I have the cutoff set at around 60 Hz. I tried recreating my Sylenth patch in Serum but also can’t get it to sound the same. I think it has to do with the Distortion effect – I’m not sure what setting gives the same sound that Sylenth/Primer gives. I’ve attached an audio file of my Sylenth patch below, for reference. Let me know if it sounds close enough to what you’re looking for. If so I’ll keep trying to reproduce this sound in Serum.