Around 1970 production was changed to a die-cast metal box, with a large pedal featuring a rubber cover that had the words "Super-Fuzz" embossed on it.
The later models also featured an internal trim pot for controlling the octave balance.
The controls are 'Balance' (volume), 'Expander' (fuzz amount), a two position 'tone' switch, and an on/off footswitch on top.
There are two unique features of this device that set it apart from other distortion and fuzz pedals.
The second unique feature is a tone switch that engages a 1 kHz filter that "scoops" the mids, giving a very fat, almost bassy tone, unique to this circuit.