Class-A Headphone Power Amplifier with IRF610 and LM317 CCSPlease feel free to ask your questions and post comments about the
DIY IRF610 Class-A Headphone Power Amplifier Project in this thread.
FAQ 
I can't find an IRF610. What alternate MOSFET can I use?

IRF510, IRF610, IRF611 or IRF612 are all suitable and work well in this buffer circuit. Stay away from IRF530, IRF540, IRF630 and IRF640 types which are commonly found in SMPS as there will be a terrible roll-off of the high-end response.
IMPORTANT POSTS{coming soon}
Similar Headphone Amplifiers== Original Post ==
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. The amplifier circuit is a MOSFET follower with a CCS load.
Attachment:
IRF610-LM317CCS-Class-A-Headphone-Amp.jpg
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.
Attachment:
DIY-Class-A-Headphone-Amplifier.jpg
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 - the output from a portable mp3 player or computer sound card were sufficient to drive 16 to 100 ohm headphones.
PROJECT PAGE -
DIY IRF610 Class-A Headphone Power Amplifier