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Digital to Analogue Converter


RT Audio Design

Manufacturer: RT AUDIO DESIGN
Price at the time of the review: 1700 EUR

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


Delivered for test by: RT AUDIO DESIGN

ore and more interesting devices come to us from countries that, not that long ago, seemed to have nothing to offer for audiophiles, and today, to many people's of the West surprise, these countries deliver some widely appreciated products. Fortunately, as Heraklitus said, panta rhei. Many companies from behind Iron Curtain today are recognized an appreciated all over the world, and their products find more and more happy owners and fans.

One of such companies is a Bulgarian high-end manufacturer of electronics, but also loudspeakers, Thrax Audio. Company lead by Rumen Atarski, apart from their own products, works also as an OEM manufacturer of fantastic, aluminum chassises for several high-end brands. Compared to them RT Audio Design is a small, just starting their own, hopefully great, history company, founded by two audio enthusiasts, Tsvetan Tsencov (an electronic engineer) and Ivaelo Ratzov (industrial designer).

There is nothing really visionary in company's materials that say, that: „our goal was to achieve improved sound quality and to propose own own solutions for audio designs”. But that's exactly how most well known audio designers started their carriers like. Mr Tsvetan as the elements of company's philosophy names:

  • high quality separate power supply for all products,
  • battery power supply for DACs and RIAA preamplifiers,
  • output transformers as filter and I/V converter for DAC,
  • passive preamplifiers with TVC (Sowter) or high quality potentiometers (ALPS),
  • no signal capacitors in signal path.

Tsvetan Tsenkov
RT Audio Design | designer

The newest DAC from RT audio design Ultra USB DAC Orpheus is result of the continuous desire to improve the sound. The Ultra USB DAC Orpheus is realized on the base of audiophile chip AD1852 with differential analog outputs. Using our philosophy for output stage, we don’t use active I/V conversion and only isolation transformers.

The most audio engineers know that transformers are ideal low-pass filter and impedance buffer (reduces dependence on quality interconnectors).The phase shift in the transformer used by us is less than 2 degrees and THD is zero , because don’t use op-amps or valves buffers. We choose output transformers from Sowter model 3232 for best music sound.

The DAC consists two main sections:

  • USB to I2S converter
  • SPDIF receiver with DAC part.
The USB section is realized with XMOS 500 MIPS processor in asynchronous mode, separate clock. The USB to I2S is especially designed for asynchronous audio transfer. It can transmits PCM and DSD (DoP) audio data. This board provides bit-perfect playback at sampling rates from 44.1 kHz up to 384 kHz with up to 32 bit resolution.

The DAC section is mounted on the separate PCB with five independent low drop stabilizers LT1086 Linear technology .All components are manually soldered for best quality. We don’t use signal capacitors in signal path because they diphase music. All filter capacitors are high grade Nichicon True gold.

The power supply is very important and therefore we use 12v/2,2 Ah battery, mounted inside the DAC. No noises and hums from mains, making sound clean and smooth. You can listen the DAC 12 hours without charging. The battery charger is a specially designed low noise SPMS power supply which works with 100kHz frequency.

All products are handmade and tested personally for defects. RT Audio Design use carefully selected components from leading manufacturers(Nichicon, LCR, Yshy, Panasonic, Mundorff, Elma). In 2013 RT Audio Design took the first place in the Best sound category on HIFI SHOW SOFIA 2013.

Recordings used for this test (a selection)

  • Coleman Hawkins, The Hawk Flies High, Riverside/Mobile Fidelity UDSACD 2030, SACD/CD (1957/2006).
  • Ed Sheeran, X, Warner Music UK/Warner Music Japan WPCR-15730, CD (2014);
  • Grace Jones, Disco, Island/Universal International Publishing 53546482, BOX: Portfolio, Fame, Muse, 3 x CD (2014).
  • Harold Mabern, Afro Blue, Smoke Sessions Records SSR-1503, CD (2015).
  • Laurence Hobgood, Left To My Own Devices…, Naim naimcd049, CD (2000).
  • Maroon 5, Songs About Jane. 10th Anniversary Edition, A&M/Octone Records/Universal Music LLC UICY-10029/30, 2 x SHM-CD (2002/2012).
  • Patty McGovern & Thomas Talbert, Wednesday’s Child, Atlantic/Sinatra Society of Japan XQAM-1047, CD (1956/2010).
  • Royal Blood, Royal Blood, Warner Music UK/Warner Music Japan WPCR-15889, CD (2014);
  • Stanisław Soyka & Roger Berg Big Band, Swing Revisited, Universal Music Polska 472 844 1, CD (2015).
  • The Quartet, The Quartet, Poljazz/Anex AN 302, CD (1978/2014?).
  • Tori Amos, Under The Pink, Atlantic/Rhino 2795618, “Deluxe 2 CD Set”, 2 x CD (1994/2015).
Japanese issues available at

If we lived in a “linear” world each invention improving the way its predecessor worked, would be simply better. Period. It would do exactly what its predecessor did, only better in every possible way. The “linear” world is a fantasy though, an imperfect model that have only some things to do with a real world. But there are some it does. After all each new solution/invention is to replace a previous one, to make some aspects of it better, to offer something new/more, by using some more advanced, better elements.

We all know, that the world is not that simple – that's a fact. Which means that is real world there are always compromises – to gain something, we loose something, at least partially. Audio industry is no different in this respect. Moving from mechanical way of recording sounds on a cylinder and later on a record with no electricity involved, to recording using active amplifier circuits we involved many variables into recording process that change the sound thus averting us from an authenticity of a live performance. But at the same time we gained so much in terms of sound quality (in a high-fidelity meaning), that we abandoned the old way of recording without any regrets. Same story repeated itself with other following steps – tubes, transistors, analogue and digital, physical music mediums and music files.

Designing and building Orpheus converter people from RT Audio Design realized their vision of the sound. I am pretty sure that what they wanted to achieve was not the overall better performance but rather a better performance in some aspects of the sound, the ones they considered most important.

And it is not difficult to realize and point out which aspects these were. Mr Tsvetan Tsencov's and Ivaelo Ratzov's priorities are clear, that's why I do not use expressions like: “I think”, “I believed” or “it seems” as I am sure of what I hear. What they cared about most was the authenticity of the presentation. Me mentioning a mechanical way of recording before was no accident as it involved the shortest and simplest possible path of a signal. The result was the most natural sound possible, and I mean a level of naturalness that is hard to achieve even today.

Performance of this Bulgarian DAC includes many elements, that were possible to achieve only recently and only by a multi-thousand USD designs using latest developments in sound processing. Sound is very “realistic” and phantom images seem very palpable which, despite quite reasonable price of this device, makes it suitable even for high-end systems.

There is nothing in its performance that bothers listener, nothing that disturbs enjoying music fully. And while this is not an absolutely all-round performer (I'll explain that in a moment), while there are some elements in this performance that are results of some, accepted by designers, compromises, yet it is truly enjoyable and if its limitations are acceptable there will be no reason to pay more for another product.
The most general description of its sound could be similar to what a high quality tube preamplifier has to offer. Wonderful, colorful tonality, richness of the sound, great soundstage, and amazing palpability of the sound that makes the performance enchanting, whether it is a puristic recording of Laurence Hobgood, or Ed Sheeran's X, or finally a remastered version of Under The Pink by Tori Amos. It doesn't really matter what recording we play, what we get is a very realistic, very convincing performance.

As I already said it is quite a tube-like sound. By that I mean that both attack and decay phases of the sounds are slightly rounded, without distinct definition. When it came to treble and midrange I didn't really care, as this created presentation with high level of euphony, which in turn fitted into the sound signature of this device, as if this imperfection of the presentation only confirmed its class.

The aspect that one has to accepted if Orpheus is to be a part of one's system, or that will exclude it from potential purchases will be most likely that way that bass is presented. The upper part is slightly emphasized which makes vocal larger and more palpable. This creates an impression of a more “serious”, richer, more palpable presentation. But it also means adding something extra to the mix, additional information that is not present in the same recording when played with better balanced digital sources. And not that good definition of a lower bass add up to this aspect too. Bass in nicely extended but the lowest part of the range, say below 100Hz, is not well differentiated, is rather monotonous. And slightly colored, too.

The way it is done differs from how many solid-state transformers do it by 'hardening” part of the bass range which makes it boomy. This DAC offers colorful sound but with rounded leading edge. So it never really sounds unpleasant. You need to know though, that when listening to not so well recorded, loud, powerful music, will result in a bit chaotic presentation. I heard it when listening to Royal Blood's album, and even with more powerful fragments of above mentioned Tori Amos' album.

That's why with Orpheus I listened mostly to jazz and vocal recordings. I have no idea what music do the people from RT Audio Design listen to mostly, but I would bet that they listen to something similar. Probably also some electronic music.
In this type of music the results of eliminating active conversion stage and coupling capacitors are usually remarkable, and changes introduced to the signal (as always, there is also a cost of this solution), as transformer also has its sonic signature, don't effect listening pleasure.

Most of the time I used this D/A Converter with my headphone system. That's how I listen to the music in the evenings. I like headphone listening, I am a real fan, so I spend a lot of time with some cans on my head. Surely this is not a perfect way to reproduce music, because it involves a non-linear frequency range, some problems with impedance and so on. But on the other hand there is something particularly authentic in headphones' presentation that I miss when music is reproduced by loudspeakers.

One of the systems that I often used comprises of battery powered Bakoon HPA-21 amplifier and planar-magnetic HiFiMAN HE-6 headphones. Signal is usually delivered from Lektor AIR V-Edition CD Player with tube output stage, via 1m Siltech Triple Crown interconnect. Adding battery powered Orpheus into the mix resulted in absolutely brilliant performance – organic, rich, natural. The problems I mentioned above did not really matter anymore, what truly mattered was what this DAC did really well.


The Bulgarian converter is a result of passion and love for music. One can hear that with every recording, in every system. As any love also this one has its preferences, it is not universal. What is preferred is: naturalness, tangibility, richness, while definition, selectivity and differentiation of a lower range is not a priority. If one is OK with that, if one listens to the music that is not “hurt” by such a set of features, then, using reasonably priced Orpheus one will join a true high-end sound club.

RT Audio Design attracts attention as it looks really nice. It reminded me (I mean its style) the logo of the Super Audio CD, which I consider one of the best in the audio industry. Front panel with logo and some inscriptions is made of aluminum. It sports a very good, widely used for high-end devices power switch and two LEDs, that indicate an active input. Both: power switch and LEDs are blue - rigueur of late XX and beginning of XXI century. Unfortunately there is no way of checking sampling frequency of input signal, not to mention bit count. User is also not informed whether input is in sync with source. This is not a problem when using a CD transport, but when it comes to communication with a computer, where something might always go wrong, without such indicator user doesn't know where to look for a problem. It seems that for latest D/A Converters such an indicator is a must.

The rest of the chassis is also made of aluminum. There is a larger logo on the upper panel, which seems a nice touch further improving aesthetics of this device. They used high quality input sockets – USB comes from Neutrik. There is a small flip switch between inputs that acts as an input selector. There is also an analogue, unbalanced output with gold-plated RCA sockets. Next to it there is this also gold-plated, multi-pin power inlet. The device sports solid, good looking multi-layer feet made of aluminum and rubber.

Inside the whole circuit sits on two PCBs. The smaller hosts USB receiver and a converter to S/PDIF. It is based on a XMOS chip. It accepts PCM signal up to 32/384 and DSD (DoP) signal.
Signal runs through a short USB cable from input. I wonder whether it would be possible to eliminate this cable. This circuit sport a separate oscillator, and an input signal is re-clocked with another high quality two separately for 44,1 and 48 kHz (with multiplayer) signals. Signal is than transferred to the next PCB with thin wires and buffered by matching transformer.

Exactly the same transformer is used for S/PDIF input and placed on the main PCB. It is clear that USB signal's path is much longer. PCM signal from RCA input lands in Cirrus Logic CS8416 (24/192) receiver, that is no longer produced. Finally signal goes to a DAC chip - Analog Devices AD1852. It is capable of receiving 24 bit/ 192 kHz signal. So it seems that any signal with higher resolution has to be converted somewhere along the signal's path. DAC chip converts all signals into 24bit ones.

All that one will find in most currently manufactured DAC. What is different about Orpheus is that where in other DACs one would find lots of integrated circuits, transistors, tubes, capacitors, resistors, here one finds nothing of the kind. Nothing apart from Sowter, model 3232 output transformers working as low-pass filters, I/V converters and output buffers. This type of design is well known thanks to Audio Note's products.

The device is powered via a 12V medium size rechargeable, that is charged using an external switching power supply. Even though is is already quite “clean” power supply 5 additional voltage regulators are used that are placed on the the main PCB. Only high quality elements are used.
There is a small inconvenience regarding power supply system here. Solution used for above mentioned Bakoon, disconnects charger after one turns the device on so the power comes exclusively from a rechargeable battery. Here the charger works all the time so when one wants to play exclusively from a rechargeable battery one has to unplug the power supply. Another inconvenience is lack of any charge level indicator.

Specifications (according to manufacturer)

Frequency response: +/- 0.25 dB 10 Hz to 60 kHz
Distortion at 50 Hz (Source 40 ohms): 0.05% at +20 dBu
Output level: 2,1V
Digital format: I2S 24bit/192kHz (PCM)
Analog outputs: 1RCA
Digital input: 1 RCA SPDIF;1 USB B asynchronous 32bit /384kHz
Phase shift: under 2 degrees
Dimensions; 230mmx280mmx80mm
Warranty: 5years



- 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