on (superb) upright bass and Jon Deitemyer with his very tasteful, natural and well recorded percussion. (And I must mention the others: Neal Alger on acoustic guitar; Jim Gailloretto on tenor sax.)
Barber gives the musicians much freedom (which is one reason I have always enjoyed her approach), and she seems to have a deep connection to them. This recording allowed the Morpheus to truly present its strength in showing off acoustic music recorded in studio, and in particular (besides Barber’s voice) it showed off its ability to get the natural deep bass sound right; it is quite special. According to the recording notes, Clique! was recorded digital and mixed on an analog Neve 88 Legacy board. No analog compressor/limiter/eq and/or digital reverb are used in the mix. So, I assume the reverb I hear from Barber’s voice is natural from the studio room. (Recording and mixing: Jim Anderson. Mastering: Bob Ludwig.)
MQA example. ‘Simple Symphony, for string orchestra, Op. 4’ (composed by Benjamin Britten) from the album Divertimenti by the Trondheim Soloists. This is fully unfolded to 24/352.8 by the Morpheus from its MQA unfolded 24/44.1 Flac file sent via Tidal. The front monitor on the Morpheus displayed, ‘MQA Studio’. The recording quality is stellar. The Morpheus picked up enough to deeply impress me.
Italian jazz drummer Enrico Morello, ‘Drills in My Brain’, ‘Quite Close, and ‘What Happened on the Road’, from the 2021 album Cyclic Signs, but released as singles along the way that can be streamed on both Tidal and Qobuz at 16/44.1. Superb creative and complex drumming with much other percussion (several cow bells?); very good recording quality with lingering resonances from cymbals and tom toms displayed by the Morpheus which made me appreciate this drummer. I hope I get to hear him live now that the pandemic appears to be receding.
Glenn Gould playing the Goldberg Variations on piano. I focus here on two recordings because my father (who recently passed away and played piano as a hobby) loved that piece and so do I: the main one from the 1950s when Gould was was young, with his remarkable new interpretation showing off his extraordinary energy, creativity, skill, speed and (yes) genius. The second (after he already (since the mid-1960s) only played in the studio), from 1983; slower, more thoughtful and emotional, with (to me) gorgeous accoutrements. My father and I could never fully agree which was ‘best’; but I preferred the 1983 one because it hit me emotionally like the earlier one did not. My father, of course, had a huge advantage: He not only played piano but had seen Gould play live several times in the early 1960s in both Ontario, Canada and in Buffalo, New York (where my father then lived). He also did his best to try to play it on his piano when I was a young child; an admirable job he did but always admitting that he could not pull it off like Gould; but he tried. That is hard to forget. Anyhow, he did agree about the emotional part, and we just hung out in later years listening to both.
But I digress: The Morpheus handled both beautifully, capturing the sound and the differences in style that I will always remember. Putting aside these particular recordings, I found that the Morpheus handled piano very naturally, and I do think that is one of the most difficult instruments to get right. Another plus for the Morpheus.
Direct to amps usage
This is where the Morpheus remote control was useful because otherwise (with my preamp out of the loop) I would have to use only the front panel of the Morpheus to control volume. I spent very little time with this mode since using my preamp was so obviously better sounding: More richness and fullness, more warmth, more textures; larger sound stage, less crispiness (in voices, for example). Keep in mind that in my experience, an outstanding stand alone preamplifier (such as the PS Audio BHK) does the same magic on all other DACs I have tried that offer direct to amps; my comments here should not be construed as being the fault of the Morpheus in particular. That said, the Morpheus was one of the best sounding DACs I have heard at such a low price (of only $3399) using via direct-to-amps; so one can save a bundle by using it this way if they do not already have a serious external preamp.
Summary
The Morpheus is an exemplary example of a hybrid R-2R DAC that, at only $3399, accomplishes what it set out to do: recreate the essential sound of a true R-2R but at a much lower price, and without wasting time on trying to do much else (such as DSD, oversampling, etc.). It is light and small and so easy to use, Roon Ready with a simple and elegant look: and it comes with a very good internal volume control making it possible to use without a separate preamplifier. Highly recommended.
Further information: Sonnet Digital Audio
