There have been several threads on this question in the not too distant past. I started one in February that provided some good suggestions. (http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1108700500&read&keyw&zzheadphone=amp).
BTW, out of the past discussion, I purchased a Musical Fidelity X-Can V3, which, I believe, has a Stereophile A rating. I liked it over the SS Headphone amps that I auditioned (e.g., Grado). It's a SET amp and uses 6922 tubes. I've swaped tubes and now I'm using Siemens CCa, which provides remarkable detail and clarity. I've also used Mullard tubes, which created a lush and rich sound, but these tubes are in my hybrid integrated and will stay there awhile. The MF X-Can V3 is also reasonably priced. At the time I posted the thread, I was using Senn 600, but I've upgrade to 650s.
John
BTW, out of the past discussion, I purchased a Musical Fidelity X-Can V3, which, I believe, has a Stereophile A rating. I liked it over the SS Headphone amps that I auditioned (e.g., Grado). It's a SET amp and uses 6922 tubes. I've swaped tubes and now I'm using Siemens CCa, which provides remarkable detail and clarity. I've also used Mullard tubes, which created a lush and rich sound, but these tubes are in my hybrid integrated and will stay there awhile. The MF X-Can V3 is also reasonably priced. At the time I posted the thread, I was using Senn 600, but I've upgrade to 650s.
John