It has a JFET impedance buffer front-end and a choke-input power supply. The sound characteristic of the amplifier can be tuned by adjusting the low pass filter formed with the input capacitance of the MOSFET.
http://headwize.com/projects/showfile.php?file=murdey_prj.htm
An OTL mu follower design. Purpose of the preamp is to drive headphones. This all-tube line stage and driver can power them, without resorting to output transformers.
http://headwize.com/projects/showfile.php?file=barbour_prj.htm
A high-current output amplifier for low-impedance dynamic headphones such as the Grados. The amplifier features an new servo biasing circuit which operates entirely outside the audio feedback loop.
http://headwize.com/projects/showfile.php?file=gilmore3_prj.htm
This tube headphone amplifier kit manual has building instructions and full circuit diagram of this device.
http://hollowstate.netfirms.com/epluskitmanual.pdf
drives up to 6 headphones from a single amplifier.
http://www.procosound.com/images/HJ6.PDF
allows a RIFF/WAVE format selection from a music CD to be "digitally re-mastered" for use with headphones. It works especially well with portable high capacity CD/MP3 players.
http://www.johncon.com/john/SSheadphoneAmp/
Making Your Own HeadBanger
http://www.minidisc.org/headbanger.html
This riaa Pre-Amp is the perfect solution to getting a signal off of your old turntable and into your mixing board.
http://www.paia.com/riaa.htm