Build - Pedal Project: Tonebender MK1

Originally built on hand-drilled phenolic board, the original build style of the Tonebender Mk1 is messy and primitive, but it has its own charm. If you’d like to build a Mk1 in the traditional style, we offer an FR4 board with the original layout (P-PC-BEND-MK1) and have a layout drawing in the Files section of that listing.

This layout is inspired by the original, but designed for more standard turret board and eyelet board types. It also moves the 1k8 resistor onto the board, whereas in originals it was wired offboard to the attack pot. There is also a 1M pulldown resistor at the input to prevent pops and clicks when the effect is engaged. Leave the far left 1M resistor out to keep it original.

The Mk1 can be picky about which transistors are used. Three OC41s are included in the BoM below, but you may need a larger batch of transistors you can try out in the circuit. The “Attack” control changes the bias of Q2. There is often a sweet spot on the control where the pedal sounds best, and there is a little more wiggle room on Q2 since it can be dialed in with the Attack control.

Q1 needs some leakage current for that stage to function. If the signal coming out of the emitter of Q1 is weak or silent, it is probably not a leaky enough transistor. A leakier transistor would fix the issue, or you can connect a resistor from the collector of Q1 to its base. This allows for additional current to flow from the collector into the base of the transistor, simulating transistor leakage. It is best to start with a large value resistor (e.g. 1M5) and decrease it from there until the output from Q1 is strong. A smaller resistor results in more simulated leakage. The less leakage the transistor has, the smaller the resistor needs to be.

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 MK1.

Figure 1: Turret board layout of the Tonebender MK1.

See Figure 4 in our Guitar Pedal Footswitch and Jack Wiring article for the recommended footswitch and I/O wiring.

Figure 2: Tonebender MK1 Schematic

Figure 2: Tonebender MK1 Schematic

Parts List

100 nF2C-MKT-D1-400Film Cap
10 nF1C-MKT-D01-400Film Cap
25 µF1C-ET25-50-MODElectrolytic
500k Audio1R-VAM500KA-SSVolume Control
50k Linear1R-VAM50KL-SSAttack Control
15 kΩ1R-I15KCarbon Comp Resistor
1.8 kΩ1R-I1D8KCarbon Comp Resistor
1 MΩ2R-J1MCarbon Comp Resistor
2.2 kΩ1R-I2D2KCarbon Comp Resistor
2.2 MΩ1R-J2D2MCarbon Comp Resistor
470 kΩ1R-I470KCarbon Comp Resistor
47 kΩ1R-I47KCarbon Comp Resistor
8.2 kΩ2R-I8D2KCarbon Comp Resistor
OC413P-QOC41Germanium transistor
Other Items
Black 1590TRPB1P-H1590TRPBBKEnclosure
Black 3PDT1P-H501-L-BLKFootswitch
Dress nut1P-H54-DRESS-BLKZonk switch dress nut
Greencell 9V1S-9V-GCELLBattery
Rigid battery snap1P-BATC-SN-1SBattery snap
Mini toggle1P-H5410Zonk switch
Mono jack1W-SC-111XOutput jack
Phenolic chickenhead knob2P-K460Knob
Stereo jack1W-SC-112BXInput jack
Switch cap1P-HTCAP-SH-BZonk switch cap

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