In the last few months, due to family, I have had a resurgent interest in Headphones. Having not really listened to my Sennheiser HD650 for a few months, I thought it time to dust them off and relax. During those months away from the headphones, I also took the task of upgrading my computer, during which I decided on a sound card upgrade. This was in the form of a Asus Xonar Essence STX. Whilst mainly functioning as a gaming PC, my music library is stored on this computer and shared over iTunes.
Naturally, I started to enjoy some headphone music through this setup. Initially, the sound was a little dark, but as the hours stacked up, became increasingly more open and less laid back. This combination is both easy on the ears and non-fatiguing. The sound stage for me was more forward, instead of in the middle of my head, it was at the front, near the forehead. The details that you get from headphones is so much more then through speakers. Although I find at this stage of the burn-in period, the Asus lacks some of the dynamics and 'sparkle' of my PPA headphone amp, I am sure that with time, this will improve.
Working on the premise that most of my audio enjoyment will probably come from headphones for the near future, I started looking into building a high quality headphone amp. Naturally my criteria was a tube based design. My first DIY Audio was Pete Millet's hybrid headphone amp. That was a rewarding build and a nice little amp. It combines a tube voltage gain and a IC buffer stage. Some would say combining the strengths of both technologies. However, having built that many years ago, the I decided it was time to see how that design has progressed.
Surely enough, there is a thriving community of Millet amp builders and has spawned several evolutionary designs. Looking through the forums and the net, it seems that most of the improvements lie in the output stage (employing a diamond buffer) and the biasing of the tube (i.e., using a CCS). Having the fore-sight to ensure that whatever I build be as reasonably compact as possible, I settled on the MiniMax Millet. Some of the progressions.
Having ordered the various parts over the last month or so, the build is ready to begin. This time around, the chassis design will be a standard DIY Tube affair. 4 timber side walls with a metal top plate. The timber will be home made with a beeswax finish. The top metal plate has been laid out and ordered through Front Panel Express. The design allows for ventilation slots above the heatsinks with the tubes projecting past the panel. Further, most of the control are also on the top panel. In this design, I have also integrated the Tangentsoft's Modified Linkwitz Crossfeed.