Build - Pedal Project: Graphic Fuzz
The Earth Sound Research Graphic Fuzz was an odd fuzz pedal that came about sometime in the 1970s. Though it never gained too much traction, it has a very unique circuit topology that remains fairly original to this day, using only a single op-amp for gain and clipping. The Graphic Fuzz can produce a nice fuzz tone, but it has quite a few quirks. ESR likened its “Filter” control to a cocked wah, and it does emphasize certain frequencies depending on how it is set. However, once it is turned up past about the halfway point, the pedal usually starts to oscillate and squeal, even in original units. With the pedal first in the chain, the guitar’s volume control can act as a rudimentary “Fuzz Amount” control. Anecdotal reports suggest that placing the Graphic Fuzz after a buffer will eliminate the squealing, but will also eliminate the resonant effect of the filter control.
The original pedal used an LM741. Metal can versions of this op amp can be difficult to find and expensive these days, but this build will also work with Alfa AS301AH, which is a relatively inexpensive metal can op-amp that is currently in production.
The original Graphic Fuzz used battery power only, and the pedal used a voltage divider to generate 4.5V which was used as a "virtual ground". If the battery is replaced with a power supply in the original circuit, the pedal will operate with no issues, but it cannot be daisy-chained (see our PNP "Positive Ground" Pedal Considerations tech article for more info). This build has been modified to allow the circuit to work when using daisy-chained power. A schematic of the original battery-powered Graphic Fuzz and the modified daisy-chainable Graphic Fuzz can be seen below.
Figure 1: Turret board layout of the Graphic Fuzz.
See Figure 2 in our Guitar Pedal Footswitch and Jack Wiring article for the recommended footswitch and I/O wiring.
Figure 2: Graphic Fuzz Schematic, original battery power
Figure 3: Graphic Fuzz Schematic, modified for daisy-chaining
Parts List
| Value | Qty | SKU | Type |
|---|---|---|---|
Capacitors | |||
| 100 nF | 4 | C-MKT-D1-400 | Film cap |
| 10 µF | 2 | C-BC-10-100 | Electrolytic |
Potentiometers | |||
| 10k Audio | 1 | R-VAM10KA-SS | Volume Control |
| 1M Audio | 1 | R-VAM1MA-SS | Filter Control |
Resistors | |||
| 10 kΩ | 3 | R-I10K | Carbon Comp Resistor |
| 1 MΩ | 1 | R-J1M | Carbon Comp Resistor |
| 220R | 1 | R-I220K | Carbon Comp Resistor |
Semiconductors | |||
| AS301AH | 1 | P-Q-AS301AH | Op amp |
Other Items | |||
| 2x5 | 1 | P-HTBU-2X6-D | Board |
| Black 1590BB | 1 | P-H1590BBBK | Enclosure |
| Black 3PDT | 1 | P-H501-L-BLK | Footswitch |
| Black/red LED | 1 | P-LPW-FLATBK-R | Prewired LED |
| Lumberg switched DC jack | 1 | P-JBLB-IN-S | DC jack |
| Mono jack | 1 | W-SC-111X | Output jack |
| RCA-style knob | 2 | P-K499-33 | Knob |
| Stereo jack | 1 | W-SC-112BX | Input jack |