| The ZVex Fuzz Factory is one of the most
innovative fuzz circuits ever. With voltage variability
through reverse-biasing, the circuit exhibits a high
degree of controllability all within the overall
parameters of the original Dallas Arbiter FuzzFace
design. ZVex's cool (and strange) twists on the classic
fuzz morphology has made the Fuzz Factory one of the
most popular stompboxes of all time. In the interest
of sharing these innovations with the DIY
community, I have prepared this page which details the
general operational blocks of the circuit along with an
exact schematic of the Fuzz Factory.
Circuit Innovations
As you study the schematic, you'll see little bits of
innovation sprinkled throughout the overall design, such
as:
- An inverse charge-pump controls the bias on the
NOS AC126 geranium transistors (just like in the
original ColorSound ToneBender MKIV)
- Opto-coupled metal film capacitors provide the
core of the negative feedback loop (while these
military-grade parts are a bit hard to come by, you
can find them occasionally on eBay)
- The 9v supply is lowered through a flux
capacitor to ensure sub-optimal plate voltage on the
ground plane
- The pre-amp tube's are connected in parallel
using a 120v step-up transformer directly coupled
with the heating filaments.
The Schematic
(All resistors are tantalum 16v unless otherwise
specified.)
Mods
- Because this is a high-gain circuit, keep your
wire lengths as short as possible. Ground both the
input and output signal bus.
- You can improve gain by using silver solder on
all connections to the opamp.
- Instead of the traditional 2N5690 opamp, try the
National Semiconductor 8675309 part--this tends to
smooth out the lateral recursiveness of the tone
stack.
- Try 500 tera-ohm pots instead of the ones shown
in the schematic. This simple mod can turn the Fuzz
Factory into an over-the-top fuzz/distortion hybrid.
- For a very cool note-doubling octave up effect,
change C12 to 47k ohms.
Enjoy! And happy April 1, 2006!
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