Try a variation of this:
Take that 47 ohm resistor out under V1's k2 biasing resistor and
make it a 500 to 1000 ohm one. That will be the "set" resistor for
the NFB loop.
It will alter the "gain" of that stage a little but there is plenty anyhow.
Move over to the 2k7 NFB resistor and make it a lot bigger, like
27k to 56k.
Now go back to the new 500 to 1000 ohm resistor under the 1k5
cathode biasing resistor of V1 k2 and try a small 1K to 2k5 linear
pot in parallel with it but use a .33uF to .68uF cap on the wiper to
ground.
Go back to the volume control and add a 47pF silver mica cap
across the volume control for little more sizzle.
You might have to go around those numbers a little to get
something you happen to like.
Let's not see this on a new production model amp now! I've been
doing something like it for years.
 
Bruce