INTEGRATED AMPLIFIER

RCM
BONASUS

WOJCIECH PACUŁA







Until recently I thought, that the only Polish company that produces hi-end devices, able to compete with other world class products, is the Krakow manufacture Ancient Audio . And I explain immediately what I mean with the terms 'produce' and 'hi-end'. These two terms describe devices, ready in terms of sound and make, a product, that is produced in certain quantities (I mean produced in at least 5 pieces) and with a certain manufacturing quality level. Devices made in one or two specimens, prototypes and similar, that are present in any country, do not fall into this category. Probably many of those are really quite nice, well sounding machines, but they are not 'products', they are not something what you could place on a store shelf and say it is for sale, they are not repeatable or possess safety certificates, etc. Back to what I said earlier: before I saw and listened with my own ears to the Bonasus from the Katowice based company RCM . The first ingredient - manufacturing quality - I knew, the amplifier was first presented on last year's High End show in Munchen, and this year, together with ASW speakers, was an equal partner in the system. The manufacturing quality of this year's edition (due to US safety regulations the amp -Bonasus was presented on the Las Vegas show -was a bit enlarged) is exceptional. The only thing left -is to listen to it...

This was more difficult than anticipated. And not because the manufacturer is unfavorable for such doings, but because the test demanded sacrifice. To see it from the right perspective it must be said, that the amplifier weights 54kg, and this little thing is placed in a quite - for a tube device - compact enclosure. Blood was spilled and it ended with stitches on the chin of the person that was delivering the amplifier to me -a moment of distraction, maybe slippery steps, or something else -anyway in a moment a hand was crushed and a chin was cut. It is really a solid piece of an amplifier. Fortunately, as in my case, there is a big chance that it will be installed sole handed by the manufacturer or dealer, and he will be responsible for treating all the injuries.

LISTENING EXPERIENCE

The Bonasus amplifier sounds different than most push-pull amplifiers, while being one of those. It also sounds different than two similarly priced amps tested this month: Jadis DA-30 and Art Audio Lab m 14.4. It will be easy to decide if this is something for us, even judging only based on this reviews. The sound of the RCM amplifier resembles in general the sound of Mobile Fidelity remasters (reviews of the newest discs HERE). It has lots of natural smoothness, something, that without the resolution, we have here (and on the MoFi recordings also) just does not work, but something, that together with this resolution creates new quality. Main part in this way of expressing the reality play the timbres. The splendid interpretation of the arias from the disk "Opera Proibita" (Decca/Universal 475 7029, CD) by Cecylia Bartoli were shown with grace, without any effort and resistance. The voice of Bartoli seemed to come directly from heaven -was clean and sonorous along the whole spectrum. Combining these two elements can in many systems be the key to achieve musical (please note that I do not use the term 'audiophile', as we are talking about something more than that) nirvana.

When we put on well recorded jazz, and also as well played as on the newest disk of the trio e.s.t. "Tuesday Wonderland" (ACT 9016-2, CD, test HERE), momentarily strong and clean sound of the piano will catch our attention. Here we could also hear the very good work of the basedrum. The basedrum had a nice, strong, but also soft attack, just like a basedrum should, the bass was drawn in a clear way. In absolute categories, comparing with the, splendid in this area Monster Power MPA2250 amplifier, it is not the last word in the area of dynamics or control. But it is very good, and for the tube -even better. The basedrum can strike with dynamics and drive, even on large floor standing speakers. In the piece "Brewery of Beggars" we will appreciate the thorough drawing appearing from the good timbres. Bass had a fast and short pace here. It did not have the incredible weight, like in the m 14.4 AAL, or those rounding like in DA-30 Jadis, but was most even from the three. It's lower end was slightly laid back, but it can be corrected with the source or speakers. Give the Bonasus a player like the Lektor V and speakers like Duevel Bella Luna and we will have a perfect combination. Experimenting will be the best guide. On the slightly warm recorded disk of theJim Hall Trio "These Rooms" (Denon, CY-30002, CD) it can be heard extremely well -the combination of charisma and strong bass. Here we could finally characterize what is the main strenght of the Bonasus, namely the clean and easy way in which it delivers the music.

In the sound of this amplifier there is no shadow of brightening -whether in the top frequency range nor in the upper mid-range -there aren't also any discontinuities, that many times accompany it. After listening to the piece "Beer Roots" from the disk "American Dreams" (Dreamworks 50233, CD) further observations regarding the bass could be made. I mentioned earlier, that in comparison with z Jadis i AAL, or even the Lebenem CS-300 (test HERE) the case is not that straight forward. This recording contains very low reaching bass, even more, for some time it plays loud, on one level. This poses certain demands to the equipment -for example devices that handle impulses very well, like NAD, don't have the power to sustain, and after the first knock loose the impetus. It was different with the Bonasus. It played the descent to hell a little quieter, but the whole on a steady, and still strong, level. It means that we will not have a shot like from the mentioned amplifiers or the Monster, but the current efficiency will be higher (maybe except the Monster, but this is understandable).

The overall concept of sound from the Bonasus amplifier of the company RCM is similar to the CD player Prime from the company Ancient Audioused by me: plasticity, timbre and an approach to resolution from the whole and not from detail, more an aspiration to fill-up the sound and "carve it" later. It gives a relaxing, nice sound, with characteristics of the hi-end, meaning without accretions from the so called hi-fi.
And I was thinking, that only in Krakow, in Ancient Audio, Polish amplifiers of such manufacturing quality and hi-end sound are made...

THE MAKE

The amplifier was prepared using tested patterns, however significantly modified. The whole chassis, including transformer covers, was made from marvelously, really marvelously prepared aluminum and steel plating. If somebody tried to do something with this material, knows that it is a really painful way to make something of it. In the Bonasus everything is top notch - starting with the anodized front panel and ending with the enormously thick openwork bottom plate. Even the feet were done sole handed (meaning by the same Polish company that made the chassis). The design is also very intriguing. The front is divided optically in two sections by a deep vertical groove: on the left we have two indicators (VU-meters), displaying the output level or the tube bias. Cunning and helpful. A pity, that the meters are not scaled, we know only where the 0 dB level is. On the other hand, aesthetics profited from that, as the white, backlit surfaces contrast nicely with the company logo. On the right hand side, two small knobs were place -one of those controls the VU-meter mode, the other one powers up the amplifier. The device can be switched off or put on standby -the tubes have the heating turned on, but without the anode voltage. It elongates the valves life span significantly, and allows immediate startup of the amp, without gong through the powering-up procedure. If we power-up the Bonasus from the off state, the tubes are heated first without anode voltage (soft start). And two more knobs, the big ones -one is the input selector and the second one is the volume regulator. Much is happening on top. First of all the voltage is rectified in rectifier tubes 5AR4 (GZ34) made by Sovtek. There are two, one on each channel, just like two power supply transformers and suppressors. Bonasus is a dual-mono device. In the preamplifier and phase reverser Sovtek's double triodes 12AB7 (ECC85) are used. This is not common practice, 12AT7 and 12AU7 are mostly used for this tasks. However historically, actually the ECC85 was most commonly used in phase diversion. This tube is used here also in the buffer. The power amp works based on four (two per channel), working in class A, in push-pull setting, power pentodes 6CA7 from Electro-Harmonics. This valve is a direct replacement for the EL34, but by most companies treated as a it's variant. Electro-Harmonics manufactures it like in old times, with an enlarged bulb, that aids the work conditions of the tube. From the specifications we can see that the tubes were not stretched to the maximum, because from those we can get a maximum of 16 W by 8Ω. The usage of those, and not other, tubes was not driven by the desire of achieving high power, because we can get the same from two, parallel 300B triodes.

After unscrewing the heavy bottom plate we have a chance to look inside. And there -the audiophile dream come true. On one hand the circuit is most important, but on the other the quality of the components, their placement, etc. plays an equally important role. The quality of the elements is outstanding here: in the intrastage coupling capacitors of the US company Auricap are used, in the cathode coupling very large French SRC polypropylenes. In the cathodes of the power tubes Mills resistors and superb RIFA capacitors (bipolar capacitors of the company Evox-RIFA) were applied -due to the needed large capacity polypropylenes could not be used. The power supply looks fantastic, with many Nichicon capacitors, coupled with smaller polypropylene SRCs. Additional polypropylenes filter the input valves current. Connections were made in the point-to-point fashion, with thick silvered copper wires (at least it looks that way). Tube holders are ceramic and have gilded pins. The power-up delay, stand-by and input filter circuitry are placed on a separate board. Because the tubes were placed in front, the signal from the gold plated RCA connectors, soldered in the relay board, goes first to the solid potentiometer (I don't know the make -it is not an ALPS though) and later, by means of quite long wires, to the tubes in front. Let us mention, that it is a true rarity, that a global feedback loop was not used, at least the manufacturer claims that. That is the reason for the not so big output power. By the way, it is interesting how they did that -the major brands use at least a 6 dB feedback. The whole is perfectly made, and only the biggest companies approach this level. One of the sighns of pursuing perfection is filling of the transformer and suppressor covers with a special dampening substance, very expensive and difficult to apply. That, what I could desire more, comes from idiosyncrasy, meaning I would like a headphone output, maybe also a remote control. These are additional things, there being is related to personal preference. One element I would change, are the big screw heads, visible from the front. They are inserted, but their nickel surface is in great contrast to the elegant, satin front panel. To do justice let us say, that I talked to one of the owners of the Bonasus, who didn't even notice that detail.



RCM
BONASUS

Price: 25 000 zł

Distributor: RCM

Contact:
RCM s.c.
ul. Matejki 4
40-077 Katowice

Tel: 032 / 206-40-16
032 / 201-40-96
Fax: 032 / 253-71-88

e-mail: rcm@rcm.com.pl

Manufacturer web page: RCM



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