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.

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

Figure 3: Tonebender MK1 Schematic

Parts List

100 nF1C-MKT-D1-400Film cap
10 nF1C-MKT-D01-400Film cap
10 µF1C-BC-10-100Electrolytic
220 nF1C-MKT-D22-400Film cap
220 pF1C-D220-500Ceramic cap/mica
2.2 nF1C-MD0022-630Film cap
100k Linear1R-VAM100KL-SSVolume Control
100k Linear1R-VAM100KL-SSFuzz Control
100k Linear1R-VAM100KL-SSTone Control
10 kΩ5R-I10KCarbon Comp Resistor
18 kΩ1R-I18KCarbon Comp Resistor
220 kΩ2R-I220KCarbon Comp Resistor
3.3 kΩ1R-I3D3KCarbon Comp Resistor
47 kΩ1R-I47KCarbon Comp Resistor
1N601P-Q1N60-KBKGermanium Diode
OC413P-QOC41Germanium transistor
Other Items
Black 1590BB1P-H1590BBEnclosure
Carling DPDT1P-H497Footswitch
Cliff Mk3 style knobs3P-K342Knob
Greencell 9V1S-9V-GCELLBattery
Rigid battery snap1P-BATC-SN-1SBattery snap
Mono jack1W-SC-111XOutput jack
Stereo jack1W-SC-112BXInput jack

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