Hi-Fi
September 24, 2013

Unison Research S6 – Powerful amp that warms up to you

By Lam Seng Fatt

First of all, be warned that this is one heck of a heavy amp – it weighs 55 lbs, thanks to the miles of copper wires in its transformers. So, don’t break your back carrying this around.

The Unison Research S6 integrated amp looks good with typical Italian flair, especially in its curves and wooden accents. The wooden bits serve two purposes – to make it look better and to control vibrations.

The S6 uses three EL-34 tubes in the output stage per channel connected together in triple-parallel configuration that operates in single-ended Class A ultralinear mode. Its power output is 35 watts per channel and though that may seem low, it was more than sufficient to drive my not-sensitive-at-all ATC SCM40 floorstanders.

Other specs are frequency response of 20-50KHz, input impedance of 47 kOhm and output impedance of 6 Ohm. It has five line inputs and outputs for tape and speakers.

The tubes came neatly packed in foam cases. The EL-34 tubes were Russian-made Tung-sol while the ECC82 valves are for the input stages. It was quite easy to push in all the valves even though the fit was a bit tight.

A flick of the toggle power switch and the tubes were glowing and they became slightly brighter as they warmed up. The toggle switch seemed a bit fragile and I was actually worried that I would break it when I carried the amp with the front panel against my stomach.

Biasing the tubes was simple – just press a button and turn a knob until the needle is smack in the middle. You have to do it every now and then as the biasing can change with time.

The biasing switches.

I started off using the Roksan CD player as transport connected to the Wyred 4 Sound DAC. From the W4S DAC to the Unison Research S6 integrated amp, I started off with Alphacore Micropurl Silver interconnects. The speaker cables were the Kimber 12TC.

I played a variety of CDs and after a while, I noticed that the images, especially that of the singer, were a bit ‘fatter’ than what I was used to.

So I switched the interconnects to a pair of Kimber Silver Streak which I had borrowed from HiWay Laser for review. The Kimber Silver Streak matched with the valve amp better than with solid-state amps and the ‘leanish’ character of the Silver Streak counteracted the ‘fattish’ character of the valve amp and the result was very good.

Note the pretty wooden trimmings.

After listening to a few more CDs, I decided to experiment again – this time with the speaker cables. I have realised that valve amps tend to handle high-capacitance speaker cables better than solid-state amps.

So I rummaged around in the drawer and found a pair of Goertz MI2 speaker cables. With the Goertz, the bass went a bit lower and tigher and the sound, especially the mid-range and vocals, became smoother.

Though the amp churns out only 35 watts, it never ran out of juice even when the volume was turned up. However, the amp runs very hot and do not leave any CDs on top of it unless you want to fry them.

Three EL-34 tubes in the output stage.

Even rock songs were rendered with enough slam. Though the bass was not as tight or deep as with the better solid-state amps I have heard, the S6 did not have the flabby and loose bass that I have heard using other valve amps.

The timbres were not the most accurate I have heard, but the overall sound quality created by the Unison Research was not as warm, romantic and euphonic as other valve amps. The S6 did not have the classic valve sound.

Though it could play rock with some measure of conviction, I preferred it playing slower-paced songs. With vocals and light jazz, the amp could really sing.

Unison Research amps are distributed in Malaysia by A & L Audio Station. The S6 is available at a special price of RM15,888.