The history of the ADR Compex Limiter F760X RS goes back to the late ’60s in England when Audio & Design Recording made the single-knob F600 compressor module. It used a diode bridge gain changing circuit and had fixed attack and release times. Later on, the single-channel F760X-N compressor module used a FET gain cell, had a variable attack, release, and ratio controls, and also included a peak limiter and expander/gate.
The original circuitry was kept intact other than adding better voltage regulation in a few spots as well as increasing local DC power decoupling to get better separation. The F760X-RS and F765 are being built by Q2 Audio in Royal Oak, MI.
The Q2 Audio F765 is the compression and limiting sections of the famous "Compex Limiter" built into a single 500 Series slot. The audio path contains the same blue Phillips type capacitors and BC series transistors as the original Compex.