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-Q2N404Germanium 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

Still not satisfied? Follow us on Instagram for additional builds, project photos, and more!

Note that the information presented in this article is for reference purposes only. Amplified Parts makes no claims, promises, or guarantees about the accuracy, completeness, or adequacy of the contents of this article, and expressly disclaims liability for errors or omissions on the part of the author. No warranty of any kind, implied, expressed, or statutory, including but not limited to the warranties of non-infringement of third party rights, title, merchantability, or fitness for a particular purpose, is given with respect to the contents of this article or its links to other resources.