Mad Professor Stone Grey Distortion

Here's the Stone Grey Distortion from Mad Professor. It's reminiscent of the Distortion +/OD250 circuit, but with a hex inverter stuck after the opamp. It also uses 2 JFETs in the feedback loop of the opamp for clipping. Original op amp is the TL051, but other single opamps can be used (Tl061, 71, etc). Should be an easy fit in a 1590B. Mind the jumper under the CB4069UBE.