Arcam rPAC USB/Headphone DAC

I just wrote this for my blog so I thought I would post it here too.
 
 
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[size=medium] A&R Cambridge Ltd. (or Arcam to the rest of us) are well established in the field of hifi audio, but it could be said that the rPAC represents a departure from their usual products. It's true that they've made DACs before, but not combined with headphone amplifiers, not USB powered portables and not this reasonably priced. [/size]
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Data is transferred to an asynchronous USB for the Texas Instruments PCM5102 DAC chip to convert - up to 24bit / 96khz - audio into glorious analogue. There are also RCA sockets for connecting the DAC to an external amplifier or powered speakers. A logo of this calibre on such a multi-talented device for only £150... This seems too good to be true. [/size]
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    SOUND[/size]
[size=medium] The rPAC has a very clean and open sound. The experience is very neutral but if I had to pick I would say it's very slightly on the warm side. This slight push in the bass is nothing offensive and suits Classical or Electronic music equally well. My most notable impression from the rPAC is a great sense of smoothness. There is plenty of detail on tap to impress here as well, it never fails to impress when rendering fine details. The soundstage is great too, giving a great sense of dynamics to the depth and dimension. This is easily the best USB powered sound that I have heard. [/size]
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Although being USB powered doesn't seem to impact the sound quality it does limit the volume level somewhat. For mosr headphone it will not be a problem but anything above 300ohms may struggle for some people and/or some music (depending on the individual a bit of course). With the 600ohm Beyerdynamic DT880 the rPAC managed loud levels only if there was little or no exterior noise. A less than quiet environment and there could be issues. As USB powered audio volume goes the rPAC is among the better ones that I've tried, the Audinst HUD-Mini is much more problematic for example.[/size]
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It's a testament to how clear the sound is that even the best compressed music is starting to feel dull on the rPAC. I keep moving over to my lossless collection and everything feels more alive. I know this is a hot topic, I am sceptical about these things, but this is how it's making me feel about music. Anything less than 320kbps feels really grating to my senses.[/size]
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This paragraph probably shouldn't be in the I had some sporadic issues with the rPAC cutting out. A quick hissing noise and then it seems to crash completely and needs reconnecting. This seemed to happen more on certain computers. On one computer certain USB ports that it was connected to caused Windows 7 to BSOD (Blue Screen Of Death), and that is very bad! [/size]
[size=medium] The rPAC itself crashing seemed to happen mostly while Spotify was playing and perhaps this is related to it the rPAC demanding 24bit audio. I noticed this when running Foobar and JRiver (MC17), both programs force the music to be up-sampled to 24bit or they refuse to output anything to the rPAC. I am assuming that the reason you don't normally have issues is Windows fixing the problem without asking you. I noticed the Audiolab M-DAC also insisted on an up-sampling from the software if you try to force it to NOS (Non Over-Sampling) mode.[/size]
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    MUSIC[/size]
[size=medium] Previously I've avoided talking about specific music tracks in the DAC and amplifier reviews. I was worried that it would get confusing, but I'm going back on this as I feel it will help better describe certain sound characteristics. [/size]
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1. Rodrigo Y Gabriela: "Buster Voodoo" - Listening to all Rodrigo Y Gabriela's music is sublime on the rPAC. This track shows how well it handles fast paced music, but also how powerful and sharply detailed the guitars sound while not feeling harsh. There is a real sense of smoothness here that is intoxicating. 
2. opendoorsclose: "Night" - (Soundcloud) This Electronic track was made by a good friend of mine. Like most electronic music this is a great test of the  frequency extremes. Bass kicks hard, but is also well formed and nicely textured, treble is nicely articulate and not overwhelming. I also like this track for dynamics and soundstage, all of which come out really well here. The rPAC is really great for Electronic music, but to be fair it's great for everything. It just makes the bold sounds stand out even more and I can't argue with that.
3. Chopin:  "Nocturnes No. 6 In G Minor, Op.15 No.3" - The rPAC displays great poise forming the notes of the piano throughout this piece. Mostly this track is quiet and calm, but just after two minutes in this is broken up by a moment of drama, both ends of the scale sound utterly immersive. The rPAC is able to dish out smooth musicality and delicate detail with equal amounts of impressiveness?
4. Chris Tilton: Fringe (Season 3) "Escape From Liberty Island" - Ever since Chris Tilton's stunning 'Black' game soundtrack I have been following his career.  From their early collaborations you can feel Michael Giacchino's influence in Chris' work and that's no bad thing. 'Fringe - Season 3' conveys a really great mood to the TV show and this is my favourite album/season of the three for it's sound. It comes through here with great presence, yet intricate delicacy. There is no hint of muddling when the track gets complicated and it has a lovely sense of depth too. 
5. Stevie Ray Vaughan & Double Trouble: "Voodoo Child" -  Yes I know this is not the original, but it's really good! I stumbled across this one going through my Dad's collection. If you have a Spotify account then you'll have access to several great versions of this track, including the original "Voodoo Chile" from the 'Live In Stockholm - 1969' album. This version by Stevie Ray is my favourite mastering of the guitar work and let's face it - this track is all about epic guitar. The opening is a great example of the 

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[/size] [size=medium] I own most of these songs on CD, they are ripped as lossless files and played on a PC. The audio is output through a generic USB cable, using WASAPI - event style on JRiver's MC17 - buffering from the RAM. I also chose these songs because they're on Spotify, so if you have a premium subscription you should be able to find them easily and check them out for yourself in decent quality.[/size]
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[size=medium]     COMPARISONS[/size]
[size=medium] The Yulong U100 is similarly priced to the rPAC and also good as a desktop DAC because it has RCA line outputs which are useful if you split your headphone usage up with the odd bit of computer speakers. The Arcam's audio signature is a little bit warmer than the U100 but not by much, I've heard warmer that I still think are great so I think this will provide a happy mid-ground that is likely to suit most people. The Yulong is priced a little higher than the rPAC, it's also much larger and needs to be plugged in to the wall for power but what it lacks in portability and convenience it makes up for with superior texture and soundstage.[/size]
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The Epiphany Acoustics EHP-O2D's audio signature is warmer than the rPAC's, which is no bad thing. It is worth noting because between the rPAC, the Yulong U100 and the Epiphany it's this aspect that'll make people prefer one over the other. It feels a little unfair to be comparing the Arcam to two units that are not USB powered however. The fact that it's close to these two is a real achievement but it is behind them in excitement levels. If you want portability then ignore the Yulong and Epiphany because they are not better enough to make up for this lack of convenience. [/size]
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Perhaps something like the Audioquest Dragonfly can get closer to the mains powered DAC/amps but I haven't tried that one yet.[/size]
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The Audinst HUD-MX1 is a great performing DAC, but for me it gets heavily overshadowed by the sheer performance of the Arcam. The two units share RCA line outputs and a similar footprint. The MX1 is a little less warm, which could be considered a good thing, but I preferred the rPAC's presentation here. At £115 the MX1 is a bit cheaper than the Arcam, but the rPAC feels way more special than it's price. The detail, bass, mid-range, treble and especially the soundstage feel much nicer on the Arcam but as well as all that there is real sense of smoothness to the sound. [/size]
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    BUILD[/size]
[size=medium] The rPAC is an interesting design. It's neat, well engineered and slick. Breaking away from the common shape of most similar devices it stands out as one of the more well thought out designs. I would call it looked unique if I hadn't seen the Calyx Kong, which apart from a slightly different button layout and no line-outputs is very similar.[/size]
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If you look at Arcam's line-up now you will see another similar looking unit to the rPAC, called an rLink. Try not to mix these two up because the rLink doesn't feature a USB input and thus requires additional power. The rLink is also a DAC only, in other words; it does not feature a headphone amplifier. Other than that the two devices are similar.[/size]
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[size=medium]     FEATURES[/size]
[size=medium] The rLink shows that the rPAC's 96khz maximum sample rate is due to a limitation the USB interface (or rather it's drivers) because the rLink supports 192khz with the same DAC chip. [/size]
[size=medium] The only buttons you get here are for volume, they are however very well engineered, shiny and have a reassuring feedback when pressed. Although I prefer analogue dials, I can see that not having one makes the device more sleek and durable - thus better for portability. You get one button for up & another for down, but if you press both buttons together you will discover a mute feature. This is a nice touch, although I tend not to use it myself. The buttons have plenty of granularity to the volume level, great for IEMs and high sensitivity headphones alike. I kind of miss having a display here as there is no feedback as to where the volume is set. Switch from low sensitivity headphones to high and you will probably get a bit of a shock. The unit is set to maximum volume when you get it too so be warned.[/size]
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    ACCESSORIES[/size]
[size=medium] The rPAC comes with a healthy set of parts. Apart from getting a 'thank you' card from Arcam there is a nice shiny manual (although there's not a lot for it to tell). You get a felt bag for carrying the rPAC around, this is nice an big so you can also get some cables in there too. Of course you get a USB cable, it's a simple one but most people won't care about that. Last, but not least, you also get a set of interconnects so that you can hook the DAC directly to another amp, again they are a 'basic' pair but this is a nice touch as they really didn't have to include these.[/size]
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    DIMENSIONS[/size]
[size=medium] The frame of the rPAC is just a bit bigger than a deck of cards (100 x 62 x 25mm). The 300g weight feels a lot for something this small - that's nearly three times that of the - all metal - Fiio E17. This makes it feel substantial and sturdy, but this bulk is almost entirely due to a very thick frame (which is most of what you see on the outside), the circuit board and chips weigh next to nothing. It feels rather overkill for strength so perhaps this added weight is assure a good footing when it's sat on a desktop. Moving me on nicely to my favourite part of the design - the solid rubber base. Looking almost the same as the metal top this keeps the design neat and slick. It's so much nicer than stick-on rubber feet, which are common on most other DACs.[/size]
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    FINAL WORDS[/size]
[size=medium] Try as I might I just couldn't find any real weaknesses to the rPAC armour. It's neat, has great features and superb build quality, but most importantly the audio isn't just good, it's stunning![/size]
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When I first saw the rPAC I was initial concerned that the AV giant was cutting off more than it could chew with their first combined DAC and headphone amplifier. I assumed that for this price corners would have to be cut everywhere and that audio quality would suffer. It's up against some tough competition from Asia too. Companies like Yulong and Audinst have had more experience with these niche products and have done an absolutely stunning job so far. After listening to the rPAC however my scepticism quickly melted away. As a desktop DAC I would put this near the top of a very long list but as a portable USB DAC it's a truly stunning machine that will be hard to beat.[/size]
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With it's balance of warmth, clarity, detail and three-dimensionality the Arcam rPAC is now my favourite DAC and headphone amplifier for laptop listening. It's not the smallest or lightest of them, but the build quality is as good as it's sound and the addition of RCA line-outs really adds to it's versatility. [/size]
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If you're looking for the ultimate in transparency (which suits my warmer headphones a little better), or have very hard to drive headphones then I would perhaps push you towards the Yulong U100 but if you want a sound presentation that is more on the sublimely smooth side whilst not sacrificing much detail or soundstage then the Arcam is very easy recommendation. The fact that the manages this while running from USB power is nothing short of spectacular. [/size]
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[size=medium] OK here are some rather pointless photos of the internal circuit board, but perhaps they will entertain some. I guess I've got the bug for taking things apart now . It's a very simple device to disassemble but unlike the Audinst HUD-Mini there is nothing fun to play with, like op-amps. [/size]
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I'm kind of curious to know what the 20 pin header, labelled 'CON1', is for. It looks like the ones you get on computer sound-cards. Anyone know what this is for?[/size]
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[size=medium] Here is the PCB sitting in the lower half of the chassis, next to the under side of the top half. Underneath is the felt draw-string bag that comes with the rPAC. As you can see by the under side of the chassis - the dark colour is sprayed on. I imagine any scrapes/scuffs to the top plate and corners will show through to the lighter metal, but so far I haven't seen this. [/size]
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Hey guys,

I have seen this little box recently and it intrigued me a lot. It has an impressive build quality.



It has a very thick aluminum case and it feels like a tank can get over it and wouldn’t hurt it.

Ok…Now I am curios..would it hurt it? Why am I thinking of this?

Because of this crazy video:

Hmm…All i need now is a tank… Does anybody knows a guy…with a tank?

I managed to get a test unit and while I had a good feeling about this small box, it still managed to surprise me.



Let’s get to business shall we? For testing, I have used Sennheiser HD800, Focal Spirit One, Audeze LCD2,  Fiio E17 and Burson Conductor.

Here are my impressions on some songs:

Pink Floyd – Time

The treble is really detailed and sparkly at the beginning. The bells were nicely separated and had a very present ring. The presentation was detailed and I just loved the drums coming from every direction which you can easily pinpoint. The voice was natural and had a nice texture.

Sons de la frontera - Al jardin de la alegria

This was a nice surprise. The sound was airy, articulate, controlled & detailed. Loved how the guitar strings snapped with full extension as they were right near me. During the test I liked the sound presentation so much as I listened to 4-5 other songs from that album.

Rodrigo Y Gabriela (Pirates of the Caribbean: On Stranger Tides) Angry And Dead Man Alive

Wow…I just loved this song…I really got caught in the moment. I don’t know about you but I just love articulate sound and this combo, rPac+Spirit One, was just awesome. The guitars gave me goosebumps. The drums…had a very very good impact and round full sound.

Leonard Cohen – The Traitor

Again loved the guitars. rPac goes very well with the articulate nature of the Focal Spirit One. Leonard’s voice seemed natural and present as it should be throughout the song.

Dire Straits – Sultans of Swing

Really nice PRAT. Really toe tapping! I really feel that the separation of instruments is quite good in this small package. The sound articulate as always and the bass was fast and with good extension.

Infected Mushroom – Army of Mushrooms  - Wanted To

The PRAT was awesome. I really love the well extended bass with the rPac. The sound was fast, energetic and really engaging.

Amandine Beyer & Gli Ingogniti – The Four Seasons -  L autunno Allegro

The sound was quite open and dynamic.  On this piece, however I realized the background wasn’t quite black. I changed the stock usb cable with a Chord Usb Silver Plus and the problem was solved. The difference was quite noticeable.



Comparison to Fiio E17

Given the price point you would ask yourself how it would compare to FIIO E17.

These units are pretty close but there are some differences between them and it may be a matter of choice after all.

Sound wise

The rPac had a more detailed sound with better decay, the sound was more articulated & better rounded at both ends, with better instrument separation, better bass extension and more energetic.

E17 has a warmer presentation & a cleaner sound than the rPac and that is mainly because the E17 runs on battery while the arcam is powered by the USB. I have tried a better cable with rPac and it really improves the sound.

Sound wise, I prefer the rPac to E17.

Amplification

I have tried Sennheiser HD800  with both units. rPac was maxed out for normal listening, while the E17 had more until reaching maximum, so it seemed like e17 had more juice. However I felt that the control was quite better on the rPac, and it did reach a good normal listening volume. So rPac quite impressed me with this. I ended up listening to a whole bunch of songs with the pretentious HD800 & the arcam unit (never expected this…wow) .  There I was…minding my own business when the rPac surprised me as hell with this.



Build quality

The e17 is almost half the size of the rPac.

Both have a very sturdy aluminium case, but the rPac really looks impenetrable.

While the E17 has a usb input, SPDIF In, aux out & headphones out, the rPac has only the USB In, headphones out and RCA out.

The E17 has a nice menu while the rPac has only volume buttons on it having a rather spartan but pleasant design .

While you can use Fiio separately as amplifier and as dac, the rPac could be used just an external dac with other devices.

Also the E17 has a battery than can become really handy in some situations, and also contributes to a cleaner sound.



Conclusions

I really loved this little box and I recommend it with ease to anybody who wants portable sound. Don’t forget that it really benefits from a good USB cable.

Pros:

1. Excellent build quality 
2. Good amplification and DAC with good instrument separation, wide soundstage, articulated & detailed sound, excellent PRAT, good decay, well extended & punchy bass, nicely overall rounded sound, sparkly but not bright treble
3. rca out

Cons:

1. no battery
2. can’t be used just as amp (only as dac)
3. has only volume buttons with no screen or menu (i don’t find this upsetting but there might be people that would)

 

by HeadMania

Hey head fiers! The rPAC is a great bit of kit! I got to compare this to Fiio e17 and the Arcam was just this little bit better than Fiio in every regard. It was just more musical - sound was more full, punchier and more detailed. Can't really comment on soundstage coz the headphones i used were closed back ones and not very good for imaging! And since i own the Arcam's rDac a standalone dac i compared the rPAC's analog output ability! The rDac is about twice the price of the rPAC so as i thought the little rPAC was not able to output a soundstage as detailed as rDac and i felt like there was a little treble roll off or some sparkle missing in the very highest frequency's! So in overal i would say if your after a little usb/dac/headphone amp and don't want to go the Fiio route i would highly recommend trying the Arcam rPAC!

I spent a few hours with this unit today, and tried it with about 8 pairs of headphones. My setup was Macbook Pro -> Audirvana Plus v2 player -> rPAC
The unit is very simple - no display or indicators, just plug and play. Feels nice in the hand too, small but solid.
I was really pleased with the combination of the Audeze and the rPAC, which was articulate and perfectly balanced and natural. It had enough power to drive the Audeze and Beyerdynamic T5p easily but some phones needed maximum volume to get loud and I think it was the Hifiman HE 560 which just didn't get loud enough.
I only had time in the shop to compare it with one other DAC, the Asus Xonar Essence STU. I preferred the Arcam - it seemed more tonally balanced and overall more natural sounding.
 
UPDATE: Later I found out that it seems the rPAC can be made to work at up to 192kHz too. These are the instructions, but try this at your own risk. I have not tried it myself:
 
download the driver from: http://www.arcam.co.uk/ugc/tor/rpac/Software/rPAC_firmware_1.0.5_driver_1.61.0.zip
This software is Windows only.
 
Whilst holding down the volume up/down buttons plug in
the rPAC to a free usb port.
install the software downloaded above.
done.
Look in device manager and you will see that the
driver is now authored by ARCAM rather than by
Microsoft.
There is also a firmware update included in the
above package that may help with choppy audio
on Win8 (also Linux/OSX) machines
Hope this helps someone.

I couldn't be happier with my purchase. Using it (temporarily) as an amp for my K702s and Hifiman RE-262s and as a DAC for my HT and stereo system, I am very impressed. The amp section, a huge upgrade from the headphone amp in my Pioneer Elite VSX-52, has given the AKG's famed anemic bass a well needed boost (I don't EQ) and has improved my Blu-Ray audio experience as well. Easy to just put it in a bag with my laptop and headphones and go-an incredibly convenient product to use. I would highly recommend this to anyone frequently on the go for a "one stop shop" audio solution. 

Full review here:
http://www.pandatechreview.com/arcam-rpac-review/
http://www.head-fi.org/t/624610/new-arcam-rpac-review
 
 
 
 
Snipet here:
 
Sound Quality:
 
Headphone out:
The sound of the Arcam rPAC as a whole is quite mellow. It doesn’t stand out overly, but nor is it just like flat soda and lifeless. The DAC and amp together gives a soft and not as pronounced but more mixed in low frequency bass hits. It is noticeable however that the rPAC as a whole however does have nice staging that is not visible on many other units which quite surpised me. As a whole the staging although it did have a more pulled back and surround kind of effect was still burdened by it’s amplifier section.  A few other things were that on times when the song would get into a very emotional or violent moment be a quickening and sudden drop of bass and quickening of tempo or massive highs, the rPAC would in a sense quiver delivering an ill sound that can only be described as unmatched. Where the highs wouldn’t exactly go to where  I want and the bass would have a slight muddy upslur instead of a steady and smooth transition. The lower frequency range of the rPAC unit is also not as drastic or as welcoming as I would have liked. The bass was a bit muddy and didn’t exactly punch with not a whole lot of detail to it. Adequate depth of the bass was there though.
 
The rPAC’s sound has good staging but in the end is still burdened by it’s lack of actual depth to the actual contents of the song. The highs weren’t harsh which were good but they were a bit overly sharp in the sense that the high frequency piercings would linger a bit after or had trouble “dropping” and keeping with the rest of the song at times and smoothing out. The highs would also constantly run into the vocals and mids mixing up the upper and center mids and muddying them up or distorting them.
 
DAC Out:
Basically as a whole unit, the rPAC does have a few sonic ills to be noted but can also be forgived, as I will get to later on. The majority of the rPAC’s ills actually stage from the amplifier section of the unit and how it is and on purpose or by design underpowered and also not of much high end. This was confirmed by using DAC out of the rPAC into the reference amp of this price range, the Objective 2 of which mine is a custom one made for high performance desk use with a Burr Brown op amp, RCA in, quarter inch out and various gains and JRC NJM4556. I used the DAC out of the Arcam rPAC into the O2 and also used the DAC out of the Audio Gd NFB 12.1 into the O2 to compare a popular desktop unit the Audio gd to the rPAC.  Both and all units were at around the same price range. 
The results came back were as I expected with most of the ills of the device stemming directly from it’s amplifier stage. The staging that I noticed and liked in the rPAC was still there and even better and more pronounced and clear and detailed and the qualms for the most part were less pronounced was gone. The vocals were warmer and more forward and more detailed. The highs were smoothed out but yet again another problem came and it was that the highs were noticeably more fatiguing now. They were smoothed out by a good amount while still maintaining that sharpness but it did have some fatigue in them when listening now.

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Overall headphone out:
 
Highs:
Sharp but is sonically problematic. The highs are nice and sharp but it gets very jumpy around in that range where it wouldn’t smooth out and go as the song wanted to and would constantly muddy up the vocals and mids. They weren’t harsh but nor were they detailed. I guess you can say it was a bit everywhere in it’s own confined space. They were still highly useable though as they were still sharp and could still pierce through songs.
Mids and vocals:
Prominent with adequate depth and separation. Staging of the separation is also a nice feature and add on. Not as natural as I would like them to be however as they were a bit thin compared to other units.  I would call this section to be a quite normal really. The guitars and vocals and other instruments had a nice and warm sound that wasn’t too warm or metallic. Nothing wrong with them, but nothing exciting with them either. They don’t have an affinity for male or female vocals, of European/American or Asian accents.
 
Lows:
The lows of this song have a good amount of depth and kick. Able to kick with the song without overpowering or being too little. However like any amp. It’s only easy to tell apart if that amp has problems with it’s design or implementation which this one didn’t have so really it’s nothing special past many out there. However what was easy to spot out was the punch of the lows of the unit. Which wasn’t very punchy. A bit muddy actually, more comparable to something for subs than a headphone. They didn’t have the detail or actual “oomph” to go along with many songs as with comparable units.
 
Conclusion:
The rPAC’s headphone out is underpowered by design but does have enough juice for most headphones, although most of the ones that it does have juice is, is below the devices own price range. Driveability is not 100% proportional to price but it is something that does have a relationship with and most won’t have headphones past the price of their amp and DAC at this price point.
The rPAC is underpowered or doesn’t have enough for many reference class headphones at this price because it uses USB for power. Consumer USB ports generally give out 500mA’s of power so the rPAC has to be designed to be in those limits for both the amp, DAC and other lighting and
components on it.
 
The sonic qualities of the rPac are ok for the price. Nothing special besides it’s staging that isn’t very enticing with this section. Some sonic problems however do put a damper on thigns such as a mellow sub detailed low frequency response and extension and a high frequency range that can muddy and lose control easily. Of course these are still better than a $20 device, one should be note all these sayings on the device are price related as I wouldn’t and can’t test and compare the rPAC to a thousand dollar popular device as I could probably call everything out then as can the rPAC to other devices at another price point.

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Overall DAC out:
 
Highs:
 Take 75% of the qualms of the previous section and remove it and add some others and that’s about it. The highs have signifigantly improved, the highs of course are still in their confined area but this time don’t muddy up the mids (for the most part) and is for the most part smoother than before. It is still sharp and piercing with a nice new revitalizing of detail but also a new revitalized fatigue came with it as well. IT’s a lot nicer but also a bit more fatiguing to the ears.
 
Mids and Vocals:
They were largely unchanged but now instead of normal with problems are just normal. They are more pronounced and detailed with a bit more depth. The upper mids that had problems before due to mingling with the uncertain highs are for the most part rectified with this output.
 Seperation and spatial have and are the biggest things anyone will notice. The separation was improved as other sectors before were being muddied up making it hard to even tell what was separate at some parts.  The spatial aspect is also improved and is something you would want for your speakers or even games.
 
Lows:
They are more detailed with a lot more body and punch than before but still falling short of the Dual WM8741 Wolfson Flagships found in the Audio gd. Again the lows in my opinion still hold more for those with subs as they although aren’t punchy, do have more buddy and the “oomph” that you would want with a sub.
 
Conclusion:
DAC fixed line out on the rPAC is signifigantly better than the headphone out. It truly shows off the spatial object placements that the rPAC has. This is not a hear it and it is there aspect as much as it is one that you hear after being tuned to it and comparing. IT is subtle but there and a good add on. I will more or less say that the DAC out encompasses exactly what Arcam wanted, DAC lineing out to speakers with sub units. If the headphone out was like the DAC out with the O2 then this would be a very good device for many.
 

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Overall Conclusion:
The Arcam rPAC is a very interesting unit, it packs Asynchronous USB, headphone out, no external power source, RCA fixed line out, stepped buttons, and good build in all the same unit which is farily compact at such a price. I would not recommend this device as a desktop unit alone for headphone audiophile's as there are many other that do it's job a multitude of times better but for one that can use all it's functions, this may be a good unit for you. It continuously outputs a singal to both RCA line out and headphone out allowing for ease of use and plug and play without affecting sound. It is small with a good build and only requires the USB cable it comes with for power. This unit is somewhat of a home entertainement unit you can bring around everywhere for your or your friends speaker setups. Just plug into your computer and then into your speaker or recievers and boom. Good sound with a good build, wherever you go. A few other devices from FiiO like the E7 and E17 can line out their WM8740's for the same purpose and are even cheaper but I was not able to test them at this time for their DAC out sound.
 
All in all, I would only recommend this device to those that have read this review and know what they are getting and can put this device to good use. I can imagine someone picking this up and taking it to a next location and simply plugging it in. With it's Asynchronous USB features that some tout is better than optical or coaxil S/PDIF with even less jitter. The value of this device for those that can use it is high, but for those that just want an headphone amp and DAC as this headphone forum usually is more inclined towards, it won't score as high there.
 

Being a Brit you might think I would be biased in favor of the Arcam rPAC but I am sad to say this DAC has let me down big time. The overwhelming choice of headphone DACs out there puts the Arcam in a difficult position. Arcam has a good reputation in mainstream HiFi and is obviously trying to carve a niche into the headphone world also, but this attempt falls way short of the competition IMHO.
 
I compared this with a FIIO E17, NuForce uDAC2 and Audioquest Dragonfly.
 
Source headphones for my trial included: Sennheiser HD650, AKG K550, Audio Technica M50 and Westone 4Rs with custom tips.
All music files tested were FLACs and the source computer was a Macbook Air running Fidelia.
 
The real issue regarding the rPAC is the lack of resolution. I would say it has a 'warm' sound and softens the edges of anything played through it. Some people may actually like this effect but for me the warmth actually removes layers of subtlety and finess that so many recordings have. Voices sounded, once again, warm but any subtle voice oscillations were lost and everything ended up sounding rather flat. Instrumental playback also had these traits and blending the two together ended up with a cocktail of two dimensional blandness compared with the DACs mentioned above.
 
I realise my comments may annoy some lovers of this DAC so I will point out the things I liked. The build quality is very high. The unit has a certain weight to it that gives you confidence that the engineers putting this together actually have put some care into its construction. The sound, although lacking in resolution and depth, does have a warmth that many will find pleasant and I am sure prolonged sessions will not fatigue the listener.
 
In summary then, a competent DAC but nothing to write home about and unfortunately does not resolve or have anywhere near the depth of the competition in this price bracket. Sorry Arcam....must do better in todays drenched USB DAC climate!