Thought some readers might be interested in these notes.
My old favorite headphone amp is an Antique Sound Labs MG head OTL.
I think it was somewhere in the neighborhood of 400 bucks...about ten years ago.
I use Senn HD650 cans.
Recently, I picked up a Chinese headphone amp on ebay. Search on
Class A 6xxx 12xxx 6N11 12AU7 Tube valve vacuum Hybrid Headphone Amplifier AMP
Cost me 40 something bucks, plus 12 or so on shipping.
The MG head uses a 12AX7, and a pair of 6BQ5's
The ebay one uses a single 12AU7.
I spent a lot of time switching back and forth between the two, and my wife did also.
Very hard pressed to tell the difference.
I thought the big ASL sounded a bit more tight, but my wife thought the ebay one had more clarity (airey).
The ebay one with its laptop-type power supply did have a bit of hum, when the volume was cranked with no input signal, but no hum under normal listening volume.
My point is...for anyone wanting to play with some hollow state hi fi...the ebay item sure is fun!
Even has a pair of blue LED's by the base of the tube to make it glow neon blue-like. Too Cool!!
Has a switch to allow you to play around with different tubes....6911/6DJ8, and 12AX7 ....but have not
fooled with that yet.
Cheap enough to have some fun with, or an ipod amp!!
YMMV, have fun!!