with two clipping diodes and an op-amp, it's likely a son of tubescreamer type thing or a 250/dist+ type thing. I would guess the former, but if you can tell if the clipping diodes are in the feedback loop of the op-amp you'd have more information. Can you get a shot of the other side of the board?
Also, tell us what the name of the pedal is or a shot of the exterior.