Just curious, Stan, on operation of the HP socket. On the 7510, it would turn off the variable out to the power amp when phones were plugged in (even if just my 1/4" adaptor was plugged in w/out phones attached, which seemed unusual to me).
But on my new 7520, the phones and power amp play simultaneously.

Just curious as to the design thinking. Something to do with cleaner signals and the variable ohm range of phones?