Monday, January 11, 2016

Hi-Fi Headphone Amp

Long after the Headphone Bass Booster I did another amp!

This time, the reason for this project was the stupid powerless soundcard built in laptops. You can fry your ears with treble but when it comes to bass it's worthless and annoying. I looked for some second hand headphone amps without luck and I disliked the price of brand new ones. There are lots of speaker amps second hand with headphone output, not very expensive, but I didn't have room for those big ones. Eventually, I decided to make one myself with reused parts, for free.

As usual, this isn't intended to be a tutorial, but I'll post some pictures to show you.

After the design and test stage it was time to put everything on a PCB.

The project is based on a Philips TDA1521 from an old TV. This IC is a Hi-Fi 12W amp with plenty of power for the purpose. I read good opinions about those TDAs, and they're easier and better than op amps. It was required a good power source however, which was the biggest problem to solve. Fortunately, a relative donated to me a laptop adapter (switching PSU, 19V, 4A), with more than enough power.

I knew I had room in the case, so I included a ferrite bead in the input to help with the high frequency noises that can come from bad filtered PSUs and reach the audio stage in laptops.

I'm no master at crafting I know, so the case parts fitted poorly (you'll see later). I didn't have many power tools either, so it was awful and tedious to fabricate. Actually, the aluminium cover (from an old VHS player) took 478965423667 hours to complete.

I added a big heat sink and some paste for the cooling system. I hope this not to warm up much when amplifying headphones, but as I included rear outputs for speakers, the heat sink may be necessary sometime.

The big white cord hides the shielding for the potentiometer wires, which was completely mandatory, to remove almost all the hum.

And this is the final product. Note the volume knob with rubber!

Some fancy LEDs with polarized paper makes it cool.