Distortion Pedal Preliminary Diagrams.

A few days ago, I showed you this.

I decided, however, that keeping diagrams on a whiteboard that is often used for other things is impractical. So from whiteboard, to digital camera, to…

Schematic v1

Huzzah for EagleCAD! Well, the initial schematic is completed, though I also decided to develop a PCB design so I may eventually print off the design and build the board myself, unless I would rather use a proto board.

Note that I limited the design to the bottom layer, and as a result, added an additional jumper for a single wire between LED1 and the DRIVE switch wire inputs. This is just to a) obliterate the requirement for a more tedious double layer PCB, and also to provide better tracing spacing (haha! a rhyme) so it’s more hobby friendly. Also note that I filled in the PCB ground tracings, less etchant to use, faster prep time, and also, less noisy circuitry as a result. Finally, despite EagleCAD’s fair autoroute feature, I ended up re-routing many traces as Eagle thinks 90% angles are acceptable on tracings. It did, however, allow me to generalize the spacing and area where I could trace.


Comparison to Source (http://www.instructables.com/id/Distortion-For-Cheap/step4/The-Schematics/)

First a few notes: While I have seen a few other schematics that use similar designs, I felt like basing my variation of the pedal off this design to start with. For one, the amplifying section of the circuit (which I have modified to divide onto its own and become simply a “BOOST” circuit) is fairly standard among op amps, meaning I’d easily have other resources later on to draw from if needed. The clipping diodes in the “DRIVE” portion of the circuit were also of simple principle, simply clipping the amplitude of the waves, causing the distorted effect.

Changes I made: Well, for one thing, I wanted to try and design something that would perform in a similar way to a Fender HotRod Deluxe amplifier in terms of channel switching. If I wanted to bluntly kick in the pedal, all I have to do is hit one button. However, to change from just a volume boost to a driven sound, a second switch would be added (similar to the Drive/More Drive switch on the HotRod’s pedal). In terms of the circuit, this was straightforward; create a complete bypass switch for BOOST, sending the input signal directly to the output, without passing through additional circuitry. For DRIVE, I did something similar, where there was a bypass switch, it only prevented the op-amp signal from continuing through the drive circuitry, and was instead sent straight to out. When activated, distorted signals would be produced and sent to the output.

In terms of the actual circuitry: Across the battery terminals, a .1uF capacitor was added in order to reduce some electrical noise generated by battery, and to filter it as it progresses towards the IC. The value of R1 was heightened a little, to just lower the boost a little and to become more practical in the circuit, and R2 became a potentiometer to control levels of the BOOST. As for the potentiometer added in the drive, I felt like experimenting with the shaping of the clipped electric waves, dancing between the LED and the Schottkey diodes. LED was added to the drive switch to determine if it would be bypassed or not.


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