This is cassiopeia the stereo vacuum tube saturation module in the api 500 format.
Cassiopeiea & lyra make use of the “natural” characteristics of vacuum tubes operated in saturation. In other words, these tubes are operated outside their originally designed specifications. This is achieved by using the SATURATION potentiometer for the incoming signal. The more this control is turned clockwise, the less the vacuum tube can operate inside spec. The resulting effect is beneficial because it creates overtones. The beautiful thing about using tubes in this context is the reason that clipping occurs in a soft way. The INTENSITY control gives the option to blend in the saturated signal with the original unprocessed signal. This is very handy in cases where the SATURATION control is cranked up but just a small amount of the wet signal is beneficial to the output. The last element needed is the OUTPUT control, which allows the user to give the correct level to the following device in the entire signal chain.