Tonebender MkII Distortion Pedal

The Tonebender MkII has been a staple in rock and roll for generations and has been used by guitarists such as Jimmy Paige. Distortion Pedals generally work via changing the shape of the waves that are typically produced by a guitar. This is done by passing the signal through a series of resistors and capacitors. The multitude of variations of distortion devices stems from simply changing the values of certain components to adding new components or competent loops. I hope that this Instructable will make this undertaking easy to understand and yield a working product. The parts list and schematic diagram for this project can be found at Fuzzcentral.com.

http://fuzzcentral.ssguitar.com/mkII.php

Good Luck! And feel free to leave Feedback.

Parts List

Resistors:
3 - 100k Ohm (Brown, Black, Yellow)
1 - 10k Ohm (Brown, Black, Orange )
1 - 8.2k Ohm (Gray, Red, Green, Brown)
1 - 470 Ohm (Yellow, Purple, Green, Black)

Potentiometers
1 - 100k
1 - 1k

Capacitors
1 - 47uF Electrolytic
2 - 4.7 Electrolytic
1 - 0.1 Polyester Film
2 - 0.01 Polyester Film

Transistors
3 - PNP

Other
1 - DPDT Switch
1 - Stereo Input Jack
1 - Mono Output Jack
Black Wire
Red Wire
Solder
Soldering Iron
Ammeter/Voltmeter

Schematic Diagram

This schematic looks much worse than it actually is. If you break the formation of it down into loops it's not quite as scary. ***Ground on this diagram goes to the positive lead of the battery***

Step 1

Start with the stereo (3-pronged) jack. Make sure that it is a Stereo jack and not a mono 12a (also three pronged) jack. The prong closest to the input of the jack is connected to the larger J-shaped part of the jack. This part connects to the positive lead of the battery. The middle prong is the Ring. The Ring typically goes to the negative terminal of the battery , or in this case into to the circuit. Finally, the lowest terminal is the ground.

Step 2

The lead coming from the ring of the jack connects to the lead from the .01 uF capacitor. The second lead from this capacitor goes to ground. The lead of the capacitor connected to the wire also is then connected to the negative lead of the 4.7uF capacitor. The positive lead of the 4.7uF capacitor is then connected to a 100k ohm resistor. The other leg of this resistor goes to ground.

Step 3

The next step involves a transistor, the 10k ohm resistor, and the .1uF capacitor. First, the middle leg of the transistor gets hooked up to the .01uF capacitor and 100k resistor junction from the previous slide. The right leg of the transistor (the emitter) goes to ground, whilst the left leg will be attached to the 10k ohm resistor and the .1uF capacitor.

Step 4

This step will require another transistor, and two 100k ohm resistors. The middle lead of this transistor will connect to the end lead of the .1uF capacitor. One of the 100k resistors will be attached to this junction as well. The second resistor will be attached to the left lead of the transistor. The right lead will go the the ground.

Step 6

The middle leg of the third transistor is attached to the junction from the leg of the second transistor and the 100k resistor. The left leg of the transistor connects to the 8.2k (blue) resistor. A 470 ohm resistor (green) is then used to bridge the gap between the 100k ohm resistor and the 8.2k resistor.

Step 7

Next, a .01uF capacitor is to be soldered to the 8.2k/470k junction. The 100k/470k junction is then attached to the 10k resistor from earlier. This then attached to a 50uF capacitor which is wired with the positive leg going to the ground. The 50uF/10k junction then leads back to the negative end of the battery.

Step 8

Attach three wires to both of the potentiometers. Holding the potentiometers with the leads facing to the right, the uppermost one (3) is an input, the middle (2) is the output, and the bottom (1) is the ground. Starting with the 100k potentiometer, attach the input (3) lead goes to the open lead from the .01uF capacitor. The middle lead goes to the input of the output jack, and the last lead goes to ground.
The uppermost lead of the 1k potentiometer attached to the junction of the rightmost lead of the third transistor and the open lead from the 100k resistor. The middle lead attaches to the negative end of the remaining 5uF capacitor. The positive end of this capacitor and the last lead of the potentiometer go to ground.

Step 9

To complete the circuit, run wires connecting all of the grounds to the positive lead of the battery. For this I stripped one long wire and connected all of the grounds to it and then connected the end back to the positive terminal.

If all goes well, this should create a working distortion box for your guitar.

Bypassing

Creating a bypass pedal for the circuit is not a tough adaptation considering the complexity of the rest of the circuit. A bypass switch is a switch with when closed plays through the circuit board and adds the distorted effect. When open, current only flows to the jacks, skipping the distortion and playing through the amp normally.
To achieve this, start with a dpdt switch, or a switch with three sets of two leads on it. Designate one side of the switch as input and one side as output. Remove the output lead of the input from the .01uF capacitor, and attach it to the middle input terminal on the switch. Te output of the middle terminal will go to the input of the output jack (detach this from the potentiometer first as well). With this setup, current will flow into or out of both jacks regardless of which way the switch is flipped. Next, solder a lead connecting on set of terminals. This will act as the bypass as current will skip straight from the input jack to the output jack.
The input of the third set of terminals will be wired to the .01uF capacitor, occupying the spot where the input jack's lead was removed from. The output of the switch then should be wired to the middle lead of the 100k potentiometer (where the output was removed from).