From a 1985 article in Guitar Player Magazine (http://schematicheaven.com/howard_dumble.htm)

Why is the Overdrive so sensitive?

It's a different kind of signal handling. In the Overdrive, I approach gain levels that are extremely intense; within the linear region, I have a signal gain capability of one million. So if you stuck 10 microvolts in, you'd get 10 volts back. And I do it with stability, and it's still very musical. The best way to approach an Overdrive is real slow. Walk up to it, look at the knobs, have it turned down real low, and then get a feeling for it. Learn what to do with your fingers to make it respond well. If you walk right up to it, it has a tendency to absolutely frighten some people. The secret control on the Overdrive's panel section is the ratio control, which controls how much overdrive is fed back into the circuit. If you turn that up, it's Rock City.

True, don't know how long it took me to discover this twiddling with my Overtone (ages) but it sure is the key.

Cat