Icon Audio Stereo 60 Mk3 Signature, Exquisite

Icon Audio is a small company devoted to tube amplifiers, based in Leicester (United Kingdom), although its products actually originate, in the first instance, in the Far East: yes, David Shaw (the company's driving force) was a pioneer more than a decade ago in what is now so fashionable, finding a Chinese manufacturer to cut costs. More than that, at a time when Chinese tube amplifiers were nowhere near what is on the market today, he saw the possibility of taking advantage of the basis of what the Chinese were beginning to manufacture, with his own designs and, in some cases, modifying specific parts once they arrived at his workshop. I am sure that, thanks to his advice, the Chinese learned many tricks and that a good number of the (apparently) dazzling amplifiers that now populate many online stores owe something of their success to the father of Icon Audio...

Let's move on to our guest, which is -no less- the top-of-the-range integrated amplifier in its catalog: the Stereo 60, now in its third iteration, or Mk3 (the "Mk" designation is very British and suits David, in his quest to improve his products), is the most powerful thanks to its use of two pairs of KT120s in the output stage, and it claims no less than 85W in ultralinear mode, which drops to an also remarkable 42W in triode mode. The name comes from the previous versions (and an alternative version of this one) that use KT88s in the output stage, with which output drops to 65 (previously 60) Watts. The unit we tested, moreover, is the Signature, meaning it has better tubes (from Full Music) in the input and phase-splitter stages, and the audio signal-path capacitors are all Jensen copper and paper-in-oil types (their installation is one of the things done in Britain, all by hand, of course). The standard version is available for 2,338 euros and, looking at tighter budgets, its catalog offers several lower-power options (using EL34 and KT88 tubes, among others) that compete in a crowded market.

Description

The packaging reveals exquisite care for the product, and that is to be appreciated: it arrives in two boxes, a very heavy one containing the amplifier itself, protected by custom-cut high-density foam, and a second, lighter box containing the beautiful methacrylate cover that will protect the tubes (if we don't want to leave them exposed), the tubes themselves, perfectly labeled in their original boxes, the manual and a multimeter that we will use, following the instructions, to set the bias (bias current) of the power tubes, a nice touch.

This amplifier's tube complement is quite original: most of these designs are more than half a century old, and the trick lies in how the designer combines their characteristics and, of course, in the quality of the components used and how they are assembled. Here we have two very generously dimensioned output transformers (compared with those usual in amplifiers of about 40W per channel) that receive the high-voltage signals from the two pairs of KT120 power tubes. In each channel, the signal will have passed through a 6SL7 (input) and a 6SN7 (phase splitter), both dual-triode tubes with an octal base (eight pins), larger than the more common noval tubes, which are more modern and compact (but less appreciated by many enthusiasts and designers). Among the latter is the amplifier's ninth tube, an 0D3 regulator: it provides regulated high voltage without solid-state devices (in pursuit of a purer tube sound).

The tubes supplied are excellent: the KT120s were Tung-Sol, the 0D3 regulator a JAN, and all the others Full Music, as I mentioned above. We will install them in their sockets (all ceramic), though not before having taken (in our case, you know how curious we are...) a good look inside the unit to assess its construction. This is very traditional: the only printed circuit board is the one for the remote-control circuit (for the volume, which uses a motorized Alps potentiometer) and the power-on timer, and everything else is point-to-point wiring, a fine piece of craftsmanship with good grounding where necessary to avoid noise. The components are of a good standard and in some cases outstanding, such as the aforementioned Jensen capacitors, to look no further. A component that will give us years, even decades, of service, and if it ever needs an overhaul, any specialist technician will be able to do it, which is why this one, like other audio components, can truly be called an investment.

Of the four rear inputs, three are for the source selector (CD, Tuner or Aux) and one is for direct selection (Tape), and the selected source is sent to a rear recording output, as well as to the volume potentiometer. This solution is very common in tube integrated amplifiers, which are really a power amplifier with a simple passive preamplifier (that source selector plus the potentiometer). Here it goes further, offering the possibility of also using the integrated amplifier as a power amplifier (with another preamplifier, or if it is integrated into a home cinema system with an audio/video processor), for example by connecting that preamplifier to the Tape input and using the front selector to choose it, with the volume at maximum. Since in this use the gain of the preamplifier plus that of the amplifier would be too much (and there would be more noise), Icon Audio has provided for reducing the gain with a rear switch, whose "low sensitivity" position reduces it considerably (it does so by adding 10dB of negative feedback, a common solution).

On the front we have the source selector (plus the Tape selector), the volume control in the center (remote-controllable) and three more controls: on the left a rotary one that switches the unit on, to the right of the volume one that puts it into standby, and to its left the one that selects between Ultralinear and Triode output modes. The Standby switch is very useful: when we switch on the amplifier, current reaches the tube filaments, and a timer mutes the output for one minute. But the central tube, which regulates the high voltage, is inactive: in this way the amplifier stays at operating temperature and the tubes have their filaments ready, but without high voltage present they do not wear out as much. Let's say we can leave it like this if we use it even sporadically throughout the day, or over the weekend, switching it off completely only when we are not going to use it for more than 24 hours.

The four power tubes (the amplifier can use any compatible tube: KT88 or 6550) come pre-adjusted from the factory (where the amplifier has been tested beforehand), but differences in power supply (mains voltage) and the time elapsed since that test may have changed the operating point. That is why the manual strongly recommends adjusting the bias current as soon as it is set up, to prevent any tube being far from its optimal operating point for whatever reason (which, apart from not delivering optimal sound, could damage it). There is a potentiometer for each tube, and with the multimeter supplied (or one of our own) all we need to do is adjust them to read 330mV (the adjustment is quite critical, by the way; small movements of the potentiometer change the reading a lot). After a few hours of operation, and with the amplifier warm, it is worth checking that everything is still in order; in my case a first adjustment was enough, and they remained perfectly stable at that value.

Testing

KT120s are the power tetrodes capable of the highest dissipation in their family, and their use in an amplifier in ultralinear mode, with a power supply as beefed up as the Stereo 60's and output transformers so well dimensioned (no wonder the unit weighs more than 30 kg!), results in that spectacular rated output of 85W per channel, which can reach practically 100W on one channel momentarily, and the tubes could go even further (they are not being pushed hard). The size of the transformers also suggests a low output impedance, so this integrated amplifier can take on loudspeakers that are difficult in that respect (demanding in terms of current, as well as power), such as my B&W 802Ds, and in fact for a few days I had it in the room where those loudspeakers are, for music but also for movies (it is my home cinema system), without any problems or surprises; even in lively scenes, there was no lack of grip from the amplifier.

But the real place and purpose of an amplifier like this is a top-quality stereo system, so once this first acid test had been passed -with flying colors- I moved it (a heavyweight, by the way) to the basement, where my favorite monitors were waiting for it. There, initially in ultralinear mode (maximum power), it was immediately apparent that we are dealing with a very high-end component. To begin with, in total silence, no noise can be heard from the unit itself (a certain sound from the transformers is common), even with your ear pressed against it, and as for noise filtering through to the loudspeakers, the tweeters had only the slightest hiss (inaudible beyond 30 cm) and the woofers no hum at all. Outstanding, and rare for a tube component.

And when playing music, that high mark is maintained: it is impressive how a powerful tube component grips the loudspeakers, and how it does so without any stridency, maintaining the particular fluidity and smoothness to which most tube components have accustomed us. Here, however, there is something more, perhaps due to the design, perhaps to the tubes used or -I would say- largely thanks to those very special capacitors: there is always an especially clear illumination of the soundstage. It is not just the classic veil lifted from the music but something more; as I say, it is as if we had more light on the performers and could better appreciate their inflections, their movements, their breathing... A hyperrealism that is not excessive; quite the opposite. What awaits us in triode mode?

Time for a change. Normally, in other amplifiers offering this selection, triode mode is limited to low-level listening or to high-sensitivity loudspeakers, since the little power available does not allow more (rarely more than 20W). Here this Icon Audio sets itself apart from the competition thanks to its two pairs of KT120s, which offer more than 40W operating as triodes, perfect for my monitors and also enough even for the 802Ds and for most of the music I listen to (and at the level I listen to it, since I still have great respect for my ears).

Now, with half the power, a different approach to the musical message can indeed be noticed: the expansive, dynamic sound is a little less so, and the more intimate pieces (a soloist with few accompanists, or chamber music) retain their scale, although with the edges of the soundstage slightly less overflowing. The clarity and transparency are retained, but the sound is slightly warmer; in recordings with overly compressed vocals or voices too close to the microphone, it takes more to reach that unpleasant point. It is difficult to choose one mode; in that system (stereo monitors), if I had to choose I would probably go for this one (triode) but... the good news is that we have both at the flick of a switch (first going into stand-by to avoid possible damage; be careful).

Conclusion

Heavy, and somewhat peculiar in appearance, so dark and with its copper plate or methacrylate protective cover, the fact is that those who have seen the Icon Audio at home have fallen in love with it, and those who have also heard its music immediately asked me about its price and for more details. It is not one of the British manufacturer's most affordable models, quite the contrary, but its performance-to-price ratio is no worse than that of its smaller siblings, many of which are considered real bargains in their respective segments. In addition, its considerable power and its connectivity options allow it to preside over a system that perfectly combines stereo music listening with home cinema. Highly recommended.

We like

-High-level sound: transparent, smooth and powerful enough to drive difficult loudspeakers.

-Long tube life and quick warm-up thanks to the "standby" mode.

-Good value for money.

-Remote control for volume.

-Silent operation.

-Excellent packaging and presentation (includes a multimeter for adjustments).

Could be improved

-Being able to select sources and "mode" from the remote control.

-A preamp output (for use with a subwoofer).

Specialists' rating: 5

One test I had been meaning to do ever since I saw the rear switch, the one that changes the sensitivity by altering the amount of negative feedback injected into the circuit, was to see how it affected the sound. Remember that a total of only 4dB is used in high-sensitivity or integrated mode, and 14dB in low-sensitivity or power amplifier mode, a difference significant enough to have an impact on the sound. The difference in gain means that, as with the comparative tests between ultralinear and triode modes, one of two things must be done: either measure our listening level precisely using a tone and a multimeter if we intend to detect the changes in the short term (otherwise the change in volume would deceive us), or carry out tests over several days to get used to the new sound.

I favor the former over the latter, for the sake of precision and because there is always time afterwards to continue listening in one mode or the other for several days (whereas, if we do not carry out the tests by measuring, we would always be left wondering what we would have noticed). The differences, volume aside (the gain changes considerably; that is, the volume has to be turned up a lot when the sensitivity is reduced to maintain a similar listening level), are subtle but in line with what I have tried on other tube components (preamplifiers or integrated amplifiers) when the feedback is changed: with less NFB (negative feedback) the sound gains a certain liveliness, it is somehow more effervescent, the sound sources seem to shine and breathe more, microdynamics are better and the sound is more expansive. An example to make it clear: with a mono recording, in which there should in principle be no stereo effect and the sound image should be firmly anchored between the two loudspeakers, with the Icon Audio in integrated mode it does sound that way, but that central sound source seems to have more dimensions than when we switch to power amplifier mode (more feedback). There, the sounds seem to concentrate at a single point, and what I was listening to sounded much more artificial: Oistrakh playing violin concertos sounded much more realistic with less feedback (high-sensitivity mode) thanks to that greater expansion of the sound; it seemed less mono, less squeezed together with the orchestra...

On the other hand, in power amplifier or low-sensitivity mode, the bass seems more defined and precise and the stereo soundstage better delineated (more precise, but with less air around the instruments), and it might be a good choice for action movies... which is, after all, what it is intended for if we use this integrated amplifier as a power amplifier with an audio/video processor. It also makes it easier to use: connect it to the preamplifier or AV receiver, set the switch to low, and turn the volume all the way up.

Icon Audio Stereo 60 Mk3 Signature, Exquisite

Specifications

Distributor: AV INTEGRA 93 464 15 00



Maximum output power: 85W RMS per channel in Ultralinear mode (42W per channel in Triode mode) into 8 ohm. Total harmonic distortion: less than 0.2%. Maximum power consumption 500W. Damping factor (DF) 13 into 8ohm in Triode mode. Signal-to-noise ratio 97dB and frequency response 20Hz (-0.2dB) to 55kHz (-3dB). Sensitivity for maximum power: 300mV (950mV in "Low Sensitivity" position). Negative feedback (NFB): 4db (14dB in "Low Sensitivity" position). Tubes: 0D3 (regulator), 6SL7 (input pair), 6SN7 (splitter pair), KT120 (one pair per power channel). Connectivity: 3 RCA inputs (CD, Tuner, Aux) plus 1 direct input (Tape) and 1 recording output (passive). Remote control for volume and mute. Wire or 4mm banana outputs for main loudspeakers, connections for 8 or 4 Ohm impedance. Dimensions (W x H x D) 440 x 230 x 430 mm. Weight 35 kg.