Inspire by Dennis Had IHA-1 Dragon Version


Member of the Trade: Acorn Audio
Pros: Very sensitive to different tube pairings, resolving, not treble harsh, uses somewhat mainstream tube options
Cons: A bit lean in the bass, pre-outs may hum with active speakers, only available from a single seller so no way to demo outside of places where Moon Audio is present


The IHA-1 is the concoction of Dennis Had, formerly of Cary Audio, who has a reputation in the audio community for his tube power amps. After Drew Baird, CEO of Moon Audio, used an Audeze LCD-3 to showcase to Dennis just how far headphone technology had come, he decided to give a commercial headphone amplifier a go – distributed by Moon Audio exclusively. He also sells his other amps on eBay separately, but I have no experience with those. Essentially, the IHA-1 was Dennis taking elements from his years of designing highly-regarded tube speaker amps and distilling them down to something that could be enjoyed with headphones.

I received mine on the 9th of August, 2017. It was a personal purchase, done purely out of curiousity as several of my peers had one and liked it considerably. Based in the United Kingdom, I wasn’t able to demo it anywhere as it is sold exclusively by Moon Audio – who are based in North Carolina, USA. I did meet Drew at the 2016 London Can Jam however, where I listened to the Focal Elear and Utopia out of this amp. At the time, I had no reference point for what I was hearing – all I knew was that it was really, really good. Over the next few months, I found myself with an Elear and then eventually a Utopia – but I wanted to know more about that amplifier with which I had first experienced these headphones.

After filming an unboxing video, I was pleased to hear that the amp immediately sounded like a considerable upgrade over my other options at the time – with the stock tubes. I fell into a downward spiral of tube exploration based on expensive curiousity over the next few months – culminating in me buying one of the most sought after rectifiers out there for it. After that, I retreated and worked with what I had. Ten months after purchasing it, I’m ready to present my findings.


Specifications (According to Moon Audio)

· Stepped DACT 100K attenuator running a pair of 6SN7's at over 1 watt of output power

· Output impedance of 4.4 ohms

· Transformer Pro Balanced output

· 2 analogue RCA input selector positions, including a mute position

· 4pin XLR Headphone output

· 1/4" headphone output

· Pre-amp RCA Outputs with switch that mutes the headphone output

· A Sovtek 5Y3GT tube is standard

· A RCA 5U4GB Rectifier New Old Stock Tube is available for an additional $100

· A pair of 6SN7 Electro-Harmonix tubes come standard

· A pair of 6SN7 New Old Stock Tubes are available for an additional $100

· Direct coupling and transformer output are included as part of the standard configuration.

· 10 inches wide 8 inches deep, height varies based on tubes used.

· Frequency Response 12 Hz to 32 KHz + - 0 dB

· Power output into 40 ohms 1.7 watts less than 1% THD 2nd harmonic

· Amplifier gain: 18 dB

· Noise Floor -87 dB

· Dual Headphone outputs 1/4” Pro-Type/ 4 pin XLR Pro-Type

· Switchable line level dual channel line preamplifier output (optional)

· AC voltage 120 or 240 VAC 50/60 Hz

· Output power tubes X 2 6SN7 dual triodes

· Vacuum tube rectification 5Y3

· .090 aluminium chassis

· Powder Coat: Copper/Clear Coat

· Dimensions: 10” x 8” x 6” high with tubes installed

· Weight: 15 lbs



Build Quality & Features

For the younger members in the community, particularly those who have dabbled in audio production, the look of the IHA-1 will probably remind them of the Focusrite Scarlett series due to the deep red colour. Others will notice that the tube glow is quite dim on this amp, the Feliks Elise lit up the same pre-amp tubes far more – as far as aesthetics go. The compactness of the IHA-1 surprised me, as I had forgotten the exact size in the year since Canjam London 2016. After shopping around and seeing amps with so, so many tubes plugged in – the IHA-1 seemed quite approachable with its two pre-amp and single rectifier design. When it comes to build quality, it is quite solid -although I noticed one day that a small piece of plastic had chipped off at some point.


It should be noted that this amplifier is not balanced. It is single-ended, despite the 4-pin XLR output on the front existing. Also, rather interestingly, there is no volume or sound degradation if both the XLR and ¼ inch outputs are used simultaneously. Two sets of single-ended inputs exist in the back, with a front dial allowing you to switch between the two and putting the amp on standby mode – cutting off any sound. The volume dial is on a stepped attenuator, and I usually never really go beyond the 12 ‘o clock mark. However, I have heard of people saying this amp (even with the Lundahl transformers) isn’t loud enough for them entirely. That boggles my mind a bit.


The Lundahl transformers are an upgrade I opted for, costing $250 more than the fully stock IHA-1. To my knowledge, these don’t add more wattage to headphones – but rather more clean gain. I find this essential if you are planning on using planar magnetic headphones with this amplifier. I also opted to get the pre-outs in the back added for an additional $100, as this was an option back then but has since been made mandatory and had its cost added to the baseline price. These had significant hum when used with my active speakers, and nothing I tried could eliminate that. I surmised that they were designed for passive systems and stopped using them. At the time I purchased it, the stock tubes were a pair of NOS Raytheon 6SN7s alongside a JJ 5Y3GT – with upgrade options being a pair of Sylvania 6SN7 GTA or GTB pre-amp tubes alongside a RCA 5U4GB. These have since been changed, as you can see in the specifications list – and I assume Moon rotates according to availability.



The IHA-1’s main strength, if you share my obsessive inclinations in hobbies, is a double-edged sword. It simply morphs with the tubes you plug in, and is a very capable blank canvas in doing so. On one hand, I have no doubt that a large number of users will be perfectly happy with the stock tubes, but I also do not doubt that others will find the payoff from trying different tube pairings to be quite substantial – as the differences are not subtle.

The sound of the amp itself is also very much to my liking. I’ve tried a variety of sources with it and felt that it did not stretch nor narrow the soundstage in any way by itself. Its own tendencies are geared towards detail retrieval and trying to remove itself from the chain as much as possible. It’s because of this that I’ve found it (with a tube pairing that I am familiar with) an easy amp to evaluate source gear with.





The bass amount might, however, be a detraction for some people - particularly those who are used to certain solid-state offerings with elevated punch. I don’t find the IHA-1 thin or unsatisfying at all, and with certain tubes it is far from that – according to my preferences. But, I will admit, it’s a bit leaner than the aforementioned solid-state amps. It’s interesting because I had heard through the grapevine that the IHA-1 was an amp that was very similar to a solid-state in sound despite injecting the benefits of tubes as well – but the bass immediately gives it away if you are someone who is used to a lot of slam.

The midrange is remarkably transparent and clean sounding, with no emphasis in lower or upper registers. The former is something I heard with the Feliks Audio Elise, and when I reviewed it last year I pointed out this tonal difference with the IHA-1. That being said, if a slightly warmer and more euphonic experience is something you desire from your tube amp – you can always swap in some tubes to cater to your needs (and I’ll detail some pairings below you might want to check out). I, personally, prefer a more even ascent up the frequency spectrum with the IHA-1 – so I did swap out the stock Raytheon 6SN7 pre-amp tubes, although I find them very capable and a good stock option on Moon Audio’s part.

While I would not characterise the IHA-1 as a bright amp, I would again mention that this isn’t a warm and gooey experience that some enjoy tube amps for. It can be taken there, but it will never quite go all the way. The treble is delicately balanced yet has the ability to soar, and does not seem etched with the majority of the tube pairings I have tried. It also doesn’t become too rolled with others, changing just enough without removing an important aspect of the listening experience.

Now that I’ve attempted to explain the tonality of the amp, I’d like to mention that what I enjoy the IHA-1 mostly for is its ability to bring out more detail in tracks. Not to be dramatic, but I heard this even the first time I plugged it in with the stock tubes. Even today, writing this almost a year later – I’m hearing the same benefits from the stock tubes even though I haven’t used them in almost as long as I’ve had this amp. Track separation is very well done, depending on source, with the stereotypical “hearing things I didn’t hear before” in full effect if it is a significant upgrade to your source chain. Paired with a Schiit Yggdrasil and driving a Focal Utopia, I often find myself in the position that music I’ve listened to for a long, long time (predating my involvement in this hobby) makes another shift in how I hear it. More is exposed, and it’s a struggle (for some) to not chase further than the stock tubes to enhance this ability.


Pre-Amp Tube Pairings

Raytheon 6SN7 GTB

I understand why this was included in my set as a stock pre-amp tube option. These manage to display the capabilities of the IHA-1 sufficiently while retaining a bit of the stereotypical tube warmth that some expect. I’ll admit that the sweetness in the midrange is quite compelling with this pair and could be a reason why someone would return to it after an upgrade. Disadvantages are that it can, compared to better offerings, mask detail a bit and that it’s quite laid back.

Sylvania 6SN7 GTA

These are possibly available from Moon Audio to add to the IHA-1 order for an extra $100. My favourite 6SN7 option, the Sylvanias veer towards the brighter side of things but have very well-controlled bass alongside sparkling and detailed highs. The midrange isn’t as lush as the Raytheon 6SN7, but has more texture to my ears. Be cautious when pairing with bright rectifiers such as the RCA 5R4GY, as it might be too much treble for some.

Ken Rad 6SN7

Warmer than the Raytheons and even more masking of detail, the main reason for using the Ken Rads is the bass slam injection. Fuller in the lows, these tubes are punchy and quite good for EDM and other electronic genres – but not something I would want for jazz or classical.

Raytheon 6BX7

Interestingly, Drew told me that they had made revisions to the amp that made it no longer support this tube set, despite me reading somewhere that it was Dennis Had’s favourite for the IHA-1. Simply put, they work in my unit at least. Considerably lower in output than the 6SN7, the 6BX7 has what I can only call a more mature warmth to it than the Ken Rads and Raytheons. It’s somewhere between them and the more articulate Sylvanias. However, you will need to crank the volume on the amp even further to volume match these, and there is a slightly higher noise floor than the 6SN7s.

Rectifier Tube Pairings

JJ 5Y3S (Stock Option)

The major failing of this rectifier is in its sub-bass control. This wasn’t quite apparent with headphones that don’t dig down as deep, but when you do plug in one that does – it’s very noticeable. Flabby and sluggish, these will slow down punchiness in such headphones and be an unsatisfying listen. I recommend replacing them even if you don’t use headphones with well-extended lows.

Electro-Harmonix 5U4GB

The cheapest replacement for the stock JJ that I can think of. A mere $15 on eBay will gain you a considerable upgrade in lower-bass control. Overall sound is leaner than the JJ and not very euphonic at all. To my understanding, these are current production tubes made in Russia. I find them quite capable, but far from my favourite pairing for the IHA-1.

Mullard GZ34 Reissue

These are current production tubes based on the legendary Mullard black-base tubes made in Blackburn way back in the day. The difference is that these are made in Russia by, allegedly, Electro-Harmonix – who purchased the original machinery from the UK factory. Considerably cheaper than the original tubes, I had hopes that these would match them. However, that wasn’t the case. These sound more like the Electro-Harmonix 5U4GB than original Mullard GZ34 black-base tubes. Lean and a bit etched in the treble, these do not sound stereotypically “tubey” at all. Detail retrieval and bass control is similar to the cheaper Electro-Harmonix 5U4GB as well. A headscratcher, this one.

Telefunken GZ34 Black-Base (Not Fat Base)

The black-base GZ34 can be found for anywhere between $50-100 and beyond. These are warmer than their reissues, but have a more organic sound that will immediately be appreciated by those chasing “tube” characteristics. They also have ample bass compared to the re-issues, that were a bit lean throughout. Treble is a bit rolled, however, and detail retrieval is more or less equal to 5U4GB variants. Staging is a bit narrow too. Despite the aforementioned “organic” sound, these are possibly some of the most solid-state sounding options you can grab for the IHA-1 due to their very focused presentation that does away with any slightly “romantic” diffuse/ethereal sound that some might expect from tubes.

Philips Metal-Base GZ34

By far the most I’ve spent on tubes, the metal-base GZ34 earns its reputation due to its incredible melding of detail retrieval with a focused sound that somehow still retains a slight etherealness to its signature that makes some genres very satisfying to listen to. There is a slight lingering to the decay, which is an addition to the IHA-1 which doesn’t have such a characteristic by its own nature, that is very romantic sounding without overstaying its welcome. It’s very delicate and effective.

I wouldn’t recommend it for its bass capabilities however, as it is quite lean in that area. The midrange is the highlight, as detail is presented effortlessly alongside texture. What sets this apart further over the aforementioned rectifiers is its timbre, as it takes the ability of the Schiit Yggdrasil Analogue Stage 2 to recreate live acoustic instruments and takes it a step further – especially pianos. Furthermore, it does all of this in a non-fatiguing way as the treble is not harsh nor hiked. In fact, I’d go so far to say that it’s ever so slightly rolled off in the high treble (especially compared to the likes of the RCA 5R4GY) – but it doesn’t bother me due to all the other benefits it brings. Do I recommend it? Yeah, but you’d have to be insane to buy it for its current market price – and I seemingly am.


These were available to add to your IHA-1 order for an extra $100 – although their market price is lower than that. A considerable jump from the stock JJ 5Y3, the RCA 5U is a warm tube with a bit of bloom for those who desire it. Its bass control is also a substantial upgrade over the stock option. Its strength is a musical sound, but it lacks some detail retrieval and resolve compared to other options – if such attributes are important to you.

Westinghouse 5U4G

My favourite of the warmer, bassier rectifier options, the Westinghouse sounds like an upgraded RCA 5U4GB with more resolve to it. Its bass managed to balance being ample and well controlled to a level that all these other rectifiers simply do not – as they veer towards being lean and controlled or ample and bloomy usually compared. What I like furthermore is a bit more sparkle in the treble that helps this be a great all-rounder tube, more so than the metal base GZ34 even and great value if you can get it for $50 or less.

Brimar 5R4GY

This goes neck-to-neck with the metal base GZ34 in terms of detail retrieval, beats it easily in staging width – but loses out in timbre. The Brimar is lean in the bass and a bit rolled in the treble, but it has stellar detail reproduction. While I do like it overall, the problem lies in its timbre being off for several instruments – making them sound a bit muted and not letting them soar quite as much as they need to. That being said, these probably have the most upper-midrange emphasis out of all the rectifiers detailed in this article. Strings have considerable air to them, but the treble is where drawbacks begin. Also, the lower midrange is a bit scooped – which can slightly hamper male vocals and guitars, areas where the 5U4GBs are better. I have parted with this tube as I wasn’t using it much, but its detail retrieval and instrument separation made it a tough sale for me regardless.


Cheaper than the Brimar 5R4 variant, the RCA has the most treble sparkle of any tube detailed today. Well-extended highs and more representation in the lower-midrange makes this the clear winner of its counterpart – in my opinion. That being said, it takes a small hit in detail retrieval and track separation – and the staging width is narrower, although still wider than the other rectifiers.

If you had to pick any two rectifiers from this list today to cover your bases, with a max budget of $100 for both, I would say the RCA 5R4GY and the Westinghouse 5U4G would serve you well.



This amplifier is my second-favourite audio purchase of 2017, it’s really about as simple as that. Ten months down the road and my opinion of it hasn’t dampened. Any disappointments I may have had in the early days, such as the hum in the pre-amp section, have faded as I doubled down on its best usage – driving dynamic-driver headphones paired with my Schiit Yggdrasil. I found my favourite tube pairings and have familiarised myself with them over time.

Despite the praise I see online for this amplifier, I still feel that it is slightly underrated in the audio community as a whole. The Head-fi thread pales in size compared to the popular and cheaper Feliks Elise and the far more ubiquitous Schiit offerings. I don’t know if this lack of marketing push is intentional on the part of Drew and Moon Audio, perhaps they don’t want to overload Dennis with orders? I can’t say, but I am absolutely enjoying mine and can confidently say that it took my appreciation of the hobby to the next level ten months ago.
Pros: Drives headphones well. Scales up with a better power tube. Good variety of options depending on budget.
Cons: Front panel is not the most attractive. No gain setting options.
A couple of years ago I happened to be in North Carolina, visiting friends who live near Moon Audio, so I took the opportunity to visit and try out some of the gear there and spend some time chatting to Drew and his wife Nichole. It was also a chance to pick up a reasonably-priced (ie: in the hundreds of dollars) set of custom-length silver interconnects, something that would normally cost in the thousands from companies nowadays. 
I already own one Moon Audio cable, a Silver Dragon for the MrSpeakers Ether. I bought it second-hand as I only had a prototype DUM cable for them as I had bought one of the original first-production models. Like the Black Dragon, I didn't find the cable particular remarkable -- nothing jumps out about the sound when using them. That experience became a precedent for my experience with the Dragon IHA-1 Inspire.
The IHA-1 was designed by Dennis Had, previously of Cary Audio, and very well-known for his tube amp designs. I had only seen Cary Audio gear in various high-end stores, but never auditioned any systems using them, so this was to be my first experience with one of his amps. 
The IHA-1 is a relatively straight-forward design, with one power tube, by default a Electro Harmonics 5Y3GT, but compatible with any 5U4 type rectifier or 274B tube. Headphone (or optionally pre-amp) drive is provided by 2 6SN7 tubes, one per channel, and output is via transformers. 
The amp can be ordered with upgrades: Lundahl transformers and/or NOS (New Old Stock) tubes. While the former is obviously a factory option, people with existing tube collections may not need the latter. For review purposes, the model sent had the NOS tubes included and a rolled a couple of my own collection in for comparison. 
I've found that every amplifier manufacturer has its own "house sound" of sorts. For those of you who already know their way around tube amps, the Moon Audio "house sound", which is apparent both in their NOS tube selection for the amp, as well as their cable designs, can be best summarised by the chrome-top Sylvania 6SN7 that came with the amp -- a smooth, even sound that doesn't jump out at you, where the detail is there, but presented in a manner without drama.
What was most lovely about the Inspire IHA-1 was the almost total lack of noise (it took using IEMs to find any, and then it wasn't at all a problem with the less sensitive pair) and the general even-handedness with which it drove everything from the Sennheiser HD800 to HiFiMan HE1000 V2. It doesn't present the music with warmth, as in the manner of the almost syrupy sound the Woo Audio WA8 had, but if something like FiiO's X7 is "steel", Audio-gd is "black opal" and the WA8 is "brass", then the Dragon Inspire might be "marble".
I didn't have enough tubes or adaptors to do a lot of rolling, but I dropped a pair of GE red-base 5692s in place of the chrome-tops, which gave a more lively, if a bit more aggressive presentation. For the power tube I had a spare Mullard metal-base 5AR4 that I had bought as a pair.
I'm pretty much a fan of the High Definition Tape Transfers jazz albums, some of which are magical. The Mark Colby Quartet in DSD256, decimated by Audirvana into PCM and fed to the Yggy as 178.6k is wonderful stuff, much of the dynamics present in the instruments despite the original recording age. Listening with the HE1000 V2, my Mullard metal-base GZ34 seemed to open up the soundstage and deliver more of the dynamics of the instruments than the RCA 5U4GB, while keeping the smoothness and liquidity of the Sylvania 6SN7s.
NOS selection RCA 5U4GB on left. Mullard metal base GZ34 on right.
Even with the Mullard the amp doesn't quite have the big-iron relaxed and spacious sound of my ALO Audio Studio Six with the HE1000 V2, even after I'd rolled Sylvania 6V6GTs in to even up the comparison.  What might be an interesting battle would be with all upgrades against the similarly-priced Apex Sangaku, though that amp, from memory, was most enjoyable with planars and less inspiring with the HD800.
As my loaner had the optional pre-amp outputs included, I used it with my ADAM ARTist 3 speakers. While not the same as using it with a proper system, I can usually get a fair idea of how an amp’s pre-amp functionality this way. Flipping the switch on the back to change to pre-amp mode, the result was as satisfying as it was using headphones.
The smoothness didn't detract at all from the dynamics of the San Antonio Symphony Orchestra performing Concierto Andaluz for 4 guitars & orchestra from the Mercury Living Presence CD set. The amp brought through both the fine detail of the instruments as well as demonstrated much of the capabilities of my Schiit Yggdrasil in this mode. It did this to a sufficient degree that I could switch the USB converter that I was using with the Yggdrasil and easily make out the subtle different in how the music sounded as a result.
Noteable that with my speakers set at the centre "0" volume setting, with the Yggdrasil as source, I had the volume, which starts at the 6 o'clock position, at around 9 o'clock. I expect this might be higher with speakers that aren't in near-field as mine are.
Functionality-wise, my only complaint might be that the gain might be set a bit low for some people, or some equipment, as I had the volume up at 3pm, though that was with the above-mentioned jazz, and other music had it closer to 12 o'clock.  I'm also not a fan of the locking version of the Neutrik headphone jack, though it might save someone accidentally shorting the amp for an extended period of time should the plug be yanked half-out.
When I first visited Moon Audio, I tried out a custom tube amp that Drew had in his showroom. At the time it, along with Black Dragon cabled HD800s was too smooth for my tastes, much as putting all green-label chrome-top Sylvanias in my Studio Six was. But now I've had a chance to get used to this with a variety of headphones, I appreciate it more than before. 
Overall, the Dragon Inspire drove headphones effortlessly, from IEMs up to top-of-the-line full-sized models and is a highly capable amp. In my system, it was only bested by an amp that is far more expensive. It’s not the kind of amp for someone looking for warmth and lushness, but for good, all-round tube performance, with the option for a bit of variety, and even a bit of a sound upgrade, via tube rolling.  Given the price of the amp, I'd thoroughly recommend it.
Thanks to Drew from Moon Audio for lending me the amp for review. 
@MLGrado The MELZ tubes? I have one here. I found that they could be a bit thin-sounding, but otherwise very clear. I only wish I had pairs of all the 6SN7s I have, but I think the results would have been consistent with the reputation for each.
I highly recommend 6SN7w's from VTS. Purk liked TSRP in my peak/volcano but I have tried that and b65 and preferred 6SN7w. The Apex sound and Inspire sound quite a bit alike to my ears as well. Clean and crisp with just a bit of lushness to make it engaging. Really wonderful. I have had the lp27a and fire bottle SE recently. The lp27a will be up for sale but the fire bottle SE is a keeper.
You said "I've found that every amplifier manufacturer has its own "house sound" of sorts."  Is there somewhere these house sound are reviewed.  I currently use a Garage1217 Project Ember, when at home but am in the market to upgrade, maybe.  I go to RMAF every year but can not spend the time... and the noise make it impossible for me make up my mind while on site.

Frank I

Columnist/Reviewer at Headphone.Guru
Pros: transparent and nothing between you and the music
Cons: need to be matched with the right source for volume levels

Back in 1997 I visited my brother-in-law in Rochester, NY and not having much to do (because of the frigid weather in the region) we decided to go listen to some high end gear in a few local audio boutiques. Two-channel audio was king in those days and I had been looking for a new amplifier, so we decided to venture out and explore.
There was a shop in Rochester that was carrying B&W speakers and Steve McCormick’s DNA amplifiers. We made that our first stop and it became my first introduction to an amplifier designed by Dennis Had. The main system was playing Holly Cole. The speaker was a B&W floor standing model. The vocal was seductive and lifelike. The baby Cary 300B mono amplifiers were being used in the system.
I remember that the sound was liquid and palpable and was unlike anything I had ever heard or experienced before. Little did I know at the time it was the beginning of a love affair with tubes (and that passion still burns in my heart and soul as strong today as it was then). The amplifier really made realize what was possible in music reproduction. The baby mono amps were priced at $3500 pair (not inexpensive) and unfortunately were not in my budget at the time.
When Drew Baird (of Moon Audio) had told me that Dennis Had was coming out of retirement and was inspired to do a headphone amplifier, my head start buzzing. Those feelings and fond memories of those early day auditioning the Cary sound immediately came to mind.
Dennis Had has been building and designing amplifiers since he was a young boy. His time with Cary produced products that are in still in production today and have achieved a legendary status. The newly created Inspire Dragon is old school in design philosophy. Dennis believes in single-ended topology in his designs and still builds amplifiers the old-fashioned way; using simple circuits and minimal parts. The Inspire IHA-1 Dragon was designed after Dennis realized that there were lot of people using headphones and the designs had matured to where they needed good and clean amplification to bring out the best sound and musicality. After listening to various headphones, Dennis became so excited and decided to build his own amp.


The Dragon IHA-1 is a simple circuit that Dennis designed to provide the purest output available. There are no parts in the signal path. The amplifier sports two 6SN7 driver tubes driven by a 5Y3GT rectifier. The rectifier acts more like a power tube.   The features of this amplifier are available from the Moon website and listed here: headphone-amp.html.
The amplifier is is painted in a high quality clear coat attractive paint finish that resembles a fine Merlot. The Dragon has a DACT 100K attenuator that runs a pair of 6SN7 tubes and puts out 1W of power. The Electro Harmonic 5Y3GT rectifier is included as part of the standard tube package, which also includes two Russian 6SN7. Tube rollers will be able to substitute any 5U4 type rectifier or 274B tube.
There are two headphone outputs in the front. One ¼ inch singled and a 4-pin XLR output as well. The amplifier is transformer coupled allowing for the use of just about any dynamic or planar headphones available today. The amplifier weighs a hefty 15 pounds.


The Dragon was setup with the Chord Hugo driving mostly lossless files from my iMac. The majority of my listening was done with my LCD X and HD 800. Also used were the Hifiman HE560 and the Alpha Dog planar headphones. The Oppo PM-1 saw some listening time as well. The Dragon volume control was used with the Oppo BDP 105. While using the Hugo as a source I used its digital volume control. The Hugo had sufficient gain and was able to drive the Dragon to loud levels.
Michael Buble’s “Close Your Eyes”, from the album To Be Loved, is a beautiful song. The track immediately will draw you in with its wonderful lyric and the song is a personal favorite that reminds me so much of my wife. Michael vocal is pristine and the Inspire Dragon made me feel the song. I became intensely involved with the lyrics.
The Dragon emotionally drew me in and had me thinking of that special person who is so important in my life. Buble’s voice is inspirational and brought tears to my eyes. I completely forgot about the gear and connected emotionally with the lyrics. Shelby Lynne’s vocals on “Just a Little Loving”, is well recorded and the vocal is one of my favorites in evaluating amplifier performance. The Dragon was articulate and had her vocal centered in the front of the soundstage. Shelby voice was clear and had body and you could feel her delicate and deliberate phrasing while singing this beautiful track.
The Dragon, utilizing the stock rectifier with the upgraded Sylvania 6SN7 chrome top tubes, delivered the right amount of texture. The sound was clean and dynamic. The bass line was very identifiable with the Electro Harmonic rectifiers. Using the Sophia 274B, I felt that the bass was not as defined and far less dynamic. The Sophia tubes were simply less enjoyable.

The midrange delivery of the Dragon is classic “Had” design. I was transported back to that time in Rochester when I had first heard the magic Cary 300B sound. This amplifier has that wonderful midrange tonality. Listening to Chris Botti’s trumpet on Impressions, “Prelude No. 20 in C minor” has that rare sense of “you are there” feeling. The trumpet was dead center and slightly up front with air around the instrument, which made it stand out in the performance.
Closing my eyes, the performers around Botti were defined and focused in their own space with excellent separation. The delicate lyrical tonality of his trumpet was all there. The instrument sounded live and realistic. There were no artificial or electronic glare or glaze. The music was so delicate and inviting and the Dragon brought out the best in Botti’s performance.
On the second track “Per Te”, with Andrea Bocelli, I became focused on the trumpet in the opening of the track because it was so delicate. The tonality was beautiful and absent were any hard or harsh sounds coming from the trumpet. The trumpet started to fade and Bocelli’s vocal started coming in and was inspiring. The beauty of the lyrics, although sung in Italian, felt universal as the Dragon disappeared into the music. All that was left was the beauty of Bocelli’s vocal and exquisite musical tonality. Never did I feel there was anything missing, the midrange was special and the treble was also musical. The magic that tube amplifiers provide with tonality usually is only heard in live performances. And the Dragon had that magic.

Bass with the Dragon is excellent. The use of the stock rectifiers brought out a well-defined and tight bass. Much more than the Sophia 274B rectifier, which I found, was a little light in bass delivery. Kenny Barron’s, The Art of Conversation, has Dave Holland playing acoustic bass. On the opening track, “Oracle”, I could hear the texture of the bass notes with excellent extension and definition. The instrument was focused and spooky in realism while rendering its own space within the soundstage. There was separation and space between Holland bass and Barron’s piano. Kenny was to the left and you could hear and feel his involvement with the instrument as his hand was moving across the keys and Holland’s bass was in its owns space and had excellent extension.
Pat Methney’s masterful work with Charlie Haden on Beyond the Missouri Sky – an album filled with terrific melody and tonality – is exceptional. Pat acoustic guitar is beautifully placed in the forefront and his delicate playing on “Waltz for Ruth” is something special. Haden’s bass is almost behind Methaney and on some lesser equipment it is hard to notice the separation of the two performers.
The Dragon did not disappoint in being able to distinguish the separation and I was able to visualize some distance between the performers in the soundstage. Haden’s playing is exceptional and the Dragon was letting it all come through in a defined space within the soundstage.
Listening to large-scale recordings like Copland’s majestic Fanfare for the Common Man, the Dragon was able to deliver a terrific performance. It had sufficient speed and dynamics to make this track come to life. The performance was all there and the soundstage was layered and I could hear every section of the orchestra. The Inspire Dragon was able to make it a believable performance. The Dragon never clipped while playing this wide dynamic recording. Many amplifiers I have used have struggled in reproducing this track.
The Hugo volume control was being used with the Inspire dragon. I noticed I was getting more volume at higher levels with difficult to drive headphones. The Hugo added more gain and could drive the little Dragon to concert hall sound levels.
The amplifier performed well with any headphone. Whether I was using the Alpha Dog or the HD 800, the Dragon did not have difficulty in driving either headphone. The Alpha Dog can be difficult with some amplifiers because it is not as efficient as some other planar designs and loves power. The Dragon easily drove the Alpha Dog and is a synergistic and good match.


The time I had spent in 1997 up in Rochester audio boutiques had opened my eyes and ears to tube amplification. Dennis Had’s baby Cary amps forever changed my life with how I would listen to audio components. The sound was more musical than any solid-state amplifier I had heard in audio at the time. The sound was magical and for me made me want to explore and eventually purchase tube amplification.
My lifelong love affair with tube amplifiers is still as strong today as it was back then. The Dragon delivers clean sound with nothing getting in the way of the performance. The musicality and tonality of the amplifier is there with nothing left out. The design is simple with no parts in the signal path and nothing in the way of musical delivery. Headphone enthusiasts can utilize just about any efficient headphone with either a XLR-4 or singled ended cable. The Dragon delivers for me everything I look for in a good tube design; it always had me involved and never left me wanting for anything during my listening sessions.
The Return of the Legend was well worth the wait as Dennis Had has brought an affordable music lover’s product to the marketplace. So if you want to see what the fuss is all about with the Dennis Had design, call Drew Baird over at Moon Audio to arrange an audition. The Dragon is the triumphant return of a masterful artisan designer and is highly recommended for any music enthusiast. It’s a well-designed product that offers both performance and excellent value and an easy recommendation.
- See more at:


Headphoneus Supremus
Pros: Sound Quality
Cons: ?

I’ve had my Dragon Inspire IHA-1 now for a sufficient time period to post my thoughts. I will use a subjective 5 point scoring system.
Power Conditioning:  Blue Circle Audio FX2 XOe and Blue Circle Audio PLC Thingee FX2
Power Cables: Sablon Audio Gran Corona
Audio Chain: MacBook Pro running Audirvana Plus > TotalDac D1 usb cable/filter > iFi iUSB > Light Harmonic 10G split usb cable > Berkeley Audio Alpha usb/spdif converter > Siltech HF9 aes/ebu > Bel Canto DAC 2.5 > Siltech 220i interconnect > Jeff Rowland Capri preamp > Siltech 220i interconnect > Dragon Inspire IHA-1 > T1’s/TH900/3000ANV
Build Quality:  4.5 out of 5
The IHA-1 is a relatively heavy (for the size of the chassis) unit and appears robust.  Everything is tight, knobs have no loose play, the unit sits flat on a flat surface, no issues whatsoever. 
The paint job is terrific and you need to see it in person to really appreciate it.
The tube sockets and headphone inputs are very solid and I believe they will last a very long time and continuous tube rolling and plugging and unplugging of headphones should not be a problem.
When using my TH900's or my 3000ANV's and there is no music playing, I can hear a barely audible faint hum in the right channel.  It disappears when music is playing.  It does not bother me, but I wanted to mention it.  With my T1’s, I can’t hear the hum at all.  Out of curiosity (not concern) I corresponded with Dennis Had and Moon Audio about this and it is not a defect.  It is a counterpart to the design of the amp and the sonic goals for this amp.
Aesthetics:  4.0 out of 5. 
The faceplate of the IHA-1 has a bit of “old school” “no nonsense” look to it.  I like it, but think it could be improved a bit with perhaps a different faceplate.  The terrific paint job makes up for the rather utilitarian looking faceplate.  I do like the overall size of the chassis.  Let me state again- the paint job is outstanding!
Sound Quality:  5 out of 5.  I'd like to give it a 6 

I don’t believe one can review the IHA-1 without mentioning the tubes being used.  The IHA-1 is very transparent and if your headphones are of sufficient quality, you will very easily be able to tell differences when rolling in different tubes.  After a bit of experimentation, I settled on a NOS Brimar U52 for the rectifier tube and NOS Sylvania 6BX7’s, which provide a bit less power than 6SN7’s, but I find them to be the most enjoyable (I understand the 6BX7’s are Dennis Had’s favorites, and I can see why).  If you need more power, you can swap in different tubes.
If I had to summarize the sound of the IHA-1 in one word it would be “magical”.  I don’t mean to sound like a new age hippie (because I’m not), but this amp transports me to another planet.  On the planet are two things- me and the music, and after a while, it is just the music.  Everything around me… all the possible distractions melt away from my consciousness.   My tendency to analyze the sound tends to drift away as well.  I get swept up in the emotion of the listening experience.
Breaking the sound down into separate aspects, I would say the IHA-1 earns a solid 5 in every single sonic aspect I can think of, except for the bass, which I would give a very good 4 or 4.5, which is down to tube designs vs. solid state designs and not a design issue with the IHA-1.  I would personally take the IHA-1 over any solid state amp without hesitation.
Forcing myself to analyze the sound, I would describe it as very holographic.  The sound is exceptionally three-dimensional, round, full, highly detailed, airy and slightly warm.  And by “warm” don’t take that to mean “rolled off”.  It is not rolled off at all- it seems quite extended.  Treble and midrange are spectacular.  Bass is very nice as well.   Bass is perhaps not as hard hitting as a top level solid state amp, but still quite good.  For context, I listen to EDM more than any other music genre and the IHA-1 is able to keep up in the bass department.
The IHA-1 also excels at timbre, fullness of tone, dynamics and soundstaging.  With the right recordings, the ability of the IHA-1 to recreate the recording venue is breathtaking. I can’t point to any weakness or sonic shortcoming.   It just sounds “right”.
I really don’t know what more I can say.  Dennis Had is a genius.
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Jeff Y
Jeff Y
You did forget to mention something... it's "only" $1599!
Great review but have you tried this amp out with any iems?
(also is that Lufthansa for your avatar-thingy?)
Your experience re sound quality mirrors my own. I have settled on the EML 274b mesh as opposed to the U52. I primarily listen to Audeze LCD3fs and have no hum with the 6bx7s.  I changed my knobs for machined aluminum, large diameter replacements.  I think it helps make it look a little less retro. The one thing I do not want to change is the sound. Amazing.
@Jeff Y: Yes, Lufthansa :) Unfortunately, I don't own any IEM's so I am not able to provide any comments with that combo.
@Bellasperson: Cool idea on the knobs.  Do you have any pics that you can post?  I am curious to see how it looks with the aluminum knobs.


100+ Head-Fier
Pros: holographic sound, fantastic microdynamics, solid build, limited production/hand-built, legendary audio designer, perfect ergonomics
Cons: price, visual aesthetic is "love it or leave it," not the best pairing for ultra-sensitive (noise) or ultra-demanding (power) cans
You may not have heard of Dennis had, but you've likely heard of his products.  Dennis Had and his wife Donna founded Cary Audio Design in 1989, but the story I've been able to piece together (go Google a bit, I'll wait) is also rich and fascinating. As he mentions in his eBay listings, he built his first single-ended 6V6G amplifier for a 7th grade science fair and has been hooked ever since.
Had left Cary a few years ago, but he continues to design and hand build single-ended tube audio components as a hobby. His "retirement hobby" is our gain. Had releases a handful of his designs on eBay semi-regularly (I've seen quoted a figure of 1-2 per week but have seen far less than that recently), usually consisting of amplifiers (stereo and mono pairs), integrated amplifiers, and headphone amplifiers. True to his original beliefs, they are all single-ended designs focusing on simplicity and the listening experience.
Had's affection for single-ended designs are well-explained in a 1995 Stereophile interview:
More than anything, the virtue of single-ended is the simplicity, and that the signal is handled in as linear a fashion as possible. In a push-pull amplifier you split the signal into two halves and then recombine those halves at the amplifier output. I felt that the power amplifier should just replicate what the CD player or turntable is outputting and maintain the integrity of the waveform. Single-ended makes the most common sense from an engineering standpoint and also has the least number of parts in the signal path. You're not taking the signal and dividing it up.

The Dragon IHA-1 is a custom version of the Inspire IHA-1 offered irregularly on eBay. It is distributed exclusively through Moon Audio and as I understand it was inspired by Drew's introducing Dennis to some Audeze headphones. There's a quick video with Baird and Had about the amp if you want to learn more at Moon Audio's site.
The Dragon Version has some changes versus the model that most commonly appears on eBay. I'm not aware of the internal changes if there are any (and I don't have the heart to crack mine open), but externally some differences are readily apparent. First, the front plate is black and the paint job is a copper-red metallic finish that would feel at home on a vintage American muscle car (versus walnut veneer on white). Second, the LED is blue instead of read. Third, the output jacks are upgraded, with professional locking 1/4" and 4-pin XLR connections (this is a single-ended design, but the 4-pin jack takes its connections from the output taps of the output transformers; my listening has been exclusively via the 4-pin jack). These take the place of a pair of 1/4" inputs and are mounted to the chassis rather than through the faceplate. Fourth, the potentiometer has been replaced with a dual DACT stepped attenuator.
On the back of the unit there are two pairs of RCA inputs, a fuse holder, and an IEC inlet. The amplifier comes with a standard power cable.
The design leverages dual triode 6SN7 tubes in class A single-ended mode with zero feedback. Had recommends the (lower gain) 6BX7 but any 6SN7/SBL7 should work (e.g. the RCA 5692). The tube rectifier is 5Y3/5U4/274B types as well as 5AR4, though Had recommends against indirect heating in this application.
The design is direct-coupled and output is via custom air-gap output transformers. It produces just over a watt into 32 ohms and a bit under a watt near 600 ohms. That should make it powerful enough to drive most loads.
Make no mistake, this is a low-production bespoke product: The fit, finish and polish are good but this unit will not win any design awards. The front panel is connected to the chassis with some sort of adhesive and bits of hair and fuzz around it remind you of that fact under any close scrutiny.  The output transformer sheet metal bends aren't particularly uniform and the labels on top of the transformers are crooked. The RCA inputs in the back aren't labeled 1 or 2 (they do have channel indicator rings, however), though it's easy to figure out which is which. There are at least four different styles of type on the front face and they look like they were placed without any real thought to design and layout. The amplifier's packaging is "toss it in a box wrapped in 100 feet of bubble wrap. The entire bottom of the amplifier is covered in Dennis's scrawl, except for the part obscured by the rubber foot (no joke). I happen to thing it's a nice touch on a very personal product, but others may not. The blue LED looks sort of like an awkward afterthought; I'm pretty sure I prefer the red of the stock unit. Those looking for the attention to detail and incredible fabrication of e.g. a Woo or HeadAmp will sneer in disgust. It's not that the Dragon IHA-1 is outright ugly, but it looks a lot better in the dark.
The tube sockets are solidly anchored; I have no concerns when changing valves. For that matter, everything about the amplifier is solid. The transformers aren't going anywhere, the RCA jacks are firmly installed, and there's no play, wiggle, or shake in the amp. Despite the entire previous paragraph, everything mechanical and functional about this amplifier is clearly sorted and well thought-out. Had may not be a champion of the visual aesthetic, but his design shows mastery of the physical and functional. The input selector switch has a firm and positive throw. It's never going to be triggered by accident and it's obvious when a change has been made. It's intuitive that going left is the left input and going right is the right input, and that mute is in the middle; operation of the amp in pure darkness reminds the listener that this amp's ergonomics were designed for somebody using it ... not somebody looking at it. The attenuator knob has perfect knob feel and was left pleasantly small. For me this is important; I find large knobs to have enough size and mass that positive identification of detents becomes difficult as attenuators age. The rectangular shape of the knob makes it easy to identify and turn with a couple of fingers in the dark.
I'm not a huge fan of locking connectors for headphones. They feel great, but they increase the risk of destroying a cable, headphones, or the amp itself if I do something clumsy (I regret this happens more often than I'd like).
The form factor itself is deceptively small; it's about 2/3 of the depth and width of a typical (~17") stereo component. This isn't that weird since there are a lot of goofy sizes in head-fi. The unit has tall feet and can take up a lot of vertical space when coupled with a large rectifier. The layout is rather compact with the three tubes, capacitor, and three transformers all packed together in pretty close quarters. The three transformers provide a substantial amount of mass, but I would not call the unit heavy as much as solid.
Operation is easy: Plug in the tubes, flip the on switch, wait a few seconds, roll the input selector, and listen to some tunes. At least, I think that's how it works as there aren't any instructions included. I can imagine Had saying "why would you need any instructions? I made this thing as simple as possible, you can't mis-use it!" Or, maybe not, but that's what I'd like to imagine.
Included by default are a Sovtek 5Y3GT rectifier tube and a pair of EH 6SN7s. In that trim, the amp runs $1599. The upgrade tubes optioned are NOS Sylvania 6BX7 output tubes ($100) and a Sophia 274B ($160) rectifier.
For those new to tubes, the output tubes don't look like much when they're running; in some cases (like the Zalytron 5692) the getter in fact completely hides any sort of illumination. They can run hot, however, with surface temperatures around 250 degrees. There's no tube cage on this thing, so be careful. The rectifiers range from mildly interesting-looking to downright gorgeous under operation; the giant Sophia tube is more in the gorgeous direction, with its bright direct heaters and stamped "mesh" plates. It's nowhere near as warm on the surface and could probably be handled during normal operation if somebody was particularly weird.
With both of my signal paths, I find I'm using the volume knob roughly from 9 to 3 with the majority pretty close to noon. I feel like there's an appropriate level of gain gradation in this range and don't feel the amp suffers from the stepped attenuator plague of wanting a setting in-between a particular set of detents. Where in other amps with stepped attenuators I often have problems finding the goldilocks level, this has not been a limitation in use with the HD800/LCD-3F.
This brings us to the only thing that should really matter for those considering the purchase of this amplifier: How does it sound? Well, that's a good question! I'll offer my initial impressions, but will caution that these are at best preliminary: I reserve the right to update this as I have more time with the amp, roll more tubes, and rotate more headphones through it. 
I've spent about 20% of my time listening to the amp with Sennheiser HD800s and the remainder with Audeze LCD-3Fs. Both cans were wired with Moon Audio Silver Dragon cables and terminated with 4-pin Neutrik connectors. I did not (and indeed may never) try the 1/4" output yet. I like both, but I love the Audeze cans on this amp especially; the pairing is special.
Before I continue, one final disclaimer: My desktop headamp listening experience is most extensive on the HeadAmp GS-X (mk II modules), Woo WA7/WA7tp, and the Oppo HA-1. When I used blanket generalizations like "compared to other amplifiers" I'm referring more to this canon than the entire universe of headamps. 
It's for me somewhat difficult to describe how this amp sounds; the easiest way I can really describe it is that it's a very good lens through which one can listen to music through a certain set of tubes. If the tubes sound a certain way, the amp sounds a certain way. In rolling several different valves I never latched onto a sound signature of the amplifier itself. I don't mean to be evasive about this, but I remain struck by a notion that this amp is all about getting out of the way and letting the tubes do their thing -- good or bad. 
So, the problem then is I have a hard time latching on to the common refrain about such a design that the amp sounds warm. With certain tubes it sounds a little warm, I guess, but I don't think warmth is an intrinsic property of this amp. Instead I would describe the sound signature of the amp and tube configuration having more the characteristic of "not dark" than "warm." The presentation strikes me as having a neutral mid-range, with austere bass and neutral to just shy of neutral treble.  While the bass does not have incredible slam and impact, the precision of the attack and release more than make up for it: There is plenty of low-range extension and it doesn't leave me thirsty. The low-end signature of the amp reminds me of that of the HD800s; the pair combined amplifies the effect. Whether or not I'd call it "accurate" bass I think the word that comes to mind most is "realistic."
I rolled with a few rectifiers and half a dozen output tubes, but fell into immediate love with the pairing of a Sophia Princess 274B (from Moon) and a pair of CBS-Hytron 5692s (from Upscale Audio) and haven't changed since. I wanted to love the Sophia 6SN7s just because they looked amazing next to the 274B, but it just wasn't meant to be. Stop looking when you find the one you love, or something like that? So, all of the feedback about the amplifier in this review comes from the Sophia/Zalytron pairing unless otherwise noted.
Soundstage remains a nebulous concept for me with headamps: I wouldn't describe the presentation as particularly broad or narrow versus other amplifiers. Positional clarity or lack thereof similarly is not particularly unique or distinctive. The word that does come to mind is that the audio presentation is "holographic." It's not that the performers are suddenly in front of me on a stage and I can tell you how far away they are and how far they sit apart; those are the terms and sensations I still reserve for loudspeaker systems. Instead, the sound itself is incredibly three-dimensional and provides a great deal of texture and depth. I'll use the holographic term as somewhat of an analogy: A lot of paintings have a great deal of depth and texture and intrigue, but they look the same no matter how the light strikes them or how they're tilted. The hologram has more to it than that; one finds different things depending on what they're paying attention to and it can be somewhat overwhelming to try to take it all in at once. Good music is confusing and overwhelming and rewards careful as well as casual listening. This amplifier is not a scalpel for surgical analysis of music. It seems to be more designed to step back and say "look, there's all this crazy stuff going on that you never realized before!" Wow. Give me a few minutes...
... dear reader, I got lost listening to the amp for a few more hours, but I'm back again. Sorry about that.
The holographic sound is what grabbed my attention with this amp, but I want to talk a little bit more about what retains it: More than anything, the microdynamic capability of this amplifier is astounding. I have not been exposed to an amplifier that delivers better microdynamics.  To all of those folks ready with the pitch forks, there are plenty of amps I haven't heard yet, especially in the high-end valve realm. The texture and detail capability is impressive. It doesn't matter if I'm getting slammed with loud beats, a pin drop is still distinct. The speed and precision of the amp is incredible. I listened to songs I've probably heard at least a thousand times, and with each one I was discovering new depth and richness of sound that I never experienced in the past. This didn't just happen when I was listening for it; the amp has a way of grabbing your attention and saying "listen to this, just get lost in this passage, you've never heard it like this before..."
... sorry, got distracted again. I'd say I lost a few hours of my life, but it was definitely a gain.
If folks are interested I can try to comment on other aspects of the sound quality, but for me this part is the kicker: The amp is incredibly euphonic for me for the reasons listed above (holographic sound and microdynamics). It makes me want to listen to the music and it makes it incredibly hard to listen to the equipment. If there's a dragon to chase in head-fi, that's mine. I hate listening to equipment. Listening sessions that end with "I wish this X had more Y" just fill me with disgust. I'd rather end up with "okay, just one more track..."
It could be said that everything I'm hearing is just second harmonic distortion and I'm in love with distortion and not signal. To that I say "that's entirely possible!" But, I enjoy it just the same. There's plain and there's French Vanilla, and I'm enjoying the French Vanilla with this amplifier. There is probably something intelligent that could be said about how the amplifier lacks clinical accuracy and 100% authentic reproduction, but I'm not the guy to say it. Count me as a believer in whatever it is this thing is doing to the music. 
The capabilities and pleasure of the amplifier have continued as I've expanded beyond the HD800 and LCD-3F. 
First up, the Oppo PM-1 puts on a good showing. These headphones are surprisingly sensitive, so the full range of the attenuator knob is not necessary. Volume levels quickly get into uncomfortable territory around noon or so. Still, I have not had any difficult finding the "right" volume level in the gradations available to me before 1 or so. I like the LCD-3F with this amp more because I like the LCD-3F more, but I think the PM-1 shows very well here. Due to their high sensitivity, Oppo's headphones make the low-level hum in the right channel more obvious.
Given how the LCD-3F sings with this amp, it should not be much of a surprise that the LCD-XC also pairs rather well. I don't have too much to add beyond that they sound a bit more closed than the 3F. Go figure, right? Since they are closed, they also make the low-level right-channel hum ever so slightly more obvious when there is no signal present.  
Happy with how the HD800 sounds and very happy with how the LCD-3F sounds, I wanted to explore the amp with some of the more extreme cases I had in my inventory. In the grand tradition of "Will it blend?" and "but does it play Crysis?" we must also confront whether or not the amplifier can drive the HE-6. With the 6BX7 I have to max the gain to get to a "normal" listening level. The 6SN7 pulls things up just enough to have a couple of detents to play with, but I would have a hard time recommending this as being the go-to amplifier for the HE-6; it's just not going to get loud enough for many with that particular set of headphones. With that said, for the volume levels the amp is capable of, the headphones do sound great. So, more sensitive Hifiman models (I have no personal experience) may work better, or this could still be a great pairing for those that don't listen too loud.
At the other end of the spectrum, I plugged my 4-pin-terminated JH13Pros into the amp. I would not recommend this particular pairing; the general noise levels are too high for my taste with this particular in-ear monitor.
Back in a very different direction of hard to drive, I plugged the AKG K701s into the 1/4" jack (good news, I can now confirm it works too). The amp is able to drive these cans and there's still a little room to play in the high end of the gain (more so than the HE-6). With that said, the sound lacks a bit of control compared to e.g. the GS-X in some quick comparisons. The pair sounds decent, but a little thin for my tastes.
Let's talk about the downsides. Optioned out with some tubes for rolling, this amp is bumping up against two thousand dollars in the US.  That's endgame or well beyond endgame pricing for a headamp. It might be somewhat difficult to call anything in that league "a value." I would not say the amp is embarrassed by gear at a similar price point. To sum up, on value my feeling is that the amp punches within its weight class and I'm rather taken with it. For those interested in getting more bang for the buck, the eBay IHA-1 lacks the upgrades mentioned above, but it also comes in a bit cheaper at $1200. At the end of the day, this is an extremely low-production hand-built product and one is getting both the benefits and detriments of that.
I think I've already beaten the amp up a bit in terms of looks and fit/finish so I won't go into that point further.
It comes with zero functionality beyond being a two-source unbalanced headamp. There's no line out, pre out, or speaker out. There's no balanced inputs. There's no gain switch (the only real option to adjust there is in tube choice; the 6BX7 provides less gain than the 6SN7 types). About the only display or indication is the blue LED. I tend to prefer this sort of simplicity of focus and purpose, but it's important to keep in mind this terminates a signal path in one's system and nothing more.
Finally, there is a very mild hum in the right channel; it starts when the amp is turned on and rapidly attenuates after the first few seconds of amplifier operation. After 15-30 seconds it's virtually inaudible and incredibly difficult to hear even with quiet passages in the music. Had responded to another member explaining this in detail in this post. I'd recommend reading that for any concerns on this point. I think this would only bother or impact people with extremely sensitive headphones/in-ear monitors, and it's really only noticeable when there's no signal present otherwise. I don't tend to listen to headphones without a signal present, so this has not been a problem for me! Had clarified in e-mail that it's down about 78dB from the music signal, so when I say mild, I mean mild. I was not clear on whether it's because of the circuit design or the physical layout; I attempted to get clarification on this point but did not hear back from Had. In my experimentation, this is less noticeable when using 6BX7 tubes than 6SN7; several other head-fi folks only notice it with the 6SN7. I did experiment with different power cords, isolation transformers, power regenerators, and other voodoo devices. None had any particular impact on this hum.
Power Cables: Pangea AC14SE
USB Cables (don't make a difference, but they look pretty): Wireworld Ultraviolet
Line-Level Cables: Kimber Kable Timbre (digital: Ultraplate, analog: WBT)
Phono Cables: Kimber Kable TAK-Cu
Power Conditioner: Furman P-8 Pro Series II, Torus Power RM15Plus
Digital Chain: Macbook Pro, Audiophileo1/PurePower, NAD M51
Analog Chain: Sumiko Blackbird, Pro-Ject RM-10.1, Simaudio Moon 320S/310LP
Headphones: Sennheiser HD800, Audeze LCD-3F, Hifiman HE-6, AKG K701, JHAudio JH13Pro
The following are the recordings I focused on when listening critically; have put a lot of additional software through the amp when I was just listening to the music. Except where noted, I auditioned each in both vinyl and red book from my own CD rips.
Opeth - Pale Communion, Ghost Reveries                           
Porcupine Tree - Lightbulb Sun
Steven Wilson - The Raven That Refused To Sing
Nine Inch Nails - Hesitation Marks (Digital copy is direct FLAC)
Aphex Twin - Syro
Stravinsky - The Firebird Suite (Reference Recordings, analog only)
Miles Davis - Sketches of Spain
I am a Moon Audio Ambassador, but that role has nothing to do with the purchase or evaluation of this amplifier. I purchased it with my own funds and reviewed it independently.
20141115 - a few clarifications, fixed a few typographical goofs.
20141117 - added a few more headphones, clarified current state of noise understanding
20141117 - further clarified hum concern, linked to BlakeT's information on this (thanks!)
20141118 - added a brief section about the PM-1, LCD-XC
20141130 - minor wording tweaks
20141207 - minor wording tweaks, type-o squashing, admitting I might just like second harmonic distortion
These are things I'm still intending to explore, and may provide updates in these areas over time:
  1. Tube rolling!
Worth reiterating @BlakeT on this, I agree 100% with "To be very, very clear, this hum is really subtle and I can only hear it when music is not playing.  It does not bother me at all.  I love this amp and could not be happier with my purchase."
Audeze LCD3F, 6BX7, EML mesh 274b, 4 pin or single end, no hum
Audeze LCD3F, HD800 S, ABYSS PHI 1266, Sophia 6SN7 and Philips 5R4GYS. Hum only apparent with IEMs like UE 18 Pro. I do wish for more gain with the HD800 and Abyss however.