Icon Audio HP8 MKII Headphone Amplifier
Michael Johnson—Tubes have always been an enticing, yet relatively frightening proposition for me. I was always drawn in by the aesthetic and potential sound benefits of tubes. The lack of power versatility always scared me away from integrating them into my speaker setup, but once I began to get into the headphone side of things, I felt a little more freedom to experiment.
It began with a pair of Sennheiser HD600 and a Woo Audio Wa6 (1st gen) amplifier. This combination was the darling of the head-fi community at the time, and I must admit it brought me many years of smooth enjoyment. Eventually, last year I found myself an owner of the excellent Focal Clear Headphones, and moved to a tube/solid-state hybrid amplifier to best accommodate the Focal’s impedance of 52 ohms.
Enter the Icon Audio HP8 MkII ($1,495), a class A triode headphone amplifier sent over by Warren Lavender at Audioarcan. The HP8 is unique because it utilizes a multi tap output transformer with 3 output impedance settings. Did I finally have a pure valve design flexible enough for my low impedance dynamic driver cans?
Note: the version I had for review was the ‘Signature’ model at $1795. For the $300 premium, the Signature includes 2 David Shaw (Icon designer and owner) white ceramic CV181 (6SN7) output tubes, 1 Gold pin 12AX7 tube and Mundorf Capacitors.
Build and Features
Icon Audio has a very clean design language that is consistent across all their units. The 16lb, relatively compact desktop design features a solid copper top plate, which in addition to providing substantial damping, is the only real design ‘flare’ on this amplifier. Icon Audio has chosen to let the tubes be the visual centrepiece, which I think is a wise decision. The box on the rear houses the hand-wound output transformer. The connections are likewise just as simple, with two sets of gold plated RCA connectors on the rear (input and output) as well as a ground, while the front features two knobs for volume and output impedance respectively, a quarter-inch headphone jack, and a real live mono/stereo switch!
The star of the show is of course the tubes, emerging from their sockets buried in the copper top plate. The HP8 is powered by two 6SN7 tubes for output and one 12AX7 for input. My Signature ships with the two David Shaw upgraded CV181 tubes and an Electro-Harmonix gold pin 12AX7 (pictured below).
Under the copper hood, Shaw has managed a very impressive purist design. This amplifier is designed in the United Kingdom but manufactured in China. It is perhaps because of this Icon is able to do things like full point-to-point hand wiring (no printed circuit board), hand wound transformers, and include high quality Japanese parts such as a Blue ALPS volume pot and steel EL transformers. The specs are also nothing to scoff at, with a THD number of only .2% (not bad for a pure tube design), and a max output of 800 mW per channel.
I was impressed with the build quality and heft of the HP8 as a whole, it certainly was more aesthetically pleasing than my Woo Wa6. I did however notice that the faceplate on my unit was severely crooked, which put a bit of a damper on the clean lines of the unit. I’m sure this is something easily corrected by a technician or even perhaps the user themselves. Still, not something one wants to see when they open their brand new 1.5K amp.
In Use
The HP8 is fairly simple as headphone amps go. It contains no DACs, WiFi, streaming, or anything of the type. It does one thing and one thing only, takes line level input and transforms it into output suitable for your headphones. Fortunately, I could run all my sources through my McIntosh C712 preamplifier and use the ‘Tape Out’ connection to run an Audioquest Golden Gate interconnect to the HP8. From there I could and did test the HP8 with a variety of sources including vinyl, CD, and high resolution files.
Sound
I started using the HP8 with my Sennheiser HD600 as I knew their 300 ohm impedance would be an easy match for any tube amp. I immediately remembered why I liked this neutral headphone as it provides an even and open sound, with its only sins being of omission. Listening to my SACD of the Netherlands Philharmonic playing the Brahms Piano Quartet Op. 25 (arr. Schoenberg), I found a lot to like about the presentation, big, bold, rich, but also fairly clean and detailed. It had been a while since I listened to the HD600 so I was unsure what was impressing me, the headphones or the amp. I still had my Woo Wa6 (1st gen) at the time, and decided to use it to listen to the same work. While both amps have a liquid smooth midrange and satisfying high register extension and airiness, the Woo definitely lacked the bottom end extension and control of the HP8. In fact the HP8 made the HD600 sound ‘bigger’ than I was accustomed to, taking the even yet polite sound and injecting it with more impact. Despite the high impedance of the Sennheiser’s, I only needed to run the HP8 at the ‘Medium’ output setting to get more than sufficient gain.
Ok, so, the HP8 had more to offer for my entry level, high impedance Sennheisers, but what about my reference headphones, the 52 ohm Focal Clear? These low impedance dynamic driver headphones can be driven by virtually anything. Owners of such headphones may wonder why external headphone amps are necessary at all, as many people have ‘headphone out’ sections on their preamp or integrated. Well, the Clears may be easy to drive, but they are incredibly transparent. I set the HP8 to the ‘Low’ setting and got out my notepad.
I started with a record I recently imported from Japan, Julie IV, Ima Boku Ha Shiawase Desu (I’m Happy Now), the fourth solo album by former Tigers and PYG vocalist Kenji Sawada. This record is a unique album in his discography as he strays away from the pop-rock he was known for on his previous outings and embraces a more intimate folk and country sound. Much of the album features dueling acoustic and electric blues guitar, as well as various piano and organ overdubs. One of the first things I noticed was how well the HP8 portrayed different instruments harmonic qualities. The last time I listened to this album on my speaker setup, the various guitars tended to blend into one another, but here they were individual voices with their own timbral characteristics. I could hear the different picking styles employed as well.
On the second track ‘Higai Mousou’, Sawada is accompanied only by two acoustic guitars, with one playing a thick full rhythm strum while the other plays a very metallic sounding slide guitar, often imitating the vocal line. The twang of the slide guitar was incredibly bright and sharp as it should be, while never falling into grain or sibilance. Overall, I was focusing on the playing of the instrumentalists, which is a very good thing—we are transported further towards the illusion of live performance. Sawada’s vocals were crystal clear and liquid, with the beautiful upper midrange that only tubes can provide, however there was never a feeling that things were “glossed over”, I could hear the small inflections and grunt of his baritone. The most impressive thing the HP8 handled in this recording was the bass guitar. It was rich and larger than life, with a strong melodic identity. It never blended into the foundation of the sound, but stood on its own with clarity and authority.
I then put on Lynyrd Skynyrd’s outstanding debut album Pronounced 'Lĕh-'nérd 'Skin-'nérd reissued by Analogue Productions at 45rpm. Here I got more of what the HP8 does with male vocals, and that’s present them with an incredible sense of air and flesh. On the opening track ‘I Ain’t the One’, you can hear the slight gurgles and palpitations of vocalist Ronnie Van Zant. There is some intensive drumming on this album, and one of the things I noticed most was how well rendered cymbal sounds were with this unit. There’s a nice air and decay around all the cymbals and they are easy to distinguish from each other. There is no sibilance or glare that obscures the overtones.
Moving to digital, I played my 96/24 file of London Calling by The Clash. Listening to this album on the HP8 is a joy, I found myself just enjoying the energy and admittedly didn’t take many notes. Bass was tuneful and satisfying, but also there was a real groove and pulse. Sometimes the combination of gear and music just makes you nod your head, and that’s the end of it. Just to be thorough (and actually do my job), I hooked up my usual amp pairing with the Focals: the Monoprice Liquid Platinum. The Monoprice is a hybrid tube/solid-state amplifier, designed by Alex Cavalli. It puts out a ridiculous amount of gain and exerts some real precision and control of the Focals. The bass on the Monoprice went a bit deeper and had a bit more punch and snap but man did it suck a lot of the tone out of the sound by comparison. The bass on the HP8 had more texture which in turn made it sound more full. I would call the Monoprice a more ‘percussive sound’, but it lacks the open, liquid midrange of the HP8. It sacrifices a lot of air and decay for greater extension in the bass and treble and more impact. The thing about ‘punch’, though, is that if it’s not accompanied by tone and the right overtones, it loses its novelty somewhat quickly. I was able to really crank the HP8 on this raucous punk album, whereas with the Monoprice I was a bit more afraid of the volume knob.
I also listened to my CD rip of Genesis’s Selling England By The Pound, particularly the opening track ‘Dancing With The Moonlit Knight’, switching back and forth between the Monoprice and the Icon Audio. Again, I think the Monoprice was able to provide a low end impact that a pure tube design just can’t match. However, on all other fronts I preferred the Icon. On this track after the opening, the first verse contains a very soft and subtle kick drum. On the Monoprice it was felt a little more, however it was just a ‘thud’ sound, impact and no tone. On the Icon, it had a little more resonance and natural tone. It sounded more like a real instrument, a real vibrating drum head. The Monoprice also got a little bright when the synths were at their full power—I found myself reaching to turn down the volume. On the later track ‘After the Ordeal’, I found the organ much more full bodied on the HP8, it really felt like a pipe organ was in the room moving air. The Monoprice also did a good job reproducing this difficult timbre, but it didn’t sound quite as effortlessly natural, it almost felt like a digital recreation by comparison. The upper treble was also incredibly sweet and airy on ‘The Cinema Show’, showing more than sufficient sparkle and upper end detail.
Maybe I shouldn’t speak so ill of the Liquid Platinum, it is a really excellent sounding amplifier at $799, and like the HP8, it is incredibly versatile. But, with my headphones, the HP8 brings much more openness and richness to the sound, which I think justifies the price increase (nearly double). The HP8 is not as quiet as the Monoprice in operation however. In my system on my (rather poor) apartment power grid, I do get a bit of background noise, however, it never distracted me from the music in any way and was really only audible in between tracks. I’m a vinyl listener after all, I would rather hear vivid sound with some slight background hiss, than sterile sound with inky black backgrounds.
Near the end of the review period, I streamed a lot of various tracks on Tidal HiFi, including things like the Cowboy Bebop (Official Series Soundtrack), Morrissey’s You Are the Quarry, August Burns Red’s Constellations, and Alexandre Tharaud’s recent piano album Versailles. The latter provided one of the most engaging piano renderings on headphones I’ve heard in a very long time. Throughout all of it, however, I began to notice that I was hearing something I wasn’t used to on the Focal Clears: soundstage depth. Not that the Clears are usually completely devoid of this, but it’s always been the one caveat to this otherwise perfect headphone—the stage feels a little bit close and somewhat small. With the HP8, I was noticing a bigger perceived distance between the musicians, and a more significant perceived distance from my head. I felt more space, something very relieving after having more or less given up on such a sensation. Even when I ran the Clears with the $2,500 Focal Arche amplifier last year, I never got quite the spaciousness I’m hearing here with the HP8, or the fun factor. Yes, it was more detailed and exerted ultimate control (it was designed for Focal headphones after all), but I certainly don’t remember it being this big of a sound or this much fun to listen to.
Final Thoughts
I went into this review very skeptical of a pure tube design wowing me, especially with my reference headphones being a low-impedance design. I was shocked by how natural the $1795 HP8 MkII Signature sounded with my chosen headphones, how much air, separation, and natural decay it showcased in all types of music. It is not a rolled-off or overly romantic sound like some other tube amps suffer from, but it is a lush and full presentation with plenty of dynamics and detail. Not only that, but it is immense fun. More so than any headphone amplifier I’ve paired to the Focal Clears. This unit just made me want to recline, close my eyes, and tap my foot. If you couple the fun factor with impressive specs, and a rock solid, old-fashioned build quality, you have a piece that stands out as an ‘arrival point’ for personal audio.
The versatility of the HP8 via its output transformer is the real appeal here, as many pure tube amplifiers are more picky about pairings. Icon says this amp will work with anything above 8 ohms, and while I believe them, I would personally suggest this amp for headphones greater than 20 ohms or so. It drove my 52 ohm Focals just as well as my 300ohm Sennheisers, and I would certainly recommend this amp for statement headphones like the Sennheiser HD800/HD800S, Audeze LCD-3/4, the HIFIMAN HE1000 or the Focal Utopia. With 800 mW x2 of Class A power on tap (a number up there with many solid state designs), it has plenty of gain for all of them. This amplifier is, of course, just an amp, no frills attached, so it may not suit those looking for compact desktop all-in-one solutions with DACs, streaming, or other state-of-the art digital audio applications. If you have all those bases already covered in your chain, or want a high end headphone section for your main system, the Icon Audio HP8 MkII Signature is one of the best sounding headphone amplifiers I have heard, and its polished looks certainly makes it easy on the eyes as well as the ears.
The synergy was so enthralling with my Focals that I contacted Audioarcan to place an order for an HP8 of my own, the best endorsement I know how to give.
Further information: Audioarcan
