Assuming that the Distortion is off, you are likely just overloading the signal somewhere. There are many signal sources in Evolver, and many sources of gain. If too many are used at levels that are too high, you will likely get some distortion. For example, if you are using all four oscillators, you should have the levels lower, in the 40 - 60 range. Likewise, if using all three delay taps, lower the levels of each.