The revised Millett Hybrid headphone amplifier (revMH) was developed at the DIY subforum of head-fi.org, based on the original low voltage tube hybrid headphone amp from Pete Millett. The revMH got his home at DIYForums.org, where this discrete Diamond Buffer (dDB) has been developed (development thread).
During the construction discussion and prototyping several designs have been tried, in the end the diamond buffer design from Phil Larocco (aka PPL) (known from PPA v2 headamp) was chosen since it performed best and met the space and heat dissipation constraints. Kudos to Phil for sharing this great design. Special thanks go to Ti Kan (aka amb) for his very helping ideas during constructing discussion and the RMAA measurement of the final buffer. Furthermore to Nathan Maher and Drew Dunn for putting generous effort into preproduction runs, GB (group buy) PCB (printed circuit board) production and GB handling.
The dDB is a direct drop in replacement for buf634 or opa551. The revMH was designed with a discrete buffer replacement in mind, dedicating space for a replacement board. So as long as you built your revMH with parts that stay within their designated borders (particulary C2L/R) the dDB is a direct drop in replacement for buf634 / opa551 where nothing has to be changed or altered.