Integrated Amplifiers

While the Stereo 40 MkIV 6L6 just about drives my Wilson Sasha DAWs [HFN Mar '19] when connected to the 4ohm taps, I used it mainly with Falcon Acoustics LS3/5As [HFN Dec '18] – a dream match – and (for reasons that will come clear) Quad ESL63s.

Back To The Future
My initial impression was that, even with digital sources, this amplifier is like an ode to analogue. That's because (and here it all falls into place) it sounds like Quad IIs on steroids. Indeed, I was reminded of John Howes' custom modified Quads [HFN Aug '09], as well as the Radford STA25 Mk IV – the latter number surely a coincidence? What I am trying to convey is that the Stereo 40 MkIV oozes vintage valve 'humanity': warmth, a touch of velvet in the treble, no signs of bellicosity.

Then again, I didn't hammer it, suspecting that it wasn't voiced to optimise the sounds of AC/DC or ZZ Top. That said, the latter sounded just fine because there's an inherent 'tube-iness' in their albums. Remember, too, the amp works in ultralinear mode rather than the more romantic triode mode. You can order the latter from the factory, and I can only imagine how lush it sounds.

It seemed only natural that LPs from a musicologist like Ry Cooder, with his love of acoustic instruments and the liquidity of his bottleneck work, would benefit from the Icon Audio karma. Wallowing in 1972's Boomer's Story [Mobile Fidelity MFSL 1-405], I was reminded how elegiac this roots music can be. Most emblematic of the sensation was 'Rally 'Round The Flag', written during the (American) Civil War.

Somehow, the historic feel of Cooder's 50-year-old performance was enhanced by hardware born 160 years after the song was composed. It was the fluidity of slide work contrasting with the twang of other acoustic instruments, shimmery resonances which possessed such natural timbre that if someone told me Boomer's Story had been recorded in 1956 by the geniuses at RCA or Mercury, I wouldn't blink.

Was this too easy a ride for the amp? Like feeding string quartets to BBC LS5/9s or bass-heavy rap to Cerwin-Vegas? A Japanese release of The Beatles' Help! [Audiophile Master Collection AMC8005CD] provided the answer: the Stereo 40 MkIV 6L6 may possess instant synergy with primarily acoustic sessions, but the crispness and detail of these high-res recordings showed its prowess at retrieving ultra-fine, low-level details.

Low-End Laurels
I have no idea how many times I have heard 'Dizzy Miss Lizzy', the most aggressive track on the album and a wall of noise worthy of Slade a decade on. Somehow – was it the disc? – the Stereo 40 MkIV 6L6 uncovered layers of lower octave information usually buried in the mix. With tracks such as 'Yesterday' and 'You've Got To Hide Your Love Away', the opposite was delivered with the very same aplomb – utter delicacy and refinement, with plenty of air in a super-wide soundstage. And you are probably guessing where this is leading.

If most hi-fi components excel in one area, precious few attain perfection across the board. This amp's forte is the reproduction of vocals. Textures, little stylistic tics, breathing – this could be called 'The Amplifier That The LS3/5A Was Waiting For' and the hyperbole of that observation would be hard to challenge. But the wider range of the Quad ESL63 showed that it has another trick up its sleeve.

Bass was never a particular strength of vintage valve amps, nor Quad ESLs or LS3/5As, but somehow the Stereo 40 MkIV 6L6 managed to extract convincing lower reaches from both, although – unsurprisingly – the Sasha DAWs demanded more grunt. At all times, bass and scale were far better than merely satisfactory. The entire experience was authentic, as evinced by the big band sounds of the Living Strings' double open-reel tape, Music From Camelot/Mame And Other Songs [RCA Camden TC3 5004].

As the latter of the two titles proudly proclaims 'Plus Trumpet', it was an ideal test for the Stereo 40 MkIV 6L6. Would the strings stay sweet or turn steely? Would the brass have attack, punch and staccato transients?

It was almost a master class in why tape is the superior source, Icon Audio's 'austerity amp' defying the removal of a few (admittedly non-sound-related) functions and a small reduction in power. Still the strings soared, with no edges to set teeth a'grinding, while the vivacious brass bursting from the speakers was enough to impress Al Hirt. This amp may have limitations in power, but used judiciously? It's only January, but it could be Bargain of the Year.

Hi-Fi News Verdict
We often receive queries about cost-effective valve amps, so the no-nonsense Icon Audio Stereo 40 MkIV 6L6 has made our lives easier. It's a no-brainer if you 1) must stay below £2500, 2) own sensitive speakers, and 3) eschew frippery. The sound? So warm, lush and transparent that you'll soon be musing about Klipsch Heresies, Quad ESL-57s or JBL L100s. A blast from the past – with the emphasis on 'a blast'.