Build - Pedal Project: Tonebender MK3
Coming after the Mk2 tonebender, the Mk3 is also a 3-transistor circuit like its predecessor, but the circuit topology is quite different. Q1 and Q2 form a darlington pair and operate as a single gain stage. Perhaps most notably, the Mk3 has had a simple “Tone” control added, which provides more tone-sculpting options than were found on a lot of fuzz pedals that came before it.
The Mk3 topology is perhaps most similar to the Baldwin-Burns Buzzaround, which was a favorite of Robert Fripp of King Crimson. The Buzzaround did not have a volume control, but instead had a “Balance” control which functioned similarly to a volume control, but also had an effect on the bias of Q3. The controls on the Mk3 are less unusual, with a simple Volume control instead of Balance. On a Mk3, the “Fuzz” control works by increasing resistance into the base of Q3 when turned counter-clockwise, reducing the current that enters the base and the overall gain of the circuit. On a Buzzaround, the “Sustain” control is wired as a voltage divider controlling how much signal enters the base of Q3.
The Mk3 circuit or a variant was found in a few different fuzz pedals of the era, some of which were built by Sola Sound/Colorsound - e.g. the Park Fuzz Sound, Rotosound Fuzz Box, Carlsbro Fuzz, etc.
This is a PNP build and uses battery power only. With no LED indicator, this pedal will last a very long time on battery power. If you would like to build this pedal with a DC jack, please see our PNP "Positive Ground" Pedal Considerations tech article.
Figure 1: Turret board layout of the Tonebender MK3.
See Figure 4 in our Guitar Pedal Footswitch and Jack Wiring article for the recommended footswitch and I/O wiring.
Figure 3: Tonebender MK1 Schematic
Parts List
| Value | Qty | SKU | Type |
|---|---|---|---|
Capacitors | |||
| 100 nF | 1 | C-MKT-D1-400 | Film cap |
| 10 nF | 1 | C-MKT-D01-400 | Film cap |
| 10 µF | 1 | C-BC-10-100 | Electrolytic |
| 220 nF | 1 | C-MKT-D22-400 | Film cap |
| 220 pF | 1 | C-D220-500 | Ceramic cap/mica |
| 2.2 nF | 1 | C-MD0022-630 | Film cap |
Potentiometers | |||
| 100k Linear | 1 | R-VAM100KL-SS | Volume Control |
| 100k Linear | 1 | R-VAM100KL-SS | Fuzz Control |
| 100k Linear | 1 | R-VAM100KL-SS | Tone Control |
Resistors | |||
| 10 kΩ | 5 | R-I10K | Carbon Comp Resistor |
| 18 kΩ | 1 | R-I18K | Carbon Comp Resistor |
| 220 kΩ | 2 | R-I220K | Carbon Comp Resistor |
| 3.3 kΩ | 1 | R-I3D3K | Carbon Comp Resistor |
| 47 kΩ | 1 | R-I47K | Carbon Comp Resistor |
Semiconductors | |||
| 1N60 | 1 | P-Q1N60-KBK | Germanium Diode |
| OC41 | 3 | P-Q2N404 | Germanium transistor |
Other Items | |||
| 2x10 | 1 | P-HTBW-2X10 | Board |
| Black 1590BB | 1 | P-H1590BB | Enclosure |
| Carling DPDT | 1 | P-H497 | Footswitch |
| Cliff Mk3 style knobs | 3 | P-K342 | Knob |
| Greencell 9V | 1 | S-9V-GCELL | Battery |
| Rigid battery snap | 1 | P-BATC-SN-1S | Battery snap |
| Mono jack | 1 | W-SC-111X | Output jack |
| Stereo jack | 1 | W-SC-112BX | Input jack |
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