Riviera Levante integrated amplifier Measurements

Sidebar 3: Measurements

When I unpacked the Riviera Levante amplifier and lifted it onto the test bench, it struck me that this is actually eight amplifiers in one. It has balanced and single-ended line-level inputs. Its output stage can be operated in class-A or class-AB. It was supplied with two choices for the two input stage ECC81/12AT7 tubes: vintage Mullards or modern JJs. Add to those variations that the Levante has a headphone output and an optional phono stage (not fitted to the review sample), and it became clear that I had a lot of testing ahead of me.

I decided to focus on the Riviera amplifier's behavior with the Mullard tubes and the unbalanced inputs, performing every test in both of the output-stage modes. I then repeated some of the tests with the balanced inputs and finally looked at how the amplifier's behavior with the JJ tubes differed from how it had performed with the Mullard tubes. All the testing was performed with my Audio Precision SYS2722 system.

I first preconditioned the Riviera Levante by following the CEA's recommendation of operating it at one-eighth the specified class-AB power into 8 ohms for 30 minutes. At the end of that time, the heatsink temperature was 108.3°F (42.4°C) and that of the top and front panels was 92.5°F (33.6°C). Switching to class-A operation, the heatsink temperature had increased slightly after another 30 minutes, to 113.1°F (45.1°C). While I was preconditioning the amplifier, I measured the output device rail voltages. They were ±29V in class-A, ±50V in class-AB.

The amplifier inverted absolute polarity with all its inputs at both the loudspeaker and headphone outputs. The maximum gain into 8 ohms was lower than average for an integrated amplifier, at 36.6dB in class-A and 36.35dB in class-AB for both balanced and unbalanced inputs. The maximum gain at the headphone output was 21.6dB for both types of input. Changing to the JJ tubes reduced these gains by 1dB.

The unbalanced input impedance was 44k ohms at 20Hz and 1kHz with the Mullard tubes, dropping to 36k ohms at 20kHz. The balanced input impedance was 42k ohms across the audioband. With the JJ tubes the unbalanced input impedance was 34k ohms at 20Hz and 1kHz, 30k ohms at 20kHz.

The headphone output impedance was moderately low, at 18 ohms across the audioband. Set to class-A operation, the Levante's output impedance at the loudspeaker terminals was 0.5 ohm from 20Hz to 20kHz. In class-AB, the output impedance was slightly higher, at 0.65 ohm at all audio frequencies. (These figures include the series impedance of 6' of spaced-pair loudspeaker cable.) In class-A mode, the modulation of the amplifier's frequency response, due to the Ohm's law interaction between the source impedance and the impedance of my standard simulated loudspeaker, was ±0.4dB (fig.1, gray trace). The response into an 8 ohm resistive load (fig.1, blue and red traces) was down by 3dB at 180kHz, which correlates with the Riviera's accurate reproduction of a 10kHz squarewave into that load (fig.2). Figs.1 and 2 were taken with the unbalanced inputs, the Mullard tubes, class-A mode, and the volume control set to its maximum. The frequency and squarewave responses were identical with the JJ tubes, in class-AB, and with the balanced inputs. With the volume control set to –20dB, the high-frequency –3dB point dropped to 110kHz, but the audioband response remained flat. Measured at the headphone output, the response was down by just 1dB at 200kHz.


Fig.1 Riviera Levante, Mullard tubes, class-A, volume control set to maximum, frequency response at 2.83V into: simulated loudspeaker load (right gray), 8 ohms (left channel blue, right red) 4 ohms (left cyan, right magenta), (left green) (1dB/vertical div.).


Fig.2 Riviera Levante, Mullard tubes, class-A, small-signal 10kHz squarewave into 8 ohms.

Channel separation was okay at 70dB in both directions below 3kHz, dropping to 53dB at the top of the audioband. The Riviera's unweighted, wideband signal/noise ratio, taken with the unbalanced inputs shorted to ground but the volume control set to its maximum, was 70.6dB ref. 2.83V into 8 ohms (average of both channels) in both class-A and class-AB modes. This ratio improved to 72dB when the measurement bandwidth was restricted to the audioband, and to 80dB when A-weighted. The background noise included spuriae at 60Hz and its even- and odd-order harmonics (fig.3), the latter higher in level than the former, particularly in the left channel (blue trace). (The odd-order spuriae are probably due to magnetic interference from the massive power transformer.)


Fig.3 Riviera Levante, Mullard tubes, class-A, spectrum of 1kHz sinewave, DC–1kHz, at 1W into 8 ohms, volume control set to maximum (left channel blue, right red; linear frequency scale).

With both channels driven, the Levante's maximum power in class-A is specified as 30Wpc into 8 ohms and 60Wpc into 4 ohms (both powers equivalent to 14.8dBW). We define clipping as when the THD+noise in an amplifier's output reaches 1%. By that standard, the Levante didn't meet its specified powers, the 1% THD+N power measuring 16Wpc into 8 ohms (12dBW, fig.4) and 21.3Wpc into 4 ohms (10.27dBW, fig.5). However, relaxing the criterion to 3% THD+N, the Riviera amplifier clipped at 49Wpc into 8 ohms (16.9dBW) and 79Wpc into 4 ohms (16dBW). The picture was similar in class-AB. The Levante delivered 12Wpc into 8 ohms (10.1dBW) at 1% THD+N, 125Wpc at 3% (21dBW, fig.6), and 18Wpc into 4 ohms (9.54dBW) at 1% and 195Wpc into 4 ohms at 3% (19.9dBW, fig.7). The AC mains voltage was 119.1V with the amplifier clipping in class-A into 4 ohms.


Fig.4 Riviera Levante, Mullard tubes, class-A, distortion (%) vs 1kHz continuous output power into 8 ohms.


Fig.5 Riviera Levante, Mullard tubes, class-A, distortion (%) vs 1kHz continuous output power into 4 ohms.


Fig.6 Riviera Levante, Mullard tubes, class-AB, distortion (%) vs 1kHz continuous output power into 8 ohms.


Fig.7 Riviera Levante, Mullard tubes, class-AB, distortion (%) vs 1kHz continuous output power into 4 ohms.

The upward slope of the traces below the actual clipping power in figs.4–7 indicates that the distortion increases in almost a linear manner with increasing power before the onset of actual waveform clipping. This will be due to what is called a "bent" transfer function. (The transfer function of an amplifier with no distortion is a straight line.) I suspect that this bent function will be due to the input tube rather than the amplifier's output stage. I examined how the THD+N percentage changed with frequency at 4.89V, which is equivalent to 3W into 8 ohms, 6W into 4 ohms, and 12W into 2 ohms. With the Mullard tubes the distortion into 8 ohms (fig.8, blue and red traces) was 0.47% at low and middle frequencies, rising slightly in the treble. It also rose into 4 ohms (cyan, magenta traces) and into 2 ohms (green, gray traces). The distortion was slightly lower with the JJ tubes (fig.9), but the behavior was otherwise identical.


Fig.8 Riviera Levante, Mullard tubes, class-A, THD+N (%) vs frequency at 4.89V into: 8 ohms (left channel blue, right red), 4 ohms (left cyan, right magenta), 2 ohms (left green, right gray).


Fig.9 Riviera Levante, JJ tubes, class-A, THD+N (%) vs frequency at 4.89V into: 8 ohms (left channel blue, right red), 4 ohms (left cyan, right magenta), 2 ohms (left green, right gray).

These levels of distortion would be very audible if they comprised the fifth and higher harmonics (footnote 1). However, fig.10 indicates that the relatively subjectively benign second harmonic was dominant in both class-A and class-AB output modes. This waveform graph was taken with the Mullard tubes. Though HR found the JJ tubes to sound different from the Mullards, the JJs produced an almost identical THD+N waveform (fig.11). This was confirmed by the spectra of the amplifier's output at moderate power into 8 ohms with the Mullard tubes (fig.12) and JJ tubes (fig.13). The second harmonic is by far the highest in level, at –40dB (1%) with the Mullards and –43dB (0.7%) with the JJs. The second was also by far the highest-level harmonic present in the headphone output, at –47dB (0.42%, fig.14) at 1V into 300 ohms. Finally, when the Levante drove an equal mix of 19 and 20kHz tones at 10W peak into 8 ohms in either class-A or class-AB with both Mullard and JJ tubes, the second-order difference product at 1kHz lay at –44dB (0.6%, fig.15), with the higher-order intermodulation products at 18kHz and 21kHz 10dB lower in level. At the same voltage into 4 ohms, the intermodulation products rose by 3dB.


Fig.10 Riviera Levante, Mullard tubes, class-A, 1kHz waveform at 10W into 8 ohms, 0.95% THD+N (top); distortion and noise waveform with fundamental notched out (bottom, not to scale).


Fig.11 Riviera Levante, JJ tubes, class-A, 1kHz waveform at 10W into 8 ohms, 0.75% THD+N (top); distortion and noise waveform with fundamental notched out (bottom, not to scale).


Fig.12 Riviera Levante, Mullard tubes, class-A, spectrum of 50Hz sinewave, DC–1kHz, at 10W into 8 ohms (left channel blue, right red; linear frequency scale).


Fig.13 Riviera Levante, JJ tubes, class-A, spectrum of 50Hz sinewave, DC–1kHz, at 10W into 8 ohms (left channel blue, right red; linear frequency scale).


Fig.14 Riviera Levante, JJ tubes, headphone output, spectrum of 50Hz sinewave, DC–1kHz, at 10W into 8 ohms (left channel blue, right red; linear frequency scale).


Fig.15 Riviera Levante, Mullard tubes, class-A, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 10W peak into 8 ohms (left channel blue, right red; linear frequency scale).

With its output stage capable of being switched between class-A and class-AB operation, Riviera's Levante reminded me of the Marantz MA-5 amplifier that I reviewed for Hi-Fi News magazine in August 1983, which, like the Levante, could output 30W in class-A and 120W in class-AB. But unlike that Marantz, which featured conventional levels of negative feedback, the Levante's measured behavior is dominated by the designer's decision not to use feedback, especially around the input tubes. His reasons for doing so are discussed in the review, but my experience has been that the resultant harmonic signature will lend this amplifier a distinctive sonic character.—John Atkinson

Footnote 1: I created tracks on Stereophile's Test CD 2 to allow listeners to hear at what percentage of second, third, and seventh harmonic they become aware of the distortion.
Riviera Audio Laboratories s.r.l.
US distributor: Tone Imports
(646) 425-7800

georgehifi's picture

"Quote: This input stage is polarized not to be a perfect push-pull but to have the distortion shape of the ear"

I'd love to see how that distortion shape of the ear was measured?

Cheers George

Jack L's picture


Me too. I'm very interested to know how our ears are measured.

IMO, it is either the amp maker's trade SECRET or simply trumpet-blowing
sales pitch !

For $16,500, only JJ or Russian Mullard triodes are provided. Profiteering here goes ! Give us consumers a break, please.

Even my humble home-brew phono-preamp, I purposely used Mullard ECC82 made in U.K. for the linestage. U.K. Mullards sound better than another other makes, IMO.

Jack L

Herb Reichert's picture

Google that question?



Charles E Flynn's picture


You are all familiar with the skull and crossbones graphic used to denote poisons on product labels.

Your assignment, should you decide to accept it, is to design a graphic suitable for use in the reviews of audio products that indicates that the highly-experienced John Atkinson has determined that an amplifier has a "distinctive sonic character" or a loudspeaker has a "'tailored' frequency response in the treble".

Should you choose not to participate in this challenge, which your faculty acknowledges involves unusual subtlety, it will have no effect on your grade.

johnnythunder1's picture

it is imported by Tone Imports. Luscious sound and gorgeous design. Italian audio equipment is always interesting to look at and to listen to. Romantic and euphonic. Sometimes the design is excessive and a little "Gucci" but other times just beautiful like a handmade instrument.

JRT's picture

On this non-inexpensive ($16.5k) integrated amplifier, I don't much like the seemingly low budget amateurish design aesthetics. The front panel design is an inconsistent hodgepodge of text fonts, sizes, directions of orientation and marking methods on a panel with a disorganized haphazard layout of the control switchgear. The industrial design aesthetics matter, and since they obviously lack enough talent in that, they should hire or rent a skilled professional industrial design consultant. There is certainly no shortage of that talent in Italy.

Also, integrated amplifiers are a bundle of compromises. While integration does reduce manufacturing costs and simplifies consumer's system design and space claim, it comes at the expense of a major reduction in system design flexibility, reduced optimization to the requirements of a specific application, and with greatly reduced long term reliability.

Expanding on the point of reduced system reliability, consider that once this device is out of production, out of warranty, and suffering obsolescence in the internal monolithic integrated electronic components (especially in the control subsystem), when an important functionality eventually fails the entire unit becomes trash, dumpster fodder. With separates, a failed subsystem component can be replaced or upgraded when and if it fails and cannot be repaired, and only that small fraction of the whole system becomes dumpster fodder.

In comparison to this integrated amplifier, some very good separate components can be had within similar $16.5k budget.

For example, look at the US made Schiit Freya plus for $949, which includes relay switched resistor network stepped attenuation. In addition to the balanced inputs, the unit also converts single ended inputs to a differential throughput and balanced output. It includes quiet low distortion solid state gain stages and a bypassable/defeatable pair of circlotron tube stages using 6AS7 dual triodes. That allows for a choice of either clean gain or bypassable added tube based euphonic distortion effects, as desired for different various program material.

Maybe add a pair of US made Benchmark AHB2 amplifiers configured as bridged monoblocks at $3k each for high purity gain and balanced inputs.

You could also add a Schiit Modi 3E external DAC for $129, and a short pair of well made inexpensive nonesoteric low capacitance single ended interconnects (eg. under $40 for the pair of 18 inch interconnects from Blue Jeans Cable).

Also add a couple of balanced audio cables consisting of some non-esoteric and moderately priced well made low capacitance shielded twisted pair or StarQuad terminated with XLR connectors. Maybe take advantage of the low noise balanced interconnection by locatimg the amplifiers adjacent to the loudspeakers, allowing use of short loudspeaker cables. With balanced interconnection, there is no need to locate the front end near the amplifiers.

Sum total is well under half of the $16.5k budget with less noise, lower distortion (when not using tube based stages), and with use of separates providing flexibility of system modularity and with that improved reliability via the possibility of future replacement or upgrade of the separate components.

The balance of the budget could buy better loudspeakers and/or better subwoofers and/or a couple of PSI Audio AVA C20 active bass traps and/or passive room acoustics treatments. ...things that matter significantly in playback system performance.

johnnythunder1's picture

tells you how to build a watch. thank you for the filibuster reply to a simple comment about a well reviewed product (by a reviewer who's ears I trust.) I'm happy that you love Benchmark audio products. Personally I think they look like power supplies for welding or medical equipment. I'm sure they give you a lot for your money and give you musical pleasure. Thanks for telling me how we all should think and feel about reproduced music.

MatthewT's picture

"Stop liking what I don't like."

johnnythunder1's picture

that was awesome !

Govna's picture

The measurement mafia is sharpening their knives ;)

Not surprisingly Michael Lavorgna gushed over this amp as well. Look forward to hearing one.

tonykaz's picture

It sure is pretty.

It could sit nearby the LazyBoy, warming the heart, with it's Chrome & Gold.

but so could a pair of gorgeous Woo Fireflys which probably look better. ( to my vintage taste )

I'd like to see some assurances that the Silk-Screening on the Front panel will survive usage considering todays environmental limitations banning old school enamels in favour of water based inks. A safe route would have the panel laser etched instead of printed .

I'd like to discover and learn what System the Manufacturer intended for revealing this device's full potential ! ( not that I'd purchase , hmm )

Tony in Florida

JRT's picture

...is available in black, white, and various other colors, exhibits good permanency, and is well suited to applications such as silk screened printing on the front face of control panels, in filling milled or deeply engraved markings, and in ink stamping reference designations and item identifications on other surfaces.

tonykaz's picture

This stuff is pricy compared to standard Nazdar Solvent based Inks. ( x4 )

It still is Solvent based and they do promise good adhesion.

It looks like the front panel is Silk Screened which has me thinking that epoxy setup/curing would ruin the screen so batch printing involves shooting a new screen.

We have laser etchers now-a-days, at the price of this device I'd think they'd etch instead of print.

I've had the letters fall/wear off touch panels. ( funny tape labels end up on the fronts )

We could call the Manufacturer in Italy, presume English is spoken but I'd bet their Chassis provider doesn't know what ink is used or how well it's applied.

Tony in Florida

LarryRS's picture

Herb wrote: "but in the higher audiophile ranks, this type of amplifier is not common. Besides the Rogue, the only other hybrid in Stereophile's Recommended Components is the $93k/pair Ypsilon Hyperion Monoblock." The Lamm Industries M1.2 Monoblocks, PS Audio BHK Signature 300 Monoblocks and PS Audio Stellar M1200 Monobocks are also on the Recommended Components list.

Herb Reichert's picture

for the big 'catch' . . .

Now I must call Paul and Vladimir and beg forgiveness.

all hail the hybrid !


LarryRS's picture

Probably Bascom too, though Paul I'm sure can pass it along.

Glotz's picture

I miss those amps and pre's... sigh.

donnedonne's picture

Herb - Great review as always. I own and love one of these. The option to fine-tune through a couple of relatively cheap tubes is a fun feature. Seems like new-production Russian Mullards were used in the review - I'd love to try some NOS British ones.

Might be fun to read a follow-up by one of the folks who have reviewed Lamm. The Lamm gear is (even) more expensive, but it's interesting that the brains and ears behind Lamm and Riviera have seemingly similar listening/measurement theories.


Glotz's picture

Novel design and well implemented.

Glotz's picture

After this and JVS' newest darTZeel reviews, I remain convinced they are the best delivery methods.

SteveM324's picture

I really like hybrid amps and I owned a Counterpoint SA220 back around 1994 and used it to power Apogee Centaur Major speakers. I have a hybrid Audio By Van Alstine 600R power amp that uses 2 12AT7 tubes and it has a MOSFET output stage that provides 300 w/Ch. I didn't like the stock JJ tubes in this amp so I replaced them with NOS Mullard 4024 tubes. This amp is a great value at $3500. Stereophile should review Audio By Van Alstine products. TAS reviews AVA products and the 600R and the FET Valve CF preamp are on their recommended list. Since Stereophile reviews other direct from manufacturer products such as Tekton speakers, they should start reviewing AVA products. I'm not affiliated with AVA in any way. Maybe I'm unaware of the history of AVA and Stereophile. Steve Guttenberg reviewed one of their least expensive 60 w/Ch amps recently and raved about it.

Jason Victor Serinus's picture

Several products ago, I reviewed a 176 lb. stereo amplifier. Now a friend and I just tried to install a 90 lb. component, only to discover that it's 1/2" too wide for my rack. Art Dudley, please shine a bit of your light on this poor acolyte. As you do, please remember how much you are missed.