Page 29 - Hi-Fi World (January 2020)

REVIEW

in Russia by the New Sensor Corp. the rear panel labelled Sensitivity. position bias-adjust rotary switch.
who are based in New Jersey, USA. This alters feedback, substantially Four positions show bias level at
The claim here is that this KT88 affecting how the amplifier works each output valve on the meter, for
perfectly reproduces the structure – and its sound. The choices are monitoring and adjustment purposes.
and strengths of GEC’s original, Low sensitivity (L) which means high The fifth Off position shows output
released in 1957 and universally feedback (14dB), High sensitivity level to the loudspeakers, warning
admired for its sound, as well as (H) which means low feedback of potential overload if volume is
durability. You can see the KT88s in (5dB) and a central zero position wound too high. Once bias has been
a linear row of four at back, just in that eliminates feedback completely set, by turning the small top-panel
front of the big, black transformers. – radical. potentiometers with a screwdriver,
Alternatively it will accept Mullard High feedback (L) gives it should not need re-adjustment for
EL34s. performance like a transistor many months.
I hope all that gets into amplifier, Low feedback (H) like To the right of this switch lies
perspective what Icon Audio’s a classic valve amplifier and zero the old-style panel meter that lights
Stereo 40 MkIV is about at a basic feedback is there for those that may up deep yellow at power on. It looks
level. Power output is plenty high prefer the sound – as some do. I sturdy and industrial, something
enough to go extremely loud, and think the best compromise is H (low from an old power station perhaps
its output valves are classics that are feedback) but the other settings – and of course it grabs attention.
durable yet inexpensive – important have appeal. With this amplifier you What modern amplifier enjoys such
because after 3000hrs use they need get to choose, whereas with most glitz? It makes them look drab. To its
replacing; with 10 hours a week use others you get what you’re given. right lies the Ultralinear/Triode lever
that means 5 years life. Feedback alters gain, distortion, switch and in the middle sits the
Physically, the new Stereo 40
MkIV isn’t outsized, measuring
390mm (15.4in) wide, 410mm
(16.2in) deep and 230mm (9.1in)
high. As amplifiers go, not so big.
But at 22kgs it’s a two-person
lift – seriously heavy. Caused by
the massive mains and output
transformers it uses for quality
reasons. A strong shelf or hi-fi rack
is needed – and a rack needs around
254mm / 10in between shelves to
allow heat to escape. Nearly all
racks are 19in (480mms) wide so
it will fit easily here – but it has
to since side access to the mains
switch is needed.
Modern technology means the
Stereo 40 MkIV comes with remote
control of volume. Inside there’s an
Alps Blue motorised volume control:
you can turn it manually or use
the heavy but small metal remote
supplied. The power supply is solid-
state, reducing weight, size and cost,
and improving power output.
Where this amplifier differs from
most is the amount of tweakability A hard-wired internal assembly, with neat wiring looms. There are
you get. The front panel has a small also printed circuit boards for remote control etc, two fuses
lever switch marked Ultralinear/ (bottom left and right), plus a big choke (bottom right) to clean the
Triode. Ultralinear is standard mode power rail. It is a specialised and expensive component.
that gives highest power and best
measured performance; Triode
lowers power by a small amount frequency response and output volume control, moved by a motor
to 30 Watts maximum but gives a impedance (damping factor) so when the remote is used. Then
slightly clearer and easier sound. when you use this switch a lot alters comes a loudspeaker/headphone
Differences aren’t great but it’s – and in a big way, which is why it is selector switch with accompanying
possible to arrange Triode working rarely seen. However, I chose to fit headphone socket.
without much kerfuffle so Icon make a feedback-off switch to our World To the right of the headphone
it available. Commonly, users settle Audio Design 300B amplifier in 1993 socket is a stand-by switch that is
on Triode mode I’m told, as I have just to show what it offers sonically only seen in valve amps: it turns
with our Icon Audio Stereo 30SE in- (a big, open spacious sound) and still off HT to prolong valve life, whilst
house reference valve amplifier. use it at home today. leaving the heaters up and running.
A bit more challenging is a A busy front panel says much And to its right is a Tape/Source
small three-position lever switch on about this amplifier. At left is a five- switch for those running classic

www.hi-fiworld.co.uk JANUARY 2020 HI-FI WORLD 29