Pros: Compact, Versatile, Great Sounding, Fun
Cons: Bass Roll Off, Menu System
What is it?
The Grace Design m903 reference headphone amp / DAC is a device that is typically used in audio production / audiophile setups to take one audio source and give life to some other audio device. In my case I let it drive my HD-650 headphones with stock cable.
Here are a few things to note prior to reading any further. My headphones have been fully burned in for over 150 hours which is standard for Sennheiser products so the audio response from your setup may differ from mine.
What is inside the m903 anyway?
Courtesy of Michael Grace
DAC: PCM1798 ( lower power usage, a tad more noisy than the 1792/1794 )
Current to Voltage: THAT1570
High Pass Filter: OPA1612
The DAC power supply and line out are separate from the head amp power supplies
The input clocking is the same as the m902
Volume Control: Cirrus CS3318
The CS3318 has 7dB less noise than the PGA4311
For $1795 US you receive quite a package. You get a headphone amp, a speaker pre-amp, and DAC. The connectors are quite fantastic making the m903 one of the more favorable mid-range audio devices due to sheer versatility. The headphone amp / DAC is comparable to my Ultra Desktop Amp /DAC which is in the same price range.
As the mantra of great sounding music tells us one first starts with a decent source. I ran audio from Foobar2000 straight into the DAC via USB. 44.1 kHz Sample Rate and 160kbs Bit Rate. With a good transfer one can achieve nice audio from the mp3 format. I compared the m903 to the Ultra Desktop running nearly instantaneous A/B tests with all of the same cables, headphones, music files, and closely matched volume levels.
The soundstage presented by the m903 is awesome and only slightly reduce in comparison to the Ultra Desktop. The mids and highs on the m903 are swift, immediate, and enjoyable. The soundstage can go from left/right, up/down, and the many combinations with ease. The audio presentation was anything but one dimensional.
Tested: Buddy Miller & Julie Miller - [Written In Chalk CD1 #05] Long Time
This is the only place I thought the m903 fell behind compared to the Ultra Desktop. The grace has decent enough impact, but it really had a little trouble driving my HD-650's into perfection. The Ultra Desktop does a great job at that. I did get close with the tested track.
Tested: Sean Jones - [Kaleidoscope CD1 #05] So Wonderful
The bass is adequately represented and is especially so if your source contains it. Remember that the m903 is pure and true so you need a great track with pure bass in it to hear what it can really do.
Tested: Karsh Kale - [Realize #03] Tour Guide
No questions here the mids were as strong if not slightly stronger that the Ultra Desktop. They were also a bit more up-front which for me was slightly fatiguing over long listening sessions. The mids were beautiful and articulate.
Tested: Ella Fitzgerald - [Verve Unmixed CD1 #07] Wait Till You See Her
Another easy test for the m903. Even with my HD-650's I could here detailed and very quick highs. No problems with the highs that I could hear.
Tested: Michael Jackson - [The Essential Michael Jackson CD1 #16] Billie Jean (Single Version)
Quality and Design:
The box itself is not too heavy nor too light. It comes with well thought out exterior design and button layout. The back panel is well constructed and the source selector is bomber. The only gripe I had here was the feel of the volume control. It wiggles up and down easily. I would love to see / feel the Music Hall 25.2 volume knob on this bad boy. The knob grips are a bit weak as well. I found no major Quality Control issues and the 5 year warranty is simply awesome. The box it came in was very nice and there is a plastic pressure sleeve in the box to minimize shipping damage. The packaging was minimalistic much like the Ultra Desktop. The feet that come with the unit can be tightened down far enough the start to dig into the bottom of the chassis. I had to use some felt, an o-ring would also work, to keep the two metal surfaces from touching. This also allows the unit to be better balanced on all fours. Some have complained on the m902 that it will not rest level. Mine had a similar issue until I used the felt and was able to control the tightness of each setscrew enabling me to level the unit.
I give the Grace m903 an 87%. It is a very nice amp / DAC with a ton of connectivity which is why I really like it. On the other hand it runs quite hot and has a few minor issues which drops it down a peg.
If you want an articulate and great sounding device with DAC and you do not mind sacrificing 5-10% of your bass range ( keep in mind you gain the mid/highs ) as well as a device that has many inputs / outputs then the m903 is for you. If it is your price point give it a try. I would test it with some ATH-M50's and be prepared to put a smile on your face.
If you are looking for slightly more bold sound including that nice bass impact then perhaps the Grace is not for you. In my opinion, which leans generally toward the Ultra Desktop side, the m903 is awesome. It is no wonder why Headroom has both on their site. It says a lot when a company that builds something that competes directly with the m903 carries both products.
Other Tested Tracks:
Garbage - [Absolute Garbage [Disc 2] CD2 #04] Breaking Up The Girl [Timo Maas Remix]
Nitin Sawhney - [London Undersound CD1 #15] Last Train To Midnight (featuring Aruba Red)
Ani DiFranco - [Canon (Essential Collection) CD1 #06] Cradle & All
Emiliana Torrini - [Me And Armini CD1 #06] Big Jumps
I ran the audio from my Philips Magnavox CDC 735 5 disc Changer into the preamp be it m903 or Ultra Desktop and then into the TEAC_AG10D. I spent most of my A/B testing listening to the Solillaquists Of Sound -  No More Heroes which is a decent hip hop album that I do bass and treble extension testing with.
After hours of listening between the Ultra Desktop, m903, and my TEAC's amp stage I decided the following factors were the primary difference that could be heard.
1.) The m903 was well extended in the bass. It had nice crisp mids to highs and did not introduce any audible noise into the system.
2.) The Ultra Desktop was slightly more boomy and seemed to wash out the mids a bit. The audio quality was still very closely matched to the m903.
3.) The standalone TEAC did well against these two much more expensive units. The TEAC certainly sounded different with the bass slightly rolled off and some audible damping throughout the spectrum. I was surprised at the TEAC's ability to hold its own against both the Ultra Desktop and m903.
During these tests I did discover that if you have nice monitor speakers in your living room and they are resting against the floor you may notice a drastic damping effect in the bass range. As I lowered my listening level closer to the floor the bass was much more extended and pleasant. I imagine this was due to the largest of the speakers on my Polk monitors was on the bottom and the bass sound wave was quickly absorbed into the floor. If you have speakers sitting on the floor and would like to hear a more complete sound I recommend lifting the speakers to the 3-4 foot level. You may be surprised at what you hear.
In comparison to the Teac's amp stages the m903 was not leaps and bounds better. I still noticed the best improvement using the m903 as an amp / DAC for my PC as I enjoyed it the most there. It gave me the most choice in sound preference. If the sound was too harsh and shallow I would go to my HD-650's. If the sound was not bassy enough I could plug in some Grados or my ATH-M50's and the balance returned.
Balanced Outputs with Headphones:
Ok, I know you are thinking it or have at some point; "Can I use the Balanced Outputs from my m903 and run them into headphones with a balanced cable terinated with TRS?" The answer is of course YES, but the m903 is not designed to drive balanced headphones. How does the sound a/b to a stereo headphone output on the m903?
The output from the m903 Balanced Outputs ( L2 ) seen on the back panel will be more spacious and mellow. The mids and highs on the HD-650's I tested with were mellow and the bass was tighter. To me it turned my HD-650's into a nice mellow Grado SR-80. For some this is a bad thing comparing the price points, but to others this may give optionality. The solution to rolling off the mids and highs with the HD-650 is here!
Eben Grace had a few things to say about the intended use for the balanced outputs from the m903.
"You can run your headphones from those rear panel balanced outs, but
that's not really what they were intended for - they are really line
outputs for connecting to a power amp or powered monitors. It's not going
to hurt anything, but really the headphone outputs on the front panel are
much better suited (output power and impedance) to drive your 650's."
I tested the following tracks using direct a/b comparison going from balanced to stereo. All of the gear in between and the music was all the same even the headphone cable. I used a XLR to stereo adapter and of course XLR to TRS for the balanced testing.
Emiliana Torrini - [Me And Armini CD1 #02] Me And Armini
The difference between balanced and stereo was subtle, but noticeable. When the stereo out was tested the sound was clear, extended well into each side of the frequency spectrum, and articulate. With balanced outputs the sound was clean, slightly reduce on the high end, and emphasized on the low. The soundstage was a bit more colored and less harsh.
Karsh Kale - [Realize #08] Saajana
I actually preferred the stereo output rather than the balanced output on this track. The stereo appropriately rolled off the highs just enough and kept the soundstage intact. The balanced outputs seemed to cut too much off of the highs and mellow the mids a bit too much for my tastes.
Weird Al Yankovic - [Straight Outta Lynwood Disc 1 #02] Pancreas
The same held true with this track as it did with Karsh Kale. The mids were a little more in your face with stereo and the balanced made them mellow. I felt that the bass was actually tighter with the stereo output.
Ani DiFranco - [Canon (Essential Collection) CD1 #11] Gravel
In stereo this track is amazing with the HD-650. I would be surprised if the balanced output sounded better. The sound was not worse in balanced mode. It sounded a bit more "live" and the soundstage expanded pleasantly. If you wanted a more up front experience you could go stereo here. If you wanted a long listening session that was bit more colored and bass emphasized then go balanced.
Balanced vs Stereo:
In the end with an HD-650 I preferred the stereo output most of the time. It was a bit harsh at louder volume and I found myself turning the output down. With balanced outputs it was easier and less fatiguing at the same output level.
Should I go balanced?
I would say if you are considering balanced headphones, cables, outputs, amps, etc and you have not heard the difference for yourself I say no. The differences may be disappointing. If you have an extensive array of headphones, amps, and grow tired of your favorite cans becoming to fatiguing over time then balanced may be a good, somewhat expensive, way to achieve this. If you are out there and have connected the balanced outs from your m903 to some nice monitor speakers and would like to include your review of that particular setup here please send me your review and I would be glad to post it. I do not have self-powered monitors to test this nor will I be receiving any in the near future. Perhaps this is where the sound differences become obvious and more importantly useful, be it for fun or technical reason.
What do I really think?
I think that the m903 is an amazing piece of equipment. Although it is brighter than the Ultra Desktop Amp/DAC it has just as much fun powering the top tier of headphones. Personally I feel a wonderful balance with a dark headphone like the AH-D2000 or the DT990 with the m903. These headphones would otherwise be perhaps too bassy. The thoughtful technology found within and performace out of the m903 is just outstanding. I think Grace Design prides themselves on their masterful m903 and that says a lot from a company that makes some really high end gear. I find the customer service there top notch and honest.
2013 Update: Driving a Balanced Headphone Amp and m903 Amp Measurements
In late 2012 I acquired a balanced headphone amp. I chose the Balanced Ultra Desktop amp ( BUDA ) from HeadRoom as I am already familiar with the Ultra Desktop Amp sound. The reason for the implementation of the BUDA was to help improve upon the low end reproduction on the m903. I ran extensive tests going between some Kimber Kable PBJ RCA connectors and some inexpensive, but high quality, Seismic Audio XLR to TRS patch cables. Both the Grace m903 and BUDA are capable of handling balanced and unbalanced signals. To my ears the only difference between the balanced and unbalanced modes was a 6db increase in sound level in balanced mode. Audibly the signals appeared identical which makes a ton of sense when you look at how each is utilized.
Due to the lack of low end on the m903 I suggest using it as a DAC more than a headphone amplifier. Even the JDS Labs 02+ODAC Combo sounds just as good as the m903 at nominal listening levels as far as the amp is concerned. Tyll Hertsens over at Innerfidelity.com measured the Grace m903's amp performance and I have provided a link to that below.
Compared directly against headphone amps like the beyerdynamic A1 or JDS O2 there is room for some obvious improvement. Both the A1 and O2 show better linearity seen in their SIMPTE IMD charts. Both amps have significantly less roll of both in the bass and treble than the m903.
The m903 sound particularly great with the HiFiMAN HE-400i. Note: the pads on my pair of HE-400i's have been flipped so the thickest part of the pad closest to my face, not back of my head, which smooths out the up-front nature of this headphone.