VCL-4 is a faithful emulation of the silver face revision of the op-amp-based successor of THE classic late 60s opto leveler. It provides you with unintrusive to extreme program dependent and musical opto compression. The switchable ratio option makes for a flexible solution over a wide range of source material. During the modeling process Fuse Audio Labs rebuilt the entire original circuit on strip board, however replacing the original opto-cells that were made up of an LED and an photoresistor with suitable Vactrols. Every part of the circuit including the receiver stage, the side-chain and Vactrol LED driver circuit, the Vactrol itself as well as the push-pull driver stage and the output transformer has been accurately modeled.