Here I've laid out my Android USB paraphernalia. The three on the left are all OTG connectors that would allow your Android to host and power an external digital audio converter or DAC. The two on the right are digital audio converters I got from HiFiMe. The conventional audiophile wisdom that I grew up with said that the turntable stylus cartridge and speakers were the two most critical pieces of equipment in an audio system. The DAC is the modern equivalent of the cartridge on a turntable as it has a equally dramatic effect on the sound of an audio system. The two DACs I've used from HiFiMe are the best I've ever heard. A simple A/B comparison with the headphone jack of my Fire tablet is night and day.
The Fire 7" (2015) Android tablet is a complete surprise. I bought it on a whim when Amazon had it on sale for $35. I never expected to use it for audio. Not only does it work with OTG and an external DAC, it will also take a 128Gb micro SD card. Mine had a sporadic problem recognizing the micro SD card until I bought the SD card Amazon recommends for the Fire tablet, but I can't complain at the price. With one of the HiFiMe DACs it sounds fantastic. It's coherent, vibrant and punchy. The sound is definitely better than any combination of iOS devices and DACs I've used previously.
The two HiFiMe DACs I have are the $30 Sabre Android DAC based on the Sabre ES9023 dac chip and the $70 Sabre 9018 USB DAC based on the Sabre ES9018k2m DAC chip. Both are outstanding, but I can't tell them apart. The specs suggested the 9018 would be a bit louder, a good thing when your amp has 3 watts per channel like my APPJ, and at first I thought it was. Honestly though, my ears can't tell the difference between the two on my system. The cheaper Android DAC has the convenience of a micro USB connector that will connect directly to your Android device without an OTG connector.
You might want to get a OTG connector anyway. I got a fancy one that has one micro USB for power in and three standard female USB ports that can host a DAC. The nice thing about the fancy connector is the Charge/OTG switch. Because of the USB spec, a host device cannot be charged. In the Charge position, the switch allows you to charge your Android device when it is not playing music. In the OTG position, power is provided to the DAC reducing drain on the tablet's battery.