I had an idea!!! Biasing diodes...

[R.G.]

There are several. Perhaps the most common ones are the Fox Tone Machine and the Green Ringer, both of which trickle some current through the diodes to get them almost on on order to do a better full wave rectification job.

The Vox one is still the most straightforward circuit for this.

Opamp circuits use either diodes or transistor base-emitters tied to a voltage string to do waveshaping. These circuits usually have to have the set points fairly far apart though, not all that good for effects sized signals. Could be done, though. The ETI Hyperfuzz does it.