An overdrive guitar pedal is kind of like a less harsh distortion pedal. Technically speaking, whereas a distortion pedal clips an amplified waveform at a particular height, the overdrive pedal actually rounds the top of the clipped wave. While this still makes it a bit fuzzy when you crank up the gain, it sounds less extreme than a distortion or fuzz pedal. What is cool about this pedal is that it adds a little extra warmth to your signal when you are strumming gently, but when you really strum hard, the audio spikes up into crunchy distortion territory. While this is generally a very subtle effect, it is actually quite robust in terms of the different types of sounds that you can get out of it. It is great for adding a little something extra to any effects chain.
Step 1: Materials
You will need:
(x1) 2N3904 NPN transistor (Radioshack #276-2016)
(x1) 0.1uF capacitor (Radioshack #55047557)
(x1) 0.047uF capacitor (Radioshack #55047555)
(x2) 0.01uF capacitor (Radioshack #55047551)
(x1) 100K logarithmic potentiometer (Radioshack #271-1722)
(x1) 100K linear potentiometer (Radioshack #271-092)
(x1) 10K linear potentiometer (Radioshack #271-1715)
(x1) 2.2M ohm resistor (Radioshack #55049482)
(x1) 33K ohm resistor (Radioshack #55049446)
(x1) 22K ohm resistor (Radioshack #271-1339)
(x1) 3.3K ohm resistor (Radioshack #271-1328)
(x1) 680 ohm resistor (Radioshack #55048032)
(x1) PC Board (Radioshack #276-150)
(x1) 9V battery snap (Radioshack #270-324)
(x1) 9V battery (Radioshack #23-853)
(x3) Knobs (Radioshack #274-415)
(x2) Stereo audio jacks (Radioshack #274-312)
(x1) Foot switch
(x1) BB project enclosure
(x1) 5" x 4" x 1/8" rubber sheet
(x1) 5" x 4" x 1/8" cork sheet
Step 2: Circuit
The overdrive pedal schematic is largely based on two different circuits. The transistor stage of the schematic is based on the Trotsky Drive Pedal by Beavis Audio Researsch (itself based on the Electra Distortion module). However, instead of using a rare Russian NPN transistor, I used a 2N3904. All-in-all, this part of the schematic is largely just boosting the incoming signal, controlling the gain, and doing a little bit of filtering.
The lower half of the schematic is based on Jack Orman's page on tone clipping, and it is in this part of the circuit where all of the real overdrive magic is happening. Basically, there is a high pass and low pass filter in parallel, each of which is followed by its own pair of clipping diodes. Aside from the filters themselves having unique tone charachteristics, each pair of diodes also has its own clipping charachteristics.
The 10K potentiometer in the schematic sweeps between the two different filter / diode pairs. This potentiometer gives the pedal a very adjustable and unique sound. By swapping out the filter components and diodes for different values, you can experiment with the pedal and find your own perfect combination.
Step 3: Wire the Switch
Connect a 4" red wire to each of the central terminals.
Connect a 4" green wire to each of the outer terminals.
Step 4: Drill Guides
Step 5: Drill the Top
Drill the center foot switch crosshair with a 1/2" drill bit.
Step 6: Drill the Sides
Step 7: Clean
Mount all 3 potentiometers in place, with the 10K potentiometer being in the center, and the 100K logarithmic potentiometer being to its left (while the pedal is face down). Fasten them firmly in place with their included mounting hardware.
Step 9: Jacks
Step 10: Switch
Step 11: Connect
Step 12: Wire the Pots
Connect a 4" green wire to the center tab on the logarithmic potentiometer.
Connect 4" green wires to the outside tabs of the 10K potentiometer.
Connect a 4" green wire to the center tab of the 100K linear potentiometer, and a 4" red wire to the righthand tab.
Step 13: Wire Ground
Connect a 3" black wire to the same jack. This wire will later connect to the circuit board.
Connect the black wire from the 9v battery snap to the remaining unused tab on the stereo jack.
Step 14: Wire the Output
Step 15: Attach the Circuit
Remember that the remaining green wire from the foot switch should connect to 'Audio In.'
Step 16: Insulate (optional)
Glue the cutout to the inside of the lid.
Step 17: Power
Step 18: Case Closed
Step 19: Knobs
Step 20: Use
If it does not sound like the pedal is doing much of anything, press the switch.
You should now be ready to rock and roll.