This is an old-school, classic, opamp-based overdrive/distortion. It is perhaps closer to the Proco RAT, than to for example the MXR Distortion +. It goes from mild (kind of) overdrive to saturated fuzzy distortion. It’s built around the 1458 dual opamp (hence the name), which basically is two LM741. After being clipped in the opamp stage, the guitar signal is clipped again by two silicon diodes. A simple tone control that cut highs RAT style), a volume control, and an output buffer. That’s it.
This is currently my favourite distortion. A treble booster in front of it sounds great too.