HiFi Rose RS520 streaming integrated amplifier Measurements

Sidebar 3: Measurements

When I unpacked the RS520 sample reviewed by RvB, I heard something metallic rattling around inside the amplifier. The nut holding one of the speaker binding posts to the printed circuit board on the back panel had come undone. I found the binding post inside the shipping box, and when I removed the top cover, I found the nut inside the amplifier. I reattached the binding post, but when I removed the top panel, the two ribbon cables that connect it to the main circuit board detached. As hard as I tried, I couldn't manage to reattach these cables. I requested a new sample of the RS520, which was promptly supplied. I measured serial number EBK302CB000118.

I performed the measurements using my Audio Precision SYS2722 system. As the HiFi Rose is a class-D design and class-D amplifiers emit relatively high levels of ultrasonic noise that would drive the analyzer's input into slew-rate limiting, all the measurements other than frequency response were taken with Audio Precision's AUX-0025 passive auxiliary low-pass filter. (The AUX-0025 mitigates noise above 80kHz and eliminates noise above 200kHz.) Without the filter, 760mV of ultrasonic noise was present at the left channel's loudspeaker terminals, 860mV at the right channel's, both with a center frequency of 570kHz. After a few hours of testing, the amplifier's top panel was warm, at 98.4°F/36.9°C.

I left the amplifier's Software Volume Control turned off for all the measurements. The Pre output level was set to its default value. Looking first at the single-ended analog line input, with the HiFi Rose's volume control set to its maximum—the control operates in accurate 0.5dB steps—the voltage gain at 1kHz into 8 ohms measured 28.5dB from the speaker terminals and 1.7dB from the preamplifier output. The line input preserved absolute polarity (ie, was noninverting) from both output types, and the input impedance was low, at close to 3.3k ohms across the audioband. (The specified input impedance is 100k ohms.)


Fig.1 HiFi Rose RS520, line input, frequency response at 2.83V into: simulated loudspeaker load (gray), 8 ohms (left channel blue, right red), 4 ohms (left cyan, right magenta), 2 ohms (green) (1dB/vertical div.).


Fig.2 HiFi Rose RS520, line input, small-signal, 1kHz squarewave into 8 ohms.

The preamplifier output impedance was 302 ohms from 20Hz to 20kHz; the impedance at the speaker terminals was a low 0.11 ohm at 20Hz and 1kHz, rising to 0.4 ohm at 20kHz. (These values include the series resistance of 6' of spaced-pair speaker cable.) Consequently, the variation in frequency response with our standard simulated loudspeaker, taken without the AP low-pass filter (fig.1, gray trace), was minimal, though the output rolled off earlier in the top octave with low-impedance loads (fig.1, cyan, magenta, and green traces) than it did into 8 ohms (fig.1, blue and red traces). A slight rise in response can be seen above the audioband into 8 ohms, which correlates with an overshoot and ringing on the waveform's leading edges with the RS520's reproduction of a 10kHz squarewave into this load (fig.2). Fig.1 was taken with the volume control set to its maximum; the superb channel matching was preserved at lower settings of the control.


Fig.3 HiFi Rose RS520, line input, spectrum of 1kHz sinewave, DC–1kHz, at 1W into 8 ohms with volume control set to the maximum (left channel blue, right red) (linear frequency scale).

Channel separation above 2kHz was okay, at >60dB in both directions, but decreased to 50dB at 100Hz and below. With the Audio Precision ultrasonic filter, the RS520's line inputs shorted to ground, and with the volume control set to the maximum, the wideband, unweighted signal/noise ratio (ref. 2.83V into 8 ohms) measured 54.4dB in both channels. Restricting the measurement bandwidth to 22kHz increased the ratio to 76dB, and an A-weighting filter increased it further, to 84.5dB. Spectral analysis of the HiFi Rose's low-frequency noisefloor (fig.3) revealed no AC power-line–related spuriae, though the 1kHz tone has a sideband at 880Hz (1000Hz–120Hz). This graph was taken with the volume control set to its maximum, but the spectrum didn't change significantly with the volume reduced by 12dB.


Fig.4 HiFi Rose RS520, line input, THD+N (%) vs 1kHz continuous output power into 8 ohms.


Fig.5 HiFi Rose RS520, line input, THD+N (%) vs 1kHz continuous output power into 4 ohms.

The RS520 is specified as delivering a maximum output power of 250Wpc into both 8 ohms and 4 ohms (24dBW and 21dBW, respectively). With our usual definition of clipping—when the THD+N reaches 1%—and with both channels driven, the RS520 clipped at 275Wpc into 8 ohms (24.4dBW, fig.4). The downward slope below 50W in this graph indicates that the reading is dominated by noise, with distortion rising above the noisefloor at higher powers. I couldn't test the clipping power into 4 ohms, as the amplifier went into protection at 357Wpc (22.55dBW, fig.5), well above the rated power.


Fig.6 HiFi Rose RS520, THD+N (%) vs frequency at 12.67V into: 8 ohms (left channel blue, right red), and 4 ohms (left green, right gray).

The distortion levels at 12.67V, which is equivalent to 20W into 8 ohms and 40W into 4 ohms (fig.6), were very low above 500Hz. (To avoid having the measured percentage corrupted by high-frequency noise, even with the auxiliary AP filter, I used a brickwall low-pass filter set to a 40kHz passband, which is why this graph only extends to 10kHz.) However, the THD+N rose below that frequency, exceeding 0.1% (–60dB) in the low bass.


Fig.7 HiFi Rose RS520, line input, 1kHz waveform at 20W into 8 ohms, 0.006% THD+N (top); distortion and noise waveform with fundamental notched out (bottom, not to scale).


Fig.8 HiFi Rose RS520, line input, spectrum of 50Hz sinewave, DC–1kHz, at 20Wpc into 8 ohms (left channel blue, right red; linear frequency scale).


Fig.9 HiFi Rose RS520, line input, spectrum of 1kHz sinewave, DC–1kHz, at 20Wpc into 8 ohms (left channel blue, right red; linear frequency scale).

The distortion signature appears to be primarily second harmonic in nature at 1kHz (fig.7) and third harmonic at 50Hz (fig.8). As shown in fig.6, the distortion was much higher with the 50Hz signal than it was with the 1kHz signal (fig.9). Note the sidebands of the spectral spike at 1kHz in fig.9 at ±120Hz. I experimented with the grounding between the RS520 and the Audio Precision, including connecting a wire between the ground terminal on the amplifier's rear panel and the analyzer's chassis ground, but I could not eliminate these sidebands.


Fig.10 HiFi Rose RS520, line input, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 50Wpc peak into 8 ohms (left channel blue, right red; linear frequency scale).

Intermodulation distortion was very low (fig.10), the difference product at 1kHz lying at –94dB (0.002%), the higher-order products at 18kHz and 21kHz at –79dB (0.01%).

Turning to the RS520's digital inputs, I used the Audio Precision's optical and coaxial S/PDIF outputs and sent test signals to the amplifier via Ethernet from Roon and by USB from my MacBook Pro. The RS520's S/PDIF inputs locked to datastreams with sample rates up to 192kHz. Apple's USB Prober app identified the HiFi Rose as "RS520-DAC" and showed that the USB port operates in the optimal isochronous asynchronous mode. Apple's AudioMIDI utility indicated that the RS520 accepts 16- and 32-bit integer data sampled at all rates from 44.1kHz to 768kHz via USB.

With the volume control set to its maximum, a 1kHz digital signal at –20dBFS resulted in an output level of 4.52V into 8 ohms from the loudspeaker output, which is 0.3dB below the clipping voltage into this load with a 0dBFS signal. The HiFi Rose's gain architecture is well-arranged. Nevertheless, I turned off the speaker outputs for the digital input testing, examining the signal at the Pre outputs. Data at 0dBFS gave a maximum level of 2.08V from the preamplifier output.


Fig.11 HiFi Rose RS520, digital input, "Minimum Phase Fast Roll-off" filter, impulse response (one sample at 0dBFS, 44.1kHz sampling, 4ms time window).


Fig.12 HiFi Rose RS520, digital input, "Minimum Phase, Slow Roll-off" filter, impulse response (one sample at 0dBFS, 44.1kHz sampling, 4ms time window).


Fig.13 HiFi Rose RS520, digital input, "Apodizing Fast Roll-off" filter, impulse response (one sample at 0dBFS, 44.1kHz sampling, 4ms time window).


Fig.14 HiFi Rose RS520, digital input, "Corrected Minimum Phase Fast Roll-off" filter, impulse response (one sample at 0dBFS, 44.1kHz sampling, 4ms time window).

With S/PDIF and Ethernet data, the HiFi Rose's reconstruction filter can be set to one of seven types with the front-panel's touchscreen. With the filter set to "Minimum Phase Fast Roll-off," which was both the default filter and the only filter operating with USB data, the impulse response with 44.1kHz data (fig.11) was typical of a long minimum-phase type, with all the ringing following the single sample at 0dBFS. As expected, the "Minimum Phase Slow Roll-off" filter was a shorter minimum-phase type (fig.12). The "Apodizing Fast Roll-off" (fig.13), "Linear Phase Fast Roll-off," and "Brickwall" filters were all long linear-phase types, with equal amounts of ringing before and after the single high sample. The "Linear Phase Slow Roll-off" filter's impulse response was shorter, and the "Corrected Minimum Phase Fast Roll-off" (fig. 14) filter was the familiar hybrid type seen in our reviews of other digital processors that use the ESS Sabre chip set (footnote 1).


Fig.15 HiFi Rose RS520, digital input, "Minimum Phase Slow Roll-off" filter, wideband spectrum of white noise at –4dBFS (left channel red, right magenta) and 19.1kHz tone at 0dBFS (left blue, right cyan), with data sampled at 44.1kHz (20dB/vertical div.).


Fig.16 HiFi Rose RS520, digital input, "Corrected Minimum Phase Fast Roll-off" filter, wideband spectrum of white noise at –4dBFS (left channel red, right magenta) and 19.1kHz tone at 0dBFS (left blue, right cyan), with data sampled at 44.1kHz (20dB/vertical div.).


Fig.17 HiFi Rose RS520, digital input, "Slow Linear-Phase" and "Slow Minimum-Phase" filters, wideband spectrum of white noise at –4dBFS (left channel red, right magenta) and 19.1kHz tone at 0dBFS (left blue, right cyan), with data sampled at 44.1kHz (20dB/vertical div.).

With 44.1kHz-sampled white noise (fig.15, red and magenta traces), the RS520's "Minimum Phase Fast Roll-off" filter response starts to roll off above 20kHz but doesn't reach full stop-band suppression until 44.1kHz. Aliased images at 25kHz and 63.2kHz of a full-scale tone at 19.1kHz (blue and cyan traces) can be seen at –47dB, though the distortion harmonics of the 19.1kHz tone are all very low in level, at close to –80dB (0.01%). The "Linear Phase Fast Roll-off" filter behaved identically, but the "Corrected Minimum Phase Fast Roll-off," "Apodizing," and "Brickwall" filters all had a sharply defined null at half the sample rate (fig.16). The slow linear-phase and minimum-phase filters both rolled off slowly above the audioband, with a null at 44.1kHz (fig.17). With these two filters, the rolloff actually started slightly lower than the Nyquist frequency (half the sample rate). At 44.1kHz, for example, the rolloff started at 16kHz.


Fig.18 HiFi Rose RS520, digital input, spectrum with noise and spuriae of dithered 1kHz tone at –90dBFS with: 16-bit data (left channel cyan, right magenta), 24-bit data (left blue, right red) (20dB/vertical div.).


Fig.19 HiFi Rose RS520, digital input, waveform of undithered 16-bit, 1kHz sinewave at –90.31dBFS (left channel blue, right red).

Increasing the bit depth from 16 to 24 with a dithered 1kHz tone at –90dBFS lowered the noisefloor by 20dB (fig.18), meaning that the RS520's digital inputs offer between 19 and 20 bits' worth of resolution. With undithered data representing a tone at exactly –90.31dBFS (fig.19), the three DC voltage levels described by the data were well resolved, and the waveform was perfectly symmetrical (though overlaid with high-frequency noise).


Fig.20 HiFi Rose RS520, digital input, "Minimum Phase Slow Roll-off" filter. HF intermodulation spectrum, DC–30kHz, 19+20kHz at 0dBFS peak, sampled at 44.1kHz.

The second-order intermodulation product at 1kHz with an equal mix of 19 and 20kHz tones with a peak level of 0dBFS lay at a very low –100dB (0.001%, fig.20), and the higher-order products at 18kHz and 21kHz were almost 10dB lower in level. Though this graph was taken with a slow rolloff reconstruction filter, the aliased products at 24.1kHz and 25.1kHz are suppressed by more than 30dB.


Fig.21 HiFi Rose RS520, digital input, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz: 16-bit TosLink data (left channel blue, right red). Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz.

The HiFi Rose's rejection of word-clock jitter with 16-bit data was identical with USB, Ethernet, and S/PDIF data. While the odd-order harmonics of the LSB-level, low-frequency squarewave were all at the correct levels, indicated by the sloping green line in fig.21, the spectral spike that represents the high-level tone at one-quarter the sample rate has relatively strong sidebands at ±578Hz, of unknown origin.

HiFi Rose's RS520 amplifier offers generally excellent measured performance, though its class-D output stage has a higher level of ultrasonic noise than I usually find with such designs.—John Atkinson


Footnote 1: See, for example, fig.4 here.

COMPANY INFO
HiFi Rose
932 Yangjae-daero, Songpa-gu
Seoul
South Korea
(312) 841-4087
ARTICLE CONTENTS

COMMENTS
MZKM's picture

If the distortion/noise/jitter were better (not saying it’s for sure audible), this would be an excellent product. I’d say 8/10 as-is.

I’ve seen a few of these at the Florida Audio Expo, this model powering the MoFi SourcePoint 10s, really nice to have a nice display and HDMI out.

tenorman's picture

Very enjoyable, informative and well written review . Cheers

RvB's picture

Thanks for the kind words!

JRT's picture

The low resolution of the images included in this article make it overly difficult to read the rear panel markings. I subscribe to the magazine, and well understand that higher resolution images are available there, and I have also read the author's description in the text, but the following image excerpted from the marketing webpage for this product at the HiFi Rose website might be useful for easy reference to some others in your readership.

Also... I did not see mention of this in the article, but the marketing webpage for this product at the HiFi Rose website mentions that an external CDROM may be attached for direct real time playback, or to allow digital audio extraction (CD ripping) facilitated by HiFi Rose's proprietary variant of Google's Andriod operating system utilized in this streamer-DAC-integrated-amplifier.

Some other info which may be interesting to some:

edit:
After reading the article, and after reading the information on the marketing webpage for this product at the HiFi Rose website, and after downloading and reading the manual, it is still not clear as to whether or not the preamplifier outputs can be utilized to feed a signal to subwoofers while also using the power amplifiers' outputs to power a pair of loudspeakers, with all sharing the same volume control. Else the only way to send shared volume controlled signal to the subwoofers would be with high level signal from the power amplifier outputs powering the loudspeakers.

JRT's picture

The author mentioned, "...I'll note that the $5999 NAD M33, which I reviewed for a different publication, comes close; it's specified to produce 200W of Purifi Eigentakt power per channel with an 8 ohm load."

My understanding is that the various NAD products utilizing Purifi's Eigentakt modules (or authorized copies thereof manufactured under licensing agreement) have been utilizing the Purifi 1ET400A Eigentakt module which is limited to 25A peak current output. A more recent Purifi 1ET7040SA Eigentakt module can deliver higher 40A peak current with similarly very clean performance.

Buckeye Amplifiers is offering their "Purifi 1ET7040SA Amplifier, Monoblock v2" for $950 each (so $1900 for stereo pair), in direct sales. It is a no-frills design, especially in the external aesthetics, but does include balanced inputs (XLR ports) and switch selectable input gain.

As compared to the amplifier which is the subject of this review, the Purifi Eigentakt modules are very much more load invariant, and so can exhibit much flatter frequency response, reduced linear distortion.

edit:
A couple of other very good alternatives from Buckeye would be the Buckeye "Hypex NCx500 Amplifier, Monoblock" for $750 each, and the Buckeye "Hypex NCx500 Amplifier, 2-channel" amplifier for $1095.

Chick Korean's picture

The manufacturer initially rated this unit at 250WPC on their site. The US distributor's advertorial shortly thereafter for the same product rated it at 200wpc, so I emailed the distributor to inquire about the discrepancy and they informed me that '200W was more accurate'. The manufacturer subsequently changed the output rating on their website to 200 wpc.
At any rate, I eventually purchased one last year and I strongly objected to the user interface of the device itself and it's app. I returned it to the dealer and ordered a NAD M33 instead, with which I am very satisfied indeed. The built in BluOS is a dream and the app is still among the very best in the industry. BTW, the above mentioned M33 as reviewed in this publication by Kalman Rubinson in 2020 measured 255Wpc into 8 ohms and 460Wpc into 4 ohms. Another publication's bench test resulted in similar numbers. Yes, it is 40% more money than the Rose, but well worth the investment. And...it's a (Chinese manufactured) Canadian (engineered) product to boot.

https://www.stereophile.com/content/nad-masters-series-m33-streaming-integrated-amplifier

I should add that I thought the Hifi Rose sounded pretty good to me at first blush, although I did not keep it long enough to either break it in nor to familiarize myself with it's sound qualities over time. BTW, published spec at the Hifi Rose US website remains "200 watts x 2 into 8 ohms", and not 250.

Ortofan's picture

... comparison with the combination of a Cambridge CXN v2 Network Player and an NAD C 298 power amp (which uses Purifi modules)?

https://www.cambridgeaudio.com/usa/en/products/hi-fi/cx-series-2/cxn

https://nadelectronics.com/product/c298-stereo-power-amplifier/
https://www.stereophile.com/content/nad-c-298-power-amplifier

georgehifi's picture

"though its class-D output stage has a higher level of ultrasonic noise than I usually find with such designs.—John Atkinson"

You found the same with the RA180 of Rose's, also a GAN output device Class-D amp of theirs.
Yet the Technics SE-R1 also GAN device seems to have none of this from what I've seen, wonder if it has something to do with the 3 x higher switching frequency (1.5mhz) and output filtering they use on it to keep the left over switching noise rubbish and phase shift away from the 20hz to 50khz range?

Cheers George

mr_bill's picture

I see it streams Apple Music - which I have seen no other streamer do.
This is truly Apple Music and not just Airplay2?
If it really is Apple Music does it stream the high res Apple Music files too?
Does anyone know the answer?
Thanks,

JRT's picture

FiiO R7 ($700) streamer, DAC, preamplifier, headphone amplifier, etc. can stream high resolution lossless Apple Music or can stream from other sources to analog or digital outputs without forcing any sample rate conversion. Most Android-based implementations will force sample rate conversion to 48kHz, but this one does not.

comp.audiophile's picture

To clear up some question about the Apple Music implementation.

https://community.roseaudio.kr/t/information-about-apple-music-service/2892

In-app Apple Music does not support lossless streaming. Currently, the audio source of Apple Music Official SDK (Apple Music Kit) only supports AAC.

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