Pocket Headphone Amplifier

If it’s too loud, you’re too old.

…older me is wishing it wasn’t so loud though.

This is one of the first circuit boards I’ve made back in the winter of 2006/2007. Back in high school I rode the bus to and from school and to drown out the noise on the bus, I needed more audio power.

Originally I was looking at the CMoy pocket amplifier:

OPA2134PA-CMoy-Headphone-Amplifier-Schematic

I had one issue with the design though, two 9V batteries, stuffed into an Altoids tin, took up a lot of space, and left very little room for the actual circuit board. I searched digikey, looking for an amplifier that would allow me to use just a single battery, and provide at least 1/2W per audio channel. After a bit of searching, I found the TDA2822 and just used the typical application circuit in the datasheet:

tda2822

The only modification I had to make was to replace the 10k pull-down resistors on the inputs, with a dual-gang log pot to give me volume control. After that I designed the PCB using Express PCB at the time, and then using a sharpie, I drew the CAD design on to the copper clad and etched the board. And here’s how it turned out:

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