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An outstanding tube amplifier that conveys music with wonderful finesse and refinement

A Review On: Icon Audio HP8 MKII

Icon Audio HP8 MKII

Rated # 96 in Desktop Amps
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Posted · Updated · 20138 Views · 21 Comments

Pros: Effortlessly natural sound. Works beautifully with the Sennheiser HD800

Cons: Nothing of note

UK Headfi enthusiasts who want to add a bit of tube goodness to the amplification must look across the pond to their American friends with more than a little envy. While a number of specialist makers cater for the US market, options in the UK and even Europe are rather more limited. The surge in models from China provide an alternative to the US, but once you factor in the cost of shipping, the inevitable import duty/tax, and the question of what to do if there’s a problem, the attractions of a home-grown product become obvious.


Until recently I’d always favoured the fit-and-forget simplicity of solid state amplifiers, but reviews of tube-based amps always seemed to describe attributes that appealed to me. A visit to a Headfi meet gave me the chance to audition a few tube-based rigs, which confirmed the impression.


So step forward Icon Audio and their HP8 mk2. It ticks all the right boxes, but doesn’t have much of a following on Headfi. In some ways I can understand why. Not withstanding the cost of importing these amps to the US which is clearly an issue in developing a following on Headfi, Icon Audio hardly do themselves any favours. You don’t get any slick packaging or a fashionable ‘i’ prefix with the HP8. And their marketing is at best understated - they make Harbeth (my favourite speaker company) look pushy by comparison – and that takes some doing! But it’s all to the good. Instead of wasting your money underwriting their marketing campaign, you’re paying for what really matters, the thing that makes the sound. And in that respect, Icon Audio can hold their heads high, because this amp is simply excellent.




Before I get stuck into this review I’d better make a few things clear. I know nothing about tube amps from a technical point of view and not much about anything technical to be honest. I can wire a plug and boil a kettle but that’s about it. I don’t have any particular prejudices when it comes to equipment or music and I listen to a wide range of genres. So this review is best considered as an informal impression rather than the kind of rigorous appraisal others provide. I’ve no doubt it will be written off by some, but I can only say it reflects my impressions based on what I actually hear.


Equipment used in this review:



Apple MacBook Pro (mid 2010) running Fidelia
iBasso DX100



Audio GD Reference 5.2
Meridian Explorer with iFi iUSB power supply conditioner


Amp used for comparison

Violectric HPA v200



Sennheiser HD800 (I mostly used these during the review and found the Icon’s middle gain setting preferable)
Audeze LCD 2r2 Bamboo
Sennheiser HD600


Music was either Apple Lossless files copied from CDs or high-res downloads at a range of resolutions up to 24/192.


I purchased the HP8 without having heard it. As I wanted to get the best I could out of the design I bought mine direct from Icon Audio and opted for their uprated SE ‘signature edition’. This comes with Jensen caps and improved valves: a gold-plated-pin JJ Tesla for the pre-amp and a pair of Shuguang Treasure CV-181Z, which are 6SN7 equivalents. I let the amp run in for about 24 hrs before listening and felt it continued to improve for a considerable period – at least 100 hours. The Treasures have been in situ the most, although I’ve recently tried the well regarded NOS Sylvania JAN-CHS-6SN7W, which date back to the 1940s, and Full Music 6SN7s which, like the Treasures, are a modern valve. I’ve also rolled the ECC83 as you’ll see below and definitely feel that tube choice can help maximise the performance of the amp. Of the ones I tries, none were bad and all had an impact in different ways, so I’d strongly recommend experimenting. However, the basic character of the amp remained consistent throughout.


So what does it sound like? Well, I’d describe it as having a rich, full-bodied sound with excellent weight and a sense of effortlessness that is vital for headphone listening. However, it’s capable of real delicacy when needed and I find it conveys rhythm and dynamics well too. It may be a muscular performer but it’s light on its feet. Finger and toe tappingly so.


What I particularly like is the naturalism with which it portrays the sound the instruments are actually making. This might sound like a given (isn’t that what all hi-fi equipment aims for?) but rarely in my experience is it really achieved. All too often there’s something ever so slightly unnatural and unreal about recorded music replay, particularly in the digital era. Well not here, the music sounds ‘real’ through this amp, three dimensional, full of life and vividly portrayed. You get a real sense of how the music is being played too, all those subtle textural cues that help you sense how the musician is actually making the sounds, and that helps tremendously with the sense of realism.


But these euphonic qualities do not mean that the Icon is throwing a beautifully, lush and golden veil over the music. If the original recording is bad, the HP8 doesn’t disguise it. However, I found that the choice of valve could be used to subtly mould the sound, depending on the source material, your other equipment and what you wanted to get from it. That said, I found one valve combination had a special ‘magic’ that meant ultimately that I preferred it to anything else – but this might not be true with a different front end or headphone – as ever system matching is essential.


In contrast to the HP8, I found the well-regarded Violectric v200 – which was the amp I mainly compared the HP8 to – sounded strangely ‘flat’ and less ‘colourful’ – drier perhaps. Not just two dimensional in the sense that the sound stage was flatter, but somehow less realistic in the fundamental sense that you never quite forget that you’re listening to recorded music played through an electronic device via a pair of headphones. By contrast, the Icon just does everything sufficiently better that I frequently forgot completely how the sounds were arriving in my ears. This isn’t to say that the Violectric is a bad amp – it clearly isn’t – just that the Icon is a better one. And, although the Violectric is frequently described as having a slightly warm, tube amp character, I found that in comparison to the Icon it was still quite obviously solid state.


Maybe at this point I should mention the tubes? Here’s a short summary of their sonic impact, which largely followed what I’d been led to expect from reading up about these valves in advance of trying them.


Supplied tubes


12AX7 ECC83

Modern JJ Tesla: It was fine as a starting point. It did nothing wrong but I felt quite quickly that it was probably holding the amp back. With running-in well advanced the HP8 didn’t seem to be shining quite as I’d expected it to, although the sound was well balanced, rich and reasonably detailed. Experiments with some alternative NOS tubes quickly showed this to be true, although the JJ Tesla wasn’t completely disgraced by any means. However, in my view there are better options available if you want to max out the Icon’s performance.



Shuguang Treasure CV-181Z: I found these valves worked extremely well with the HP8. They seemed to have a good balance of positive qualities and no obvious faults – other than their high price! The best qualities of the amp were well revealed by these tubes and I felt the other 6SN7 tubes I tried made only a relatively small difference to performance. However, I did prefer the Full Music 6SN7 which, while similar in general performance and tonality, really seemed to make the amp sing.


Other 12AX7 ECC83 I tried:


NOS Tesla (remake of the famous Telefunken ECC803s) mid 1970s vintage.
Basically silent. Crisp, clean and slightly analytical. Sonically cooler than the Brimar or Mullards, the Tesla was very extended with a slight hardness at the top end. Excellent sound stage – deep, wide and well-defined. I found this tube didn’t gel well with the Sennheiser HD800 (too analytical) and was a little fatiguing. It was better with the LCD-2r2. 


Mullard MC1 – 1958, one of the most famous ECC83s of all time. Mine was a used example and wasn’t quite as quiet as the Tesla, although the hum was never objectionable. The Mullard was a very fine performer and bought a sweetness to the sound, particularly the midrange. I felt it added a touch of warmth too. Both the Mullards were outstanding with my HD800.


NOS Mullard F91, late 1950s. Quieter than the MC1 and a touch more neutral, this brilliant valve provided an open door on the music - almost holographic - with wonderful detail and 3D imaging. The highs were very extended but without harshness, except where already present in the recording. It added a touch of warmth perhaps, but overall I found it well worthy of its reputation.


Brimar 1952 - No hum issues. Hard to describe but somehow made the Icon a more muscular performer with bigger, bolder, weightier sound. However, this tube also had great finesse and could reveal delicate textures very effectively. I loved it with classical music but it was a fine all-rounder too. It definitely had a slightly different character to the Mullards, but hard to actually describe.


Other 6SN7 I tried:


Sylvania JAN-CHS-6SN7W black base, tall bottle mid-1940s

Initially, I was very impressed by these valves. The top end, in particular was spectacular, with cymbals and high hats amazingly revealed and percussion generally very impressive. These tubes seemed to bring out the rhythmic side of the music which added to the impact of some genres more than others. On the downside, I found the presentation a little ‘tense’, and the high end over emphasised on the HD800, eventually finding them a little too fatiguing.


Full Music 6SN7 (same as Sophia Electric 6SN7 I think)

I’d read mixed reviews of these valves and wasn’t expecting to be particularly impressed, but the Full Music was an outstanding performer. Their general sound was similar to the Shuguang Treasures, but combined with the Mullard tubes it provided a completely beguiling combination in the HP8, sounding wonderfully effortless and open, while offering the most holographic insight into the music of all the combinations I tried. The sound stage was beautifully realised with a high degree of instrument separation. Placement was excellent, particularly with well-recorded classical music. Any thoughts that the HD800 could be considered thin and bass light were completely dispelled by this set up. The Full Music provided weight and punch in abundance, but without any obvious loss of top end sparkle or detail – actually detail was if anything enhanced. The midrange was outstanding too – smile on face time almost constantly. I found this the most transparent and lifelike of the combinations I tried and this was true with both instrumental and vocal music.






It's hard for me to say whether the ‘SE’ upgrades are worthwhile compared to the standard model because I didn't do a comparison. I went for the upgrades on the basis that I wanted to give the HP8 the best chance to impress me, which it certainly did.


On the basis of the sound quality for what I paid, the good news is that the upgraded HP8 is certainly worth it. However, be aware that the valve recommendations they offer are based on the need to supply modern production valves. In the case of the ecc83/12ax7 I'm certain you can improve on their recommendation. The Shuguang Treasure CV181 are splendid though, and will give you a very good idea of the performance of which the amp is capable. I happen to prefer the Full Music/Sophia Electric 6sn7 but it's very much a matter of personal preference and component matching. No doubt there are other great NOS alternatives too.


That's pretty much all I can say. Having lived with my Icon Audio HP8 mk2 for some time now, I doubt I’ll go back to a solid state amp for my Sennheiser HD800s and, based on my detailed comparison against the Violectric v200, and what I can remember of other amps I’ve tried recently, I’d expect it to compete very strongly with anything at it’s price point. 


Perhaps the best thing I can say about it is that it encouraged me to listen to more music. I regularly found I'd play a track while writing this review, and then find I'd end up listening to the whole album. In terms of its sound, it's the first headphone amp I've used that I've been 100% happy with. I've no doubt there are higher end options that offer even more, but I reckon many people will be very happy with how the HP8 sounds.



lovely review...i like the non technical way its expressed, ya i can boil a kettle of water as well as u do...tats about as technical i can get. :P
must admit i am eyeing this amp as a possible upgrade to my dv336se.
trouble is i cant find a big fault with the DV..humpffff...unless there is an icon at 300 british pounds ..lol.
Nice review, really captures the soul of this wonderful amp.
Really nice review of an amp i have had my eye on for some time now. I wonder how it would compare to my souped-up Bottlehead Crack? i am thinking it might be more of a sideways upgrade/slightly different presentation etc.
Wonderful review, Painterspal. I must congratulate you on your excellent photography. Really captured the joy of this product in the group shot. It seems like a wonderful tube amplifier and one that seems to be great with both low and high impedance headphones. I hope I can hear this amplifier in the future. :-)
Wonderful review.
I agree with your review. I own a 2nd hand standard model and am very happy with it indeed. Like you I have settled on the middle output resistance setting, though I preferred the others at various times. I also use it with HD800s. With ATH-W1000X The background hum was a bit much though, so YMMV with low impedance headphones.
Quick addition - Using a Tera Player as the source+DAC sounds wonderful.
Superb review. I have this amp and could almost hear myself when reading it. Every single thing you said is spot on! Thanks for taking the time to write it :)
Thanks all - very much appreciated!
very useful review.Thanks for taking the time to write it.
Great review. But does it sound better than the Little Dot?
Have heard some reports of users reporting hearing a HUM. Listening at low volumes can be a problem. The only thing holding me back on this one.
The best thing about this review is the honesty that comes across. Not overloaded with superlatives (which can be a bit tiring) but the main point comes through loud and clear - this is a really superb headphone amplifier! I am now itching to get the HD800! Thanks for the review. Fortunately no hum in my unit.
Thank you for taking the time to write such nice review.
This amp sounds like a winner
Wonderful review.
Really nice review made me do a few searches on the Jenson Caps in the upgraded version a couple of interesting things turned up. Positive they are highly praised for their great sound. Downside is there have been a few reports of the odd leaky one, also worth noting it seems they have a 250 hour life at a maximum temperature of 85°C so keep an eye on temps and ventilation not one to leave on all day.
 Great review!  Really easy read and really informative.  I have the amp and I love it but I have issues with it being too bright, which is something that people say just isn't so about the headphones I'm using (Denon AH-D7000).  And on the back of this review I'm now looking for some Full Music tubes.  I already have a Mullard CV4004, which is excellent and completely got rid of the hiss that I had with the stock tube that came with it.  I'm using Sylvania 6SN7s and they sound great but the treble is too bright with these headphones.  I think if I was using Senns they would probably be a better match, but I am really looking forward to trying this out with some Full Music tubes now.  Thanks!
Thanks for the excellent review
Nice review and a very pleasant writing style. I use the standard version of this amp, and my impressions pretty much mirror yours. Thanks.
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