This doesn’t have much to do with Trumpets, but I wanted to post this headphone amplifier I built.
I’m not using it in a very demanding application (it’s for watching TV with headphones), but it works really well, it’s totally superior to the FIIO E6 I was using, more gain and less noise.
It’s based on a TI TPA6021A4N, which has some nice features: digital volume control, a shutdown mode which prevents pops at startup and shutdown, and most importantly for hobbyists, it’s available in a through hole 20 pin DIP.
Someone has already done a layout for this:
http://www.paulinthelab.com/2014/04/tpa6021a4-2-watt-stereo-amplifier.html
It’s pretty much the circuit from the datasheet, with some tweaks:
– Bigger input coupling caps ( 1uf vs. .47)
– Smaller output coupling caps (220uf vs 330 uf). I changed these to 470 uf to get less low end roll-off with lower impedance headphones.
I did find that I couldn’t fit the caps connected to pins 4-8 next to each other so I had to tweak things slightly.
As far as capacitor selection, I used poly film for all the 1 uf caps, ceramic for the .47 bypass caps, and aluminum electrolytics. Things might have fit better using a ceramic for the bypass cap on pin 6 and it probably wouldn’t have impacted anything to use ceramic caps for the unused differential inputs on pins 5 and 7. You definitely don’t want to use a ceramic cap in the audio path.
One interesting note, one of the several construction mistakes I made was I missed a cut so the amplifier was operating in bridge mode. It was very unhappy!
Here’s the amplifier in an enclosure, I went a little overboard and got a fancy extruded aluminum enclosure. I used this technique for the labels:
http://www.instructables.com/id/An-easy-way-to-create-professional-looking-labeled/
Mine came out a little faint, probably due to lack of patience on my part, but I still like it better than a dymo label.
