Larry carlton's show-Bud volume pedal

[tomo]

Do you have an idea of the circuit of larry carlton's show-bud volume pedal?

1. FET installd
2. it has gain adjust
http://personalpages.manchester.ac.uk/s ... es/FET.jpg

3. Rick Wheeler says that "boost highs as the volume is increased ..."
http://mr335.tv/?channel=rig&videofile= ... pedalboard

I have no idea about "boost highs as the volume is increased ..."
Do you have an idea?