7X-500 500-Series F.E.T. Compressor The 7X-500 is Lindell Audio's take on the classic "1176" sound, packed in a compact 500-series format. The 7X-500 is a single channel compressor/limiter with a FET (field effect transistor) design that incorporates some new and exclusive features such as "High Pass Sidechain Filter", "Mix Knob" mix between dry and wet signal (parallel compression).