Electronics Technology Lab Report Number 8

Last week, I began work on the distortion unit of my final project. I used the circuit below, based off of a schematic I found on the internet. The circuit uses a transistor and a few resistors to distort the signal you put into it. I placed a 10k ohm potentiometer across the circuit from the input to the output of the circuit with the wiper attached to the input of the speaker. This potentiometer was meant to fade between the wet and dry signal and essentially turn on and off the distortion circuit. Somehow, when the potentiometer was turned hard to one side, it caused the circuit to overdrive very hard and create an LFO-style sound from the circuit. Unfortunately, I am not entirely sure how the circuit created this sound and in general how the circuit works.

Because of the issues with my previous circuit, I decided to find a simpler circuit. I found the circuit below online as well. It is based on a network of diodes and resistors. Each set of parallel diodes only passes signal at certain frequencies and this causes a distortion effect, or rather, a clipping effect. For my final project, I instead to control my effects units using light. Previously, I had hit a roadblock because all of the photoresistors that I could find were only two sided. The applications I intend to use them in require them to act like potentiometers and these have three pins. I found a way to get around this issue by soldering a resistor to one of the legs of the photoresistor. This creates a voltage divider with one variable resistor. This way, the photoresistor acts very much like a potentiometer even though it only has two pins. Another trick I discovered is a way to change the taper of a photoresistor. By placing a resistor in parallel with the photoresistor, you can change the curve at which the the resistance changes and therefore get a more musically useful range. Below are the schematics and videos for the circuits described above. In addition, another advancement I made was to begin to integrate my guitar into the effect circuits. I unsoldered the output jack and routed the guitar signal through my breadboard before sending it back out the jack again and it works like a charm. As I further develop my project, I need to figure out a way to reverse my photoresistors so that when they have full light the signal is unaffected and when their light starts to get cut off the effect begins to come through. I also am going to introduce a switching system so that I can bypass all of my effects and not have to worry about relying on the state of the photoresistors to keep my signal clean when I want it.