Functionality confirmed. No crackling. Based on the pot date, it appears to be from 1981. One of the jacks has been replaced. The distortion range is wider than current models, with a significant high-end presence. Compared to current production models, Russian Muff, Rams Head reissues, and op-amp reissues, I think this one is the roughest and most "fuzzy." Vintage Effects Pedal Fuzz Big Muff Electro-Harmonix Type...Electric Guitar