This is a project I created to make a portable headphone amplifier using a lithium ion battery for charging it. It uses a TLV2462 op-amp, and like my other amplifiers, it is based on a rail-splitter, in this case the TLE2426 rail splitter.
It also incorporates a current buffer, the BUF634, like my second desktop amp project. This helps drive larger headphones if need be, although the amp is designed for earphones or In-Ear Monitors.
I used an adafruit lithium charging board to handle the power supply, which can be found here. It has some pins which allow for monitoring the status, which I make use of for status LEDs.
The interesting aspect of this project is that since the battery is 3.7v, I needed an amp that could work on such a low voltage (normally you would want much more headroom). The TLV2462 is designed perfectly for this purpose since it can operate on a minimum of +/- 1.35v (so 2.7v in total) and up to +/- 3v (or 6v in total). So it works perfectly with a lithium ion battery! I have not had any issues with low battery life while using it portably since I put a 6600mAh battery in it.
I also added copper tape around the edges (which is grounded) in order to add a bit of shielding to protect against interference.
In the future I may modify it by adding a low-dropout voltage regulator (LDO), in order to allow it to perform better while running off a wall-charger.