Tremolo (electronic effect)

The first self-standing electronic tremolo effects unit may have been produced by DeArmond, in which a motor shakes a canister containing a "hydro-fluid" (not mercury as some people assume), oscillating the canister containing an electrolytic fluid that sends the signal to ground. Earliest references to DeArmond's tremolo unit date to 1941.[2] Starting in the 1950s many companies began incorporating the effect into guitar amplifiers, including the Fender Tremolux and Vibrolux: Leo Fender marked the effect on Fender amplifiers as "vibrato", conversely calling the vibrato arm on his Fender Stratocaster a tremolo arm.[3] The most notable early amplifiers with built-in tremolo functions were the 1961 Fender Princeton and the Gibson Falcon. In such amplifiers, the tremolo circuit was relatively simple, using as little as a dozen components and one half of a tube of the preamp circuit. The effect was achieved through "bias wiggle", in which the bias of a tube, in the preamp or output stage, was modulated (turned off and on, or partly off and on) in a pure sine wave. Such circuits typically had controls for speed and depth, and produced an effect described as "lush, warm, and roundly pulsing".[4]

Later amplifiers, and particularly the Fender Blackface amps of the mid 1960s and the later Silverface amps, used a much more complex circuit, producing the kind of effect that was especially popular with surf musicians. Modulation was produced using an optocoupler, a light-dependent resistor whose pulsating signal (producing a lopsided wave) affects the preamp circuit.[4]