Tubes Asylum: REVIEW: Unison Research Smart 845 Amplifier (Tube) by GEO

After watching others in this forum rave about the magic of the Single Ended Triode amp, I finally decided to take the plunge. After an approximately 15 year experience in the land of solid state spending time with brands such as NAD, B&K, Forte and up until about 1 year ago, McCormick, I decided to go tube and bought a Graaf 5050 power amp which used four 6550s and one 6922 for input and one 6922 for a driver. This was a very nice sounding amplifier. Very liquid midrange with nice body and great upper and low end resolution, especially with GEC KT-88s. Although I was very satisfied, I just had to try a SET, even if I ran the risk of not being fully satisfied.

An overriding concern for me was low end control. I own Spendor SP 9/1 speakers, which are adequately efficient (90 db) and adequately flat (8 down to 6 minimum)but the speaker is outfitted with a large 12" woofer that is fairly heavy. Those familiar with the speaker will appreciate the need to carefully match these speakers with equipment that is going to take advantage of the wonderful Spendor tone as well as provide good dynamic drive and rhythmic pace. I initally considered a 300B SET, but I feared that the bottom was going to be too soft on my speakers. I also considered other designs utilizing the KR 300B type tubes, but outside of Welborne Apollo II, nothing was going to give me the power I felt I needed. The Jota, was out of the question ($$$). After, dozens of conversations with a number of people experienced with various SET amps on my speaker, I decided that an 845 SET, would give me basically everything that I was looking for with the fewest compromises.

I have owned the Unison Reseach Smart 845 for three weeks now, and after a bit of tube swapping, I decided now is the time to write my review. I have replaced the Chinese 845s with RCA 845s and I am using a Telefunken 12AX7 as input and Sylvania 12AU7 as driver. The amplifiers are beautifully constructed. The 12"(w) X 8"(h) X 22.5"(d)units are utilize beautifully finished in solid cherry of very high quality along with black matted metal transformer covers and under chasis. There is a large ceramic shell which cradles the 845 tube and shields the transformer. This shell is very beautifully rendered and is not as cheesy a the picutres would lead you to believe.

Now on to the sound. The sound of these amps is incredible. I can only descibe the sound as wholly organic. Like many others have stated, I found that I don't listen to music like I used to. I now hear the whole band palying as one as opposed to various guys as individuals playing music together. The tone is much more life like with a texture that you can almost feel. The low level detail retrieval if fantasic. Air passing over a reed, fingers plucking a bass string, a singer breating between notes. If you have ever played bass or any instrument, you will understand how the attack of a note is critical to making music swing. The 845 is very extended on top without any hint of harshness. Cymbals ring true and the decay is spooky. Notes just fade to black. Guitar and piano chords are vivid as you not only hear the chord but you hear all of its harmonic components. These amps, and I would imagine other SET amps, bring out harmonics that you don't realize are missing until you hear it properly done. I listen to acoustic jazz and the presentation is much more life like.

The midrange on these amps is super smooth. It is here that these amps really shine. The fullness and richness of the midrange renders a "they are here" quality that is probably the hallmark of triode amplifiers. Vocals are cleary defined and you can almost physically see the performer in front of you without even thinking about it. Trumpets sound like trumpets saxophones sound like saxophones. However, they don't all sound the same. You can actually hear the "voice" of the indivual players. Everything is very immediate and these amps produce sound and scale of which is comparable to the actual sound produced in a live setting.

The low end of these amps is very good. I was very concerned with inadequate bass control because of the size and the weight of the Spendor woofer. Although the impact is not on par with my Graaf 5050, I never, feel that something is missing. The bass articulation is fantastic. The bass isn't as prominent as it was with my Graaf but, it seems more natural. The bass seems to be back where it belongs, underneath the music, providing support as opposed to being more out front or on par with the other instruments in the band. As a person who has heard at least 100 jazz performces live, I can tell you that the bass is usually on the bottom, unless directly miked (which stinks) and at times you have to focus to hear it. With these amps, the weight of the bass is always present and and you can always hear the tonic notes, which is what you want when you listen to jazz

I know that this has been a long winded reveiw, but these amps are very impressive. The were incredible right out of the box and only got better as I swapped tubes. (For those interested, the Chinese 845 isn't bad, but once you have heard the RCA 845, you can never go back. The diffence is not unlike the difference between a SV 6550C and a Tung Sol or a GEC KT-88. The difference is not subtle. Much more resolution as the music shines through)

The Smart 845 amps sound like music is supposed to sound. I find that I listen longer and more completely than I used to. I put a disc on and the next thing I know it is over. I don't jump around and change discs like I used to as the music is much more captivating. I also don't listen in fragments (i.e. the soundstage is this, the image is that, the highs are this etc. etc.). The SET experience has been worth the journey and I encourage anyone who is interested to give it a try. I know people debate which is the better tube, the 2A3, the 300B or the 845 but for my needs the 845 was the way to go. It is a very dynamic tube which retains all of the harmonic richness that is often associated with the 300B, while providing plenty of headroom and dynamic drive and low end control.

These amps are highly recommended.

REVIEW: Unison Research Smart 845 Amplifier (Tube) Review by GEO at Audio Asylum