Open Pandora


Headphoneus Supremus
Pros: Great resolution, can power most headphones, compatible with any USB DAC, up to 256 GB of storage, solid construction
Cons: Slightly bulky, computer experience required, questionable appearance, USB DACs can be a little finicky, simplistic construction
What's this? Why is there a PocketPC in the product list of a headphone forum? 
Some of you might've heard of the Open Pandora, the mutant child of a PocketPC and a gaming handheld, designed by a small group of people for retro gaming. It also serves as a fully functional Linux-based computer and is completely open, allowing the end user to do anything and everything they want to do with the unit.
So why is this on Head-Fi? As it turns out, the person who designed the Pandora's motherboard is an audiophile, and he put in a powerful dedicated audio section. This review is dedicated to reviewing this unit's performance as a DAP. 
[center] ////////////////////// //--Build Quality:--// //////////////////////[/center]
I figured I'd address this first as it is the only part of the handheld which I am not 100% satisfied with. 
As far as durability goes I have absolutely no worries about the handheld. The plastic is strong and rigid and the handheld feels rock solid, not rickety or weak anywhere, I can tell it will last me a long time.
However, there are some issues that I have with it cosmetically. The silver paint isn't well-coated. It chips very easily and blemishes in it are very obvious. The edges of the plastic are very, very noticable and gives it a look like it's about ready to fall apart. There are then the little things about it, like no labels on the switches and slots, no rubber stoppers in the screw holes, and other nit-picky things like that. My battery cover is a bit warped as well but as far as I'm aware other units aren't like this; mine probably happened during shipping or something, and it causes absolutely no problems.
Keep in mind this is all <entirely> cosmetic; the handheld has a good weight to it and the plastic is strong. The keys and buttons feel great and everything is solid and well-tuned. It feels and operates like a $500 handheld, it just doesn't look like one. Considering all of the issues that occurred during the production of this unit, I am very surprised and impressed that the handheld is what it is. That being said, if I could change one thing about the handheld, it'd be the case. It wouldn't look bad at all if it weren't for the silver paint. The old matte black case looks quite nice.
[center] ///////////////// //--Usability--// /////////////////[/center]
This is a mixed bag. As far as actually using it s a portable player, I've had no troubles. The shoulder buttons skip tracks and there's a hold switch to prevent accidental input. The suspend switch will stop the music if you need to. The volume dial is recessed so it won't get moved by accident when it's in your pocket. That's more control than an iPod Touch has without having to unlock it. It's not uncomfortable to have in a jeans pocket, but you still feel it in your pocket and it's not exactly easy to reach the buttons. I personally recommend a jacket pocket or something. I keep mine in the little hidden pocket on the inside of my jacket where it's easy to access.
Now, this handheld runs Linux, and while it wasn't too difficult for me to get used to, there were some hiccups along the way to get it 100% functional. This is not a 3DS, it's not an  iPhone, and it's not a laptop. It is not fully functional out-of-the-box. You have to buy your own SD cards, install a web browser, install a media player, and everything else you want for it manually. I personally prefer this over having lots of things installed on first boot, 90% of which I never use, but I'm not most people. You <absolutely must> be at least somewhat capable of using a computer to use this device. A lot of things that are normally done for you in Android or even Windows have to be done manually in Linux. That being said, the SuperZaxxon that the Pandora runs is significantly smoother than any Android phone I've ever used, including those with more RAM and faster processors. Operating systems like Android, iOS and Windows are built around ease of use while sacrificing performance and some functionality. The Pandora's OS is the opposite, and therefore superior in my opinion, but it most certainly is not for everyone, and I don't blame you if you'd rather use Android on it. Getting Android working is as simple as copying a single file to an SD card and running it. Check the Pandora Boards for more detailed information.
One of the main reasons for buying the Pandora as a portable player is that it can use any USB-based DAC using the USB HOST port. While this statement is not untrue, it was not very easy to figure out. I won't go into the technical details here, but you basically need to plug it in through a USB hub and select it as the audio output device and mixer device within the music player's settings. Simple enough to get it working, except not all players support this as developers aren't expecting people to be using external soundcards with the Pandora, and thus leave that part out of the code. Some players don't even allow you to choose your output device, sometimes the device doesn't show up on the output list, sometimes it does but no sound (or static) will come out. I have a list at the bottom of the review of players that I have tested and confirmed to work as well as detailed instructions on how to get it working for each.
[center] ///////////////////// //--Sound Quality--// /////////////////////[/center]
Alright, now for the big one, and most important.
Most consumer electronics such as an iPod Touch or a Nintendo 3DS use an all-in-one DAC/amp chip to handle audio. As mentioned before, the Pandora actually has a dedicated audio section on the motherboard that's completely seperate from the rest of the system. It implements the Burr-Brown PCM1773 DAC and the Texas Instruments TPA6110A opamp. It runs on its own isolated power supply and even has a proper line out via the EXT connector on the back of the unit if you want to use your own amp with it.
The amp is clean, powerful, and doesn't color the sound. It does exactly what it's supposed to. A plus about the Pandora is that the output stage of it is purely analog, none of that digital crap you see in many players nowadays. The output of the amp goes directly to the volume dial, then to the headphone jack. It's better for both audio quality and usability in my opinion; I've always prefered an analog volume control. The little volume dial has a smooth but tight movement which prevents it from being adjusted on accident. This is good, because most portable cans would harm you at max volume on this device. I have never noticed any sort of clipping even at max output into ridculously hard-to-drive headphones (Pioneer SE-500 and SE-700). 
--In comparison to iPhone 3G, my oldest player (CS42L61):
Wow, what was I listening to back then? The Pandora has so much more detail and texture, the sound of the iPhone is dark, muffled, and sloppy in comparison. There's also a tinge of THD around the whole sound spectrum, but it's especially bad in the upper register, possibly what made my M50s treble sound harsh many years ago. It's also very noisy and unrefined; lots of congestion with even moderately fast music. The Pandora has a lot more amping power and supports far more formats than the iPhone, and the battery life is unmatched. I've had times where I'd charge my iPhone before bed, and wake up in the morning with a dead battery. I can leave the Pandora on all night and wake up with half a battery left, which will last me the rest of the day with no recharging. Absolutely no contest.
--In comparison to FiiO E7 in DAC mode (WM8740 & TPA6130A):
Yuck, what's going on here FiiO? Even though the opamp chips of the two units are almost identical, the E7 has a terrible haze in the midrange and a dark, muffled sound signature. Extension in either direction is lacking, and there's a lot of noise throughout the spectrum. It's very congested and sloppy. While better than my laptop, the DAC portion of the E7 is barely decent, and it pales in comparison to any of the devices mentioned further on in this review. I suppose you get what you pay for, but at the same time the E7 is <only> a DAC, it can't play music on its own, and I'd expect at least a little bit better performance than what it provides. 
--In comparison to Sony Playstation Vita (Wolfson WM8781G):
The WM8781G is an all-in-one sound chip (DAC and amp). Both the Pandora and the Vita have a very clean sound, but the Pandora is much more detailed and actually has enough power to handle most headphones. I'm hard pressed to find a headphone that the Vita can drive to its full potential, as the amp section is exceptionally weak. The Pandora has much better low exension; the Vita seems slightly hollow and bright in comparison. The Pandora is also a good deal smaller than the Vita, and doesn't have two analog sticks jutting out of the face to get caught on things in a pocket. The Vita also only supports a handful of files; ALAC, FLAC, and AAC would not work. It only accepted WAV and MP3 out of the formats I tried. One thing I can say on the positive side is that the Vita's UI is better for portable use than say Audacious or DeaDBeeF, but since the Pandora has Rockbox as well this isn't very important.
--In comparison to the AudioQuest Dragonfly (ES9023):
At first I thought the Dragonfly was superior to the Pandora. I had only used lossless music with the Pandora, and didn't really hear how revealing it was, whereas the Dragonfly was immediately exposed to lower bitrate files was well as lossless. When I actually compared the two side-by-side, I was absolutely stunned by what I heard. The Dragonfly has more output power, but the perks stop there. The Pandora absolutely smokes the Dragonfly in every other area. The Pandora has greater resolution and clarity; the Dragonfly sounds smoothed over in comparison. Both are clean, controlled and expansive, but the Pandora has a lot more detail and texture. Using my Sony MDR-SA3000 with the Pandora is a truly unbelievable experience. The Dragonfly seems to have a tad more warmth to it than the Pandora, and slightly less content in the high section. The Dragonfly seems to be slightly more expansive, but also a tad distant at times. Considering the fact that the Dragonfly is so small, it's very good. However, function comes before form in my book, and I'd expect better performance at this price point.
Sennheiser HD600:
--Lush, natural, and expansive. Smooth yet incredibly detailed. The Pandora handles this headphone exceptionally well. It can drive them to nearly deafening levels of volume. Even more detail than the SA3000 (though not as much of a focus). I'm hearing completely new parts in my music. 
Grado RS2i:
--Extremely fast and revealing, very heavily colored. Harsh and headache-inducing out of sub-par equipment (such as my laptop), but very enjoyable out of the Pandora. Sound is full yet light, very engaging and aggressive. 
Sony MDR-SA3000:
--Fast and easily driven, dry and very detailed. Fairly neutral, primary test headphone used. Using these with the Pandora is an unreal experience, the sheer amount of detail is incredible. The Dragonfly makes them sound slightly smoothed over with slightly slower decay. 
Beyerdynamic DT1350:
--Good lord these headphones are ruthless. The Pandora reveals their true face, which is extremely analytical with instantaneous decay that reveals every nuance and imperfection in the music. The Dragonfly shows part of this character, but doesn't quite get them all the way there. On other players they sound euphonic and warm, likely due to bad DAC sections.
--An old beast from 1976, they are very difficult to drive at 250 ohms and 90 dB/mW SPL. The Pandora handles them very well, maintaining their extremely expansive sound and their immense presence. The Dragonfly can get them louder, but there's no need for that much volume, and it sounds slightly worse.
Monoprice 8320 (stock tips, no mods):
--On the Pandora, these are warm with a nice little soundstage and a wonderfully pleasant tonal balance. On other players, they're slightly cold and are a little bit rougher. The difference is night and day. One thing to note is there is a slight hiss on these when you're around sources of interference, such as a WiFi hotspot. Not too big of a concern, and inaudible with headphones.
Pioneer SE-700:
--Infinite impedance and very low sensitivity, used to test raw amping power. The Pandora does an O.K. job with this headphone, not very good, but not also not the worst I've heard them sound; it is however fairly quiet. The Dragonfly has enough power to get them to a more listenable volume, and they sound better, though it clips a bit at max volume. Considering these headphones were designed for speaker taps, this is impressive on the Dragonfly's part.
AKG K240 Studio:
--I don't really like these headphones, but they actually sound quite good out of the Pandora. Other players didn't seem quite able to handle these cans. They appear to be very DAC-dependant, much like the DT1350. 
Audio-Technica ATH-M50:
--For fun, I got out my M50s. I haven't used these in ages. While I can't say I particularly like the headphones anymore, I can say they sound considerably better out of the Pandora than they ever did out of my iPhone or my E7. 

Album: The Mechanical Rennaisance
Artist: Psyborg Corp.
Genre: Harsh EBM
Lots of impactful rhythms and aggressive, detailed synths. Lots of high-end content and very unique vocals with heavy distortion applied to them. 
Album: Nostril
Artist: Igorrr
Genre: idfk
A very unique combination of many, many different genres that's impossible to describe. Extremely aggressive and chaotic with lots of (purposeful) recording artifacts (static, hiss, clipping, pops, etc etc).
Album: Ethernaut
Artist: The Cruxshadows
Genre: Darkwave
Incredibly well-done recording job and beautiful, poetic lyricism. Lots of rock-bottom low end content and a tactile feeling to every instrument. Beautifully textured synth instruments and good vocals. 
Album: Come Read the Words Forbidden
Artist: Morton
Genre: Melodic Metal
A great album from a new band. Very solid recording job. Guitars sound rough and strong without distortion or noise, just the pure crunch and bite guitars are known for. 
Album: Rolling Thunder
Artist: Dan Gibson
Genre: Ambient
Beautiful ambient music set to the sound of binaurally recorded rain. Very soothing and expansive. 
Other music:
Rocket Knight Adventures OST (SEGA Genesis/Megadrive):
Played directly from the sound test screen using PicoDrive. WOW this game's soundtrack is amazing. The Genesis uses Frequency Modulation to make its music, which means extremely good things for emulation. The synths are rendered directly to the DAC of the Pandora. The sheer texture in all the synths is incredible and the Pandora renders it all very well. This is leagues better than the console was ever capable of sounding.
Gunstar Heroes OST (SEGA Genesis/MegaDrive)
Played in the same manner as the above. Ahh the sweet memories. Most of the soundtrack is average, but a few of the songs are exceptionally good, and they all sound flawless on the Pandora.
Dr. Wily Stage 1 (Megaman 2 (1986), Nintendo Entertainment System)
Gotta love that NES music. Dumped to PCM directly from an emulator on my computer and played back on the Pandora. The raw square and triangle waveforms offer a very good method to test the resolution of the handheld.


[center] /////////////////// //--Final Notes--// ///////////////////[/center]
There are 3 different editions of the Pandora. The Classic, the Rebirth, and the 1GHz. There are no differences in the audio section of the units, only in the amount of RAM and the CPU. 
The best player that I've found so far has to be DeaDBeeF. It's strikingly similar to Foobar2000 for Windows. It can even import EQ presets from Foobar. It has extremely low CPU draw and supports a large number of different formats, and is the player I used to do most of the testing. 
Some players require custom button mapping to use the shoulder buttons for skipping tracks. DeaDBeeF is one of these. Rockbox, however, is configured this way by default. 
If you want to use a dedicated amp, you'll need to request a cable from one of the members of the community. Numerous members make and sell TV-Out cables on a daily basis, and a line out is even easier. If you are DIY-oriented, you can make your own using the EXT connectors availible on the DragonBox shop. EDIT: Pre-assembled TV-Out cables are now available from the DragonBox shop.
USB devices that get their power from the USB port will drain the Pandora's battery faster than usual. The Dragonfly is a major offender in this case because of the massive power draw from the opamp. Portable DACs that have their own dedicated power supply (such as the E7) will not drain the battery as much. Using the USB-OTG port for these devices is reccomended, as it will drain even less power, but it will not work for devices that need a certain amount of power from the port (the Dragonfly is one of these devices).
I am working with the OpenPandora team on being able to set a USB device as the primary sound device, which would enable seamless compatibility with any player or emulator. I'll report back here with any future progress.
Players that have been confirmed to support external DACs (Tested using AQ Dragonfly and FiiO E7):
(Set output plugin to OSS in settings, set bit depth to 16, click "Preferences", select "USB Audio" and "USB Mixer")
(Not really a player, but go to Edit -> Preferences, set the output host to ALSA, and select USB audio and it will output to the DAC.)
There are too many players to test them all, and it's likely that there are others that will work. I'll post any more I find here.
Known quirks/problems with external DACs:
--Selecting a bit depth above 16-bit causes static to be outputted, likely due to the Dragonfly using asynchronous USB, might be fixable
--If the device is disconnected during playback the USB stack crashes, requiring a reboot. Stop the music first and disable USB host from the taskbar.
--Volume control is limited to software as the Dragonfly doesn't have its own volume control, won't be a problem with an E17 or a DAC/amp stack
[center] /////////////// //--Verdict--// ///////////////[/center]
Overall, I am very pleased with how the Pandora performs. It's a very engaging and unrestricted sound that is well extended in both directions, with extremely low noise and THD throughout the spectrum. It has a tightly controlled sound and is never sloppy, muddy, or boomy in any areas, and it has a lot more detail than any consumer-grade product I've touched, whether it was designed for music or not. It can handle a wide range of different formats and has phenomenal battery life, while still being able to power most headphones with ease. It handles aggressive music and instruments very well, especially guitar and other string instruments like it. 
The Pandora does exactly what it should do: Output clean, high quality sound without coloration or degradation. It's a wonderful device that does a lot of things very well, and I will continue using it for a very long time.
Is it worth $500? Definitely, but only if you will be using it to it's full potential. I would never recommend this product to someone who would only be using it as a portable DAP. It sounds good, its features are impressive, but it's not a device that's designed to do one task. It does anything and everything you want it to do, and it's a waste of money to use it for just one thing. If you're a person who likes retro gaming, audio, and customizing your system exactly how you want it, then this device is an absolute dream come true for you. I have never adored a unit as much as I adore this one.
I own this (1Ghz edition). I've never pushed the portable thing beyond good mid-fi, latest DAP I used were Cowon J3 & X9. The Pandora wipes the floor with them both -and Cowon are rather good. But they can't compare. The separation and detail level are far superior on the Pandora, bass is deeper AND better as well as treble extension, and the amp is _very_ powerful. Playing music through Rockbox on this is pure bliss. Highly recommended. I'm very curious how it would compare to the big boys -iBasso, Hisounds etc.
I echo your thoughts on the Pandora.
I just tried running a Genesis emulator on my phone (Note II) and my desktop, using them to play the RKA soundtrack, and was severely unimpressed. The Pandora just has so much more resolution. Its kind of incredible.
...great review, thanks!