 The effect varies depending on the speed of the rotors, which can be toggled between fast (tremolo) and slow (chorale) using a console half-moon or pedal switch, with the most distinctive effect occurring as the speaker rotation speed changes.The most popular Leslies were the 122, which accepted a balanced signal suitable for console organs, and the 147, which accepted an unbalanced signal and could be used for spinet organs with a suitable adapter.The Pro-Line series of Leslies which were made to be portable for gigging bands using solid-state amps were popular during the 1970s.