op-amp

Depending on the circuit, it can sound neutral and clean at low gain, become a hot overdrive when turned up, or serve as a high-quality buffer at minimum gain¹. Some designs use op-amp clipping rather than diodes², or push the op-amp itself into clipping for much of the distortion³. Op-amp-based fuzzes, such as the Electro-Harmonix Op-Amp Big Muff, produce a fuzz that does not sound quite like transistor-based designs⁴, typically described as more saturated, mid-forward, and cutting⁵⁶.