Another designer tried my mosfet compressor using a darlington pair as the gain stage device Q1. He described some improvements in performance – so I tried this as well. I love it! Using a darlington such as a MPSA14 (or a homemade one) is a drop in replacement for the MOSFET Q1. It gives a little more gain and reduces noise in the control loop slightly (allowing more freedom in changing and or eliminating C7, c8, C9). I definitely can reccomend it.