Buzz Audio Essence True Class A optical compressor for 500 Series Rack opto comp

IGS Audio One LA 500 Series Vacuum Tube Opto-Compressor

Purple Audio Action 500 Series FET Compressor

Empress Effects ECM-519 500 Series compressors (6 total)

Purple Audio Action 500 Series FET Compressor

Lindell Audio 7X-500 Series FET Compressor/Limiter

Retro Doublewide II 500 Series Tube Compressor

Warm Audio WA-1B Rack Mountable Transformer-Balanced Tube Optical Compressor