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Power amplifier


RT Audio Design

Manufacturer: RT AUDIO DESIGN
Price (when reviewed): 3000 euro

Contact: kv. Bratya Bukston
blok: 204 vhod: B floor: 2
Sofia post code: 1618 | Bulgaria


Provided for test by: RT AUDIO DESIGN

tanding out is an advantage. Every manufacturer, businessman and salesman knows that. Audio manufacturers realize that too. Even though many audiophiles claim to be very open-minded when it comes to new ideas and solutions in fact they are hard-headed traditionalists. Why, do you think, since 1960ties most audio devices feature flat, cuboid enclosure with elegant front and connectors placed on the rear? Most devices sport chassis with a wide, low profile front, with its width being usually a bigger dimension than its depth. Sure there are some exception, but their numbers are irrelevant. Audio devices are not particularly colorful either – most are black or silver; only recently white became popular.

It is easier to attract audiophiles' attention with some technology, or solution. Assuming that they even know about it :) For example, class A – many audiophiles dream about it, considering it to be a solution to all problems. Even more self-aware audiophiles like something to be added on top of that, like stabilized power supply. Yeah! That's really something. Today among biggest manufacturers probably only Naim uses those. In Poland Kunstagon used them in their products years ago. But these are rare gems.

RT Audio Design, a small Bulgarian company, was founded by Tsvetan Tsencov, the chief designer, and Ivaelo Ratzov, who takes care of the aesthetic form of their products. This company adopted all above mentioned 'audiophile's dreams' and implemented them in their products. As our review of D/A Converter Ultra USB DAC Orpheus proved, their designing ideas are interesting and their products sport nice, but not showy enclosures.

The Orpheus line, apart from said DAC, includes also power amplifiers. The latest addition is the „power amplifier push-pull class A MkII Orpheus”. It's so new that I had to wait a month or two before first batch was available for testing (the unit under review features serial number: 00002). Even though it is just a power amplifier, so its functionality description should take just a few sentences, this one seems quite unique in this respect. Yes, I am also surprised – that's a stereo power amplifier so just an input, an output, power inlet and that's it, right? Some more advanced units feature both, RCA and XLR inputs and some also a LED indicator on the front.

Orpheus is something more. First of all it is a class A amplifier, working in push-pull configuration. It means that it produces a lot of heat and delivers a limited power. Manufacturer declares that it is able to deliver 50 W at 4 Ω, which means probably that at 8 Ω it outputs no more than 20, maybe 25 W. Which is not much – many tube amplifiers offer bigger output. But class A solid-state amplifier's distortion and noise level is lower, and so is the output impedance especially if more than one pair of transistors works in the output stage (in this particular case there are two pairs). Low output impedance means high damping factor which translates into better loudspeakers' control.

Orpheus does not use a standard, non-stabilized power supply, but a stabilized one, that utilizes power transistors as active element. Such type of power supply guaranties lower level of distortion. But on the other hand it gives amplifier almost no power headroom. Power supply utilizes a separate enclosure – so what we have is a two-box design, a very rare case among stereo power amplifiers.

And that's not all. Front panel reads: „Class A/AB”. One can order this amplifier in one of two versions: operating in class A or in AB. The latter delivers output of 250W into 4 Ω. A different power supply is delivered with this version. But also an owner of class A version can turn his unit into one working in class AB. One has to remove the cover, adjust bias and replace a fuse. Upon request manufacturer delivers a detailed description how to do that. Using the same power supply (as for class A amp) amp will deliver 80 W @ 8 Ω.


Our new power amplifier Orpheus works in class A and it is a genuine reflection of our sound philosophy. We decided for an outboard fully shunt regulated power supply. Rectifier is based on fast SIC Shottky diodes supported with a large filtering capacity. The regulator features transistors as active element. Power stage delivers more than 30 A DC.

There are no capacitors in signal's path in the amplifier section which allowed us to minimized phase and frequency distortion. It improved bass control and timing too, We used professional grade drivers driving audiophile grade output transistors. The output section works in class A delivering 50W into 4 Ω loading with output impedance of 0,1 Ω. The amplifier utilizes silver internal cabling, power supply utilizes OCC copper one. All passive components are low tolerance, and we utilize no SMD. The design of the amplifier is minimalist and signal's path very short. We also used professional power connectors instead of classic IEC ones.

RT AUDIO DESIGN in “High Fidelity”
  • TEST: RT Audio Design ULTRA USB DAC ORPHEUS – D/A Converter.

  • Recordings used for the test (a selection)

    • Sonda 2. Muzyka z programu telewizyjnego, GAD Records GAD CD 011, CD (2013)
    • Czesław Niemen, Czas jak rzeka, Pomaton 3376772, „Złota kolekcja”, CD (2000)
    • Eric Clapton, Timepiece: The Best of Eric Clapton, Polydot/Audio Fidelity AFZ 190, „Limited Edition No, 0281”, SACD/CD (1982/2014)
    • Jean-Michel Jarre, Electronica. Vol. 1: The Time Machine, Sony Music Labels SICP-30788, BSCD2 (2015)
    • King Crimson, In The Court of the Crimson King, Atlantic/Universal Music [Japan] UICE-9051, „21st Century Complete Edition. Series 1 #1”, HDCD (1969/2004)
    • King Crimson, Lark's Tongues in Aspic, Atlantic/WHD Entertainment, IECP-20220/221, „40th Anniversary Series", 2 x HQCD (1973/2012)
    • Lisa Gerard & Pieter Bourke, Duality, 4AD/Sonic SON 139, CD (1998)
    • Marc Copland & John Abercombie, Speak To Me, Pirouet Records PIT3058, CD (2011)
    • Mike Oldfield, Crisies, Mercury/Universal Music Japan UICY-75880/1, 2 x SHM-CD (1978/2013)
    • Roy Haynes Quartet, Out of the Afternoon, Impulse!/Esoteric ESSI-90135, SACD/CD (1962/2015) w: Impulse! 6 Great Jazz, Impulse!/Esoteric ESSI-9013/8 (2015)
    • Smolik/Kev Fox, Smolik/Kev Fox, Kayax | Agora 92781141, CD (2015)
    • Sonny Rollins, Sonny Rollins on Impulse!, Impulse!/Esoteric ESSI-90134, SACD/CD (1965/2015) w: Impulse! 6 Great Jazz, Impulse!/Esoteric ESSI-9013/8 (2015)
    Japanese issues available at

    I would compare coming across such an amplifier as this one to finding a gold mine. No, it doesn't offer anything I haven't heard before. Every now and then I come across such special, unique amplifier – like Polish SinusAudio or British Tellurium Q (Iridium 20) to name a few – but not often enough. They are a gold mine because they treat music in a particularly unique way, interpreting it in their own way, signing it with their own 'sonic signature'. If you like this approach you might spend hours and hours listening to all of your favorite albums and then go to the shop to buy even more music to find out what will be this amp's interpretation it. That's how this unique type of amplifier works on me.

    Orpheus presents a warm, rich sound. If you're looking for a class A, warm sounding transistor that does not sound like a typical solid-state machine at all, that turns digital sources into analogue-sounding ones, you should give this amp a try. Sure, there is a bit of exaggeration in my description – it's not THAT analogue - it's as much of a stereotype, as 'warm sounding class A'. But if one was ever to benefit from stereotype it would be in this particular case.

    This amplifier only confirmed what I figured out when reviewing RT Audio Design DAC some time ago, about its designer's own musical preferences. I'm pretty sure that he loves: vocals, old jazz, chamber music as these genres sounded remarkably. Within certain limits, I mean – this amplifier offers presentation that in some areas is ostentatiously far from being neutral. I also loved the way it played classic rock and many albums with electronic music too, including latest one from Jean-Michel Jarre Electronica. Vol. 1: The Time Machine.

    This album seems to be sort of recap of the whole carrier for the artist, as if he thought it was coming to an end and wanted to look back at what he achieved and work with artists he liked and admired. In the particular case of the track recorded with Tangerine Dream it turned out to be the very last moment to do that.

    Soon after Zero Gravity was recorded Edgar Froese, band's founder, passed away. This very track became the very last work all Tangerine Dream members ever did together. Anyway, Sony Music released a large box with this album, that includes a double vinyl, a CD, a pendrive with hi-res files and with some posters. Due to some errors in production, such as black and white posters for example, I've been postponing my review of this box for some time, even more so because I didn't really feel/understand this music. You see, Jarre's music is a very personal experience for me, as I've been his fan since my teenage years. So I perceive his failures as if they were my own.

    But with RT Audio Design amplifier's sonic character and Blu Spec CD 2 (BSCD2) version of the album, it all came together, 'clicked' and finally fulfilled my expectations. I read descriptions of each track again and I finally understood Jarre's intentions.

    Orpheus brought sound closer to me, warmed it up a bit, enriched it. I should tell you that already now, that there is no too much energy in the lower end nor it is particularly well controlled. It is obvious that amplifier prefers music with a nicely sustained bass notes rather than one with fast, taut ones. With Jarre's album amplifier told a an elaborated, beautiful, interesting story. It did the same with Lisa Gerrard from Duality and King Crimson from In The Court of the Crimson King.

    This last album surprised me particularly. I listened to the HDCD version released in 2004, that offered a significantly different sound than previously released one on gold CD, or the HQCD released later. It offers less details, sound is warmer and bass not so rich. But it has a particular depth to it, that other releases lack. So until the whole discography will be released on Platinum SHM-CD (it was supposed to happen already last year, but they postponed it), this is my version of this album. Even more so, because when played on a system that is capable of presenting this particular depth of the recording, that is also highly resolving but not highly detail-oriented, it sounds so well, that each time I listen to the full album even if I do that for a test and not my personal pleasure.

    The mkII version of Orpheus delivers exactly such a performance. Upper treble is rolled-off, and bass below, say, 50-60 Hz lacks power, energy. There is also a slight emphasis in the area of 300-400 Hz, that is responsible for this amazing impression of a depth of the midrange. And yet, I didn't really feel for a second that this presentation was missing something. I can't promise you will perceive this sound the same way – if you prefer open, fast, highly detailed sound you might find this amplifier's performance boring. But for a second try my perspective: listen to percussion cymbals on Impuse! recordings that were recently re-mastered by guys from Esoteric (Japan) – this is a true effusion of sounds. Sounds that are not artificially lit up.

    And that's what Orpheus is about: the resolution is very high, resulting in rich, deep sound. In turn, the selectivity is so-so, and it resembles what such amplifiers such as: Iridium 20 by Tellurium Q, or top models of Accuphase P-series, and others, offer. That's why sustain of the sound, fully developed decay create a convincing impression of instruments' presence. Even more so, because sound seems also particularly clear. I know that from devices with particularly wide frequency range, such as my Soulution amplifier, or my Ayon Audio Spheris III preamplifier with its frequency response reaching 1 MHz. I do not mean that there are any instruments that have such a wide bandwidth, anyone who thinks that has obviously no idea about audio (same goes for hi-res files). The wide bandwidth allows an accurate reproduction of the 'useful' range though (nominally 20 Hz - 20 kHz, I'd say: 15 Hz - 25 kHz).

    Perhaps that is why the amplifier presents a very natural soundstage, space, I mean for a listening at the home. It reminded me a type of sound delivered by turntables and master-tapes, with not so precisely defined shapes of instruments, no so precisely differentiated distances, with acoustics focused around instruments and with listener having a sense of 'being' part of the music. This 'focusing' ability works not only for jazz and rock, but also with the recordings with problematic spacing, such as, for example, Czesław Niemen's albums.

    I wrote about it in my articles about Niemen's debut album, or so called: 'red album': changes introduced to the spacial aspects of the recordings made them on one hand more interesting but on the other it changes their perception. I realized that when I purchased one of the albums of “Golden collection” that was released in 2000 by Pomaton – this was the first since many, many years re-issue, personally authorized by Mr Niemen, called „The Best of…”. I bought it when I started to work on the article about Mr Czesław's “compilations”. This particular one utilized material re-master by artist himself for the Digiton release. When played using Bulgarian amplifier it sounded really good, It was easier to understand Niemen's intentions, because sound was very rich, dense, and these slightly bright elements in the upper midrange did not annoy me the way, they usually do. I also did not have this feeling of a 'tunneled' presentation that many other amplifiers deliver with this material – it was a very interesting listening session!


    This amplifier offers simply beautiful sound. But its bass doesn't go very deep, is not particularly well controlled and it is rather warm. But it's tonality, and spacing is wonderful – it creates an impression of a bubble, without clearly defined contour, that listener sits in. Micro-dynamics is remarkable, macro is definitely not that good. As with any other audio product, there are pros and cons. But that's what a high quality audio is about – nicely balanced proportions and not pretending that everything is perfect and there are no issues at all.

    Orpheus is quite a atypical device. It is surely not the right choice for every music fan. But I don't think that it was intended as an all-rounder. If such a small manufacturer as RT Audio Design is to succeed on the market, it has to distinguish itself from the competitors using its designer's sound philosophy and following it to achieve a certain type of sound. This is an amplifier for those who have clear expectations and preferences. It is a great example of a implementing man's vision of the sound into a wonderfully made device.

    The full name of the amplifier under review is: Stereo Power Amplifier MkII • Orpheus • Class A/AB. It's a two-box, stereo power amplifier. It features a dual-chassis design because the power supply section has been completely separated and put into second enclosure. Both boxes sport almost identical enclosures with a thick, 10mm, anodized and lacquered aluminum front and a very rigid, steel case. Top cover features a large brand's logo. There are two large radiators with rather rough edges on both side panels. Chassis sports nice, aluminum feet with rubber inserts.

    The power amp box sports a small, red LED on its front, acting as power indicator. The on/off switch sits on the rear of the amplifier – placing it on the front, like in case of Orpheus DAC, would be more practical. Both boxes are connected with a short umbilical. So both boxes can be placed either next to each other or one under the other (on separate shelves in the rack). Don't place them directly one on top of the other – that's not why these two elements were separated! The umbilical is a high class cable by Neotech, the NEP-3003 to be exact featuring high purity UPOCC conductors. Same wires were used for internal cabling of the amplifier. Manufacturer used one of the best power connectors available on the market, the Neutrik NAC3FX. These feature silver-plated contacts and an excellent locking mechanism. Power supply is fitted with the same type of connector so user has to make use of a generic power chord delivered with the device or a short adapter featuring Neotech OCC copper conductors if one plans to use a power cable of one's choice.

    The power supply section is filled up with components. There is a powerful 350W toroidal transformer made by Bulgarian company Unitraf. It works with an active voltage stabilizing circuit featuring power transistors, 8 Nichicon Hi-Sound 10 000 μF each capacitors and four smaller ones filter and stabilize voltage. Voltage is rectified using fast Shotky diodes. The same power supply might be used for a power amp working in class AB. One has to replace one jumper and adjust bias to have the amp working in class AB delivering 80W @ 8 Ω. One may also buy a dedicated power supply for AB operation and use its full output of 250 W.

    Each output stage is rather small but each features its own PCB. Current section utilizes two pair of Toshiba A1962 + C5242 transistors per channel. They work in class A in push-pull configuration. There are four Nichicon capacitors on each PCB. One finds also chips attached to small radiators there – these are drivers for output transistors. Signal travels to PCBs via nice, shielded wires. High quality input connectors and speaker bindings come from Cardas.

    Specifications (according to the manufacturer)

    Output: 2 x 50 W/4 Ω
    Input impedance: 47 kΩ
    Gain: 31
    Output impedance: 0,1 Ω
    Frequency range: 0 – 1 MHz
    THD (1 kHz): 0,001%



    - Turntable: AVID HIFI Acutus SP [Custom Version]
    - Cartridges: Miyajima Laboratory KANSUI, review HERE | Miyajima Laboratory SHILABE, review HERE | Miyajima Laboratory ZERO (mono) | Denon DL-103SA, review HERE
    - Phono stage: RCM Audio Sensor Prelude IC, review HERE

    - Compact Disc Player: Ancient Audio AIR V-edition, review HERE
    - Multiformat Player: Cambridge Audio Azur 752BD
    - Line Preamplifier: Polaris III [Custom Version] + AC Regenerator, regular version review (in Polish) HERE
    - Power amplifier: Soulution 710
    - Integrated Amplifier: Leben CS300XS Custom Version, review HERE

    - Stand mount Loudspeakers: Harbeth M40.1 Domestic, review HERE
    - Stands for Harbeths: Acoustic Revive Custom Series Loudspeaker Stands
    - Real-Sound Processor: SPEC RSP-101/GL
    - Integrated Amplifier/Headphone amplifier: Leben CS300XS Custom Version, review HERE
    - Headphones: HIFIMAN HE-6, review HERE | HIFIMAN HE-500, review HERE | HIFIMAN HE-300, review HERE | Sennheiser HD800 | AKG K701, review (in Polish) HERE | Ultrasone PROLine 2500, Beyerdynamic DT-990 Pro, version 600 - reviews (in Polish): HERE, HERE, HERE
    - Headphone Stands: Klutz Design CanCans (x 3), review (in Polish) HERE
    - Headphone Cables: Entreq Konstantin 2010/Sennheiser HD800/HIFIMAN HE-500, review HERE

    - Portable Player: HIFIMAN HM-801
    - USB Cables: Acoustic Revive USB-1.0SP (1 m) | Acoustic Revive USB-5.0PL (5 m), review HERE
    - LAN Cables: Acoustic Revive LAN-1.0 PA (kable ) | RLI-1 (filtry), review HERE
    - Router: Liksys WAG320N
    - NAS: Synology DS410j/8 TB
    System I
    - Interconnects: Acrolink Mexcel 7N-DA6300, review HERE | preamplifier-power amplifier: Acrolink 8N-A2080III Evo, review HERE
    - Loudspeaker Cables: Tara Labs Omega Onyx, review (in Polish) HERE
    System II
    - Interconnects: Acoustic Revive RCA-1.0PA | XLR-1.0PA II
    - Loudspeaker Cables: Acoustic Revive SPC-PA

    System I
    - Power Cables: Acrolink Mexcel 7N-PC9300, all system, review HERE
    - Power Distributor: Acoustic Revive RTP-4eu Ultimate, review HERE
    - Power Line: fuse – power cable Oyaide Tunami Nigo (6m) – wall sockets 3 x Furutech FT-SWS (R)
    System II
    - Power Cables: Harmonix X-DC350M2R Improved-Version, review (in Polish) HERE | Oyaide GPX-R (x 4 ), review HERE
    - Power Distributor: Oyaide MTS-4e, review HERE
    - Stolik: SolidBase IV Custom, read HERE/all system
    - Anti-vibration Platforms: Acoustic Revive RAF-48H, review HERE/digital sources | Pro Audio Bono [Custom Version]/headphone amplifier/integrated amplifier, review HERE | Acoustic Revive RST-38H/loudspeakers under review/stands for loudspeakers under review
    - Anti-vibration Feets: Franc Audio Accessories Ceramic Disc/ CD Player/Ayon Polaris II Power Supply /products under review, review HERE | Finite Elemente CeraPuc/ products under review, review HERE | Audio Replas OPT-30HG-SC/PL HR Quartz, review HERE
    - Anti-vibration accsories: Audio Replas CNS-7000SZ/power cable, review HERE
    - Quartz Isolators: Acoustic Revive RIQ-5010/CP-4

    - FM Radio: Tivoli Audio Model One