Initial measurements on the prototype tone control if anyone's interested. There is a small amount of HF instability (expected with this type of tone control) I can cure that but I don't have any low pF capacitors at home. Will have to grab a few in work tomorrow. Might shift the LF a bit lower, and the HF a bit higher, but will listen first. The HF roll-off is a 'feature' of the crappy soundcard in my measurement PC, and NOT the tone control circuit!
More difficult to make it battery powered. This needs split power rails, but fret ye not, I have a fairly radical plan
Brought home some low value caps to nail the HF stability issue so will do that this weekend. Also thinking about using fet input op-amps so I can dump the dc blocking caps (lower input offset voltage traded off against probably unnecessarily low noise)