JF Digital HDM-03S
I’ve been using this device as my main source in my primary headphone rig for months. I’ve had the picture posted and a space reserved for review, yet I just haven’t had the time to get to it. Part of the problem is that I’ve been waiting until I had time to fully explore the network features, as well as mess with firmware updates. But with a newborn baby in the house and plenty of reviews on deck I feel like I just need to finish what I started. This will be my attempt at a more streamlined review.
So what exactly is the JF Digital HDM-03S? First off, the JF stands for Jing Feng, with the full name of the company being Shenzhen Jing Feng Digital Technology Co. As far as I can tell they do OEM work for others as well as design their own line of music servers. There is a full line of models ranging from the HDM-01D which is purely a transport only with no analog outputs, to the top of the line HDM-03 which has a host of features. The HDM-03S is sort of a budget version of the HDM-03 – it has most of the same features in a smaller form factor, and omits the output transformers and balanced XLR outputs. Aside from that it uses the same hardware and is really the bang for the buck model in the lineup. I chose it because while I appreciate a good analog section I knew I would mostly be pairing the unit with a higher end DAC. So the full HDM-03 was not necessary.
The device is basically a purpose built computer running a custom Linux install. It has no onboard storage but can act as USB Host for a hard drive through a pair of rear panel USB inputs. It can also pull audio over a network, either wired through Ethernet or WiFi (which requires a separate adapter). There are quite a few ways to use the thing – aside from playing FLAC or WAV files up to 24-bit/192kHz, it can also function as a stand-alone DAC via a pair of digital inputs. I use it as a transport with an external DAC by utilizing the coaxial SPDIF output, but it also has extremely capable RCA outputs and even a nice headphone out. Once connected to a network it can stream audio from a UPnP server as well as internet radio through its built in database. It can also stream directly from Foobar2000 over Ethernet. It can even record audio in 24/96 from the digital inputs and save the result as a WAV file. This really is a remarkably versatile device.
Click any picture to expand
The HDM-03S sells on TaoBao (a China based site similar to eBay) for 6200 Yuan which equates to about $1000 USD. I had a friend make the purchase for me and he was able to successfully communicate my request for the proper voltage, which is not user adjustable and must be set at the factory. I don’t know how often they sell to US customers as I’ve never heard of anyone else using one of these. The closest option I’ve seen for US buyers is from fellow Chinese hifi company Opera Consonance. They sell a unit similar to the HDM-01, called the D-Linear 7, through Grant Fidelity. I believe JF Digital provided the processing and enclosure, while Consonance handled the audio side of things. The interior looks more simplistic but it may still sound great. That device goes for $1250. It’s a bit more expensive than the JF models but it does come with a warranty and after sales support, and I believe they throw in a wireless USB adaptor as well. Consonance just released another model called the Reference 7. I can tell it is based on the same JF Digital platform but is probably reworked on the inside since it has a balanced tube output stage. Pricing will be somewhere north of $2500.
DESIGN
Externally the device measures 12 inches wide, 14 inches deep, and about 4 inches tall. Weight is roughly 16 pounds. It looks like a slightly scaled down version of an Audio GD Reference 7 DAC since it shares a similar construction including the rounded corners. It’s heavy and seems built like a tank, ready to stand up to abuse. I notice design theme similarities with Classe gear, and I believe the new Ayon S3 streaming audio device uses a nearly identical enclosure. I speculate that Ayon is sourcing the same manufacturer for their enclosure as JF Digital and Audio GD because the similarities are just too close.
The front panel is dominated by the 5 inch touch screen display. This is the main interface used to interact with the device. It uses a resistive panel rather than capacitive, which generally doesn’t hold it back much since all it requires is simple button pressing. Basic functions are accomplished by touch but for certain things the included remote control is required. A power button is the only physical button on the entire device.
The rear panel features RCA outs, coaxial digital out, coaxial and toslink digital in, Ethernet in, two USB ports, and an IEC power cable receptacle.
Internally, the design is very ambitious. Processing is handled by a 32-bit dual core 600MHz CPU with a dedicated DSP chip and 2GB of RAM. Because it is a dedicated audio device running a custom operating system instead of a multi-purpose PC or Mac, those specs are more than plenty. A fairly large portion of real estate is dedicated to the power supply section. It’s a linear design utilizing dual shielded toroidal transformers; one for digital with multi-stage post regulation, and the other for analog with a class A high speed active parallel servo design. A Wolfson WM8805 digital receiver handles signals from the digital inputs while the internal playback is sent straight to the DAC section in I2S form. The D/A conversion is handled by a pair of Wolfson WM8741 chips in dual mono configuration. From there the signal is sent out to the output stage built around quad OPA627 opamps and dual AD797 opamps. The DAC chips are supported by a custom made 1ppm precision system clock. Elna and Nover capacitors are used throughout. The headphone stage pulls the signal from the output stage and utilizes a TI TPA6120A2 for amplification. Volume control is accomplished in the digital domain and applies to both the RCA out and the headphone section. As with many designs using the Wolfson WM874x chips, the user has access to 5 digital filter settings, as well as a digital de-emphasis which can be turned on or off. That means plenty of ways to tweak the sound to your liking.
Power supply is robust
Headphone stage
From right to left: WM8805, dual WM8741, quad OPA627,
dual AD797, TPA6120A2
Main processing section, complete with mystery chips
that have their markings removed
USE
The HDM-03S can play nearly any type of file you can think of. FLAC, WAV, AAC, MP3, WMA, ALAC, APE, and probably more that I can’t think of. The front panel says it handles 24/192 streams but I’ve successfully played up to 24-bit/352.8kHz tracks as well. I assume there is some internal downsampling involved there since the Wolfson WM8741 chips top out at 192kHz. But it’s nice to know that whatever file I may throw at it, the HDM-03S will handle it well. It even supports CUE which can be troublesome to other devices.
Operation is best expressed in pictures. So I took plenty of those. As you can see, the main screen lists the song title including the extension (.FLAC, .WAV, etc). It lists the sample rate, time played or time remaining, and has all the basic transport features as buttons for touch operation. Volume level is displayed but it must be adjusted via remote control. After a short amount of time without activity, the display switches to a mostly black screen with just the title scrolling across. In later firmware versions album art is enabled but I didn’t like the way it worked. It seems the device would show any artwork in the folder being played, no matter the size. It took a while to redraw larger files, cut off space for title text, and generally didn’t add much to the experience. I do fine without it.
General navigation is a bit different than most audio streamers like this. Instead of selecting by metadata like artist, album, or genre, it simply displays a list of folders. So basically it goes back to a drag and drop style of arranging music on an external hard drive. It seems surprisingly effective though once the number of folders becomes high enough, navigation gets harder. You find yourself scrolling through quite a few before arriving at the one you want. I’ve come to love it though – it reminds me of browsing through a physical media collection. I might set out to find a certain jazz album, but prior to finding it I spot something else I want to try and end up listening to classic rock instead. The device does support the PlugPlayer app for iOS devices, so proper navigation is likely easier to do that way. Which brings me to my big issue.
I haven’t been able to get the device online yet. I tried three different USB WiFi adaptors. One ended up being defective all around but the other two do work on my various computers – but the HDM-03S doesn’t recognize them or even seem to give them power. I haven’t been able to figure it out. I could lug it into the other room and use an Ethernet cable but I just haven’t had the motivation yet. Without network connectivity, the device is still very useful for me, but I do need to figure it out one of these days.
Unfortunately my unit shows all incoming data as 44.1kHz
even when they are higher
First find your album
Then pick a song
Song plays
Screen eventually goes to this mode
Handles most files types: MP3
FLAC from standard Redbook format
48kHz
88.2kHz
96kHz
176.4kHz
192kHz
Even 352.8kHz (which is quite rare to find)
LISTENING
I’ll cut right to the chase – this is a top class transport, a very good DAC, and a reasonably good headphone amp.
As a transport, it does exactly what I hoped it would, which is sound better than anything else I’ve heard. I’ve had some good to excellent transports around the house and done direct comparisons with many of them - Theta Miles, Lexicon RT20, Squeezebox Touch, NAD C446, Pioneer N50, Marantz SA-1 with extensive Audiomod upgrades, Classe CDP10, Rega Saturn, Esoteric SA-10, McIntosh MCD205, modified Sim Audio Moon CD-1… and I’m sure some others that I’m forgetting. The majority of these devices are highly regarded, with many priced in the multi-thousand dollar range. The Marantz SA-1 was $7500 when new and has another $7K worth of upgrades on it. Yet none of these could quite do what the HDM-03S can in terms of feeding a top quality, pure, low jitter signal to an external DAC. I really do think this device may have maximized what is possible from a standard SPDIF connection. Perhaps some megabuck $30K transport can do a better job but I’m unlikely to ever own such a device. The only competition I can see is one that doesn’t play by the rules of an SPDIF connection – I’m referring of course to asynchronous USB transfer. I believe the potential is higher for a well done async solution compared to even the best SPDIF signal. The hot ticket right now happens to be the $300 Squeezebox Touch with a custom add-on enabling a USB 2.0 output. This can pass 24/192 data asynchronously to compatible DACs with stunning results. I need to do more comparisons to see how much improvement that brings…. for now I can just say that no other SPDIF transport I’ve heard can touch the HDM-03S (in my experience).
So what differences do a great transport make compared to a merely good transport? The answer really depends on your DAC. Some DACs are happy with any reasonably good signal, and don’t seem to scale much higher. At that point there is no use in spending more money chasing a better transport. My Yulong D100 is one of those types – I don’t feel it sounds any better being fed by the HDM-03S compared to using a reasonably good transport like the Pioneer N50, Theta Miles, or just the stock SPDIF output of the Squeezebox Touch. So in that case there is not much benefit. But in DACs where it does seem to be more significant, you can expect things like tighter focus, a better defined soundstage, superior imaging, a more natural presentation…. All those “squishy” audiophile type definitions that can be difficult to describe or comprehend. Readers familiar with my style know that I’m not really the type to ascribe night and day differences in sound quality based purely on a transport. Yet it does make sense to me that a superior signal would be an easier “load” for the DAC to handle; even DACs with exceptional jitter reduction capabilities would be working with a more pristine signal right from the start, therefore guaranteeing the accuracy only hoped for by an ideal de-jitter process. So I don’t feel that I’m crossing the line into snake-oil nonsense here. As always, the reader is free to disagree with me.
When using the analog outputs, the HDM-03S sounds very good as well. It has a smooth analog feel to it that rivals many of the better stand-alone DACs I’ve heard. I compared it to the Rega DAC recently and to my ears the two sounded nearly identical. The Rega was ultimately superior by a small margin, having a more open top end with less veil, but it was a fairly close call. For those familiar with that unit, you’ll know what I mean when I say the balance of detail and musicality is very nicely done. Perhaps not the last word in ultra-analytical sonic precision but very involving and rhythmically correct. There’s a slight warmth over the presentation and it tends to make all music sound as good as possible. This is probably not the DAC you would use in a mastering session because it would tend to hide flaws in your mix. But for someone merely concerned with listening, it is a very nice sound.
As I mentioned the Rega DAC sounded nearly identical with the HDM-03S. I also hear a strong similarity to the Yulong Audio flagship Sabre D18 unit. That machine is the better DAC overall, taking the same recipe a bit farther to maturity. So ultimately the HDM-03S is not quite on par with my reference units like the Anedio D2 or Violectric V800. But those are dedicated DACs costing more than the HDM-03S, and they don’t have nearly as much functionality. If I had to rely solely on the JF Digital machine as my only DAC I would certainly be able to get by happily. I would rank it close to my Yulong D100 MKI or Matrix Quattro DAC in terms of overall ability, just trailing the D100 MKII. I’d also rate it slightly higher than the Pioneer N50 I recently reviewed (and enjoyed).
The integrated headphone amplifier is probably the weakest link of the whole device. Not that it is bad – on the contrary, it is generally pleasing with a warm smooth tone reminiscent of the RCA output. It has good performance overall and most people would probably be more than satisfied with it. As a bit of a headphone snob, I have many other dedicated amps to choose from, so I usually prefer one of my reference units instead. Comparing the headphone out to a quality budget standalone amp like the Matrix M-Stage or the Yulong A100, the built in amp is a bit hazy and indistinct, but does have very nice tonality and good low frequency control. Resolution is fair and imaging is clear enough to be convincing. I guess what I’m trying to say is that the amp is very respectable but doesn’t stand out as much as the RCA or digital outputs.
System takes just over 1 minute to cold boot
Progress bar lets you know how close you are
SUNDRY COMMENTS
A downside to the whole experience is the lack of after sales support. It’s not just the language barrier either – I get the impression from the manufacturer website that they aren’t as focused on individual sales as they are on finding OEM partnerships. For example, there are several firmware updates, but there is very little info as to the changes each one brings. Each time I’ve updated I’ve had a nervous feeling like I may be about to ruin the machine. There is also the matter of finding a matching WiFi adapter which has been mildly frustrating. Most companies would have a list of recommended adapters, or a forum where fellow users can post their results, or something to help the situation. Not so in this case. I'm also scared that I may somehow damage the remote, which would be a big deal. Many functions are only accessible with the remote. I'd have to contact the manufacturer and hope I could get a new one. I should hurry up and program my Harmony remote to duplicate this remote, just in case.
There also appears to be a recent upgrade to the main processing module. The website doesn’t really say how one can update to the new version. It does list the specs, which happen to be the same as I already have in the HDM-03S (the newest of all the different models). So perhaps I already have the newest processor installed? To make matters worse, the new module is not quite a plug and play upgrade – each model has a different set of instructions for some hardware modification necessary to support the upgrade. It involves cutting traces and soldering. Since instructions exist to do this process for the HDM-03S, do I then logically conclude that I don’t have the updated processor after all? I don’t know. There are some very recent firmware updates that specifically state they only work with the upgrade. If I try them, will I brick my unit? I need to have someone translate for me to get answers to my questions. For now I’m keeping it as-is with the older but solid firmware.
CONCLUSION
The HDM-03S is a quirky device. With a little refinement and polish, it could easily be rebadged and sold as a much more expensive product. The sound quality is certainly there - this is quite simply the best SPDIF transport I have ever experienced. Yet those little quirks keep it from becoming something that has mass appeal for the general user. Lots of folks are accustomed to browsing by artist or genre and would have a difficult time with the folder-based navigation of this machine. But it works for me, and I feel like a bandit having only paid what I did for it.
By way of analogy: many people still prefer the experience of vinyl. It may have started with the sound quality but has become something more than that. They maintain expensive turntable rigs that have far less convenience compared to a music server or even a CD player. Yet they have become used to browsing their physical media, organizing it, cleaning it, selecting the particular album they wish to play. And in that way the aspect that is considered detrimental by many, becomes an enjoyable ritual by few. I’ve seen the HDM-03S referred to as a “digital turntable” according to Google Chrome translation. I think it’s an appropriate term. Scrolling through the directories, less than perfect as it may be, has become my ritual through which I have found many hours of enjoyment.
I don’t know if anyone else around here will ever own a JF Digital product. But for me this has become the foundation of my fairly substantial equipment collection. I’ve had some great network audio devices come and go through my system and have enjoyed them very much, but nothing has come close to replacing the HDM-03S. It isn’t the perfect device for everyone but it comes rather close for me. I can’t see it being displaced in my system anytime soon, and down the road I know I’ll have to spend an obscene amount of money to do any better.
I do use a portable USB hard drive plugged straight into the USB port. It works well even for ultra-high resolution files - no network lag. The downside is that it doesn't really do metadata - file naming and organization is a must.
Analog RCA outs are actually very good. On par with my Yulong D100 MKII, though having their own personality. It takes a really high end DAC to improve on this unit, assuming you like the smooth laid back tone.
I do use it the way you described, feeding a headphone amp directly. It works very well. I