See the DIY IRF610 Class-A Headphone Amplifier Project page for more details.

All this F5 talk has got me horny for a Class A amplifier, so here is a little headphone amplifier project that I am just putting the finishing touches on. It is my first real solid state project and it seems like a good starting point before I tackle something serious.

It uses an IRF610 MOSFET and a LM317 regulator as a constant current source. Below is a shot of the head amp built on a Radio Shack protoboard.
It came together rather easily. At first I tried it with a unregulated wall wart power supply. Major hum. Below is a shot of additional capacitance on the supply and connecting the power ground to the signal ground through a parallel cap and resistor. It reduced the hum by quite a bit, but there was still enough hum to make it annoying. Adding another cap and a small inductor helped to reduce the hum some more, but through headphones you only need a little hum to make it annoying during quiet parts of a song.
With a regulated wall wart power supply, there is no hum and this headphone amp sounds nice from an mp3 player or computer. Gain is less than one (I measured ~0.8) so you need a good voltage drive. I am working on a schematic and web page which should ready in the next day or so.

Cool project Gio. Is this your own design? How did you decide on this circuit?
Ri

It is mainly the Szekeres headphone amplifier http://headwize.com/projects/showproj.p ... dd_prj.htm with a CCS. I decided to go with this one since I have been wanting to try something Class A for a while now and because I had all the parts for this project on hand.

I'll get more details posted shortly.

Cheers

Ok, full details about this build have been added to the website. See the DIY IRF610 MOSFET Class A Headphone Amplifier Project page for more information, photos and a schematic.

Below is a final shot of the amplifier. I stuffed it into an external CD-ROM enclosure. The end use for this head amp will be work, so this is the perfect enclosure as it will sit next to a computer.
The sound is very good and really improves the listening experience from a portable mp3 player. It drives a pair of Grado SR80 headphones nicely.

Soon I will have to try a Solid State Class A project for speakers!

Wow, what a great idea. I just love it. We have a bunch of old external cdroms at work and I bet I can score one. What power supply from radio shack will work with this?

Any regulated wall wart should be fine. 750mA should be fine. While I have not tried this one from Radio Shack 273-029, it says it will go up to 12V and 1A. That should do the trick. I would try find one that is closer to 15V.

Thank you

Gio,
With the LM317 configuration, does it get as warm as the mosfet?

It is pretty hard to tell with the heat sinks in place and bolted to the chassis as they barely get warm. But if I was to guess, I would say the MOSFET gets warmer than the LM317. The temperature is about the same to the touch, but the heat sink I used on the MOSFET is larger.

Gio
You hit the nail on the head when you said even a little hum in headphones is akin to driving kitchen forks in your eyes. Not your exact words but for sure you have to have a dead quiet PS when driving headphones. Batteries are best but in high drain devices, not practical. As you are well aware I have been enjoying my headphone driver (HPd) "Woody" for a week now. My PS is a 24V 3.5A computer power pack and is fully regulated. I have a 10uf poly snubbed by a .1uf poly sitting across the supply internally to the driver. Though the hum was well in the background, on very quiet passages or between tracks the hum was just there but a distraction (kitchen folks!). The hum completely vanishes with an additional 5600uf cap across the supply but I could not get this into an already crammed case. I could fit a 2200uf cap though and this is sufficient. But in WoodyII I will include an additional 5600uf cap on the PS to kill Mr Hum once and for all.