The Nomad OTA Compressor is based on the Valve Wizard Engineer’s Thumb, a DIY classic that was first invented in 2012.
Unlike most OTA-based compressors such as the Ross or Dyna Comp, the Engineer’s Thumb uses the LM13700 as a current-controlled feedback resistor in an op-amp gain stage. This reduces noise and significantly increases headroom compared to other designs. The audio path of the circuit actually has a lot more in common with optical compressors such as the Flatline Compressor.
The Engineer’s Thumb has four official revisions, with the most recent being from 2019. While most DIY projects are based on V1 or V2, the Nomad is based on this latest revision, with all of the suggested modifications for a true 5-knob compressor. It’s a simple and cheap build with a deluxe control set.