[Nexus 7 (2013) Q&A] NoD~:
I have a strange issue after installed my Nexus 7 as a car stereo setup in my Subaru (see setup blow)... Whenever I turn up the volume, specifically the subwoofer, the USB system basically "resets" itself. As if, I unplugged and plugged it back in very quickly. At first, I thought my USB DAC was bad, because I plugged my audio feed directly into the tablet with no USB devices connected and all worked fine, but if I have my hub plugged in and then the reset happens (with audio from tablet still), the reset still happens and my OBD2 adapter (USB) brings up torque. I plugged that same USB DAC directly in, with no hub, to my OTG cable and used its audio feed, same issue. I thought maybe the voltage drop was too harsh and causing issues with my charger, so I ran a 120v usb charger setup (like a factory phone one) with an extension cord to my vehicle to isolate its own charge system to the tablet with the same results. OK, Maybe it is just vibration? (forgot to note: subwoofer is freeair, laying in the back seat... still testing, box isn't done yet, so the vibration level is next to nothing currently.) I grabbed my usb cable system with the volume low and shook the life out of it... never did the reset. Again, only when the subwoofer volume goes up and anything is plugged into the USB port on the OTG for external devices does this ever happen.

The Setup:

I have a dedicated 4A 12v-5v charger and it seems to charge the tablet fine. I have a 90 degree charge adapter in place. I also have an OTG Cable so I can hook up USB to my dedicated USB hub that I have a "backup" power cable plugged in (into the same 5v charger the tablet is).

Audio chain wise, I have plugged into my USB hub a USB DAC. After that, a noise blocker. From there, I wired in a potentiometer for volume control. From there, it goes to the 4 channel amp and the mono subwoofer amp (which also has a dedicated volume controller that came with the amp)

Power wise, I have a dedicated run of "oversized 4awg" (basically, 6 awg wire) from under the hood and no more than 5' of cable to a fused distribution block, then to the amps. I also have a ground wire of the same size that from come the battery ground that all amps connect to (as well as chassis, so about an overkill of a grounding system). The factory wiring harness was spliced into for connection to a relay that feed from the constant on factory wire, feeding the 5v usb charger and the remote turn on trigger for the 2 amps (so it shouldn't be overloaded at all).

Items (can't give links, so giving exact item name):

4A 12v-5v charger(Amazon - Icstation LM2596 DC to DC Voltage Regulator Dual USB Charger Step Down Power Supply Buck Converter 6-40V to 5V 3A DC 5.5X2.1mm Port )

90 Degree USB adapter(Amazon - Micro USB Extension Cable - Riipoo Left Angle Micro B USB Extension Cable, 25 CM, Micro USB 5 Pin Male to Female, Sync Charging and Data Transferring Cable for Samsung, HTC, Huawei, Sony and More)

OTG Cable (Amazon - DSYJ Micro USB Host OTG Cable with Micro USB Power for Samsung S7 S7 Edge, S6 S6+ S6 Edge, S5, S4 & Nexus 10 9 7 4 Player + ALL OTHERS )

USB Hub (Amazon - UNITEK Portable USB 3.0 4-Port Ultra Slim Data hub, with Micro USB 2.0 Power port and Built-in USB 3.0 Cable LED for iMac, MacBook, MacBook Pro, MacBook Air, Mac Mini, Chrombook, Surface Pro )

USB Dac (Amazon - Fiio K1 Portable Headphone Amplifier&DAC and USB DAC, Titanium)

Noise Blocker (Amazon - Mpow Ground Loop Noise Isolator for Car Audio / Home Stereo System with 3.5mm Audio Cable (Black))

Potentiometer: (Amazon - 10K Audio Taper Stereo Potentiometer 1/4 Shaft)

4 Channel Amp: (Amazon - Audiopipe 4 Channel Micro Amplifier 1000 Watts)

Subwoofer Amp: (Amazon - Audiopipe Class D Micro Amplifier 500 Watts)

I'm pretty stumped at this point. Any ideas?