Integrated Valve Amplifier Icon Audio Stereo 40 MkIIIm


Tech Specs

  • Comprehensive manual supplied
  • Built in meter “Easy Bias” system
  • Full instructions for valve change included
  • All hand wired point to point
  • No printed circuit board to ‘colour’ the sound
  • Japanese ALPS volume pot.
  • Class A, all Triode front end
  • Output circuit Ultralinear or Triode switchable
  • 4x EL34/KT88 precisely matched for best performance
  • 1x 6SL7/6N9 first stage valve, 2x 6SN7 phase splitter
  • 274B/GZ34 valve rectifier for ‘Soft start’ and smooth sound
  • Standby switch to save valve life and power
  • 2x 40w RMS per channel output
  • 2x 20 Watts RMS in Triode mode
  • Signal to noise level -90db
  • Freq response better than 20hz-20kHz +0 – 1db
  • Power bandwidth 10hz-30khz
  • Total harmonic distortion 0.15% at full output
  • Suitable for 4 to 16ohm loudspeakers
  • Supplied with attractive valve cover.
  • Choke regulated power supply
  • Solen audio caps, or Jensen copper foil in paper and oil
  • Silver PTFE audio cable
  • Custom hand wound Tertiary output transformers
  • Gold plated Input & speaker terminals
  • Four line inputs – CD, Tape, Tuner, Aux
  • Tape monitor circuit with ‘Record Out’
  • 250mv input sensitivity.
  • Power requirement 220-240volts (115v adjustable)
  • 76 Watts standby, 140 W Min, 240 W max.
  • CE, ROHSS and WEEE
  • 39cmW, 41D, 21H, 25kg (a minimum of 30mm height should be added to allow for ventilatio


The Icon Audio Stereo 40 is a straightforward design which offers all the traditional Hi-Fi enthusiast needs and nothing they don’t. There are no tone controls, no Bluetooth, no wireless multi-room streaming, no printed circuit boards, no-nonsense. With that said, there are some clever design touches…

A four-position switch, accompanied by a vintage styled backlit meter, allows the user to check and adjust the bias of each valve via top-mounted trimmer pots. The range of bias adjustment allows for a choice of outputs valves to be fitted, including EL34 (as tested) KT88, KT66, 6550 and other types; opening up the possibility for sonic experimentation.

The Icon Audio Stereo 40 allows the user to run the output valves in pentode, ultra-linear operation for the highest output, or in triode mode. Triode mode results in half the power output but a slightly sweeter, more “open” tonality; it was in this mode the day’s listening tests were conducted.

The remaining valve complement consists of a 274b rectifier and octal based pre-amplifier valves including the 6SN7 and 6SL7. Three switchable inputs are provided along with a tape monitor, and conveniently, remote control of the volume.

Anyway, enough of the jibber-jabber, what does this thermionic beauty actually sound like?

Icon Audio Stereo 40

The Stereo 40 mk3 is an integrated amp that actually even features remote control. The height of luxury, as far as I’m concerned. The amp itself is a push-pull design using either EL34 or KT88 valves. When I asked David if it was fully class A I got a complicated answer that I think I can summarise as ‘yes’. In accordance with its name it delivers 40 watts and has separate speaker terminals for 8 ohm and 4 ohm speakers, like most valve amps. There’s a perspex cage provided to protect the valves from your children and the other way around, which is good in my opinion. When switched on, the amp goes through a 30 seconds startup sequence to protect the precious valves. Even the volume control turns itself all the way down, and then partly up again, during this procedure. In use the amp will become quite hot, and leaving it on all the time is seriously not recommended, but it does feature a standby mode.

The review sample wasn’t the standard, vanilla Icon Audio Stereo 40, but a version that used better capacitors, copper foil paper in oil ones from Jensen, and the best KT88 valves. The amp can also be used with the more basic EL34 valves. As I haven’t used the simpler versions, I cannot comment on the differences, but David told me that most people go for the upgraded versions.

The amp can be switched between triode and ultralinear modes, with the latter producing the most power. I preferred the ultralinear mode, but I have to admit that I didn’t hear much difference between the two. The only other feature on the amp is a tape loop, which I consider completely unnecessary in this day and age. A single selector with a few more inputs would have been preferable, but a real problem this isn’t, obviously. More serious is the lack of a preamp output, or power amp input. There’s a tape-out, as mentioned, but that has fixed volume. Icon Audio claim the Stereo 40 can be used as a power amp, but this requires the volume control to be set to maximum, which I don’t find the most elegant solution, specifically as it will turn itself down again each time you switch it off and on.

The amp worked very well during the review period, with a few exceptions. The remote controlled volume didn’t always work, for some reason, and the amp had a slight tendency to hum when I used it with a subwoofer. I suspect a ground loop, as my sub is connected to the speaker terminals, and it would probably make more sense to connect it to the pre-out, if the Stereo 40 would have one! There are also some minor quality issues with the phono connectors, some of which didn’t allow my interlinks to fully penetrate them. For the rest the Icon Audio Stereo 40 mk3 seems robust and well put together. The remote control is a particularly nice one, made from almost solid aluminium. One thing to remember, if you’re not used to valve amps, is the sheer size and weight of this amplifier. It really is enormous, and needs a lot of space above it too, for cooling. Lifting it is almost a two person job, and you need to hold it at the back, as almost all the weight is in the three gigantic transformers. You’ll need a big, and strong, rack to accommodate this amp.


The first thing that hits you between the eyes when you try the Icon Audio Stereo 40 for the first time is actually something that isn’t there. It is the absence of a big difference with my own Usher R1.5 power amp, driven by my Django preamp, or with any other decent amp for that matter. I was expecting to enter a completely new, magical world, but it all sounded quite familiar. Bass was not as tight and powerful as with the Usher, but that happens to be a particularly strong point with that amp and the Icon Audio was doing a more than adequate job. With some speakers it actually sounds better in the bass, but more about that later. The fact is that the overall balance and presentation are not that different to any other good amp, which is a good thing as it proves that the Stereo 40 is principally a neutral and faithful amplifier that doesn’t put its stamp on the music or lets itself be known in any other obvious way. So far, so good.

It didn’t take me very long, however, to start hearing the more subtle differences. Yes, the bass was a bit warmer, and the midrange was somewhat richer, but what mostly drew my attention was the top end. I’ve been looking for an amp that can reproduce the upper frequencies without edginess while still being open and articulated, and I’ve always felt I had to compromise. Until now, that is, as the top end of the Stereo 40 is just about perfect. Clean, detailed, dynamic, open and completely natural and fatigue-free. It wasn’t as jaw dropping as the Kondo amps at Definitive Audio, but there was more than a hint of Kondo magic in there. Most importantly, there’s nothing soft and veiled about the top end of this amp: it actually is livelier than my Usher amp, while being much cleaner at the same time. And the Usher is supposed to be ‘valve-like’! I’ll never use that word again, I tell you!

This really was completely according to my expectations, except that I hadn’t expected it to be so transparent too. There’s a beautiful richness there, but it isn’t slow or woolly at all, more the opposite really. Lifelike and articulated would be a better description. It makes for great listening, especially with voices and does wonders for the soundstage too. It really enables you to look deep into a recording, but without ever becoming analytic. It also is completely unforced: all that detail is there for you to explore and enjoy, but your attention is still free to wonder around in a recording.

The bass is the only region where the Stereo 40 is just average. There’s nothing wrong with the bass, and it actually has a nice warmth and fullness about it, but it isn’t the last word in control and texture. Still, it isn’t bad either, and actually goes rather well with the midrange and the rest of the spectrum. Had I not owned the bass miracle that is the Usher power amp, I would probably not have noticed any shortcomings in this area at all.

All of this is when I used it with ‘normal’ speakers, like my Dynaudio Contour 1.8 MKII’s or the PMC transmission lines that were on review. The real surprise came when I started using the Icon Audio amp with the SEAS Exotic speakers. These have a tendency to sound a bit stark and overly revealing with the Usher, but turned into luscious music machines with the Stereo 40. If I still had any doubts about the qualities of the Exotics, they completely disappeared when used with this valve amp. And if I still doubted the superiority of valve amplification, I became a complete convert with this combination. It makes sense, as both basically represent technologies from the 1950’s. When I was young we used to have a valve radio that you couldn’t call hifi by any means, but that still sounded wonderful. The Stereo 40 with the Exotics has the same luscious, seductive sound, but accompanied by a full hifi pedigree. I didn’t think it was possible.

Still, the biggest surprise remained that wonderful, lifelike dynamic expression that I never expected, at least not before I’d experienced the Kondo amps. There’s something about live music that anyone can recognise, even from around the corner. It has to do with dynamics, and no audio system can completely reproduce it, but our ears immediately recognise it. It is this dynamic envelope that the Icon Audio amp reproduces better than any transistor amp I’ve ever had in my system. It feels unrestricted and alive. The fact that is combined with silky sweetness and rich tonality makes this amp irresistible, at least for me. These things are more or less mutually exclusive in a transistor amp, but here they happily go together, as if it’s the easiest thing in the world.

Listening time

The source for the day was Linn’s excellent Klimax DSM network player streaming hi-res audio from Tidal. Today’s speakers of choice were Tannoy’s oh-so-lovely Tannoy Prestige Kensington dual-concentrics. Yummy!

Deciding to jump straight in with a test of bandwidth, dynamics and timing, Todd Terje’s 80s synth homage, Delorean Dynamite was cued up. From the first few bars, the unmistakable sound of valve amplification filled the room; warm, full and characterful.

If you’ve never heard a valve amplifier before, it can be a revelatory experience compared to solid-state designs. There’s a high-end extension which is bright, sweet, smooth and airy in a way you’ll probably never hear from a solid state amplifier.

There’s a unique character to the upper mids in particular; a real sweetness which lifts detail elements from the track without being fatiguing.

By the same token, the bass and low-mids have a depth and weight which is both seductive and addictive. The rhythmic force of Delorean Dynamite carries through nicely with a real heft to the kick drum and arpeggiated bass synth. This is very much the “valve magic” in evidence.

Continuing the theme of melodic electronic music, CHVRCHES provide the emotion with their track Lies. Lauren Mayberry’s vocal sits beautifully in the mix, again benefitting from that wonderful sweetness and airiness the Icon Audio Stereo 40 offers.

Anyone who claims valve amplifiers lack depth, low-end extension and speed really should listen to the Icon Audio Stereo 40. Kick drums and bass synths positively rumble and roll with the punches whilst percussion is persuasive and powerful with character and emotion. It’s a massively impressive presentation.

Technically Impressive

It’s one thing to be able to deliver on compressed, highly produced material, but how does the Icon Audio Stereo 40 perform on material which is more open and acoustic in nature? Is there finesse to match the bombast and bravado? In short, yes, there is!

Turning once again to the beautifully recorded and performed piano performances of Lang Lang, his performance of Tchaikovsky’s Dance of The Sugar Plum Fairy from The Nutcracker Suite demonstrates great control and finesse. Transients are managed extremely well, with no audible or discernable distortion.

Once again there’s a natural and engaging sweetness to the performance; the notes all follow each other with a fluidity which is captivating and (there’s that word again) engaging.