The Unison S6 is a 30 watt Class A tube amplifier that uses 6 EL34 tubes and 2 12AX7. The sound is quite powerful and controlled in the bass region, with a beautiful midrange and extended highs. The tube warmth and liquidity are there in the right places and in the right amounts.
I had been using this amp in my reference system for several weeks now and enjoying it, but having the nature of a Tweek Geek, I wanted to see if I could get a little more out of it. I also wanted to do so without doing any major modifications. In other words, no opening up the amp and no soldering.
Preamp Tubes
The first thing I looked at were the preamp tubes. I replaced the stock 12AX7 with a matched pair of the Ray Tube Select 12AX7. The Ray Tubes immediately were more transparent, making the stock tubes sound a bit fuzzy and veiled in comparison. This was most evident in the upper midrange and high frequencies. Everything from about 2kHz on up had more clarity and more resolution.
Amp Tubes
Ray Tubes makes a Reserve version of the EL34, and I decided to shoot for the moon with these rather than the Select version. Installing the Reserve EL34's started out as having reduced highs, a little more veiled sounding, but that went away after 24 hours of leaving the amp on. Everything opened up afterward in an unexpectedly beautiful way. Yes there was more clarity and detail, yes the midrange became more tactile, textured, layered and very engaging. The thing that surprised me was the cohesiveness the EL34's brought to the soundstage and the overall presentation. I hadn't noticed that this was a weakness in the stock tubes until I heard the Reserves, then it was obvious. Especially in the highs. With the stock tubes they were a little more separate, like I could pick out what sounds and frequencies were emanating from the tweeter on certain recordings. With the Reserve tubes everything came together seamlessly.
I would say that the Reserve EL34's were quieter as well. There was just more blackness between notes and passages. This also contributed to more air and space in the presentation.
QSA Red Fuse
The S6 takes a 5x20mm, 6.3 amp slow blow fuse. I chose the Red fuse because the Violet is more known for smoothness, something I already thought I had and didn't want to overdo. WOW!!! This was the biggest improvement, by far. The soundstage exploded in all directions with depth and delicacy. Low level resolution and microdetail with naturalness opened up the musical details in a very awe inspiring and non-fatiguing way.
The Total Picture
With the tubes and fuse in place the S6 is an incredible amplifier. Magical in every aspect, creating an enveloping, cohesive, detailed, natural and dynamic presentation. I actually prefer it over my Modwright LS99 and KWA 99 combination with upgraded tubes (the Modwright for some reason wasn't super responsive to fuses). That combination is nearly $16,000. The S6 cannot compete with the Modwright in terms of sheer power, but sonically I found the S6 more satisfying in my system with my 92dB efficient Aurai speakers.
I think these tweaks make the Unison S6 a better deal than the S6 Black edition, at least for me. I don't need a built-in DAC with my integrated amp, and this way I could choose to invest that additional expense into performance of the amp itself.
Cost Breakdown
- Unison S6: $5999
- Ray Tubes 12AX7: $92 each (2 needed)
- Ray Tubes EL34: $196 each (6 needed)
- QSA Red Fuse: $1422
- Total Price with Tweaks: $8781
In conclusion, you get an amp that sounds better than the Modwright LS99 KWA99 separates (granted without near the output power) for nearly half the price of the separates. For $8781 you get an amplifier that can create an immersive, engaging, emotional music experience that performs well above the price tag. Highly recommended!