Technical Notes:
The module is based on the special circuit CEM3320/AS3320. In highpass mode this circuit has a cleary higher CV feedthrough than other voltage controlled filters. With high audio levels or slow filter sweeps that's no problem. But with fast changing control voltage (e.g. ADSR with short times or a fast LFO) and low audio levels (i.e. the audio input level is clearly below the level where clipping occurs) a noticeable CV feedthrough may appear at the audio outputs.
With typical audio input levels (~10Vpp) from about position 5 of the level control clipping will occur. This is intended to generate distorted signals if desired. If applicable the level control has to be turned back so that no clipped audio signals appear at the outputs.