The UBE Screamer from Runoffgroove was originally developed as an experiment to see if something tonally similar to the Ibanez Tube Screamer could be created with a series of CMOS hex-inverter stages.
CMOS hex inverters function somewhat similar to op-amps, albeit with much lower open-loop gain and much different clipping characteristics. Craig Anderton’s famous Tube Sound Fuzz circuit (which the Way Huge Red Llama is based on) also used hex inverters, as well as the Electro-Harmonix Hot Tubes from 1979 and many other derivatives since that time.
Circuit-wise, the UBE Screamer has little in common with the Tube Screamer it’s named for, but it succeeds in occupying a similar space in the tonal spectrum and is well worth your time to build it.
The Aion FX implementation of the UBE adds two modifications: a clipping diode switch and a second switch to change out the global feedback resistor. The original Runoffgroove article recommends selecting this resistor for based on whether you’ll be using single coil pickups or humbuckers, so we took the step of putting it on a switch so the pedal can be used in any scenario without heating up the soldering iron.