Finally finished my review:
In the last year, I changed my approach to headphone setups. At one point I had a desktop setup for the HD650 (Bitfrost + Lyr), a mobile amp with various portable cans I've owned (various FiiO products), and a small, work setup (Modi+Magni stack) for my Shure SRH840. What I realized is that a large portion of the time I was not using any of that stuff and i was often simply using my Grados or KSC75s through my iPhone because it's convenient and I could do chores around the house or walk the dog. I was spending a majority of my time with my least expensive setups.
So I decided to simplify based on a few rules:
1) Any headphones had to be drivable by an iPhone and sound very good straight out.
2) All gear had to be all-arounders, in that it sounded good with any gear I own, and all amps work well with all headphones. No more of this "this amp is for this headphone" stuff.
3) No more big desktop stacks.
But I also didn't want to compromise on audio quality either. I was unsure if this was possible, but I wanted to see how close I could get. So, I first sold off all the gear that didn't fit that program. HD650, all my Schiit gear, gone.
Headphones were the next big decision. First move was the Shure SRH840. To me, that's the best closed headphone in the $200 range (yeah, better than the M50X). Grado SR225e came next as my fun, open can. Then I demo'd the HiFiMan HE400i and knew that would be the cornerstone primary headphone.
The next challenge became the DAC/Amp. While everything had to be drivable by the iPhone, I did want something that I could use to take them to the next level. And that was surprisingly challenging.
People on here often talk about "scaling well" and primarily what they mean is that the headphones are hard to drive, and thus require an expensive powerful amp to properly power. In my experience, easy to drive headphones can actually be more challenging to properly power. Lower impedance easy to drive headphones require a lot of current, rather than a lot of pure power. You also need a low output impedance for dampening. The 02 was one of the first amps to really "get" this. But it was shrill to my ears with a lot of headphones. The Schiit Magni also offered this, but again, I didn't want a stack.
I had always been drawn to Grace units, but A) they were the size of a rack unit and B) they were $1500-$2000, which was more than I wanted to spend.
Things started to come together when I saw the announcement for the m9XX.
The m9XX on paper looked about perfect.
The ultra-low impedance meant that it would drive a lot of current (ohms law states that as the output impedance goes toward 0, current goes towards infinity), especially since it could deliver 1000mW at 32 ohms. With an output impedance of 0.08, this meant that the current it sent to headphones was literally near infinite.
The design was spot on: simple, ergonomically appealing, attractive. It had several features I found very appealing as well:
1) Crossfeed. To me crossfeed is nearly required for long listening sessions to avoid fatigue. Without it, it's like my brain gets tired trying to reconcile hearing sounds consistently only out of one ear (this almost never happens in real life, so it confuses your brain).
2) linear decibel stepped volume control. Most amps have a volume control where power levels are just some arbitrary points. often times halfway through the dial isn't half power, or half volume or anything in particular. On the Grace m9XX, each spot represents an actual half decibel. This makes it possible to fine tune adjust the volume on an IEM and a planar magnetic headphone without using a gain switch (and thus changing the output impedance as well). It also makes it very easy to understand volume differences, since the display numbers are actual decibels.
3) one output line that allows the RCA outs to still work, and one that mutes the RCA outputs. This allows a number of things: you can play two headphones at the same time, for quick critical comparisons (or listening with a friend), using a sub with your headphone (try it, it's an interesting experience) and auto-muting speakers you may have been feeding from the DAC.
4) ability to be both USB powered, but also have a high power mode that doesn't change the gain (and thus maintains the low output impedance) but adds more headroom. For many headphones USB bus power is all you need, but it's nice to have that little extra power you can send if needed, and unlike gain switches, it doesn't make things more noisy, or add impedance.
5) The DAC chip was the same as the DAC chip in my bitfrost, which even though I wanted to slim down the form factor, I loved the sound of the bitfrost.
That all looked great on paper, and combined with Grace's reputation, I decided to jump in. Even if the amp was merely decent, $499 was a reasonable price for the DAC, given the components and features.
So, I got it; did it live up to my hopes/expectations? (well, spoiler alert if you noticed the rating I gave, you know the answer to this)
Yes, absolutely it fulfilled my expectations, 100% and then some.
First, the build quality, fit, finish and feel exceeded my high expectations. Supposedly the engineers at BMW exhaustively test each car, so that the sound and feel of the door closing is just right. That's how the volume control feels when you turn it or push it down (push to mute or hold to access the settings menu). The front, back and top plate is one piece of high quality aluminum. It feels solid without being heavy. It manages to seem both robust yet elegant.
It's the apple macbook pro or BMW 5 series of audio equipment. Fit, finish, feel and performance all coming together perfectly.
Now, on to the sound part:
It manages to be incredibly transparent, spacious, with great treble and bass extension, without sounding dry and brittle. It's extremely transparent, yet musical. Nothing about it sounds unnatural. It just gets out of the way, and takes on the character of the headphones and music instead of imparting its own footprint. This isn't what you want, if you want to hear your DAC/amp in your chain. You don't hear the m9XX, you hear *through* the m9XX. You'll instead hear your music and headphones. To me, that's the ultimate compliment for a DAC/amp, that it simply gets out of the way and lets everything else do its part.
Now, coming back to what I said at the beginning, where this amp really shines is on lower impedance headphones. It can drive an HD650 very well, but to me, in some ways, driving low impedance headphones has its own challenge. Most of the headphones I own are very current hungry, that is, instead of needing a lot of absolute power, they need a lot of current to tighten up and define the bass, and refine the treble and midrange, and give shape and definition to the soundstage and accuracy to the imaging. This is the real key to the m9XX, that it can make your low impedance headphones sound like you've never heard them before. And it can drive IEMs well. And it can even sound really good on a freaking HD800. 0.08 output resistance with 1mW of power makes this ultra versatile.
High Power Mode is vastly superior to most amps High Gain Mode: more current, less noise, no increase in output impedance
Talking a bit more about how high power mode works, and why it's substantially superior to the "high gain" mode of most headphones: In high power mode, instead of increasing the gain, Grace simply adds more headroom. You'll notice that 70 on low and high gain are the same loudness. You don't get an increase in noise at all, like you do with most DACs high gain mode, you don't get an increase in output impedance. You do get more current, which most amps high gain mode don't actually send more current, they just increase output impedance. Basically High Power Mode adds headroom and the ability to use settings over 90 without running out of current on tap and getting a "OC" (Over Current) error and the consequent muting.
Now on to how it sounds with various headphone pairings I tried it with.
With the HiFiMan HE400i, the pair is just effortlessly balanced and precise.
I think the HE400i paired with the Grace m9XX could be my endgame setup. As they've both rolled past 150 hours, with 80 hours of "on head" time, this is just such an incredible pairing.
Ihis is the *perfect* pairing for long sessions. Enabling crossfeed on the Grace, and this is the least fatiguing headphone I've ever heard. The resolution and transparency means that I never have to strain to hear anything. The tonal balance, flat bass and (to me) neutrality means no frequency ever wears you out. The crossfeed makes for a less fatiguing listen as well. While the soundstage isn't vast on the HE400i, it's so coherent and imaging is so precise, that it's an effortless listen. It's present without being sibilant. The bass is full and extends, without booming (which can get fatiguing after a while to me).
The signature, right away, can almost seem boring. But it's just so resolving, transparent and fast, while being smooth and musical, that those qualities become fun in their own right. I realize instead of being like "wow, oh my god the bass" like I am with some equipment, more often I think "wow, this song is incredible." WIth this pairing it just becomes so squarely about the music as opposed to noticing things about the headphone, amp and DAC.
The word that keeps coming to mind with this pair is simply "effortless" They just effortlessly bring me my music. They get out of the way.
Finally this pairing has by far the most listenable range of volume I've ever heard. On the Grace, I find the HE400i listenable from 59 to 79. That's 20 dB of difference that I find them perfectly listenable.
With the Fostex THX00, the pair is rich, smooth, detailed and powerful
The THX00, like the other TH series cans, and the old Denon DX000 predecessors are tricky to amp, despite not needing much in the way of absolute power. They're very easy to drive, but if they don't get a lot of current, the bass can be quite uncontrolled, especially on hard fast bass transients. The Grace comes in and cleans this all up with aplomb. A can that out of other amps can sound average in terms of detail and imaging becomes quite good in those areas. To my ears the Grace gives these cans exactly what they need, a very resolving and spacious DAC and tons of current because of the Grace's ultra low output impedance in the amp section. it's been said by more than a few that it almost sounds like the THX00 was tuned for the m9XX, and it's hard to disagree. But I also think that almost any low impedance cans with powerful magnets in the drivers (the THX00 is over 1 Tesla) benefit from the current the m9XX pushes. The m9XX doesn't change the THX00's signature, it just tightens everything, smooths some of the rough edges out and adds a level of detail and transparency. Essentially it enhances the THX00's strengths (bass power, fun factor) while polishing its perceived weaknesses (detail, bass texture, imaging). What you're left with is a heck of a fun, yet technically proficient pairing.
I also spent about an hour with the TH900 with this pair and the bass on the TH900 with the m9XX was legendary: controlled, powerful, deep, no bleed over. Everything I said about the THX00 applies here, except with the TH900's even more powerful bass. If you don't like the TH900's hard V signature, this won't "mellow" it out all. Again, what the Grace does is get out of the way and lets the headphone do its thing. If you're a fan of the TH900, you'll love this pairing. If you aren't a fan of the TH900 sound, you're still going to dislike it.
With the Sennheiser HD650 the pairing is incredibly smooth, detailed and refined with gorgeously textured bass and smooth, if a bit veiled, treble
There are two approaches to properly amping the HD650: 1) something that shows the headphone's inherent character or 2) something that provides a little more treble energy to shake off the "sennheiser veil." If you want the latter, this isn't the pairing for you, because as previously stated what the Grace does more than anything is get out of the way and lets the headphone do its thing. That means this pairing does much more of the former, you hear how the HD650 really sounds. It's incredibly detailed, the bass has a sort of refined grace, the treble has a relaxed smoothness that's simultaneously detailed. To some this sounds veiled and boring, to others it's the pinnacle of engaging treble and a deep soundstage that sounds like you're watching a concert from about the level of the soundboard, as opposed to the front row. If you want to "shake off the veil" I'd go with something a bit more energetic, like maybe a Lyr (with either solid state or more energetic tubes).
This pairing really shows what the DAC section is all about though, as the microdetail somehow manages to be both precise and crisp yet musical and relaxed. It's a sort of elegant beauty that sounds really classy. It's probably not the amp I'd use if I was building an HD650 system from scratch, but I've come to realize that has more to do with some dissatisfaction I personally have with the HD650's relaxed signature. I wanted an amp that would "fix" it, and as I've already stated, the m9XX isn't going to fix any issues you have with a headphone's signature, it's simply going to reflect the base signature, and refine the more technical aspects. I think of it like a photographer making a model look as beautiful as possible with skill in photography, without using photoshop to "fix" things. It brings out the best of what is available.
Grados are frighteningly fast and energetic, gain a bit tighter punch in the midbass, and become an even more fun, if still a strictly technically flawed listen
I think there tend to normally be two camps with regards to the Grado sound: those that think it's complete trash that hipsters love and those that can't accept that there might be ANY flaws whatsoever. I tend to fall into a middle ground. The SR60e is one of the first three headphones I bought when I got into headphone audio (the Denon D1001 and Audio Technica AD700 being the others) and I'll always be fond of the sound. They can bring a lot of energy, especially to older classic rock recordings. They provide a lot of speed on the cheap. But I also realize that they're honestly technically deficient if the goal is to reproduce what is in a recording. Again, the Grace won't give them some semblance of sub bass, it's still as rolled off as ever. The Grace will, however, "perk up" the Grado upper midbass hump, providing classic rock kick drums a bit more thump, thus somewhat equalizing the perception of the signature, without changing the Grado house sound. Grados are notoriously current hungry, and the m9XX defnitely provides the current they crave. This results in a lot more refined sound. I tried the pairing with the SR80e and the SR225e. The Grace really took the SR225e to a great place. The DAC section really enhanced the soundstage and imaging. The amp section gave their already good speed the high octane it needed to become a gloriously fast headphone for metal and prog rock. The amp section also gave that bass hump some authority and depth that it normally lacks. The SR80e didn't see quite the same benefit, though you got some semblance of a soundstage (unusual for the SR80e, which to my ears has virtually no depth or soundstage width). The SR80e's at times flabby midbass tightened up. The fatiguing upper midrange smoothed out just a touch. It's not going to turn a SR series Grado into a GS1000, but it will take the Grado house sound to the next level, while staying unmistakably Grado, for good and/or ill.
Other miscellaneous pairings I tried
Just going to dump my pairing notes with headphones that are either less common or that I didn't spend a TON of time listening to:
1) TheAudio Technica ESW9A is probably my most difficult headphone to amp, in the sense that most amps tend to actually make it sound worse. As a headphone it's kind of muddy, has boomy bass, and isn't particularly transparent. Treble/upper midrange is kind of weird and veiled, but with a little sparkle on the very top. The pairing essentially brought all these qualities to the fore. It did add a bit more detail, but overall, yeah, this headphone still sounds better out of an iPhone than it does when amped. It's pretty though, and very portable. A good headphone to non-critically walk the dog, not to plug into an amp and listen to carefully
2) The Shure SRH840 is probably the easiest headphone I have to amp. It's so workmanlike that it just does its job with almost anything. The pairing worked well. The Grace, as per usual, added a bit more detail retrieval and transparency and firmed up the bass. If you want a slightly warm, soft U-shaped monitoring style headphone with good treble clarity, this is it. I love this headphone, but it won't wow you immediately. This pairing is an ultimate all-arounder when it comes to closed headphones. It does everything very, very well, but doesn't amaze you with any single aspect.
3) The Audio Technica M50X has issues with bass bloat at times, and the m9XX helped with that. The m9XX couldn't do much about the lack of soundstage though, it still sounds like you're having sound pumped into the middle of the brain, and imaging is still basically only left middle and right, no nuance. The m9XX did refine the treble a bit though. the M50X is a headphone that is notorious for sounding the same pretty much no matter what is amping it, and that held true here as well.
4) The Audio Technica AD700 has some issues with grain, and the m9XX brought that out. However, the AD700 is also incredibly detailed and spacious and the m9XX highlighted and enhanced that. At times the soundstage was almost so vast that imaging lost a bit of coherence. Crossfade helped with that, making for a large (thought not cavernous) soundstage that was very precise imaging wise. The AD700 is one of the most rolled off headphones in sub bass I've ever heard, and that stayed true with the m9XX.
5) The Koss KSC75 is an ultra portable on ear clip on headphone. But its quality is incredible for $15. THere are a lot of $100 headphones it wipes the floor with. I would never use it on the m9XX on a regular basis, I strictly use it as a portable "walk around outside" headphone. But here goes anyway: The KSC75 has great treble detail and sparkle, though is fairly rolled off in the bass (mostly due to the way it just sorta hangs around your ear). The m9XX made it sound even more spacious and detailed.
6) The Denon D1001 is essentially the same headphone as the long running and budget popular Creative Aurvana Live. I believe Fostex actually makes it. It has a budget version of the Fostex house sound regardless. It has pretty great midbass and sparkly treble. It's certainly a V-Shaped headphone, which helps hide its weaknesses (a bit congested and not super resolving). I was actually surprised how much the m9XX improved this headphone. The sometimes boomy bass was tightened substantially, and gained more extension. The muddiness was cut fairly dramatically. I could hear some grain, that the muddiness had never even allowed me to hear before. Grain is always preferable to muddiness, so this was a welcome revelation. This is another "knock around" headphone. I've owned it and enjoyed it for about 10 years now and it was nice to have some new life breathed into it. It's still not an amazing headphone, but the Creative Aurvana Live version is still a bargain (Denon long ago discontinued this, at the same time it notoriously switched from Fostex for the rest of the DX000 serious, leading me to believe this is a Fostex headphone). But I mean I don't know anybody who would buy an amp like the m9XX for it.
Conclusions:
This is an INCREDIBLE piece of gear. It's so versatile that it's astounding. I'm not an IEM guy (can't stand the feeling of having something in my ear canal) but it can effortlessly amp those with complete silence, and it can drive an HD650 very well. Heck, several people even say it's a great pairing with the Sennheiser HD800. It's so well designed from all angles: look, feel, build quality, feature set, sound quality and just some indescribable "ahhhhhh" feeling of satisfaction every time I look at it. Where it really shines are the current hungry high end but low impedance headphones that have really been a growing market segment these days. The crop of easier to drive planars and low impedance dynamics will sound better than many thought possible through the m9XX. It's not going to blow you away on a first listen though. It's not going to grow a subwoofer in your bass deficient headphone, pr give a non-detailed headphone HD800 level resolution. But it will take the headphone that it's being given and shine it as well as it possibly can. It's not going to power a HE-6, but it can handle almost every "normal" headphone with aplomb. I'm pretty sure this is the last DAC or amp I will ever own, unless there's some crazy leap forward in technology.
I think of it this way: If this thing was just a DAC, and had no features (no crossfeed, no filters, no volume control, etc) it would be a bargain at $399. If you had a unit that added the features it has (crossfeed, filters) for just that add on unit, you could charge $100. If it was just a solid state amp, given its ultra low impedance, the way the volume control and high power mode work, the cleanliness, just the amp section would be a bargain at $250. Put that all together and you have a product, that on pure sound quality alone would be a bargain at $750. Then when you combine the convenience, elegance, and quality of the build and form factor, this is easily a $800-$1000 product. It would make a lot of "best value" lists if it cost $899. Grace and Massdrop got it to us for $499, which makes it a stupefying value.
You can throw this in a messenger bag, without any worry, and you can have sound quality that will put many $2000 systems to shame. You can power everything from an IEM to a HE500 and never feel that your gear is being compromised. It's an all around solution that somehow manages to make no real compromises at a budget friendly price. If your headphones don't require s small scale nuclear power reactor to drive, I have one piece of advice about this:
If you have the chance BUY THIS THING
