In 1969 Electro-Harmonix came out with a Muff Fuzz which was the same form factor as the LPB-1 that plugged directly into your amplifier and had a switch to turn it on and off. Over the years people wanted more overdrive out of the muff fuzz and people started stacking them. Electro-Harmonix then introduced the Double Muff (Can’t find a production date) that was 2 Muff Fuzz circuits cascaded in one box.