I just had a thought: we need a list of current do-it-yourself headphone amplifiers. So here it is. I'll be updating when someone alerts me to new amps or amps that I have missed. Now, since there is a very large amount of circuit designs available, I'll only be listing available kits and PCB (if you want a circuit design only, you should check headwize).
And what do you know? I just found a brand new design that came up yesterday (31/01/2011)!
Available as a kit (and sometimes as a PCB).
Available as a PCB.
Available as a group buy (hurry!)
Uncertain (you might have to make the PCB yourself).
AMB Cavalli-Kan Kumisa III
DAO & DAO with Taylor CCS
Kevin Gilmore Dynalo
Kevin Gilmore Dynahi
Pavel Macura Audio Dispre 2 - JFET
Sjöström Audio QRV01 through QRV09
Twisted Pear Audio Ventus
Aikido 24V line-stage/headphone amplifier
Cavalli Audio Compact Tube Hybrid (CTH) (Group Buy @ Head-Fi)
Cavalli Audio Single Opamp Headphone Amplifier II (SOHA II)
Cavalli Audio Embedded Hybrid Headphone Amplifier & Revision A (EHHA & EHHA Rev. A)
Millett Hybrid MAXed
Millett Hybrid MOSFET-MAX
Millett Hybrid MiniMax
Starving Student Millett Hybrid
Aikido 9-Pin All-in-One Line-Stage/Head-Phone Amplifier
Aikido Octal All-in-One Line-Stage/Head-Phone Amplifier
Aikido SRPP+ stereo line-stage and headphone amplifier
Bottlehead Crack OTL
Bottlehead Single Ended eXperimenter's (S.E.X)
Cavalli Audio Bijou OTL
Hagerman Technology Castanet
Pete Millett "Jonokuchi"
Maple Tree Audio Ear+ HD
Oatley Electronics K272A (tube hybrid)
Cavalli Audio eXStatA (Solid State & Hybrid)
Amarok^2 electrostatic amplifier
Audiologica (CMoy, PPA & Pimeta)
AMB Laboratories (also stocks PCB for Kevin Gilmore amps)
Beezar (kits for Millett Hybrids)
DIYforums.org (Millett Hybrids)
Electric Sumo (CMoy kit)
Glass Jar Audio (kits and PCB for AMB and Cavalli amps)
GlassWare Audio Design (Aikido)
JDS Lab (CMoy Bass Boost PCB)
Headwize Library (DIY with an enphasis on the Y)