January 2003

Dubiel Accoustics (Skorpion) HV-1 OTL Stereo Headphone Amplifier
Giving Great Head On The Cheap
Review by Steven R. Rochlin
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  Here is one of those virtually unheard of "web find" products that reach my e-mail inbox from time to time. While some of these finds are home-brew turned company, others are from well-established companies in parts of the world where they have not ventured outside their home country. As an example, the world's first outside Germany review of the Lehmann Audio Black Cube by yours truly was one of those great finds. Great sound on the cheap is always a joy! Only weeks after my initial review did word on the street reach a feverish pitch. Eventually the Black Cube found its way into the homes of many thousands of audiophiles. The rest, as they say, is HIStory. If i was a betting man, the Dubiel Accoustics (was called Skorpion) HV-1 OTL headphone amplifier will also garnish such praise.

Based in Poland, Dubiel Accoustics was officially formed and began manufacturing electronics since 1979. Maybe we need to back up a bit as in 1969 their first tube amplifier, based on ECL 86, was designed for vinyl replay. After some years manufacturing silicone-based amplifier (solid-state), they decided to offer a line of tube amplifiers. This includes everything from tubes phono stage to amplifiers. As my home is chock full of equipment, the one component that could use an improvement was in acquiring a headphone amplifier. Enter the Dubiel Accoustics HV-1 at only $750!

Features include two standard stereo headphone jacks, a power switch (plus power LED) and volume control on the front. On the rear are quite solid gold plated RCA inputs, paralleled RCA outputs, standard IEC power receptacle, and fuse holder. Wood side panels round out the visual beauty of this unit. While there is a single power transformer centrally located, notice there is no sign of output transformers as this is an OTL design. Each channel uses a single 6AQ8/ECC85 for pre-amplification and 6080 for amplification. This design is said to provide a very wide frequency response from 5Hz to 70kHz (+0/-3dB). While output power is rated at 300 mW with a 40 ohm impedance, i found it more than enough for my power hungry Sennheiser HD600 setup (as reviewed here).

Using good quality parts and construction techniques, the HV-1 lends itself to greatness through the ability of not just eliminating the costly output transformers, but in also benefiting from using no output transformer at all. OTL is an abbreviation for Output Transformer Less and there is a huge audiophile cult that feels the best output transformer is none at all. Less = more. Hmmm... i detect a pattern forming as the Royal Reference 3A MM De Capo-i (reviewed this month by yours truly) also follows this technique within their crossovers.

Listen Up!
The Dubiel Accoustics HV-1 found its way in both my high-end rig and also my Roland V-Sessions electronic drumset. While it was fairly easy to tell this was a wonderful unit, and amazingly cheap, with my cj premiere 17LS, the real qualifier for me was within my Roland V-Session kit. The V-Session has a good headphone setup and by simply adding the Dubiel Accoustics HV-1 it was easy to detect the differences. After careful listening using both systems have been able to come to a fairly complete conclusion. First and foremost the subtle dynamic nuances lost with the Roland's headphone jack were much more apparent with the HV-1. As the cj has no headphone jack, i can only make guesses in this regard. It is not to say the cj Premiere 17LS lacks dynamics. Far from it! Just that without a headphone jack on the 17LS all i can do is make an overall review without a comparison.

Tonally, the HV-1 is on the accurate side of the fence over tube warmth or "lush". It is not a cold and sterile unit and to further clarify, harmonics seems quite good and precise over the rose-colored glasses variety. If you are looking to have added warmth to your headphone's sound, then i would suggest looking elsewhere. The Dubiel Accoustics HV-1 seems to be more akin to the proverbial "straight wire with gain" versus a "tone control". While the lowish signal to noise ratio of 86dB initially concerned me as headphones are like audio microscopes seeing into the sound, the 86dB rating may be very pessimistic. Using my Sennheiser HD600 headphones i could detect a very slight buzz, yet it was very low and appears to be undetectable once the music begins (with the exception of the quietest of passages). While we could all wish for perfection, at only $750 for an OTL tubed headphone amplifier perfection may be unreachable.

Be forewarned, this unit inverts the phase. This means that the plus and minus needs to be reversed within your earphones or use the reverse phase switch on your CD/DAC (provided it offers this feature). Vinyl lovers may be left out of luck, though fortunately (for me) the Sennheiser HD600's ear pieces have a removable cord that can be reversed to effectively reverse phase at the "speaker".

Summing It All Up
Forget perfection... for $750 the Dubiel Accoustics HV-1 sounds to me like an amazing real-world bargain! Stereo separation and unfolding complex musical passages was easily accomplished as was subtle hall air. Only when playing the headphones at a high volume output as the music became incredibly intricate did it seem the HV-1 ran out of steam. This could also be due to the Sennheiser's power hungry nature. For those unfamiliar with the HD600, they are among the worst headphone power pigs available on the market today in my opinion. They are power hungry monsters akin to Dr. Evil seeking world domination! Easier to drive headphones like those offered from Grado would probably never stress the HV-1. (Note: According to one of our well-versed readers, Nathanil Lewis, "Most headphone amps are voltage amplifiers. A 300 ohm Sennheiser takes 3 times as much voltage to drive as a 32 ohm Grado. So you have to turn the volume way up. The efficiency, however, is the same.") The flipside would be the possibility of making the amplifier's background noise a bit more apparent. This is the same situation i find when  using my Avantgarde Acoustic Duo with their high 104dB/w/m sensitivity (Grado) versus normal 93dB/w/m loudspeakers. The lower sensitivity of a loudspeakers tends to hide a system's background noise to a higher extent.

The Dubiel Accoustics HV-1 does so much right that it would be hard to not recommend this unit at this low pricing ($750). While i would prefer a bit more lush, the stock 6AQ8/ECC85 and 6080 seems to come from ??? so tube tweaking could benefit greatly in this department. Regardless, those who desire a good quality headphone amplifier on the cheap and with tubes can rejoice! Perfection may not come in at $750, though the HV-1 does so much right that it can't be wrong. As they say "If loving you is wrong, i don't want to be right." As always, in the end what really matters is that you...

     Enjoy the Music,

    Steven R. Rochlin

Specifications
Inputs: One RCA pair (rear)
Outputs: One RCA pair (rear), two standard 0.25" (1/4") stereo headphone (front)
Control: Front on/off switch and large volume control
Frequency Response: 5 Hz to 70 kHz (+0/-3dB)
Tubes: preamp - 6AQ8/ECC85 for pre-amplification, 6080 for amplification
Operation: "Class A", OTL (Output Transformer Less)
Input Impedance: 100

Company Information
Dubiel Accoustics (Skorpion)
Zaklad Uslug Elektronicznych
Boguslaw Dubiel
45-824 Opole, ul. Cicha 6
Poland

Voice: (0-77) 4746-406
E-mail: bodzio_wiatr@poczta.onet.pl 
Website: http://en.dubieltubeamps.pl