JHS Pedals 3 Series Harmonic TremoloIn 1960, Leo Fender introduced a circuit in his Bandmaster and Vibrasonic amps called the Harmonic Tremolo. Essentially, the amps signal was split into high frequency and low frequency components, with the output switching back and forth between the two, resulting in a dreamy effect similar to the Uni Vibe. The 3 Series Harmonic Trem allows you to utilize Leo Fenders revolutionary effect in a package much easier to tote than a vintage amplifier.