From Charles Platt’s “Hypothetical Tremolo Wheel” (MAKE Volume 15, page 82, “Stomp Box Basics: Tremolo and Fuzz”) to real-world project box, MAKE Technical Editor Sean Michael Ragan walks through building out this circuit in MAKE’s latest issue (Volume 33, page 96).

With this Optical Tremolo Box you are hearing are patterns of light, created by a spinning disk translated into rapid electrical fluctuations to produce a warbling audio effect. Audio enters the circuit via the input jack, passes through the variable resistor — the light-sensitive photocell — and outputs to the amplifier, creating the effect known as tremolo.

Tremolo itself can be found in many instruments, and includes most types of drum rolls, some singing techniques, “bends above the nut” on a guitar, or tuned and de-tuned ranks of pipes of an organ. It can also be produced with synthesizers. As a classical guitar technique, tremelo is perhaps best known by Francisco Tárrega’s Recuerdos de la Alhambra.