When Art Dudley reviewed the original PS Audio PerfectWave DirectStream D/A processor in Stereophile‘s September 2014 issue, he very much liked what he heard. “For those who’ve waited for a computer-friendly DAC that offers, with every type of music file, the best musicality of which DSD is capable, the PerfectWave DirectStream may be in a class by itself,” he concluded. It was computer-friendly because, with an add-in card, you could connect it with USB or to an Ethernet cable and use it with, for example, Roon or JRiver.
DSD? The DirectStream’s D/A conversion engine, designed by former Microsoft engineer Ted Smith, was unusual in that it synchronously upsampled all input data—regardless of format and native sample rate—to a 30-bit word length running at 28.224MHz followed by a digital-domain volume control. The data were then downsampled to 5.6448MHz, resampled to single-bit DSD128, and converted to analog with a low-pass filter.
Rather than using off-the-shelf chips, the DirectStream’s digital processing was performed by a field-programmable gate array (FPGA). The performance could therefore be enhanced by reprogramming this FPGA and supplying users with firmware updates. Art installed the first firmware update while he was working on his review, and several firmware releases followed, culminating in the “Sunlight” version in 2021. Robert Deutsch, Jim Austin, and I reported on the effects of the upgrades up to 2017’s “Huron” in follow-up reviews (footnote 1). I purchased one of the review samples in 2015 to use as my everyday DAC, fitting it the following year with the Bridge II network card in order to use it with Roon, and installing the penultimate “Windom” firmware in 2019.
Enter the MK2
PS Audio discontinued the original DirectStream DAC in 2022, introducing its replacement, the DirectStream MK2, priced at $7999, in January 2023. At 17″ × 4″ × 14″, the MK2 is the same size as its predecessor, and with its gloss-black MDF top panel, it looks very similar. However, the original’s rectangular, four-color touchscreen has been replaced by a smaller display with a Mute/Menu button to its left—a short push for Mute, a long-held push for the Menu—and a blue-illuminated five-button controller to its right. The left- and right-arrow buttons on this controller select the digital input; the up- and down-arrow buttons adjust the volume. After a long push on the Menu button, the controller buttons allow the processor’s settings to be changed.
The MK2 has seven digital inputs: two AES3, optical and coaxial S/PDIF (one each), asynchronous USB Type B, and two I2S over HDMI. The last two can be used with PS Audio PerfectWave transports. There is no Ethernet port, but PS Audio will soon release its AirLens streamer/network bridge, which will connect to the MK2 over I2S. There is also a USB Type A port, which allows a memory stick to be inserted for firmware updates.
The USB Type B and I2S ports accept 16- and 24-bit PCM sampled at frequencies from 44.1kHz to 705.6kHz and DSD data from DSD64 to DSD256, natively or by DoP. The AES3 and S/PDIF inputs accept 16- and 24-bit PCM data with sample rates up to 192kHz and DSD64 DoP data; as usual, the TosLink input is limited to 24/96 data. The two AES inputs can be linked to accept DoP DSD128 data and PCM data sampled at up to 352.8kHz.
Every digital input is galvanically isolated to eliminate noise on shared grounds (footnote 2). (The galvanic isolation is bypassed by default but can be implemented for each input if needed in a specific system, using the Menu function.) There are now two FPGAs, though Smith says that only one is used with the current firmware. While the MK2 still converts the incoming data to DSD, it upsamples it to twice the original’s 28.224MHz. The digital-domain volume control has been refined, with a new architecture with six levels of attenuation, which are automatically selected based on the requested volume level to preserve resolution. In contrast to the original DAC, there is no switchable analog output attenuator. However, the output level can be fixed with a Menu option at whatever level is selected by the volume control.
After the volume control, the 50-bit, high–sample-rate data are resampled to quad-rate DSD and converted to analog with a low-pass filter. The output stages comprise “high current, high speed analog amps” followed by galvanically isolated, balanced transformers. These transformers can handle higher currents with lower distortion than those used in the MK1 DirectStream.
Setup
I connected the DirectStream MK2 DAC to my Roon Nucleus+ server’s USB port via an AudioQuest JitterBug FMJ filter. The PS Audio’s balanced outputs initially fed the inputs of Parasound Halo JC 1+ monoblocks via 10′ lengths of AudioQuest Wild Blue interconnects. However, the PS Audio’s output dropped out at random intervals. It appeared that the weight of the cable’s DC-bias battery was pulling the cable’s custom female XLR plugs, which don’t have the usual locking button, out of the DAC’s jacks. The only other balanced cables I had to hand that were sufficiently long to reach the amplifiers were Ayre/Cardas Signatures, which I had been using several years ago. These interconnects use locking XLR connectors, and I had no further connection problems. I burned in the cables with a CD on repeat overnight before continuing my critical auditioning
The review sample had the v2.3.5 firmware package installed, but as I discuss in the Measurements sidebar, I rolled back the firmware to v2.3.3 then updated to the v2.3.6 package with the 198-Antero FPGA firmware when it became available for download (footnote 3). A long press on the Menu button and scrolling to the right brings up a display showing the firmware version and the unit’s serial number. The DAC has sufficient storage for up to 10 firmware versions, making it easy to switch among them.
Listening
My original DirectStream DAC hadn’t seen audio action for a while—I had been using MBL N31’s CD player/DAC since I auditioned its Roon Ready update in 2020, followed by Benchmark’s DAC3 B. I therefore spent a week refamiliarizing myself with the MK1’s sound before starting my auditioning of the MK2, using the KEF LS50 minimonitors. To ensure a fair comparison with the new DAC, I used the MK1’s USB connection.
The MK1 PS Audio DAC couldn’t match the low-frequency drive and authority of the inexpensive Benchmark DAC that preceded it in the system. (Readers may wonder how I could perceive this with the small KEF LS50s, but I use Roon’s parametric equalizer to add a 3dB boost below 75Hz with these speakers.) But while it doesn’t have the almost unrivaled transparency to recorded detail of the Benchmark or the combination of transparency and effortlessly musical reproduction offered by the more expensive MBL when used with its Minimum-Phase reconstruction filter, the 8-year-old DirectStream’s presentation was smooth, easy to listen to, and never got in the way of the music.
Footnote 1: All of our coverage of the original DirectStream processor can be found here.
Footnote 2: See Ted Smith’s presentation on the design of the DirectStream MK2 at youtube.com/watch?v=x7csGu1VpLU.
Footnote 3: Thorough instructions on how to update both the user interface firmware and the FPGA firmware can be found in the manual, which can be downloaded from psaudio.com/products/directstream-dac-mk2.
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