My go-to DAC and network audio player for nearly the past two years has been PS Audio's PerfectWave MkII DAC with the Network Bridge. PS Audio recently replaced the PerfectWave DAC with the DirectStream DAC, so naturally I had to get my hands on it.
Outwardly, the DirectStream DAC appears to be a DSD-capable version of the PerfectWave DAC, and it is. However, the DirectStream operates by converting all incoming signals, including PCM, to 10 times DSD rate. Processing of all signals, regardless of the format in which they were sent to the DAC, is then DSD-based. Why convert all incoming signals to DSD? PS Audio claims several advantages to DSD audio signals over traditional PCM, including: increased linearity; simpler conversion to analog (which can be done through a low-pass filter); and more analog-like behavior (i.e., soft clipping) when overloaded.
The DirectStream DAC is the brainchild of Ted Smith and is the culmination of a nearly decade-long project. Ted's background is in software engineering, and he designed a prototype of a computer-based DAC. After five years of working on his DAC, Ted visited Gus Skinas of the Super Audio Mastering Center in Colorado to see how his DAC would stack up to the competition. Gus introduced Ted to Paul of PS Audio, and the rest, as they say, is history. I was fortunate enough to spend a few minutes visiting with Ted while he was in California this summer for T.H.E Show: Newport. Ted's flowing beard and Hawaiian shirt made him easy to find in the crowd, and he was eager to answer questions from the many people who were eager to speak with him.
Ted explained that the conversion of all incoming signals is treated the same. The conversion to DSD (specifically, 10 times DSD sample rate) rather than simply being DSD-capable is what sets the DirectStream apart. All inputs are locked at all times. This combination, along with a clean power supply and accurate clock, is said to eliminate any jitter-related differences between inputs. The DSD signal is run through a simple filter to produce the analog signal. The diagram to the right (click on it to view in a larger window) demonstrates the simplicity of the DSD signal path in comparison to a traditional PCM signal path. PS Audio contends that the simpler signal path preserves many signal nuances that are lost in more traditional DAC designs.
No off-the-shelf DAC chips were utilized in the DirectStream; the processing is handled by a custom FPGA (field programmable gate array) that can handle the amount of computing power necessary without overheating and allows for a true single-bit Sigma Delta conversion. A single extremely accurate clock from Crystek eliminates any clock synchronization problems. The analog output path is fully balanced and passive. A passive audio output transformer provides galvanic isolation and acts as a low-pass filter. Adjustable output levels allow the user to further simplify their system by bypassing a preamplifier and connecting the DirectStream directly to an amplifier.
The above description is a gross oversimplification of how the DirectStream DAC works. I am afraid that any attempts to provide more insight would make this article exceedingly lengthy. Any oversimplification or inaccuracies in the technical description of DirectStream are my fault, as I was attempting to keep up with Ted's enthusiastic technical description during our discussion, and my note-taking fell behind. For those of you who are interested in learning more about how this DAC works, I recommend checking out the PS Audio website, where you will find lots of information, including some videos that provide much more detail on the technical aspects of the product.
Owners of the PerfectWave DAC can purchase an upgrade kit that basically uses the chassis and display panel of the existing DAC but replaces everything inside of the unit. The main difference between a DirectStream DAC and a PerfectWave DAC upgraded to a DirectStream is that the IR receiver on the new DirectStream unit is supposed to be more sensitive. Otherwise, functionality and performance of the new and upgraded units should be identical. A new DirectStream DAC retails for $5,995, while PerfectWave DAC owners can purchase the upgrade kit for $2,995. The optional Network Bridge still retails at $795 but is slated to be replaced by a new version in the near future.
As the DirectStream utilizes the same chassis as the PerfectWave DAC, it has the same aesthetic and the same inputs (I2S over HDMI, Toslink, S/PDIF, AES/EBU, USB). The inputs are all asynchronous, with the network input accepting up to 32-bit/192-kHz data and the USB input accepting up to 24-bit/192-kHz signals. Input selection, as well as phase, volume, balance, and polarity selections, can be made from either the included remote control or the front-panel touchscreen.
Since I own the PerfectWave DAC, I chose to go the upgrade route instead of requesting a new DirectStream sample. I started the upgrade process by reading the instructions provided by PS Audio and watching YouTube videos that provided a walkthrough. The Network Bridge in the PWD required a simple update before the installation of the DirectStream kit, which was easily performed before disconnecting my PerfectWave MkII DAC from my system.
Overall, the upgrade process went relatively smoothly and should take less than an hour, not including the time the DAC takes for software updates. (Photos of the upgrade process are available in the slideshow below.) The unit is cleverly constructed but was relatively easy to take apart. Be sure to double-check the connections on all of the cables when installing the new parts. The only hitch in the process for me came from a loose cable that prevented the DirectStream from properly initializing. Once I found that cable, everything worked fine. Firmware updates are available on the PS Audio website and are downloaded to an SD card (one is included with the new units and kits), then inserted into the back of the DAC. This is a bit clunky compared with some other devices, but it's simple enough if you have the most basic of computer skills.
After the installation of the upgrade kit, I ended up with what amounts to a complete PerfectWave DAC, minus the chassis and display. It would be a shame to have this great donor DAC sit around unused. I saw on the forums that the search is on for a chassis and display that will let the old components be utilized. If this pans out, the parts from your prior DAC can be used to assemble a second DAC or will at least have increased market value. A program where these can be turned in for some sort of credit would be very welcome to the frugal audiophile within me.
The DirectStream went into the same rack space that the PWD came from. My preamplifier was the Krell Phantom III, which fed the signal to Krell and Halcro amplifiers (obviously not at the same time; I switched back and forth). An Oppo BDP-95 was available for use as a disc transport, and a Marantz NA-11S1 was on hand for comparison. B&W 800 Diamonds were in place as the main speakers, with the B&W DB1 subwoofer anchoring the foundation. Cabling was Transparent Ultra MM2 and Kimber Select. All line-level analog signals were carried on balanced cables. I used two different USB cables: the Kimber Select KS2416 and KS2436, which are similar in design except the KS2416 utilizes copper connectors and the KS2436 uses silver.
The vast majority of my listening was of audio files stored on my Netgear NAS device. I used a wired connection to the DirectStream, as I wanted to minimize any connectivity variables that would come from using the WiFi connection. The audio files were served via J River's Media Center, which I have installed on both Mac OS and Windows 8 machines. I also used a MacBook Air with locally stored files sent out via USB. Using Audirvana+ on my MacBook connected to the DirectStream allowed me to play direct DSD files without utilizing the DoP protocol that is required with the network-served DSD files.
Click over to Page Two for Performance, The Downside, Comparison & Competition, and Conclusion...
Before sitting down to do any serious listening, I let the DirectStream play for three weeks straight to make sure it was fully broken in. The DirectStream firmware version at time of listening was 1.1.9. [Editor's note: After this review was completed, PS Audio issued a major firmware update that the company says improves every aspect of performance.]
I listened to Paco de Lucia's "Live in America" from the Burmester Art for the Ear disc. I first played this track as a 16/44.1 FLAC file via the Network Bridge input, then directly from the disc in the Oppo BDP-95 and the DirectStream's coaxial input. Through the Network Bridge, the guitar was very natural and open. The guitar was vibrant and full of body and detail, solidly placed in the forefront with a well-defined space in the background. Background noises and voices added to this sense of space. The well-balanced nature of the PerfectWave DAC MkII that the DirectStrean replaced was preserved, but there was noticeably more information being presented, which made me double check the audio file being played to confirm that it was not a higher-resolution file (it wasn't, I only have this on my drive as a 16/44.1 FLAC file). There was simply more texture and presence with the DirectStream.
In comparing the Network Bridge and coaxial inputs, there were some differences, but they were much more subtle through the DirectStream than they were through the PerfectWave DAC. The Network Bridge seemed slightly more dynamic, with faster leading edges on the guitar than when the CD was played through the coax. The sound was very, very similar between inputs, much more so than with the PerfectWave DAC MkII, which had very noticeable differences in the sonic characteristics of each input. I suspect this is due in part to the continuously locked inputs and the way the signal from each input is processed.
The next track on the Burmester album is one of my favorites: Hans Thessink's "Call Me." Thessink's voice was virtually indistinguishable between the inputs; but, consistent with the prior track, the strings had a bit more snap to their leading edges through the network connection compared with the coaxial input.
Michel Jonasz's voice on "Le Temps Passe" from the album La fabeleuse histoire de Mister Swing (Warner Music Group, FLAC) was very natural and lifelike, full of textured emotion. The drums were tight and well defined with the cymbals in the same space on the sonic soundstage. The cymbals were energetic and shimery but not harsh.
I then compared a standard CD-resolution version of Michael Jackson's Bad to a 24-bit/48-kHz version from HDTracks. Both versions were streamed as FLAC files. The increase in clarity between the CD resolution and 24/48 versions was clearly audible. The higher-resolution version had detail and image solidity that exceeded that of the standard-resolution version. The title track, "Bad," has deep synthetic bass notes that the DirectStream handled in a balanced and taut manner. In comparison with the Oppo BDP-95's internal DAC or the Marantz NA11-S1, the bass notes were thinner but just as deep and more defined. This was even more noticeable with the bass track in "Liberian Girl."
I then stepped up to a 24-bit/176-kHz AIFF audio file of the Living Stereo recording of Charles Munch conducting the Boston Symphony Orchestra playing Saint-Saëns: Symphony No. 3 (from HDTracks.com). Listening to this symphony was pure audio ecstasy. Those of you who think classical music is boring will be pleasantly surprised by this piece, with its engaging tempo and powerful pipe organs. Listening to this recording through the DirectStream, I heard a full detailed soundscape spread out before me, going beyond the bounds of my listening room. Each section was firmly anchored and full of lifelike detail. The pipe organ's bass with notes in the low to mid 30-Hz range were phenomenal but still cannot compare to hearing this live in a symphony hall. As wonderful as the sound quality was, the lack of gapless playback with the network input was distracting when listening to a classical piece such as this, which should flow smoothly between tracks.
I listened to a few DSD tracks that some colleagues were able to recommend but again relied upon one that I have both in the DSD and PCM formats: Beck's album Sea Change (Interscope). When listening to the DSD and PCM versions of this album through the Marantz NA11-S1, the differences were significant. I was curious to see if the differences between file types would be as pronounced with the DirectStream. In order to make this comparison, I loaded a CD-resolution, FLAC-format file along with the DSD files for the album onto my MacBook and used Audirvana+ for playback via the DirectStream's USB input. Standard-rate DSD files can also be played back through the Network Bridge via the DoP protocol, and I heard no difference between DSD files sent over the network and those transmitted via USB.
The track "Lost Cause" remains one of my favorite tracks and is the first one I played off the album when listening through the DirectStream. The "Lost Cause" DSD file had more detail in voice and strings, as well as more body than the FLAC file (made from the CD), but the difference was not nearly as pronounced as when I played the same two files on the Marantz NA11-S1. Considering the significant amount of detail the DirectStream was able to retrieve from a variety of non-DSD files, I suspect that the smaller differential is due to increased performance with PCM files rather than any degraded DSD performance.
The DirectStream, like its predecessor, has preamplifier functions like volume and balance controls, which allow it to be directly attached to an amplifier. When listening to the DirectStream connected directly to my Halcro DM-38 amplifier without a preamplifier in between, there was a small increase in clarity as compared to having the Krell Phantom III in between. However, taking the preamplifier out of the system precludes the use of other sources and may make the connection of a subwoofer more challenging.
Some features are missing that I would like to see included on a high-end DAC, such as the ability to accept a USB thumb drive and built-in Internet radio, streaming services and, in acknowledgement of the Apple iOS world around us, AirPlay. Many of these have workarounds. Internet radio and streaming can be accessed via a computer, but this is a bit quirky and complicated for an otherwise elegant product. Simply using the USB input can also provide a workaround if your setup allows this.
The sound quality of the Network Bridge is not a problem, but the continued lack of gapless playback through it will prove annoying for those who play classical music. Plus, the lack of double-rate DSD capability may irk the few audiophiles with DSD audio file collections that include double-rate files. PS Audio has announced a new Network Bridge that may address the lack of gapless playback but not double-rate DSD files.
Lastly, I would still like to see a headphone output, especially as the DirectStream has a built-in preamplifier section.
Comparison and Competition
The first unit that came to mind is the Marantz NA11-S1 that I recently reviewed. At $3,500, the Marantz is just over half the price of the DirectStream and has lots of convenience features not found on the DirectStream, such as built-in Pandora, Spotify, SiriusXM, and AirPlay. The Linn Majik DS-I ($4,200) garners excellent reviews as a network-capable DAC but does not have USB capabilities. Another contender is the Bryston BDP-2/BDA-2 combination ($2,995/$2,395), which provides a modular system that may better suit some systems. Another option is Cambridge Audio's Stream Magic 6 V2, which supports Bluetooth audio, network audio, Internet radio, and some streaming services for $999.
The DirectStream DAC is one of the finest-sounding DACs I have heard. Many will be excited just to see that it can accept DSD signals, but I would say that they are being shortsighted. The DSD processing of all signals is what makes this unit special. All signals, regardless of their file type, are converted to DSD and processed the same way. Does that mean a 128k MP3 signal will sound as good as a 24/192 FLAC signal? No. However, the amount of low-level information and detail retrieved minimizes the differences, making it so that the differences you hear will end up being the result of the underlying file quality rather than to differences due to the file type.
I found the DirectStream to be very natural sounding, with a balanced presentation and accurate soundstage that makes for great realism. The musical presentation was engaging, and I often found myself getting lost in the music, listening for hours or until I was interrupted by my familial duties. Strings and voices, which I hear the most of live, stood out in my mind as being very lifelike. The DirectStream did seem to be just a tad bit laidback during my first listening sessions, but this diminished (becoming slightly more forward) when I updated the firmware to 1.1.5. However, this does not mean that there is a lack of high-frequency detail. The DirectStream was extremely clear and detailed in the upper registers, and my listening notes make several references to this, including extremely clean-sounding cymbals with extended decay.
In short, the DirectStream provides excellent sound quality with all types of audio files. The unique processing of audio files minimizes the sonic differences due to file types. I would characterize the DirectStream's sound as being natural or lifelike with a balanced blend of analog smoothness and detail. The amount of detail that the DirectStream extracted from regular redbook CDs made me want to go back and listen to them again, but it was also able to take advantage of my newer, high-resolution files for some of the best sound I have heard in my system. Kudos to Ted and Paul.
• PS Audio PerfectWave MKII DAC with Bridge Reviewed at HomeTheaterReview.com.
• PS Audio Shipping NuWave Phono Converter at HomeTheaterReview.com.
• Read other DAC reviews in our Digital-to-Analog Converters section at HomeTheaterReview.com.