HiFi Rose RA180 integrated amplifier Measurements

Sidebar 3: Measurements

For logistical reasons, I measured a different sample of the HiFi Rose RA180—serial number ESL203AB000182—from the one auditioned by Julie Mullins. I performed the measurements with my Audio Precision SYS2722 system, examining the amplifier's performance in both normal mode and in bridged ("BTL") mode, following the instructions in the excellent manual. As Julie Mullins found, the RA180 doesn't recognize 5G Wi-Fi networks, but I was able to connect it to my Netgear NightHawk router's 2.4GHz network. I could control the RA180 with the RoseAMPConnect app on my iPhone, as well as with the remote control and the front-panel controls.

As the RA180's output stages operate in class-D, all the measurements other than frequency and RIAA responses were taken with Audio Precision's auxiliary AUX-0025 passive low-pass filter, which reduces the level of noise above 80kHz and eliminates noise above 200kHz. Without the filter, in normal mode, a very high 1.33V of ultrasonic noise was present at each pair of loudspeaker terminals, with a center frequency of 525kHz. The ultrasonic noise level rose to 1.6V in bridged mode. In both modes, when amplifying an input signal, the RA180 interfered with the reception of a portable FM radio that lives in the test lab.

I don't precondition class-D amplifiers before testing, but the top panel became warm after a few hours, its temperature measuring 104.6°F/40.4°C.

The RA180 preserved absolute polarity, ie, was noninverting, from both its balanced and single-ended line inputs in both normal and bridged modes. The maximum voltage gain at 1kHz into 8 ohms with the line inputs was 26dB, balanced, and 32dB, single-ended, in normal mode, and 6dB higher for both inputs in bridged mode. The balanced input impedance is specified as 44k ohms. I measured 43k ohms at all audio frequencies. The unbalanced input impedance measured 44.3k ohms at 20Hz and 1kHz, dropping inconsequentially to 29k ohms at 20kHz, compared with the specified 47k ohms.

The source impedance in normal mode, including the series resistance of 6' of speaker cable, was a low 0.1 ohms at low and midrange frequencies, rising to 0.4 ohms at the top of the audioband. The variation in the HiFi Rose amplifier's small-signal frequency response with our standard simulated loudspeaker (fig.1, gray trace) was a negligible ±0.1dB. Into 8 ohms (fig.1, blue and red traces), the RA180's response rose above the audioband, reaching +1.2dB at 65kHz, before sharply rolling off, reaching –3dB just above 100kHz. This peak is associated with a degree of overshoot in the RA180's reproduction of a 10kHz squarewave (fig.2), but there was no ringing. Into lower impedances the response starts to roll off in the top audio octave, with the most extreme result being into 2 ohms (fig.1, green trace), where the output at 20kHz is down by 2dB.


Fig.1 HiFi Rose RA180, normal mode, frequency response at 2.83V into: simulated loudspeaker load (gray), 8 ohms (left channel blue, right red), 4 ohms (left cyan, right magenta), and 2 ohms (green) (1dB/vertical div.).


Fig.2 HiFi Rose RA180, normal mode, small-signal 10kHz squarewave into 8 ohms.

The source impedance in bridged mode was higher, at 0.15 ohm at 20Hz and 1kHz, 1 ohm at 20kHz, doubling the variations in response with the simulated loudspeaker (not shown) and increasing the 20kHz rolloff into 2 ohms to –4dB. However, overshoot was now minimal in the bridged mode's reproduction of a 10kHz squarewave into 8 ohms. (In bridged mode, each channel is effectively driving half the connected load impedance, so the RA180's bridged response into 8 ohms was the same as the normal mode's response into 4 ohms; fig.1, cyan and magenta traces.)

Fig.1 was taken with the volume control set to its maximum, and the excellent channel matching was preserved at lower settings. However, a peculiar 1dB boost in the midrange and bass appeared at lower settings of the volume control (fig.3, blue and red traces). This behavior was consistent with balanced and single-ended inputs in both output modes. The cyan and magenta traces in fig.3 show the action of the Subsonic setting. The main outputs roll off rapidly below 100Hz, reaching –9dB at 40Hz. This rolloff seems too extreme for typical listening, so perhaps it could be used when adding a subwoofer to the system. However, there is no means of altering either the high-pass filter's frequency or its slope.


Fig.3 HiFi Rose RA180, normal mode, frequency response at 2.83V into 8 ohms with volume control set to the maximum (left channel green, right gray) and with subsonic filter activated (left cyan, right magenta), and with volume control set to –20dB (left blue, right red) (1dB/vertical div.).

The behavior of the bass and treble tone controls set to their maximum and minimum settings is shown in fig.4. Some overlap in their passbands can be seen in this graph, and the maximum cut or boost is higher than useful, at ±15dB in the treble and ±17.5dB in the bass. The Active Crossover controls adjust the turnover frequency level of the secondary amplifier outputs, which can be used to drive supertweeters. Fig.5 shows the behavior of this output with the frequency set to "0.85" and "2.17." The control's numerical values approximately coincide with the high-pass filter's –3dB frequency.


Fig.4 HiFi Rose RA180, normal mode, frequency response at 2.83V into 8 ohms with bass and treble controls set to the maximum, center, and minimum positions (left channel blue, right red) (5dB/vertical div.).


Fig.5 HiFi Rose RA180, supertweeter output, frequency response at 2.83V into 8 ohms with turnover frequency set to 0.85kHz (blue) and 2.17kHz (red) (2dB/vertical div.)

The RA180's channel separation (not shown) was 80dB in both directions below 2kHz, but the reading, taken with the Audio Precision low-pass filter, was affected by the presence of residual ultrasonic noise. This noise, which had a level of 1.5mV and a center frequency of 45kHz, is equivalent to an unweighted, wideband signal/noise ratio in normal mode (ref. 1W into 8 ohms, measured with the unbalanced inputs shorted to ground) of 66dB (average of the two channels). This ratio improved to 80dB when the measurement bandwidth was restricted to the audioband, and to 83.6dB when A-weighted. Spectral analysis of the low-frequency noisefloor while the HiFi Rose in normal mode drove a 1kHz tone at 1Wpc into 8 ohms with the volume control set to its maximum (fig.6) revealed a higher level of random noise in the left channel (blue trace) than the right (red). Repeating the measurements with the volume control set to –20dB reduced the left channel's noisefloor by 6dB (green trace) but the right channel's floor by 2dB (gray). In bridged mode (not shown), the levels of the low-frequency random noise in both channels increased by approximately 8dB.


Fig.6 HiFi Rose RA180, normal mode, spectrum of 1kHz sinewave, DC–1kHz, at 1Wpc into 8 ohms with volume control set to the maximum (left channel blue, right red) and to –20dB (left green, right gray) (linear frequency scale).

HiFi Rose specifies the RA180's maximum power in normal mode as 200Wpc into both 8 and 4 ohms, respectively equivalent to 23dBW and 20dBW. With our usual definition of clipping as being when the THD+noise reaches 1%, the HiFi Rose amplifier with two channels driven in normal mode exceeded its specified powers. It clipped at 290Wpc into 8 ohms (24.6dBW, fig.7) and 400Wpc into 4 ohms (23dBW, fig.8). In bridged mode with again two channels operating, the RA180 went into protection below the actual clipping point, turning off at 460Wpc into 8 ohms (26.6dBW, fig.9) and 322W into 4 ohms (22.1dBW).


Fig.7 HiFi Rose RA180, normal mode, left channel, distortion (%) vs 1kHz continuous output power into 8 ohms.


Fig.8 HiFi Rose RA180, normal mode, left channel, distortion (%) vs 1kHz continuous output power into 4 ohms.


Fig.9 HiFi Rose RA180, bridged mode, left channel, distortion (%) vs 1kHz continuous output power into 8 ohms.

The downward slope below 50W in figs.7–9 indicates that the measured THD+N percentage is dominated by noise. (A constant amount of noise becomes a smaller percentage of the measured level as the power increases.) Fig.10 shows how the percentage of THD+N varied with frequency in normal mode at 20V, which is equivalent to 50W into 8 ohms (blue and red traces) and 100W into 4 ohms (green, gray). The THD+N was very low in the bass and midrange, particularly in the right channel, but rose in the top audio octaves. In bridged mode, the performance into 8 ohms was similar to the normal mode's behavior into 4 ohms.


Fig.10 HiFi Rose RA180, normal mode, THD+N (%) vs frequency at 20V into: 8 ohms (left channel blue, right red) and 4 ohms (left green, right gray).

Fig.11 shows the distortion waveform in normal mode with a 1kHz sinewave at 50W into 8 ohms. The presence of bursts of switching noise at the waveform peaks makes interpretation difficult, though it looks as if the second harmonic is dominant. This was confirmed by spectral analysis (fig.12), though the third harmonic was almost as high in level. Repeating the analysis at the same power in bridged mode (fig.13) revealed that all the distortion harmonics were lower in level than they had been in normal mode, the third harmonic in particular.


Fig.11 HiFi Rose RA180, normal mode, left channel, 1kHz waveform at 50W into 8 ohms, 0.02% THD+N (top); distortion and noise waveform with fundamental notched out (bottom, not to scale).


Fig.12 HiFi Rose RA180, normal mode, spectrum of 50Hz sinewave, DC–1kHz, at 50Wpc into 8 ohms (left channel blue, right red; linear frequency scale).


Fig.13 HiFi Rose RA180, bridged mode, spectrum of 50Hz sinewave, DC–1kHz, at 50Wpc into 8 ohms (left channel blue, right red; linear frequency scale).

Intermodulation distortion was low in level. With the RA180 driving an equal mix of 19 and 20kHz tones at 100Wpc peak into 4 ohms in normal mode (fig.14), which will be equivalent to 50Wpc into 8 ohms in bridged mode, the 1kHz difference product lay close to –110dB in both channels (0.0003%), and while the higher-order products at 18 and 21kHz were higher in level, they still lay below –80dB (0.01%).


Fig.14 HiFi Rose RA180, normal mode, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 100Wpc peak into 4 ohms (left channel blue, right red; linear frequency scale).

Turning to the phono input's performance, this preserved absolute polarity in both MM and MC modes. The maximum gain measured at the loudspeaker outputs in normal mode was 78.4dB, MM, and 98.3dB, MC. Bridged mode increased both gains by 6dB. The input impedance, specified as 47k ohms, was 44k ohms at 20Hz and 1kHz, in both MM and MC modes, but dropped to 6.7k ohms at 20kHz, again in both modes.

I examined the phono input's adjustable equalization set to "RIAA" and the output measured at the speaker outputs without the Audio Precision low-pass filter. The error in the RA180's RIAA equalization (fig.15) was very low, with superb channel matching. This graph was taken with the volume control set to its maximum; at lower settings the midrange and bass were boosted by 1dB, as they had been for the line inputs. Assessed with the inputs shorted to ground but the volume control set to its maximum, the phono input's unweighted, wideband S/N ratios in MM mode were 72.3dB ref. 1kHz at 5mV in both channels. Restricting the measurement bandwidth to 22Hz–22kHz increased this ratio to 74.1dB, while switching in an A-weighting filter further increased the ratio to 80.6dB. The ratios in MC mode, ref. 1kHz at 0.5mV, were all 20dB lower, correlating with the 20dB increased gain in this mode, but the HiFi Rose's phono stage is still relatively quiet.


Fig.15 HiFi Rose RA180, phono input, response with RIAA correction (left channel blue, right red) (1dB/vertical div.).

The phono input's overload margins were respectable in both modes, at 13dB at 20Hz and 1kHz, ref. 1kHz at 5mV (MM) and at 0.5V (MC). However, the overload margin at 20kHz was disappointing, at –5dB, again ref. 1kHz at 5mV/0.5mV. In MM mode, an input signal at 20kHz reached 1% THD+N at 28mV, which will be marginal with normal-output moving magnet cartridges. (I performed the overload testing with the volume control set to –20dB to avoid clipping the RA180's output stage.) Harmonic distortion was very low via the phono input, the second and third harmonics with a 1kHz tone at 10mV respectively lying at –94dB (0.002%) and –100dB (0.001%) and all other harmonics at –110dB (0.0003%). And even at a peak level of 25mV, just below the MM mode's overload point, an equal mix of 19 and 20kHz tones produced a 1kHz difference product at –74dB (0.02%), with higher-order intermodulation products at negligible levels.

The HiFi Rose RA180 offers high powers in both its normal and bridged modes, especially into 4 ohms, with low, mainly benign second-harmonic distortion. I remain puzzled, however, by that 1dB boost in the midrange and bass at low volume control settings, by the higher-than-usual level of ultrasonic noise at the loudspeaker outputs, and by the phono input's limited overload margin at the top of the audioband.—John Atkinson

HiFi Rose
US distributor: MoFi Distribution
1881 W. Bryn Mawr Ave.
Chicago, IL 60660
(312) 841-4087

Jack L's picture


Indeed. I still recall my gourmet friend who goes for international foods on his offshore business trips, told me:

"Japanese cuisines are for the look (artistic-like display on the plate), Chinese food is for the taste & western cuisines are for the smell."

Yes, many auido fans like to "listen" with their eyes first. But not for me, in any audio shows, if the music does not sound right before I walk in the demo room, I don't even both to walk in at all.

If the music comes out from the demo room sounds OK, then I would walk in & sit down & listen for a few minutes. If it sounds really nice, then I would start to ask questions.

Otherwsie, I would just say thanks & walk out without further questions. That's it!

Likewise, for any audio studios ! Sound always comes first before I bother the look & price.

I design/built/upgraded audio rig at home looks like cheap crap, yet I love spend numberless hours of my leisure time there to enjoy the music masters re-performance there.

Listening with my own ears is believing

Jack L

JRT's picture

Normal human brain function, in dealing with various cognitive dissonance, can place visual perception ahead of hearing perception, where visual perception can change hearing perception.

The McGurk effect provides example of some of this.


As for the subject matter of this review, I would not want the gimmickry and whimsical aesthetics of this thing, as it reminds me too much of the old Rube Goldberg cartoons. I would rather have something far less integrated with cleaner functional aesthetics and better performance.

Jack L's picture


OK. You don't have to throw me the book !

It's common sense for any mature music lovers, like yours truly.
That's why I use my ears only for gauging any audios to minimize "McGurk effect" & the likes.

It also has brought in the huge controversail audio blind tests.

Music is for my ears for my enjoyment gauging on live performance. I don't give a rat's ass to whoever saying whatever else.

Listening with my own ears to the music is believing

Jack L

Jack L's picture


JHL's picture

...when needing erudition on (snort)


normal human brain function

which I assure you I do all the damn time, is to hunt up the initials JRT in a comment thread.

LOL. The very pretense.

You even summarize like a drone, jeenyus, as if Normal Human Brain Function could appreciate art. Or "better performance". I have zero doubt now but that it'd McGurk both. Is that the term I want? McGurk?

"Self-delusion"? For years I watched gasbags vomit on normal human engagement in music and the technical arts and applied sciences, but now? Not so much.

Long-time listener's picture

Research has also shown that people with "normal brain function" can overcome biases when they are made aware of them. If we choose to consciously reject visual influence and concentrate on what we hear instead, we can do so. It's not a big problem for intelligent people.

Indydan's picture

Hey Jack, crapping with your own butt is believing...

Jack L's picture


Indydan's picture

Hey Jack, where you at? Your wife is looking for you...

Jack L's picture


Julie Mullins's picture

Yes, many audio fans like to "listen" with their eyes first. But not for me, in any audio shows, if the music does not sound right before I walk in the demo room, I don't even both to walk in at all.

If the music comes out from the demo room sounds OK, then I would walk in & sit down & listen for a few minutes.

In general, I generally don't tend to enter rooms where the sound from outside doesn't capture my interest—unless something really captures my eyes (or I'm required to for an assignment).

Also, when I listen at home I usually close my eyes, especially for critical listening. So at that point, the aesthetics become irrelevant. BUT I prefer and enjoy having components that appeal to my visual/aesthetic sense as well; I'm living with them in my space and would simply rather have something attractive around.

Jack L's picture


Why not? Just like stylish furniture - lifestyle. Nobody can challenge it.

But my point is: sound always comes before the exterior design of the product. For yours truly, it is the sound dicates me to choose the right one for my budget & exterior design is only the bonus which is always welcome.

Listening is believing

Jack L

Archimago's picture

Hmmm. I appreciate the mechanics. The VU meters look nice. Strong nods to the '70s vintage esthetics, but obviously more "flowery".

IMO, this is clearly overdone; reminds me of the overwrought CGI effects in some Asian (primarily Chinese) movies which lack finesse. Much of it just screams "appearance for appearance sake" which I guess is OK if one has an affinity to it and truly "love" that look.

I fear that this kind of look will not age well though. I would suggest to HiFi Rose that "less is more". Aim for elegance rather than risk looking tacky as they're doing right now with this (again, IMO).

It would be interesting to see in a poll if the general audio-loving public likes this front panel!

Archimago's picture

Figured I'd poll the folks over on Steve Hoffman Forums here:

Feel free to share your opinion!

Jack L's picture


Is such polling necessary ?????

Any audio designers want to put their personality signature on the front panel designs. This is its value & presitige & should not be challenged.

Anybody ever ever challenged of the beauty of Mona Lisa ?

Come on, get real !

Jack L

Archimago's picture

Since when was this device some kind of "fine art" where one is supposed to respect the creative integrity of the design team?

Of course the appearance can be questioned! When you look at that thing, does it look like form follows function? Or maybe just a little too much flight of fancy?

It's consumer electronics. Consumers have an opinion and in fact the final say as to whether they care for it. Nothing wrong with having a poll on it and in fact, I hope the design team made sure to engage some consumer market research to make sure this targeted the intended audience.

Jack L's picture


Mona Lisa is a priceless historic fine art which has been open for appreciation to the public at large in Palace of Versailles near Paris. I still recall my wife & I got to line up for an hour or so to to get a view of the small painting from a fence-off distance of some 15 ft !!!!

Any commercial design is still some art - applied art. It may not suit everybody who always gets its own preference & like.

Like coffee, many love black & yet many love double (milk)/double (sugar) instead. So do we need to get a poll on it?

Jack L

windansea's picture

Looks like an airline cockpit to me. I would have loved this as a child. But now I think it has too much surplusage and all I want is a power switch and volume knob.

But the active crossover and biamping option sound awesome to me. I love that idea. I've wanted to biamp my time windows with active crossovers but the expense and hassle have exceeded my limits. This all-in-one option could be perfect for me.

Julie Mullins's picture

There is a lot going on there: It's packed with knobs and switches. It does make kind of an "extreme" statement, but that's part of what makes it unique.

bhkat's picture

Front panel looks like the guy who designs Nagra equipment took some magic mushrooms before designing the front panel.

MontyM's picture

Hi Julie. The RA180 was set up in one of the rooms of my local HiFi store when I visited a couple weeks ago. I agree that the look and feel of the thing is great; a conversation starter for sure, if nothing else. Sonically, not my cup of tea, but visually it definitely stood out from the other integrated amps in its price range. I generally prefer a form follows function design aesthetic, but I certainly appreciate a bit of whimsy now and again. Thanks for the review.

Julie Mullins's picture

I generally prefer a form follows function design aesthetic, but I certainly appreciate a bit of whimsy now and again.

Although it is functional in its form: Almost everything is right there on the front panel. And I agree that a bit of whimsy in a hobby/industry that sometimes takes itself too seriously is a positive thing!

Electrophone's picture

I had the opportunity to manually operate the RA-180's interesting volume control mechanism at the local dealer and am disappointed that the process is not as refined as expected. The gears don't run as smoothly as expected at this price point, leaving the impression of under-engineering.

PeterG's picture

A fun description of a cool visual design, but the central question is left unanswered--how does the amp sound compared to competition? This is especially important when reviewing a Class D where conventional wisdom is that although they are more efficient/economical, they still cannot match A or AB for the serious listener

Julie Mullins's picture

Thanks for commenting, PeterG. In part because this differs from a "typical" Class D amp in that it's built around more modern Gallium Nitride (GaN) transistors rather than silicon ones, I decided to talk about those sonic differences (and benefits) rather than focusing on direct comparisons or doing a "shoot-out." Also, I've only heard a few other GaN-based amps, such as the Technics SU-G700M2 integrated amp (and only briefly, at a show or two) that use GaN transistors—something I'd mentioned in an earlier draft of this review (that didn't appear in the final version).

windansea's picture

keep writing these excellent reviews-- they are a breath of fresh air with zero snootiness and plenty of relevant observations for those of us considering whether to purchase the reviewed product.

Julie Mullins's picture

I appreciate your kind words. More to come...

PeterG's picture

Thanks, Julie. I guess we differ on the definition of competition. I am agnostic wrt architecture--I do not really care too much if an amp is A, AB, D, tubes, SS....But I care A LOT about an amp compares to other amps in its general price range. (BTW, I think we had a similar exchange on the marble(?) speakers you reviewed a few months ago) Rock on!

Julie Mullins's picture

You make a fair comment. I'm also "agnostic" in the sense that I don't have a strong bias (pun intended) for or against tube amps or various solid-state types or topologies. Because I don't have a wide array of amps on-hand (just a few), I'd be going mostly from memory.
It's another good reason for me to keep visiting dealers, attending audio shows, checking out friends' systems, etc. to hear as much new and different gear as possible and keep staying up-to-date.
(BTW, those other speakers I reviewed that you mentioned were made of granite, made by Acora Acoustics.)

Glotz's picture

The review, of course.

Will you or another reviewer report on the Mytek Empire Monoblocks? GaN-based amplifiers are very intriguing...

mns3dhm's picture

This is a component that, should a friend buy one and ask if I'd like to listen, I'd be 'shit yeah!'. I would probably wind-up annoying said friend by asking them to run through its myriad of setup and operational options. Kinda the opposite of straight wire with gain. Thanks for the review.

Jack L's picture


Agreed ! Who needs thousands of watts for decent music let alone the musicality of Class-Ds ? I don't & would never !!

FYI, my humble dirt-cheap home-brew zero local/global NFB class-A SET delivering only 5W per channel working hand-in-hand with 3 x100W active subwoofers (L, R, L+R) can deliver 103db(C) SPL musicality nooo sweat !

Be smartly ahead of the game !

Listening to class-A SET is believing

Jack L

barfle's picture

Like others, I’m reminded of a Nagra deck. Lots of meters and buttons and knobs, and I certainly appreciate design, but it might be a bit much and might not age well. But very, very groovy.

barfle's picture

Like others, I’m reminded of a Nagra deck. Lots of meters and buttons and knobs, and I certainly appreciate design, but it might be a bit much and might not age well. But very, very groovy.

barfle's picture

Like others, I’m reminded of a Nagra deck. Lots of meters and buttons and knobs, and I certainly appreciate design, but it might be a bit much and might not age well. But very, very groovy.

SocProf's picture

I just got the latest Recommended Components issue. I'm surprised that the RA 180 was given a Class B rating and not a Class A rating. I assumed it would be a step up from my much cheaper Marantz Model 30, which earned a Class A rating. What are its shortcomings?

Also, I wonder if the bi-amping function is better suited for a 2-way bookshelf (where the tweeter gets its own binding post) than a 3-way floorstander (where the tweeter is grouped with the midrange driver). The high pass filter might actually be able to accomplish something useful for the former--protecting the tweeter from anything other than high frequency signals.

steve59's picture

The looks say swiss watch quality, the feel of the controls says, built to a price.

Markedly's picture

Visually, the amp reminds me a little of the Simpson's episode where Homer designs his perfect car.