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Integrated amplifier

Price (in Poland): 19 900 zł

Manufacture: Spec Corporation

6th Fl. Shin Kioi-Chobuilding ǀ 4-1 Kioi-Cho, Chiyoda-Ku
Tokyo 102-0094 ǀ JAPAN | tel.:/fax: 03-6272-6011


Country of origin: Japan

Product provided for testing by: Eter Audio

Text: Wojciech Pacuła
Photographs: Wojciech Pacuła ǀ SPEC ǀ Muson

Published on: June 1. 2012, No. 97

SPEC is a very young company. It was started by its owner, SPEC Corporation, in January 2010. The pretext for that was the launch of the SPEC RSA-F1 integrated amplifier , known in the specialist audio literature as the REAL-SOUND AMPLIFIER , as well as the RSP-101 filters mounted on loudpseakers, called REAL-SOUND PROCESSOR. I mentioned the latter in my editorial Small dreams in the 90th issue of “High Fidelity” (HERE). These little boxes have proven to be so cool that I have kept them as a partner to my Harbeths M40.1.
It was, however, only a foretaste of what SPEC had to offer. For although their offer also includes oil capacitors and audio equipment racks, they concentrate on amplifiers. It began, as I say above, with the RSA-F1, to be later joined by the RSA-M1 and the RSA-V1 that we review today.
They all share the same concept: the best possible adaptation of an analogue amplifier, operating in Class D. In order to achieve this, the amplifiers feature the fine, oil capacitors from Arizona Capacitors, Inc., being modern replicas of the vintage WEST-CAP capacitors, together with a sophisticated power supply and ultra-short signal paths. And of course, housing that combines metal and wood.

I took a great interest in test reviewing this amp, because when the Japanese are serious about something, they usually do it in a unique way. And Class D amplifiers deserve serious consideration. However, the review would not happen, if it weren’t for stubbornness and help of Messrs Hontai - Yoshi and his son, Elia. In order to introduce me to the subject, they sent me a brief list of the most important things I should know about the RSA-F1:
∙ the electrical circuit was designed by a talented engineer (working for many years at Pioneer), seeking to come up with the best possible single-ended amplifier based on 300B tubes,
∙ used the best available pulse amplifier system, which was used in a purely analog amplifier (the power supply is also fully analog, linear)
∙ oil capacitors used, being a reproduction of the WEST-CAP NOS,
∙ powerful amplifying system, modules for use in amplifiers are SPEC performance exceeding 90% (normal is about 25-30%), so the amplifier generates almost no heat,
∙ due to high power amplifiers and a powerful amplifier SPEC are able to effectively control almost all the available columns, including those with low efficiency, such as Kiso Acoustic HB-1, this is why the company chose the Kiso Acoustic amps spec to work with their columns of HB-1 all exhibitions
∙ base with wood used in order to obtain a saturated sound as possible,
∙ "safe" power switch, used in aircraft cockpits.
We came into this brand, because we have grown these amps sound like it. I believe that you too will love.
We like the philosophy which stands behind it. Constructor, Mr. Koichi Yazaki is enthusiastic about the sound tube, 300B amplifiers. 38 years uses a very good amplifier of this type, the amplifier of your project, which over the years added improvements to help him get closer to the "ultymatywnego" sound.
What is happening but he could not tell you is very low power of such structures, which precluded the use of columns of low efficiency. To achieve this, to get as beautiful, deep sound and high dynamics, decided to combine the analog and the latest power amplifier with a PWM pulse. Therefore, during the exhibitions in Japan SPEC amplifiers are often confused with a tube amp.
Yoshi Hontai

How can we sum it up? Maybe like this: the SPEC amplifier is an analog design, operating in class D, with NOS components, and enclosed in a housing combining wood with aluminum. Its sound was intended to closely match the sound of the 300B tubes amplifier, adding to that large-scale and power. Let's see how it translates into reality.


Recordings used during auditions (selection):

  • Blade Runner, soundtrack, muz. Vangelis, Blade Runner Trilogy, 25th Anniversary, Universal, UICY-1401/3, Special Edition, 3 x CD (1982/2007).
  • For Ever Fortune. Scottish Music In The 18th Century, Les Musiciens de Saint-Julien, Robert Getchell, Alpha, 531, CD (2012).
  • Paganini for two, Gil Shaham, Göran Söllscher, Deutsche Grammophon/JVC, 480 246-5, XRCD24 (1993/2009).
  • Diana Krall, All For You, Impulse!/JVC, 532 360-9, XRCD24 (1996/2010).
  • Dominic Miller, Fourth Wall, Q-rious Music, QRM 108-2, CD (2006).
  • Exodus, Supernova, Polskie Nagrania/Metal Mind Prodictions, MMP CD DG 0405, CD (1992/2006).
  • Handel, La Maga Abbandonata, Simone Kermes, Maite Baumont, Il Complesso Barocco, dyr. Alan Curtis, Deutsche Harmonia Mundi/Sony Music Entertainment, CD 88697846212, CD (2003/2011).
  • Jean Michel Jarre, Magnetic Fields, Epic/Sony Music, 488138 2, CD (1981/1997).
  • Jean Michel Jarre, Téo&Téa, Aero Production/Warner Music France, 699766, CD+DVD (2007).
  • Jimmy Smith and Wes Montgomery, Further Adventures of Jimmy and Wes, Verve/Universal Music [Japan], UCCV-9359, SHM-CD (1969/2008).
  • Michael Jackson, Thriller. 25th Anniversary, Epic/Sony Music Japan, EICP 963-4, CD + DVD (1982/2008).
  • Nosowska, 8, Supersam Music, SM 01, CD (2011).
  • Sara K., Don’t I Know You From Somewhere?, Stockfisch, SFR 357.6055.2, CD.
  • The Modern Jazz Quartet, The European Concert. Volume One + Volume Two, Atlantic/East West Japan, AMCY-1186-7, K2 CD (1960/2000).
  • Wes Montgomery, Incredible Jazz Guitar of…, Riverside/JVC, VICJ-41531, K2 CD (1961/1999).
Japanese editions available from .

The SPEC amplifier is an ultra-minimalist device, featuring only a volume control knob and an input selector, without any remote control, etc. That is, you can order the remote control as an option but it is realized in a quite specific way. More on this later, in the section on the amp design. The RSA-V1 comes from a small, specialized manufacturer, known only to experienced audiophiles. It is the result of love for music, which you can both see and hear. Its mechanical design combines heavy, metal enclosure with several types of wood. And finally – it has a rather distinctive sound, as if designed to work with my Harbeths. Does it ring any bell with you? No? Or perhaps it does – how about the Lavardin Technologies IT-15 amplifier? Please, take another look at the review; it will be our important reference point.
Although, generally speaking, these two devices appear to sound a totally, completely different. Decomposing their sound to a set of prime factors, we get a group of often contradictory elements. And yet, after assembling it back together, and connecting the amps to the speakers of the kind of Harbeth or Spendor we get a comparable musical message, evoking similar emotions. Although, let’s repeat it once again, using a set of different tools.

I auditioned the SPEC RSA-V1 in two completely different sound systems – my own, reference system, and also at the Nautilus audio shop in Krakow, together with the Accuphase DP-510 CD player , the Dynaudio Special 25 Signature Edition speakers and the Purist Audio Design cables. With each of the systems the amplifier sounded different.
The system with the Dynaudio and the Accuphase proved that the amplifier delivers an extremely precise and exceptionally pure sound. I also very quickly realized that it seems not to be limited by any output power restrictions, because not only did it excel at showing deep, dynamic bass, but also well-differentiated dynamics. However, all that time I had the impression that this show-off did not convey a coherent message; that all we see is a frame on which the sound is built, not a complete, finished project. This only happened for me back home, with the Harbeths.
As Mr. Hontai said, one of the companies that decided to use SPEC amplifiers during their loudspeakers presentations is the Japanese Kiso Acoustic. Is it a coincidence that the HB-1 speakers from this manufacturer garnered two awards from me based on my auditions during the High End 2011 show in Munich: Best Sound High-End 2011 and Red Fingerprint (report HERE)? And that the speakers were driven by our reviewed amplifier? I do not think so… It was a well though-out system, showing in which direction to go.

The sound I heard after hooking up the RSA-V1 with the Harbeths M40.1 was nothing short of spectacular. It is probably, or rather almost certainly the first amplifier operating in class D that I know of where the technology not only doesn’t prevent it from achieving a high quality sound, but instead in many ways it improves it, simply creating its grandeur.
With the Dynaudio speakers and the Purist wiring, I had an impression that it lacked some fullness in the lower midrange and that the upper midrange was a bit too forward. As it is known, class D amplifiers are (almost always, though there are exceptions) sensitive to the speaker cables and crossover design. The latter constitute a part of the low-pass (reconstructive) filter in the output (amplification) section of these devices. That was perhaps the reason why the amp’s audition at the Nautilus, while it floored me to some extent (its sheer power, clarity, precision, etc.), was not fully satisfactory. I did not “buy it”.
With my Harbeths and Tara Labs speaker cables the Japanese amplifier played a different tune – showing beautifully saturated, almost warm sound with a very strong, solid bass foundation. It might seem for a moment that the treble is slightly withdrawn and softened, which is part of the class D amps “trademark sound”, but after prolonged listening and subsequent return to the reference system I found it hard to confirm. It was more like a foreboding shadow. For the cymbals sounded very, very, very convincing – they were both rich and full, somewhat “tube-like”, as heard from a good 300B amp. I.e. neither withdrawn nor warm, but just right – natural in their weight, texture and density.

Anyway, we do not immediately perceive them so, because they are simply part of the midrange. And that is the most impressive sub-range of this amplifier. Not because the amplifier is limited to it, but rather because the midrange is best differentiated and constitutes a true “center”; it is here that we get the highest emotions.

I mentioned the differentiation – not without a reason. Both the treble (to a lesser extent) and the bass (more) sound great, it’s hard not to like their color and dynamics, but when it comes to differentiating the instruments within these ranges, showing clear textures, it is not their forte. The midrange though is a completely different story.
It is shown in a – seemingly – tube-like fashion, as with good, interesting amps based on EL34s. What I mean is a kind of saturation of sound, its maturity, and even “over-maturity”. This manifests itself in presenting the vocals, guitars, etc. before the line of speakers, in a tangible, very “organic” and “physical” way. It is a truly energetic presentation. With such albums as Don’t I Know You From Somewhere? by Sara K., and 8 by Nosowska it was easy – both recording actually encourage such presentation. It also may have been expected from the albums by Wes Montgomery The Incredible Jazz of Wes Montgomery and Further Adventures of Jimmy and Wes, although the scale of this phenomenon, the volume of sound took me by surprise. I did not hear small instruments suspended somewhere between the speakers, but rather three-dimensional masses, their entire network, linked together into something greater. Over imposed on it was a brilliant texture of tape-noise, the noise of air in the recording studio, etc. Nothing much, but that’s what constitutes an integral part of these recordings, ultimately giving them a specific sonic dimension. The noise was primarily midrange based, not the treble. This is not an amplifier that brightens anything.
Yes, the sound was based on its similarity to EL34. But not only that, it was just a starting point. For it is purer than any EL34 device, except maybe for the IA-30T Linear Audio Research. And it rather resembles good 300B amplifiers, and to some extent the sound of my own, unrivaled in this respect, Soulution 710 power amplifier.
It was enough to listen to Simone Kermes on her La Maga Abbandonata album with Handel arias, especially the wonderful Ombre pallida (Alcina), to appreciate the combination of high output power, purity and excellent color of the midrange and the treble. They were exactly the same emotions I experienced while listening to her live some time ago with the Venice Baroque Orchestra during the Mysteria Paschalia festival (ninth edition). Simply, beautifully splendid!

And so we come to the bass. It’s a good time to recapitulate what we have said so far and, adding a little, try to summarize the review. For the bass is strong and full, slightly warm. I cannot imagine speakers that would be a problem for this amplifier, if only they are properly matched with speaker cables. But it is here that you can hear it is a class D amplifier. With smaller speakers, such as the above mentioned Dynaudio Special 25 Signature Edition, and even with the Kiso Acoustics HD-1, it will not be heard so clearly because they simply cannot render such low bass as my Harbeths. What I refer to is a slight uniformity of sound, a kind of homogenization of this sub-range. Dynamics and bass extension are outstanding, but the differentiation of dynamics, differentiation of color, are not.
And to some extent the same also applies to the treble. It is always pleasant and smooth. Not exceedingly well defined, although selective, and as such is the exact opposite of the Harbeths. The center of the sub-range, its upper part is slightly warm, but if the recording is lacking in this respect, like Michael Jackson’s Thriller or some tracks from 8 by Nosowska, the SPEC will show it to some extent. It will not sharpen, nor brighten up, but will neither drown everything in uniform warmth. Nothing like that.
The amplifier’s advantages can be best appreciated with classical music. Or not, rather with jazz. Well, honestly it sounds even better with electronic music – Vangelis’s soundtrack to Blade Runner has not long sounded that well. And besides – everything sounded great and, as I see it now, it is difficult to pinpoint a particular musical style that would benefit the most. Provided that we can accept certain, perhaps (as it looks today) idiomatic limitations of the analog Class D.
This is not an amplifier with highest definition, especially at the top and bottom ends. The midrange is outstanding. The midbass can sometimes be too uniform and sound similar with various CDs. The high treble is warmed up and slightly veiled. Of course, only in comparison to the reference amplifier. There is no remote control and there are not too many inputs. The amplifier is not budget-priced, especially at first glance. Yet the moment we see it, have a taste of its perfect design, see the excellent components inside, we will change our mind. However, our first impression is important, and it says that we actually do not really know what we pay for.
But I’d had exactly the same situation with the Lavardin Technologies IT-15 amplifier, from which I began this review. An unknown manufacturer, no-thrills design, nothing. That is, until we take a closer look, until we listen to it with matching speakers – Harbeths, Spendors, Castles, etc. Then it turns out that this may become our last amplifier. Maybe not the “best” but definitely “enough”. And that is very much indeed.

Review methodology
The amplifier was placed on the Base IV Custom Version rack, on a wooden shelf. For some time it also sat on additional decoupling elements, Audio Replas OPT-30HG-PL/OPT-30HG-SC quartz insulators.
The CD player was connected with the XLR SAEC XR-4000 cables – I think the sound was better than with the RCA. You need to remember that the result largely depends on the CD player design, and even on the player and amplifier power supply. It is worth trying on your own. The power cord I used was the Harmonix X-DC350M2R Improved Version.
The test review was an AB comparison with A and B known. In addition to my reference amplifier, the reviewed amplifier was compared to the Struss R150 and the Hegel H200. Music samples were 2 min long.


The first amplifier from this manufacturer was the RSA-F1. The reviewed RSA-V1 is its newer, less expensive version, with somewhat simplified housing and electronics. But only to a point where it made sense.
It is an integrated amplifier based on analog amplification modules working in class D, with newly-designed MOSFET transistors. The amplifier comes without a remote, but you can order a beautifully designed, external receiver module, together with the remote control. The whole set is called the RSR-3 and you have to pay for it separately.

Front and back panels
From the outside, on the one hand the amplifier is very simple, on the other, very interesting. You can see that its mechanical design is based on the combination of the main chassis and enclosure made of steel and an integrated with it anti-vibration wooden platform. This is what gives it a deep, saturated sound according to the manufacturer. The platform is made of a combination of several components: solid oak wood with two feet in the front (the bar bears the Oak Village logo), and plywood made of European spruce cut in Austria, with one foot in the back. The feet are made of maple wood from Hokkaido Island (Japan), called hickory, recently used by Acoustic Revive in their RAF-48H and RST-38H anti-vibration platforms (the 'H' in the symbol name comes from Hickory). The front panel features only three components – the input knob, the volume knob and the power switch. The volume knob can be illuminated in blue, but the backlight can be turned off via a switch on the back panel. Both knobs are very solid, made of aluminum, really nice. The power switch is even cooler. Its design is borrowed from the cockpit of an airplane – to switch the amplifier on or off you need to pull the switch pin, releasing the latch. Next to the switch, there are two LEDs – red and green. The red one lights up when you turn the amp on and slowly fades out when you switch it off. After turning off the amp the backlight around the volume knob also fades out slowly– really cool! The quality lettering is beautifully screen printed and the Designer Audio logo is engraved in the center.
The back panel is quite simple. In the center we have two pairs of gold plated, rather plain speaker binding posts. To the right we see the inputs – three pairs of RCA and one XLR. The RCAs are high quality, rhodium plated. To the left we find the IEC mains socket, a switch controlling the volume knob backlight and a small socket for an external remote control unit.

The interior
The interior is divided into several sections, carefully shielded with steel sheets. From the inputs the signal goes via pretty Belden cables to the mechanical switch on the front panel, and then to the main circuit board with the power output stage. It turns out that the RSA-V1 is a power amplifier with adjustable volume control. It is hardly “passive” control, because it features an integrated circuit, a digitally controlled, analog resistor ladder with a logo of the Japanese Tachyonix 3310 IR01. It is apparently custom programmed. A quick check shows it to be the “International Rectifier Japan version 01” of the CS3310/PGA2310 chip. The Japanese potentiometer on the front panel is only a driver, not featuring in the signal path. After the gain level adjustment the signal goes straight to the small main circuit board. It is a complete class D analog amplifier IRAUDAMP4 DB Rev.03 from International Rectifier. It is an amplifier with a PWM modulator. The circuit is fully balanced, so it is worth driving the amplifier via the XLR connectors. SPEC designed the power output stage, on newly developed FET transistors, bolted to a tiny radiator.
One of the most important components of a class D amplifier is the output filter. In order to “recover” the musical signal from the signal generated by the PWM modulator an output reconstruction filter must be used. And it is its quality that largely determines the quality of sound. SPEC went all out and used special oil capacitors, designed together with Arizona Capacitors, Inc.
Power supply is equally important. The Japanese usually do not use switching power supplies, relying instead on linear designs – the reviewed amplifier is no exception. Under the shielding metal sheet we find a very large, really powerful R-core type transformer. The rectifier features a bank of ultra-fast, modern Shottky diodes and a number of filtering capacitors of various types. For example, we have “Super Through” and “Gold Tune” Nichicons, bypassed by oil capacitors from Arizona Capacitors, Inc., bearing the SPEC Corp. logo.
It is a very clean, well thought-out design. Although the amplifier is built around the “heart” from International Rectifier, it is supplemented with high-end, custom designed components.

Technical data (according to the manufacturer):
Output Power: 2 x 50 W / 8 Ω, sine | 2 x 75 W / 8 Ω, peak | 2 x 100 W / 4 Ω, peak
Frequency response: 10 Hz – 30 kHz / ± 1 dB (6 Ω, 1 W)
Total harmonic distortion (THD): 0.02% (at 1 kHz, 80% of nominal power)
Input Sensitivity: 300 mV rms, 37.3 dB (Volume MAX, 6 Ω, 1 kHz)
Power consumption (max): 180 W (8 Ω, 100 Hz)
Dimensions: 440 × 120 × 414 mm


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  • Loudspeakers: Harbeth M40.1 Domestic, review HERE
  • Headphones: Sennheiser HD800, AKG K701, Ultrasone PROLine 2500, Beyerdynamic DT-990 Pro; 600 Ω version, review HERE, HERE, and HERE
  • Interconnect: CD-preamp: Acrolink Mexcel 7N-DA6300 (article HERE, preamp-power amp: Acrolink 8N-A2080III Evo, review HERE
  • Speaker cable: Tara Labs Omega Onyx, review HERE
  • Power cables AC (all equipment): Acrolink Mexcel 7N-PC9300
  • Power strip: Acoustic Revive RTP-4eu ULTIMATE
  • Stand: Base; under all components
  • Resonance control: Finite Elemente Ceraball under the CD, Audio Revive RAF-48 platform under the CD and preamplifier
  • Pro Audio Bono PAB SE platform under Leben CS300 XS [Custom Version]; review HERE