Tremolo is the rapid oscillation in volume that gives the guitar its shimmery sound in surf rock, rockabilly, and country music. Link Wray’s guitar in his 1958 hit “Rumble” is a stand-out example of tremolo—required listening for anyone building a trem unit.
The heart of our Blinkie Tremolo effect is a homemade optoisolator (also called an optocoupler) made from an LED and a light-sensitive resistor. The photoresistor controls the volume of the audio signal; when the LED shines on the photoresistor, the resistance drops to near zero, and the audio comes through loud and clear. As the LED dims, the resistance climbs, and the sound fades. A timer circuit rhythmically pulses the LED, which pulses the volume, which gives your solo a throbbing retro drive. As with the Spring Reverb (Chapter 14), this trick is cribbed from early Fender amps.
Our Blinkie Tremolo has a remarkably clean output, since the optoisolator keeps the control circuit entirely separate from the audio signal, and true bypass, which means that deactivating the effect completely removes the modified sound from the signal without affecting the unmodified sound in any way.
