RIVIERA AUDIO LABS AFM-50 POWER AMPLIFIER REVIEW PART ONE


Its not a secret, that I have a soft spot for exotic, greatly designed high-end audio products in all forms and shapes. When Silvio Delfino approached me if I would be interested in a test and review, I was not needed to be asked twice to jump on board. 

Even the quick glancing at the AFM-50 reveals, that there is something very different going on with these Italian hybrid creations. In the world of so many replications Riviera Audio Labs have managed to encompass its own spirit with an instantly recognizable aesthetic cues. 

It’s not exactly easy to be be original when it comes to the industrial design, yet Rivera design team expertly encapsulated the Italian aura not only with their AFM-50 power amplifiers, but with the complete line of products.

THE BRAND - THE TEAM


Riviera Audio Laboratories s.r.l. was founded in January 2017: it aims to produce innovative quality products for the highest end of the audio market.


Riviera has brought together the complementary skills of three members to produce audio components aimed at bringing new advances in analogue sound, merging passion, technology and innovation.


First and foremost, Luca Chiomenti is the company’s audio designer and engineer. He has been designing and manufacturing Hi-Fi systems since the 1990s, combining both technical expertise and craftsmanship which now find their expression in Riviera products.


Silvio Delfino deals with imports and exports. He has tried and tested experience in global marketing and sales in the field of Italian audio high end. He now turns his considerable expertise to Riviera.


Marco Muzio is an expert in industrial design and rendering for mechanical applications; he brings to Riviera his outstanding skills to chassis design and manufacturing.

THE RIVIERA WAY


It’s an open secret to every serious audio designer that relying on traditional measurements does not necessarily guarantee audio nirvana; that is why Riviera places such importance in listening to its amplifiers.


In fact, Riviera restarts from the basics and takes great pride in having studied the literature of electroacoustic written in the last hundred years. It was necessary to redefine the electrical characteristics of an audio amplifier. Riviera’s benchmark remains the live listening experience: Riviera’s philosophy is that a Hi-Fi system must be able to reproduce a sound event which is the closest possible to what a listener would hear in a live context.


To achieve these goals Riviera has made specific choices regarding circuitry and applied technologies:
  • Zero Overall Feedback
  • “Class A” amplification at every stage
  • Hybrid circuitry, with valves (triodes) for signal processing and solid state (BJT and Mosfets) for the power stage
  • Electrical values chosen by listening

Luca Chiomenti explains further his history and what have driven him to design these hybrid power amplifiers...

"I presented my first design for industrial production to the public about 25 years ago. In the introduction I wrote: “We believe that, in the last 20 years, high fidelity has ended up in a blind alley. There is a pointless race to technical perfection. For too much time the final goal seemed to be to reach the limits of measuring instruments. This choice seemed to have forgotten the real function of an audio amplifier: to reproduce the music through an electroacoustic transducer.”


"25 years later the situation appeared even more confused. Today, there is a general agreement that the commonly used tests for audio frequency amplifiers do not correlate with the audio quality. Audiophiles largely reject technical specifications and bench tests as an indicator of the subjective sound quality. Nevertheless, perfect bench tests seem to be essential for any product on the market."


"I cannot synthesize over 25 years of (my personal) study and research on the relation between subjective experience and laboratory measurements. I based my studies on direct experiments and hundreds of pages of bibliography covering over 80 years. I hope to complete a white paper on this argument soon. Now I will try to give some focal points that are the foundation for the Riviera design"...


We must go back to the beginning. An audio amplifier must reproduce a signal with the highest fidelity… for the human ear, not for instruments. This is the point. It is critical: 

1. To understand some aspects of the functioning of the human earing system and, consequently... 
2. To define the characteristics of the reproduced signal for the human ear, not for an electronic measuring system. 


Let’s start from the ear...
  1. When we ear a pure tone, many studies have verified the creation of harmonics inside the ear and, specifically, in the cochlea. This is not a new discovery. First reports on this distortion are from Fletcher (yes, the famous of the Fletcher-Munson curve, in the ‘20s); more precise reports came from H.F. Olson (Acoustics, 1947) and many others later. It is interesting to observe that the ear generates really high levels of second harmonic: about 10% for pressure levels of 90dB (not 120dB, 90dB!). Higher order harmonics levels decrease with the order of harmonics. We can define a spectrum of the harmonic distortion of the ear. The shape of harmonic distribution is very important: there is high predominance of lower order harmonics, with a decreasing spectrum. This spectrum changes with the pressure level but this point is too complex to examine here. The key points are: 1) the high level of distortion the ear self generates; 2) the ear+brain system cancel those harmonics and the perception is that of an absolutely pure tone. In other words, the hearing system suppresses the harmonics generated by itself. Interesting, isn’t it? Even more interesting is this: the system suppresses the sound of “that” range of harmonics even if they are of “external “ origin, under the condition that the shape, the pattern, is maintained. Quite obvious: the system is programmed to cancel that shape of distortion and it cannot distinguish whether the origin of the distortion is internal or external (some interesting musical phenomena are related to this behavior, i.e. the missing fundamental note). If the harmonics differs from this pattern shape, the ear+brain system detects the harmonics as different tones. Based on this, we think that an amplifier generating a distortion spectrum similar to that of human ear will result extremely transparent and clean, even if its THD level is relatively high. 
  2. The above mentioned mechanism is dependent on the pressure level. In synthesis, the higher the pressure level, the higher the harmonics distortion that our ear generates (and accepts). This brings us to prefer amplifiers with distortion monotonically increasing with the output power. 
  3. The higher the pressure, the higher the order of harmonics that ear generates. This means that, at higher levels, an increased quantity of higher order harmonics can be accepted. 
  4. The detectable distortion depends, among other things, on: 1) the ratio between the peak and the average value of the signal; 2) the duration of each signal peak. Studies have proved that distortion can even reach very high values and still remains inaudible if the peak length is very short. 
  5. Masking is the well-known phenomenon where a low level tone in close proximity to a higher level one is not audible. This can limit the influence of IM distortion in an amplifier with a predominance of low order harmonics. This effect seems to be even higher if the distortion spectrum shape of the amplifier is close to the ear’s one. 
  6. Feedback is the classical method used to reduce THD and upgrade circuit performances (THD, IMD, bandwidth, noise and more). Unfortunately feedback reduces the lower order harmonics (less harmful and more “benign” for the ear) much more than the higher order harmonics. More and better: high levels of feedback act as a generator and “multiplier” of higher order harmonics (harmonics that ear detects as “dissonant” and noisy). Even if these high order harmonics are under the audibility level, the mechanism generates a “noise floor” that seems to be absolutely undesirable for the human ear. All this suggest to avoid feedback (specially overall feedback) or to try to reduce its use to the minimum.
Starting from this theoretical base, Riviera has defined the ideal characteristics for “human ear dedicated” amplifiers. Riviera amplifiers are optimized for the bench test that demonstrated an actual relation with the listening experience only, careless of pure technical virtuosity. 


They've focused on the following points...
  1. Optimization of distortion for amplitude and frequency: THD does not need to be extremely low, but it must absolutely follow the human ear distortion shape. This means predominance of lower order harmonics, with their regular distribution in frequency (the higher the order, the lower the harmonic level, with a relation between harmonics similar to the human ear one). Furthermore, the distortion level must be monotonically increasing with power level. The amp should have a soft clipping and, if possible, the distortion spectrum must be similar to the ear spectrum even in this area (or to the higher level possible before losing the right shape).
  2. The use of Zero Overall Feedback and minimum level of local feedback, to minimize the above mentioned negative effect that this technique has on sound result. This is the best way to reach the desired distortion behavior.
  3. A good open loop BW
  4. A reasonable DF, like in best tube amplifiers: between 15 to 20, without looking for useless records. This point also contributes to provide articulation and harmonics richness in the low frequencies 
  5. Total stability on every load
  6. Absence of protection, to avoid their negative effects on sound and dynamics
  7. Extreme care to the power supply


These theoretical points are then implemented in a real amplifier design and here is the Riviera practical implementation:
  • The Zero Overall Feedback and the minimum use of local feedback, when absolutely indispensable, is the first solution to reach the desired distortion behavior. 
  • The use of the A class in all stages is the logical consequence: we need to have the maximum linearity without “tricks”.
  • The hybrid solution is the next logical consequence: the triode is the best voltage amplifier and, mostly in a s.e. configuration, it offers a “natural” distortion shape, very close to the required one. Silicon devices (and specially Mosfets) are the best choice to handle power and low impedances; if properly used and driven, they can offer a good distortion shape too. In the topology adopted they also give the desired output impedance.
  • Protection circuits damage sound. In Riviera thinking this is a fact. So… no protection circuits (only fuses on PSU rails). Consequently a real large dimensioning, not for appearance (coke-like capacitors…) but in the real key points (PSU, transformers, power devices). A secondary consequence is the need for an adequate mechanical dimensioning too.
  • Accurate PSU design. 2 transformers and 5 separate PSU. The tube PSU is PI-filtered and stabilized (with a MOS, not a BJT); in the audio power PSU stage there is a PI filter too and the distributed capacitance: instead of 2 big-and-slow capacitors, many little-and-fast capacitors, with the last ones extremely close to each power device.
  • There was a long and accurate musical and bench optimization (I do not know how to quantify or better explain this point) 
  • Mechanical and “physical” manufacturing with a quality level of a laboratory instrument and a made in Italy design, and this point is easy to see ;-)" 

The output power is given just as a reference. Our ideas on the weight of the distortion, its composition, its acceptable value in different circumstances (static, dynamic) and the way to measure it makes it really difficult to give numbers that can be compared to other products on the market. And, probably, many words would upset most audiophiles. We can just say: try it, listen to it! 

SUM UP


I'm sure, that by now, you really had quite an insight into the Luca's and Riviera Audio Labs mind set. While they're avidly following the technical aspect of the design, unlike many on the market, they're willingly taking the very different and bold steps needed to enter the "uncharted" territories. Well, not exactly completely unexplored. Vladimir Lamm is certainly most prominent one, that had publicly declared the implementation of the pyshoacoustic model of the human ear in his designed. The other prominent name that pops up is the legendary FM Acoustics, that also supposedly uses something very unique within their own propriety circuits. 


We're living in the era where daily our minds are bombarded by the sparkling words of technical advancements and discoveries of new technologies, but at the end of the day less and less people are emotionally engage in the interaction with the device.  There are many great things, that helps us live better, faster,  safer and more comfortable, but not every advancement brings the actually potent result.


Especially in our beloved and niche industry, the inventions/reinventions, that are being made just for the sake of marketing existence are sadly in many cases just an eschewing of the eschewed. The real quest within high-end audio should always be the sonic performance, that can reveal the raw nature of the music and can act as a via medium in the interactive distribution of the music. 


While Riviera Audio Labs AFM-50 hybrid monoblocks are exploring the positive attributes of complex universe of psychoacoustics, they vividly connects to the sonic territories, that's intimately focusing on the very core of the music. Riviera AFM-50 power amplifiers are digging deeper into the harmonic structures and follow intimately the core attributes of the golden trinity of timbre, tone and colour. 


One of the biggest challenges in high-end audio is the manifestation of a believable reflection of the real music. The complexity of the data retrieval goes far beyond simple tasking and demands more than just an usual electronic affairs dealings under the hood of the amplifier. While some engineers will repeat to death, how measurements alone are the clear sign of the sound outcome, the reality strikes when the first few notes starts to manifest in the sound space. This becomes instantly clear when the acoustical, un-amplified live music takes a part of the reference aural material. 

By digging into my listening notes I've reminded myself about AFM-50 seamless correlation between the speed and proper harmonic behaviour, that I've highlighted as Riviera’s forte. 

There will be always an open and endless debate when it comes to THD, distortions, higher/lower harmonics and measurements. When Dan D’Agostino departed Krell and pursued his own sole path, he clearly noted, how he wants to produce a musical sounding machines and all the above mentioned aspect need to be subordinate to the musical sonic outcome. At the end of the day market by itself has shown, that he must be doing something very right by following his principles. 

So, if not everything is in the domain of measurements are we then dealing with the positive distortions? The proof is in the pudding as the saying goes!

Like with other fields of industry one can perfect a certain segment, but it’s hard to marvel everywhere. In high end audio things are even more complicated as we’re not dealing with the typical mechanics, but with the subtle and fragile reproduction of the music. Typical norms fails here. Still, the real world test is more or less simple when it comes to the real references. If one has accumulated enough impressions from the real world (in our case live music), than both replication and evaluating becomes not exactly an easy performing task, but much more meaningful and vigorous. Both an audio designer and evaluator are affected by such impressions and will cherish, as well as incorporate them in their work. And this matters on all fronts...

Riviera Audio Labs AFM-50 amplifiers operate in the absence of typical augmented sonic reality. They operate with the ability, that allows them to decode the original message with a grand portion of spatial cues and the right amount of properly distributed harmonics, that can easily engage one into the undisturbed and highly interactive listening. 

AFM-50 are not carrying neither typical solid state sonic imprint nor the tube attributes. The sound balance somehow embraces the best of both worlds. The illusory effect of reality resonates intimately close with the realistic density, where music can manifestes with trenchant, puissant and silky attributes. 

I'm always saying, how any circuit topology design choice and selection of the electronic parts are the clear reflection of the designer's mind. However, some of the audio designers wants to avoid like plague any association with the voicing term. Yet... There is no escaping it. Each and every choice reflects the sound outcome and Luca Chiomenti knows it by heart. This is why listening part matters and this is why Riviera Audio Labs AFM-50 monoblocks can deliver such undisruptive and perennial
music experience, that matters!

In the second and final part I'll focus on the music and how Riviera AFM-50 monoblocks have managed to portray some of my beloved albums. Silvio has also sent me some N.O.S. tube to try and this will find its place also in the follow up. Stay tuned... 

Matej Isak

PRICE


32.000 EUR without VAT

SPECIFICATIONS

 
Power 50W / 8 Ohm
Zero Feedback
Pure “Class A”,
Hybrid (triode, BJT, Mosfet)
Balanced and unbalanced inputs

CONTACT


Riviera Audio Laboratories s.r.l.
Via Nicola Fasano 26
80078 Pozzuoli Na
Italy

General or administrative information: info@rivieralabs.com
Technical information: luca@rivieralabs.com
Commercial information: silvio@rivieralabs.com