@B2288 The pictured boards will be used in the prototypes. Granted the prototypes work then, after a few minor tweaks (there are always tweaks regardless of if everything works or not), the first production run for enthusiasts should be no different to units that will ship later.
Please put a revision number somewhere on the device anyway, you never know when you discover a previously invisible hardware bug. 
@Djhg2000 Not really sure what artwork you have in mind exactly, but casting a cover in a different color (basically just different color plastic) would most certainly be less expensive. Also, we cannot use some of the artwork due to potential problems with trademarks -- that linked Ubuntu image being a good example of what we could not do
I only meant for the picture to be illustrative but now that I read my post again I see that I wasn't very clear about that, sorry for the confusion.
Basically I wanted to have some recognizable UI element printed on the back so that you could tell what the phone shipped with. Trademarks/copyright could certainly be an issue for some of those. Then again, a solid color should be recognizable enough to the right people.
@PINE64 I really like the idea of having different colors for different operating systems. Would the different back-plate designs be available separately or to be treated as limited editions exclusive to each batch?
Another idea could be to have solid colors available to all and printed artwork exclusive to each batch. For instance, the first batch could have a solid purple backing with the orange Ubuntu Phone circle (like in this picture: http://refugeeks.com/wp-content/uploads/2013/01/Ubuntu-Phone-Wall.png).
@Photojoe4 Maybe there could be some exposed pads for I2S we could access with pogo-pins through a modified case?
The Allwinner A64 has I2S on either pins PB3-PB7 or pins PB3 + PG10-PG13 according to the datasheet and according to the feature matrix on the SUNXI wiki, I2S should be supported in mainline Linux since 4.17.
Unfortunately the first channel (on the PB pin block) is shared with the SIM card pins if we use the A64 for that. Even worse PB3 (I2S0_MCLK, I2S master clock) is shared with SIM_VPPPP ("SIM Card Power Voltage"). However, the second channel (on the PG pin block) could potentially be of use if we can find another way to solve SIM_VPPPP. I'll leave it up to the PINE64 team to answer that one since this is pretty much all the information I can figure out by myself from the SoC documentation. Maybe we don't even use the built in SIM functionality?
Anyway it looks like the I2S hardware supports up to 192kHz sample rate and 32 bits depth. This is detailed in chapter 2.1.8 in the A64 manual.
The built in DAC+AMP is specified to "100dB SNR@A-weight", which means you're looking at somewhere around 90dB SNR without an A-weighted spectrum. Obviously that doesn't hold true for the whole range of 20Hz-20kHz when using the dB(A) scale, but I'd say the difference between the built in 100dB(A) SNR DAC+AMP and a high end external 120dB SNR DAC+AMP is immeasurable when you're anywhere but in a professional studio or measuring the theoretical response on an oscilloscope.
Unfortunately when I skimmed through the manual I couldn't find anything about the rated power or design impedance, but unless you had some really high impedance headphones to take out with you I'd say the built in audio path is sufficient for high quality playback. You might be glad to hear the A64 does support true line level outputs on C16/D16 in addition to the amplified headphone output on C13/C12 but I don't know if we'll get those routed on the board. Users would probably confuse the line out connector for an extra headphone connector so I would probably use a different connector for the line out anyway.
This is all very much overkill considering (1) the priority right now is to get the first phone out of the door and (2) the built in DAC+AMP combo is way better than it needs to be for outdoor use. Maybe we could have line out and/or a nicer amplifier on PinePhone 2? To be honest I'd be more interested in the former if you want to use a high quality external amplifier, just cut the internal amplifier out of the signal path entirely and use a 1:1 isolation transformer to get differential outputs.
This got a lot longer than I anticipated when I started writing an "I'll just copy some stuff from the datasheet" post but I hope I helped answer at least some of your concerns.
Edit: The dB/dB(A) comments are for the SNR but I had omitted those three very important letters
@vandys I mean a removable battery as in a battery you can remove without tools.
The Librem 5 as I understand it will have the battery on a cable connected to the mainboard and you'll need to disassemble the phone to replace it. Which to be fair means that it will indeed be user replaceable, but it also makes it really inconvenient to use as a method to implement the ultimate kill switch (physically separating the phone with it's battery). When I write an exam I don't want to risk it going off because the power button got jammed against something in my backpack.
It also makes it impractical to swap batteries during the day if I need to. Most people argue that you can just bring a charger or a power bank with you, but if you had the option, would you honestly prefer that over just swapping out the battery with a spare that fits your pocket? No need to find a wall outlet and no need to waste some of the energy you bring with you on lossy DC/DC converters. It's probably the most efficient way to carry additional energy with you and most of the phone industry has totally forgotten about it.
Seriously, how did it become acceptable to fumble around with a cable that takes your only I/O port and a brick larger than your phone just to cope with an unusually long day?
After following this thread for a while I must say I'm very interested in the PinePhone. Not having a removable battery is a dealbreaker for me so the Librem 5, despite how good it looks, is not an option. I also like how the plan it to reuse an existing battery.
I'm also very pleased to see that the anti-feature of a fingerprint sensor has been omitted. If it is on the table for a PinePhone 2 I'd like to request the ability to physically remove it from the device (and possibly cover up the hole with a supplied piece of plastic).
I have one quick question though; will it be possible to disconnect (and maybe even remove) the front camera? I don't consider it an essential feature to do so, but for me that camera is just dead weight.
Thank you so much for developing this phone!
