Hi all!
I come from Poland. I'm sorry excuse of engineer (no formal education in this direction whatsoever).
I like to fix and build things, especially audio electronics.
I'm trying to design as small as possible (
http://www.hammondmfg.com/pdf/1455C801.pdf) headphone amplifier, that could be powered from USB and Li-ion cell (specifically 18650).
Similar projects in the past where almost entirely Cmoy (Chu Moy's) deisgn derivatives, powered from the ancient 6F22 (9V). Even the legendary NwAvGuy used them!
There are some really cool production headamps out there (e.g. Fiio A5), but I wan't to flex my design muscles a bit on this one, so I've decided to complicate this task as much as possible.
First, I want to use TI's TPA6120A2 headphone chip. It can take +/-5V to +/-15V voltage.
But the case size constraints (it has to fit on the back of the smartphone) doesn't allow for 2x18650 power source.
Why Li-ion?
Best Ni-MH 6f22 on the market has about 2.5Wh of capacity. Best 18650 is above 12Wh.
Even with average 80% efficiency there will be still ca. 4 times more juice available.
So I have only two options:
1. boost 3.7V to let's say 12V and use rail splitter circuit. I think that it will be less power efficient, but will also take less space.
2. use 2 separate converters to make positive and negative 6V rails.
Which one is better? Or maybe something else entirely?
I'm going to add TP4056 li-ion charger with safety chip, cause there's no protection IC on my 18650's.
Another problem is volume control, because I find potentiometers not elegant enough, expensive, and bulky.
I'd really appreciate your thoughts on the topic.