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...