![]() The S6 covers all the bases to be qualified as a premium product.Īudiophiles fixated on specs might pass on the S6 because of its modest power rating – yet its 35 watts per channel will suffice for all but the most inefficient speakers when playing at reasonable levels. Even the remote is unique, eschewing the standard kids meal remote that many products at this price feature, in favor of a more stylish remote with a wooden body. Unison claims the S6 compatible with speakers in the 4-8 ohm range and provides a single set of output binding posts. The rest of the amplifier is straightforward, with volume, power and input selector on the front panel and five single ended inputs around back. Regardless of where you stand on tube rolling, the stock tubes are an excellent choice and should be fine for all but the most OCD tube roller. A pair of Telefunkens or Bugle Boys will push the sound more towards the classic syrupy tube sound, while my favorite 12AX7, the EAT gives the S6 a lower noise floor and even more HF extension and less grain. This amplifiers character can be changed more (and for less money) successfully merely substituting the two 12AX7s. I did not spend a lot of time tube rolling, and swapping a few different EL-34s for the Tung Sols provided different sound but no overall improvement, so I submit the designers have done an excellent job voicing around current tubes. The 12AX7 driver tubes should last in the 10,000 hour range, making this an easy amplifier to live with long term. The controlled biasing combined with not running the output tubes terribly hard should make for ample tube life. Standard issue tubes continue to improve and the current TungSol E元4’s supplied with the S6 proved close enough to the megabuck vintage E元4s on hand for comparison, that for all but the most fanatic and well heeled tube roller, you can rest assured the S6 sounds great right out of the box. After about a month, the tubes settle in and a casual check now and then will suffice. It’s wise to keep an eye on bias when your S6 is brand new, checking every few days. ![]() ![]() With a pair of stylish meters and front panel adjustability, no tools are needed – meaning no tools to lose or misplace before a listening session. Mixing it up even further, the S6 features a combination of auto bias and adjustable bias, fine-tuning the operating point of the output tubes to perfection. Rather than a traditional push-pull configuration, the S6 employs three E元4 tubes per side, in parallel, driven in single-ended, Class-A triode mode. Regardless of the flavor you choose, amplifiers built around the E元4 tube rarely disappoint when it comes to midrange magic – and the Unison Research S6 is no slouch, yet it offers so much more. (Those thinking 6550’s can’t offer subtle inner detail, look no further than the Octave Jubilee monoblocks) The midrange of the E元4 is usually described as having a warmer, more romantic, tonally rich sound than many of the other output tubes, these lower powered amplifiers often render inner detail with more delicacy than most of the higher powered tube amplifiers. This pentode tube almost always produces a more mellow sound than the 6550/KT88, which usually delivers about twice as much output power per tube. While I’ve never met an E元4 amplifier I can’t enjoy, the folks at Unison or Conrad Johnson need not lose sleep over my making a career change anytime soon. I’ve even built a few in my younger days. I’ve owned many variations on the theme – from the legendary Marantz Model 8 and the Dynaco Stereo 70, to current production amplifiers from Conrad Johnson, Prima Luna, Octave and now the S6, reviewed here. Moderately powered tube amplifiers based on the E元4/6CA7 output tubes have a legion of followers, myself included. The same could be said for the Unison Research S6 integrated amplifier, now in production for over a decade. It’s like discovering that cool coffee shop down the street, only to find that it’s been there for years and you just passed it by. Perhaps the most enjoyable part of the hifi journey is discovering something new, especially on a heavily traveled road.
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