Page 33 - Hi-Fi World (January 2020)

REVIEW

regenerated mains power supply fed this the Stereo 40 MkIV thundered body was given scale – whilst each
the electrostatic supplies and Oppo through tracks like Safri Duo’s key had solid presence as Volodos
player, the Icon being connected Samb Adagio, the opening bell strike carefully worked his way through this
to its high current filtered, un- ringing around our room, followed lovely piece. Valve amplifiers always
regenerated output. by a swelling synth and then a bass deliver a big sound – dynamically and
The Stereo 40 MkIV was both synth line that was far and away spacially – but the Stereo 40 MkIV
vividly dynamic and spacious in its more violent than you’d hear from a has impact, precision and timing
sound, Icon Audio getting very clean transistor amplifier. The combination beyond most with music such as this.
bass from their output transformers. of big, modern power supply, whistle
The sound was less easy, soft or clean KT88s and Icon’s massive CONCLUSION
warm – as classic valve amplifiers output transformers come together Although a “tried and tested classic”
are imagined to be – more vivid and here to deliver bass few amplifiers in design essence, in real life the
punchy. The combination of valve can match. Interestingly, switching Stereo 40 MkIV is a different beast
amplifier and electrostatic panel to L Sensitivity (high feedback) subjectively. What you get here is
always was made in heaven, giving pulls bass back a little, but this a modern, fast and punchy sound
a sense of life and scale transistor is interaction between amplifier that simply overwhelms most else.
amplifiers don’t match. But I’ll cover electrical damping and loudspeaker With very strong bass, a huge sound
the sonic options first. acoustic damping, so no mystery. stage and thunderous dynamics the
With Antonio Forcione’s Tears Arcadi Volodos playing Icon is a long way from valve amps
of Joy (CD) there was softness – sublimely – Schubert piano of yore. It’s a great blend of old and
and warmth in the sound with concertos (CD) was vivacious, new, finding the best in both. Add in
feedback Off (sensitivity 0). Wooden dynamically strong yet controlled and the almost unique ability to dial in
blocks lacked transient edge and with a lovely light across the sound feedback and select Triode mode and
guitar strings were mild rather stage – bright but honeyed. This you’ve got an amplifier and a sound
than lacerative. However, with no Icon puts power into piano – the that’s hard to beat at any price.
feedback images seemingly jump out,
having a dynamic about them that’s
almost puzzling – but that’s because MEASURED PERFORMANCE
zero feedback is never encountered
in hi-fi amplifiers. It’s worth hearing. In Ultralinear mode distortion at quoted – a low value.
Switching Sensitivity to H (low 40 Watts measured 0.26%. Using a 1% Bass distortion (40Hz) was also low
feedback) pulled the images back, limit 55 Watts was delivered. at 0.06% (1 Watt) and 0.13% just below
both restraining and controlling In Triode mode output measured 25 full power (L), deteriorating little to 0.2%
them, but it also brought a solid edge Watts using the same 0.26% distortion and 0.3% at H and 0.3% and 0.8% at zero
to the blocks and some laceration to limit as Ultra-linear, but 34 Watts at 1% feedback – all low values for a valve
guitar strings; they seemingly moved distortion, validating Icon Audio’s figures. amplifier.
from being fibrous to metallic. Distortion levels (1kHz) were low High feedback (L) gave very wide
Switching Sensitivity to L (high all round, just 0.006% at 1 Watt and bandwidth of 2Hz-44kHz (-1dB). Low
feedback) pulled the images back 0.15% just below (-1dB) full power, feedback (H) 7Hz-31kHz, usefully
further, slightly flattening perspectives at maximum feedback (L). With low eliminating low bass to avoid possible
– but even set like this the Stereo 40 and zero feedback around 0.04%, and core saturation from LP at high volume,
MkIV was more dynamically engaging 0.3% just below full power. At high whilst zero feedback (open loop) was a
than a commercial transistor frequencies (10kHz) 0.05% was typical usable 20Hz-12kHz. ICON AUDIO
amplifier. But since the latter use at FREQUENCY RESPONSE (L) Damping factor measured 16 (L), 6 STEREO 40 MKIV
least 30dB feedback – double that of (H) and 2 (0) so there’s choice to be had £2199.95
the Icon – it’s hardly surprising. here too. Low sensitivity (max feedback)
A bit more baffling and hard offers tightest bass, but lower feedback £
to explain is Triode mode. This can give bigger bass with acoustically OUTSTANDING - amongst
unravelled musical strands, drawing over damped loudspeakers. the best.
Skin out of the fray when singing Noise levels were minimal: there
Hedonism (CD) for example. was little hiss and hum was below 1mV. VALUE - keenly priced.
Triode just sounded better sorted The Stereo 40 MkIV measures
and a tad less confused, also lifting well in high (L sensitivity) and low (H VERDICT
Sturdily built, cheap to
Marianne Thorsen clear from the sensitivity) feedback modes, being run, vivid in sound. Add in
backing Trondheim Soloists (hi-res DISTORTION (L) acceptable even with no feedback (open tweakability and you have
24/96) when playing a Mozart violin loop). NK it all.
concerto. But the massed violins of
the soloists equally gained in dynamic Power (UL / Triode) 40 / 25W FOR
- powerful bass
presence. Although not better in Frequency response (-1dB) 2Hz-44kHz - open and vivid
L sensitivity
measured terms Triode mode is H sensitivity 10Hz-31kHz - remote control
subjectively best. And Thorsen’s no feedback 20Hz-12kHz
violin and playing were sublime, Distortion (10kHz, 1W, L) 0.02% AGAINST
shimmering out into the room with Separation (1kHz) 86dB - size and weight
- heat
a sunlit textural density that makes Noise (IEC A) -90dB
all else sound lifeless and bleached. Sensitivity (0-L) 100-800mV Icon Audio
In the end I settled for Triode Damping factor (L sensitivity) 16 + 44 (0)116 244 0593
mode and H sensitivity – and with www.iconaudio.com

www.hi-fiworld.co.uk JANUARY 2020 HI-FI WORLD 33