Media Server Reviews

Although I reviewed the original version of this elegant South Korean streamer not too long ago, in the December 2021 issue, it has already been updated. The RS250A ($2695, footnote 1) replaces the RS250's ESS ES9038Q2M two-channel DAC chip with the higher-performance ESS Sabre ES9028PRO chip and now supports PCM data formats up to 32/768 and DSD formats up to DSD512.

MoFi Distribution sent me a sample of the new RS250A. I installed the Rose HIFI app on my iPad mini and connected the RS250A to my NetGear router. My sample had serial number EBK211AB000173 and, according to the Rose app's Device Management page, was running operating system version 4.5.05, which updated to v4.6.06 as I was writing these words. The Rose app identified the RS250A as "ROSE-79." Roon recognized the RS250A as a full MQA decoder and renderer and noted that it handles 32-bit PCM data with a maximum sample rate of 768kHz.

Listening
To audition the RS250A, I connected its single-ended analog outputs to the CH Precision I1 Universal integrated amplifier, which I reviewed in the August 2023 issue. The I1 was set to Bypass mode, where it behaves as an all-analog, fixed-gain power amplifier. Loudspeakers were KEF LS50 minimonitors, sitting on 24" stands and connected to the amplifier with 10' lengths of AudioQuest Robin Hood cable. I used Roon to control volume and its parametric equalization function to extend the LS50s' low frequencies.

With the original RS250 long since returned to MoFi Distribution, comparisons between it and the new version weren't possible. But using Roon and the network connection, I played some of the same files I had used to reach my original conclusions about the streamer's sound quality: Jerome Harris's Rendezvous album (16/44.1 ALAC, Stereophile STPH013-2), which I engineered and mixed; Sasha Matson's Molto Molto jazz-orchestra album (24/96 WAV, Stereophile STPH024), which I produced; and Daft Punk's "Lose Yourself to Dance," from Random Access Memories (24/88.2 ALAC, Columbia/HDtracks), which I neither engineered nor produced but which gets me losing myself and dancing every time I hear it.

The results? I still preferred the "Corrected minimum phase Fast Roll-off " reconstruction filter for the ease of its sound. I still found the soundstaging precise, coupled with excellent transparency to recorded detail. However, as with the original model, kickdrum sounded a little tubby and bass guitar had slightly too much upper-bass bloom. This will be due in part to the CH Precision amplifier, which also has a touch of that character when set to 40% global negative feedback, which was how I had it set. Changing to the MBL N31 processor as the source tightened up the lows compared with the HiFi Rose.

After returning the CH Precision to the distributor, I continued my audition using first a pair of Parasound Halo JC 1+ monoblocks then the Audio Research I/50 integrated amplifier, which I reviewed in the September 2023 issue. My experience with these two very different amplifiers was as positive as it had been with the CH Precision. There's little more to say about the experience.

Measuring
The RS250 offered excellent measured performance for a relatively inexpensive, full-functioned product, with very low harmonic and intermodulation distortion and digital resolution of better than 19 bits. The only somewhat disappointing results I noted were the analog input's relatively low input impedance of 3.3k ohms, which might make the low frequencies sound a little lightweight with tubed source components, and some random-noise–related jitter.

I ran some of the same tests on the HiFi Rose RS250A with my Audio Precision SYS2722 system. The analog input impedance was essentially the same, a relatively low 3.2k ohms; the analog output impedance was 146 ohms, higher than the original's 100 ohms but still usefully low.

Unlike the earlier version, the RS250A inverted absolute polarity for both analog and digital inputs. This can be seen in fig.1, which shows the impulse response with 44.1kHz-sampled Ethernet data and the default "Corrected minimum phase Fast Roll-off " (CMPFR) reconstruction filter.

Like the original RS250 and the RS520 integrated amplifier reviewed by RvB in the July 2023 issue, the RS250A offers a choice of seven filters, labeled "Brick Wall" (BW), "Apodizing Fast Roll- off " (AFR), "Minimum phase Slow Roll-off " (MPSR), "Minimum phase Fast Roll-off " (MPFR),"Linear phase Slow Roll-off" (LPSR), and "Linear phase Fast Roll-off " (LPFR)." In the frequency domain, these filters all behave identically to those in the other HiFi Rose products. Fig.2, for example, which was measured with the CMPFR filter, shows the response up to 100kHz with 44.1kHz-sampled white-noise data (magenta and red traces) and the spectrum with a full-scale tone at 19.1kHz (cyan, blue).

While the RS250's low-frequency noisefloor with the network connection was disturbed by some low-level AC supply–related spuriae, the RS250A's noisefloor was clean (fig.3). Other than a slight rise in the level of random noise between 6kHz and 9kHz, an increase in bit depth from 16 to 24, with network data representing a dithered 1kHz tone at –90dBFS sourced from Roon, dropped the RS250A's noisefloor by almost 30dB (fig.4). This graph implies a resolution of close to 21 bits, superb performance for an affordable processor.

Fig.5 shows the spectrum of the RS250A's output when it was fed high-level, 16-bit J-Test data. In contrast to the original RS250, which boosted the levels of the pair of sidebands surrounding the high-level tone at one-quarter the sample rate (footnote 2), all the odd-order harmonics of the undithered low-frequency, LSB-level squarewave lie at the correct levels, indicated by the sloping green line in this graph. However, the noisefloor still rises in level on either side of the high-level tone, and a pair of sidebands of unknown origin is now present at ±880Hz.

Summing Up
I wrote in my review of the original RS250 that it was "an extraordinarily versatile, affordable product" and that its sound quality suggested that nothing had been compromised in packing so many features into its small chassis. "Highly recommended," I concluded, "both as a streaming DAC and as an all-in-one hub for a high-end audio system." With this audition, I extend that recommendation to the new RS250A. It is an elegant-looking, well-engineered, multipurpose component.—John Atkinson

Footnote 2: See fig.14 here.