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
Build the circuit as pictured in the schematic, with the exception of the potentiometers.
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 one pair of the switches outer terminals together.
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
Print out the attched drill guides and affix them to the pedal enclosure.
Step 5: Drill the Top
Drill the three potentiometer crosshairs with a 1/4" drill bit.
Drill the center foot switch crosshair with a 1/2" drill bit.
Step 6: Drill the Sides
Drill both side crosshairs with a 3/8" dril bit.
Step 7: Clean
Remove the drill guides after all of the holes are drilled.
Use the attached template to make a spacer out of rubber or cardboard for the inside of the casing, and position it in place.
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
Insert the audio jacks into each of the side holes and mount them in place with their mounting hardware.
Step 10: Switch
Insert the stomp switch into the 1/2" hole and mount it firmly in place with its mounting nut.
Step 11: Connect
Connect each of the red wires from the switch to the signal tab on one of the audio jacks. This is the tab that has electrical continuity with the long bent peice of metal that comes into contact with the plug's tip.
Step 12: Wire the Pots
Solder a green wire between the center tab on the 10k potentiometer and the lefthand tab on the 100K logarithmic potentiometer.
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 the remaining unused tab from the 100K logarithmic potentiometer to the tab on the closest stereo jack that is electrically continuous with the outer barrel.
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
Connect the center green wire from the 100K logarithmic potentiometer to the switch such that it is connected next to the red wire which is connected to the stereo jack that is also connected to ground.
Step 15: Attach the Circuit
Attach the remaining components as appropriate to the circuit board based on the schematic.
Remember that the remaining green wire from the foot switch should connect to 'Audio In.'
Step 16: Insulate (optional)
To help prevent shorts, download the attached template and cut that shape out of a non-conductive material. I used cork for this purpose.
Glue the cutout to the inside of the lid.
Step 17: Power
Snap the battery into the 9V connector.
Step 18: Case Closed
Put everything inside of the case and fasten it shut.
Step 19: Knobs
Turn all of the potentiometer shafts all of the way to the left. Place the knobs onto the shaft and fasten them in place using their set screws.
Step 20: Use
To use the pedal, simply plug it in between your guitar and your amp.
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.
Dr_K made it!