WALL-E
100+ Head-Fier
- Joined
- Dec 12, 2011
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Radon – beginnings.
The amplifier had his little debut on 27th of April 2013 at the London Head-Fi Meet. Even though it was just a prototype, this rigid, inconspicuously looking box brought my attention for the first time.
I was able to hear it performing with a few top models of headphones (as far as the acoustic conditions of the hotel room allowed). I especially enjoyed Audeze LCD2, where sound was full of energy, bass was very deep full of the lowest registers, able to punch with incredible power and speed at the same time not losing it consistency with the rest of the audio bandwidth.
Then I made also contact with the creator of this amplifier (back then it wasn’t named yet) and asked him for the possibility of making a private listening session at home using the system I had. He agreed and soon after the London Head-Fi Meet I had it at home connected to my system.
As a big tube fan I wanted to confront prototype of headphone amplifier Mr Radek of the RadioactivePages.com created with my tube amp, La Figaro 339 SE-OTL, working in class A, equipped with 6sj7gt tubes of American Tung-sol on the input and 7236 tubes on the output (BTW: my favourite configuration when pairing with HE500).
We started the listening session.
Our digital source was feeding DAC with ESS Sabre32 9018 chip used in 3in1 Burson Condutor, which output was connected to the amplifier and then HE500 headphones.
First impression we got was a pleasant tube-sounding of Mr Radek’s amplifier. It had no problems with driving such a demanding headphones like HiFi Man HE500. All registers were consistent, not falling apart, plentiful of well controlled bass, contours were not too harsh and listening was just a sheer pleasure.
The overall sound quality as for this prototype was very promising, not exactly as high as the La Figaro 339 amplifier, however designer and producer of the amplifier said that he is working intensively on the final improved version which is to be ready in about few months. This happen to be very fortunate as I was just about to build another headphone system based on the solid state amplifier.
Last fall I was seduced by the trade-in program for Sennheiser HD800 offered by Custom-Cable UK, so I started taking a look for a proper amplifier for my brand new headphones. When visiting radioactivepages.com I found out that the amplifier got into a production stage and a few first units were ready for purchase. Since the producer gives 21 day money back guarantee I ordered one home as there was no risk that if I don’t like it I lose hardly earned money. So after next few days I had a brand new Radon 222 at home.
First look – construction.
After opening the box and removing the protective bubble wrap I was able to see the amplifier in its final design version, nicely finished and looking even more eye catching than one can see on the website. Radon 222 makes very good impression at the first sight: it is heavy (>3kg) as for such a small box, has professionally finished case with front made of 8mm brushed and anodized aluminium and top and back sides made of 3mm think aluminium plates. Sides made of waxed exotic wood adds retro look, resembling a bit Japanese stereo amplifiers from late ‘80.
At the front we see a round solid power switch highlighted in red when ready to use, two Neutrik Phono sockets and a large aluminium volume knob. At the back we have 2 gold plated Neutrik RCA sockets and a power socket with grounding and protected with 2 fuses. That it all about the external look, but the most interesting and important is what is underneath the top cover of the amplifier.
After taking the top aluminium plate off first thing we see is the real dual-mono architecture, cleanliness of the construction and symmetry. As highlighted by the creator of the amplifier on his web site, this modular approach is to enable simple upgrades and tuning. Both left and right channel’s amplifiers as well as their corresponding power supplies are completely separated.
It is clearly visible that a lot of effort was put to the power supply: 230V is fed to 2 stage integrated filter made by Shurter which is then connected to two toroidal trafos cemented in epoxy resin (they have to be hi grade as it is almost impossible to hear any buzzing), each powering its own channel. Each power supply module is using 2 bridge rectifiers each for positive and negative voltage halves. Each module is also equipped with filtering circuit consisting of 4 Nichicon and 2 Panasonic electrolytic capacitors selected for their low ESR and high durability. They are supported by pair of WIMA polypropylene capacitors and surface mounted ceramic Murata XR7 capacitors which main task is to filter out radio frequency noise and improve amplifiers impulse response. Voltage stabilisation is performed by two Linear Technology chips LT1085/LT1033.
The audio path is based on discrete components (assisted by only one highest grade op amp per channel) individually selected and paired as noted by the producer, which in my opinion, deserves full respect in these days flooded by mass production. Only few hi-end equipment producers can afford such a luxury.
Blue Alps potentiometer is placed in between amplifiers to minimize the length of audio path. Its axis is connected with the elastic yet very solid axial joint which guaranties optimal mechanical performance of the potentiometer.
In short conversation with Mr Radek about the amplifier, he said that it was amplifier module he spent the most time designing it. The bar was set very high, as he said that only circuits with the very high frequency band pass are able to provide the highest fidelity of audio reproduction and fastest pulse responses. We are talking about hundreds of kilohertz in this case!
This posed many problems related with oscillations and susceptibility of the amplifier to radio frequency noise. Therefore careful selection of elements, proper PCB design, power supply bypassing as well as shielding were necessary. Next step was to eliminate all ground loops what was the most critical part of the design. As signal output provided by Jack socket already shortens both left and right channels grounds, this had to be the only common ground point. This single requirement dictated the only possible topology to choose - full dual mono architecture with separate power supply per channel.
Signals enters volume potentiometer which provides signal to operational amplifier LME49990(*) made by National, which further drives high current buffer based on two paired bipolar transistors SD669 and SD649 working in push-pull mode, mounted with the small aluminium bracket to the bottom of the case. That’s why it the hottest part of the amplifier, which is working in pure class A. Quarter of more than 8 Watts of power is sent to headphones, which should be sufficient for most of dynamic and planar headphones.
* Thanks to easily replaceable op amps Radon 222 allows you to enjoy excellent tonal characteristics selected according to you own preference.
Possibility of op amp selection was an important factor when designing the amplifier module. Mr Radek was aware of this problem so he designed it to be ready to work with large range of op amps available on the market. All around power supply we see a number of high class bypass capacitors like MKP WIMA, ceramic Murata, tantalum or low ESR electrolytic capacitors made by Panasonic. In the feedback loopback there are two 0.1% DALE resistors used.
Sound
Accompanying equipment:
Burson Conductor as DAC (working as reference DAC)
Mac Book Pro i7 with installed FLAC file player Audinirvana via USB
Marantz SA15S2 as Hi-Res SACD player
La Figaro 339 as reference headphone amplifier
Headphone output from Marantz as reference point
Headphones: Sennheiser HD800 and HiFi Man HE500
Op amps used: AD797, LME49990 and Burson suprema sound (4th generation of opams).
According to the web page this dual mono construction should provide 8W of power per channel (or 2.3W in pure class A) at THD below 0.01% at 20 ohm of load, so I was curious if this could be heard while listening. This much of power should discipline every single headphones, even planar ones.
To test it I decided to use 38 ohm HE 500 headphones. This was my first test I performed on a brand new Radon 222. At once I found out that the music was presented with unprecedented verve and dynamic range. And even when I connected a second pair of headphones, set the volume to the levels my ears wouldn’t be able to stand too long I was able to notice any signs of distortions. After satisfying my “animal” curiosity, I started more accurate listening tests at normal volume levels.
Anticipating the facts, I will only say that I liked the amplifier so much I decided to keep it, so as I write this review, both the amplifier and my HD 800 headphones are already working for 150 hours and are fully broken in. Therefore the experience I will try to describe below will mostly refer to that pair of audio equipment.
Everyone who tried putting Sennheiser flagship on, even just for the moment, knows how comfortable they are. Around the ear construction with a lot of space for ears gives comfort level unattainable for many other smaller headphones. For me they are the most pleasant to wear headphones ever. As for the sound, the things look less obvious. From the very start they show some specific tonal character that changes in some magic way presentation of the music content, still they are natural and very detailed. I would say they are detailed to that extend they are merciless for any poorer recordings or electronics used in the signal path, especially for the amplifier. Even lack of the proper CD drive may result in a flat, dull or sterile sound with no atmosphere to breathe.
Radek’s amplifier doesn’t have anything in common to what I said just above. The sound is alive, abundant in bass which is pulsating and vibrating but never out of control. It is strong but not obtrusive, pleasant in listening even soft when it’s meant to be. It doesn’t matter if it comes from natural instruments or is synthesised, it is always stable and there is plenty of energy left for the culminating punch. Radon 222 represents warm tonal character, with vast but not overblown space and dynamics.
Scene is broad, deep and all sources of sound can be easily localized and have proper size. When listening to Amber Rubarth recorded in binaural technology by Chesky Records, the rendered stage was so real, holographic, I got the impression that I am sitting inside it, able to point to where who is standing.
Listening to the subsequent albums confirmed the same natural warmth that nonetheless never crossed the lack of detail boundary. Was it strong Faith No More, melancholic Ane Brun or twisted Steve Struss from stockfish, there was never coquetry in the sound reproduction, it was genuinely attractive and well balanced, supported by the firm bass, bright upper band and well saturated mid tones.
The amplifier was able to „understand” in an instant the specifics of each recording and serve it according to the expectations in a way you just can’t stop listening. A gentle increase of the sound temperature was to encourage you to discover again the music you love and make you also enjoy the albums of slightly poorer recording quality.
Summary
In my opinion Radon 222 will be a perfect choice for many headphones. It is characterised by excellent casing design, has large reserves in dynamic power and what is most important plays different types of music with proper balance, presents all the details with ease, giving you long hours of pleasure of listening to the music.
