Wilkie, you are absolutely correct. Duh, on my part! The switched single diodes preceding the diode pairs would act as a half rectifier. I suspect there is really no way using the Rototone to add or subtract a diode to the diode pairs to effect a switched asymmetrical/symmetrical clipping situation. I believe even running the the single diode and diode pair Rototones in parallel rather than in series wouldn’t work either.