# GUIDE: Standard USB DAC and Nexus 7



## deltaechoe

So you just bought a Nexus 7, congratulations, you actually got a device that will make your ears happy. There is one caveat though, you do need to do a bit of work to get it working, but fear not, here is a step by step virutally foolproof guide to bypass the less than stellar built in DAC on the Nexus 7!

(*WARNING*: This guide does involve unlocking your device which can, though extremely unlikely especially if you follow the guide, lead to unexpected damage to the device, neither the developers of the software that I reference here nor I take any responsibility to any damages caused to your device.)

*Things you will need:*

1. A Nexus 7, obviously (https://play.google....?id=nexus_7_8gb)
2. A PC or laptop that runs windows 7 (just for the unlocking part, there are plenty of other guides on how to unlock for other OS's)
3. An OTG cable (ex. http://www.amazon.co...words=OTG cable)
4. A standard plug and play USB dac (preferably one that can run on battery power otherwise you get into problems with power management)
5. Nexus 7 Toolkit: http://forum.xda-dev...d.php?t=1766475
6. Poitee kernel: http://rootzwiki.com...-cpu-oc-072912/

*Step 1: Prep tablet for use with the toolkit*
 Swipe down from the top of the screen to open the notification area.
 Tap the settings icon next to the time and date.
 Scroll down to the Developer options area and tap it.
 Slide the switch to turn on Developer options.
 Check the box that says USB debugging
 Hit the back button to return to the previous screen
 Tap the "About tablet" option.
 Make a note of the Build number - the last item on this screen.

Another word about this step, if you have been using your tablet and it is still stock, make sure you backup all the files you have on it onto your computer as unlocking the tablet will erase absolutely all user data, including the /sdcard/.

*Step 2: Install the nexus toolkit to help unlock your tablet (windows 7 only, if you have a different os google a guide for that os and then skip to step 3)*
 Install the Nexus toolkit that you downloaded (posted in the things you will need section)
 When you start up the toolkit it will ask what model type you are using, scroll down to the nexus 7 portion and select the build that you have
Start it up, and under the initial setup click on the Full Driver Installation, this will walk your through how to install the drivers to unlock the device
(YOUR DEVICE SHOULD BE ATTACHED TO THE COMPUTER BY THIS POINT)
If you haven't done so, take a backup of the device by clicking on the backup button
Click on the Unlock button to unlock your device
Under the root button, tick the Custom Recovery box and then click on root and follow the script

*Step 3: Flash the poitee kernel*
Download the kernel that is posted above in the things you will need section of this guide
Boot up the Nexus 7 and go through the initial setup again
Put the poitee kernel onto the /sdcard/ of the nexus 7
Power down the tablet completely
Power on the tablet by holding the power button and down on the volume rocker, you should be in fastboot mode
Use the volume rocker to select recovery mode and hit the power button to select
 At this point it would be a good idea to take a backup of your current state in your recovery's backup and restore menu
If you are using CWM recovery, select wipe cache. Once that is done click on install zip from sdcard and look for the poitee kernel that you downloaded, select it and follow through with the flashing
If you are using TWRP recovery (which I personally prefer), touch the wipe tab and then touch Cache under the wipe menu, once that is done go back to the home menu and touch the install tab and look for the poitee kernel and select it, follow the prompts to install
You have now flashed the kernel

*Step 4: Final steps (the easy part)*
 Reboot back into the system, hopefully everything has gone ok and you now have poitee kernel installed, if you run into problems then reboot back into recovery and restore the backup that you took in step 3, then repeat part 8 or 9 depending on which recovery you have installed.
 If everything went smooth, then power down the tablet and attach the OTG cable to it, then attach your DAC to the other side of the OTG cable
 When you power on your tablet, the sound should be routed through the USB DAC instead of the built in one as long as you don't disconnect the DAC
 Enjoy much higher quality sound from your new tablet XD

NOTE: If you do disconnect the DAC at any point, you will have to reboot the tablet with it attached. Also to route sound out of the tablet, you always have to boot it up with the DAC attached otherwise it won't switch. Also if you are using the E17, make sure you turn the USB charge feature off so it only uses the battery, it seems to draw too much current for the tablet to handle and doesn't work well when relying on the tablet's power.


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## mike216

Awesome bud! Can try my fiio E17 finally! Where the hell is everyone! I certainly appreciate it

Sent from my SGH-T999 using RootzWiki


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## deltaechoe

E17 indeed works: http://puu.sh/159dC (this is my setup)

But any low power (or self powered) standard plug and play usb dacs should work


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## Sengir

Thanks for the tip! nice tutorial. Doesn't anybody know how to keep the tablet charging while using the usb port for DAC? Through pogo pins would be awesome but I can't figure out how to do this because simply providing +5v and GND doesn't work


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## papatel

Sengir, currently charging + USB OTG is not possible with the nexus 7. I worked around this by hardwiring the power input to the nexus to a 5V supply and removing the lithium battery.

Nice write up. Deltaechoe, do you get sound input from your microphone when you have the USB DAC enabled? I'm using a trinity kernel and and a FiiO E10 DAC with an unmodified asound.conf and I get no MIC input. In fact, any application that uses audio input behaves oddly and doesn't work. I've tried playing with asound.conf but no luck









Sounds like a stupid requirement, but I Really want voice search and VOIP calling to work from my tablet when I'm using the USB DAC...


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## Sengir

Nice idea but I assume your nexus is in a permanent install..I still need portability so I have to figure out how to do this,mainly for car use


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## papatel

Someone eventually will get Nexus 7 USB OTG + charging working. It will require some kernel driver changes so that we can force the battery charging hardware to charge at all times, regardless of USB host mode state.

Anyone have ideas/suggestions on the USB DAC + internal microphone problem?


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## Agent_Cooper

My headroom headphone amp seemed to be powered by the nexus 7...or did I miss something?

Sent from my Nexus 7 using Tapatalk 2


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## deltaechoe

It can power stuff, but I don't know the size of the current that flows


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## PaulF

Hmmm, I've tried this with two USB sound cards and booting with them attached results in no sound, but booting with them detached results in the sound coming from the tablet's speakers.

I have verified that the kernel is in-fact, correct, and that the devices properly appear in /proc/asound/cards
I have attempted to modify /etc/asound.conf, but it appears that android ignores this.

Any possible tips for what to try next?


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## Tad

papatel said:


> Sengir, currently charging + USB OTG is not possible with the nexus 7. I worked around this by hardwiring the power input to the nexus to a 5V supply and removing the lithium battery.
> 
> <SNIP>


I don't mean to sidetrack this thread, but can you confirm that the Nexus 7 boots and operates like normal when connected directly to 5V at the USB port (or POGO pins), without the battery connected? I have been looking for this information for the past week or so and have not been able to confirm one way or the other.

If so, this is good news for people who want to use the Nexus 7 in a permanent installation (e.g., in wall), but want to remove the battery to mitigate heat/fire concerns. (I, for one, am not thrilled with the idea of mounting a perpetually charging/discharging lithium ion battery to the wall).


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## Flav106

It works flawlessly thanks !!
To my knowledge, this is the only one kernel which make usb audio work on JB (Galaxy S3 apart).
Do you think it would be possible to make it work on the GNex ?


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## exzacklyright

So what's the point of ddoing this? Wwhy do people need usb?

Sent from my Nexus 7


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## Flav106

If USB Audio is enabled, we will be able to use audio DAC directly connected to USB and bypass the crappy DAC of our phones.
This is for a better sound quality.


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## Sengir

Yes, it's about improving audio quality... Does anybody know if is possible to have the external DAC working without rebooting?


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## robtrevino

I'm surprised this is not getting more attention. I have been looking for this for the past year! Thanks!


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