^ I like your breath mint box.
Thanks. I was gonna build one, but bought this one assembled with a custom pc board and op amp socket (if replacement is desired).
Nice clean build.
That design has been around for some time. I even run it off rechargeable 9v's.
It barely has enough power to make the E4's very loud, but they isolate very well so I've not had much of an issue. Many times don't even use the hp amp.