Experiment 30: Fuzz
258 Chapter 5
Schematic
The output from the 555 timer is a square wave, so it already sounds quite
“fuzzy,” but we can make it more intense to demonstrate the clipping princi-
ple. I’ve redrawn the whole circuit in Figure 5-55, as several components have
changed. The principal alteration is the addition of two NPN transistors.
If you assemble this circuit on your breadboard, note carefully that the 33K
and 10K resistors at the bottom of the amplifier chip have been removed, and
there’s now just an 820Ω resistor in that location. The bottom of the adjacent
0.22 μF capacitor is still the input point for the amplifier, and if you follow the
connection around to the middle of the schematic, you’ll find it leading to a
100K potentiometer. This is your “fuzz adjuster.”
The two NPN transistors are arranged so that the one on the left receives out-
put from the 555 timer. This signal controls the flow of electricity through the
transistor from a 33K resistor. This flow, in turn, controls the base of the right-
hand transistor, and the flow of current through that is what ultimately con-
trols the amplifier.
When you power up the circuit, use the 100K potentiometer attached to the
555 timer to adjust the frequency (as before) and crank the “fuzz adjuster” po-
tentiometer to hear how it adds increasing “bite” to the sound until ultimately
it becomes pure noise.
The two transistors act as amplifiers. Of course, we didn’t need them for that
purpose—the input level for the amplifier chip was already more than ade-
quate. The purpose of the lefthand transistor is simply to overload the right-
hand transistor, to create the “fuzz” effect. And when you turn up the output
from the transistors with the “fuzz adjuster,” eventually they overload the input
of the amplifier chip, creating even more distortion.
If you want to tweak the output, try substituting different values for the 1K
resistor and the 1 μF capacitor that are positioned between the emitter of the
righthand transistor and the negative side of the power supply. A larger resis-
tor should overload the transistor less. Different capacitor values should make
the sound more or less harsh.
You can find literally thousands of schematics online for gadgets to modify
guitar sound. The circuit I’ve included here is one of the most primitive. If you
want something more versatile, you should search for “stomp box schematics”
and see what you can find.