Icon Audio Stereo 40 MkIV

As a key player in the valve revival of the past decade, Icon Audio has made a bewildering array of tubular belles for enthusiasts with the accent always on value for money. Products such as the original Stereo 40 integrated amplifier – which arrived back in 2000 – began the company’s journey towards more accessible, user-friendly designs. Yet it hasn’t been until now that designer David Shaw has really realised this ambition.

The new £2,200 Stereo 40 MkIV is a flexible, well-made integrated that really advances the budget valve amp cause. It’s bristling with tweaky features, the most notable of which is that it can work with a range of output valves from EL34 to KT88 (including KT66/77/90, 6CA7 and 6550), so you can ‘roll’ valves for yourself to get the sound you want. It also offers a choice of Triode or Ultralinear operation; the former giving a claimed 30W RMS per channel and the latter 50W, with differing sonic characteristics. There are also other factory options including Shuguang Treasure valves and Jensen ‘oil in paper’ capacitors.

This amplifier covers the basics well. There’s a steel mesh valve cover to keep prying fingers out – should you require it – and a headphone socket for private listening. Measuring 390 x 230 x 410mm (WxHxD), the Stereo 40 MkIV is pretty compact for a product of this type too – although it weighs a chunky 22kg. This Class A design is “a mish-mash of ideas with several nods to giants of the past like GEC, Blumlein, Williams, Philips, etc.”, according to Shaw. Technologically there’s nothing particularly fancy about it, but instead the emphasis is on real-world practicality and affordability.

The new MkIV gets tweaks to the custom hand-wound tertiary output transformers with an additional third winding, claimed to subtly improve performance. The point-to-point wiring includes silver PTFE audio cable, and selected passive components are fitted. The redesigned driver circuit has a cascode configuration, and there’s a choke-regulated power supply and motorised ALPS volume potentiometer. The latter works with the supplied – and very minimalist – remote control. Build quality is good for a product of this type, and the copper top trim is a nice visual touch. The front panel meter, which looks wonderfully anachronistic, is used to set up the valve biasing; this is only done when you change valves and so doesn’t become a daily chore. The back panel has a choice of 4 and 8ohm taps for the loudspeaker outputs and there are three RCA line input pairs as well as a proper tape monitor loop. The sensitivity toggle switch has three positions; middle is service mode and there are low and high settings, too.

Sound quality
The Stereo 40 MkIV sounds very nice – in a really good way. Its faults are easy enough to hear, but its easy charm means they don’t seem to matter so much. Its key strength is power, and it comes across with plenty of confidence. It has a certain purposefulness to the way it makes music, underwritten by what is undoubtedly – for a budget valve amp – impressive loudspeaker driving ability. Not only can this deliver the power, but at highish volumes and on loud crescendos it makes it stick. It doesn’t fall apart like some similarly priced valve designs when asked to push hard. There’s no sense of the output transformers saturating too soon, for example.

This is especially the case in Ultralinear mode and with the sensitivity switch set to high, but for most of my listening I run it in Triode mode. Here it proves just gutsy enough to really tickle my reference Yamaha NS-1000M loudspeaker, and grips my more efficient Cambridge Audio Aeromax 6 floorstander (HFC 391) like an iron fist. In this mode, things are smooth and sweet, with less power and bass thump, but with a better sense of musical coherence.

Put on some bouncy classic techno such as Inner City’s Good Life, and this bottom-heavy track has the bass synthesiser modulating up and down the lower octaves in a most powerful and animated way. Meanwhile, flipping to Ultralinear operation gives it more wallop, but it also sounds flabbier and rhythmically less coherent, with a slightly more gritty midband and treble.

The Stereo 40 MkIV has a lovely, sumptuous tone. There are some valve amplifiers around that are desperate to counter the stereotype of the breed by sounding fat and warm, but this isn’t one of them. It’s only subtly coloured, but you’re never unaware of it. It takes the edge off dry, forward recordings or steely sounding loudspeakers and cueing up Squeeze’s Tempted, I revel in the silky sound of the recording. There’s no edge to the vocals and at the same time the hi-hat cymbal work is very sophisticated, while the electric organ sounds thick and full of body. Contrast that with some solid-state amplifiers at the price – which can make the recording thin and tinselly – and the Icon Audio is hard not to like.

Rhythmically it’s good too – living up to all the predictable, time-honoured clichés about ‘the magic of valves’. Music just chugs along in a carefree way and there’s no sense of it sounding forced or mechanical. Instead, you’re struck by the sense of musical occasion; Rush’s Lakeside Park is a simple late-seventies rock recording, but the Icon Audio makes it sing. It’s not famously open or dynamic, yet this amplifier just gets into the groove and lets the music’s natural rhythm flood out. Your mind wanders from considerations of hi-fi and instead gets preoccupied with the music itself – which is just as it should be. It’s odd in a way because it doesn’t sound especially fast – it’s not as if you’re wowed by its transient speed – and yet you still feel yourself getting pulled into the groove.

The soundscape it produces sounds good too as it sets up a wide left-to-right soundstage with a cavernous feel. It’s as if everything’s gone through an effects processor, and is now in ‘stereo wide’ mode. Some classic rock from The Smiths sounds larger than I remember it; The Headmaster Ritual booms out of the speaker in a most enchantingly capacious way, when sometimes it can sound small and weedy. Inside that large stereo soundscape imaging is a little vague, but instruments nevertheless have a good deal of space around them and aren’t too subsumed by others.

Downsides? The Stereo 40 MkIV still doesn’t ultimately have the grunt of a good similarly priced transistor amplifier. Bass is a touch too loose for my liking, although it’s still tuneful and sumptuous. Midband is coloured and low-level detail isn’t all it could be so don’t buy this if you’re looking for forensic neutrality. Despite this, it is a real charmer with pretty much everything I opt to play.

Icon Audio’s Stereo 40 MkIV is quite remarkable for the money. It is well made, good looking, highly tweakable, surprisingly powerful and delivers an engaging sound. A great value package that will tempt serious solid-state amplifier fans with its valve charms. DP    

Product: Icon Audio Stereo 40 MkIV
Price: £2,200
Origin: UK/China
Type: Integrated amplifier
Weight: 22kg
Dimensions: (WxHxD) 390 x 230 x 410mm

● Quoted power output: 2x 50W RMS (8ohm)
● Class A Triode front end, push pull output
● 4x KT88, 4x 6SN7 valves
● Inputs: 3x stereo RCAs; 1x tape loop

Read the full review in June 2019 issue 450

Icon Audio
0116 2440593