What volume pot are you using? Blue Velvet?
The metal nose of the volume pot is not connected to any of the pins.
If you get humming involving the volume pot, try running a wire from
one of the screws in the back to ground. That will usually cure it.
Adding the buffer will increase the output power considerably as well
as improve the sound quality. A TO-220 BUF634 is easy to work with
and hard to kill.