This I created a simple audio amplifier using an LM358 op amp. While not built for audio, these little op amps will boost your signal even if they do provide quite a bit of loss in signal quality. The circuit that we used uses a resistor across the op amp to control the gain. In order to calculate the output voltage of the amplifier circuit, you can take the input voltage and multiply it by value of the resistor across the op amp divided by the value of the resistor before the op amp. In this case, the first resistor has a value of 2.2k ohms and the potentiometer over the op amp has a value of 10k ohms. Divide them out and you get about 4.54. This ratio is the amount of gain that the circuit can provide. The minimum gain for the circuit is obviously zero. When the potentiometer is set to a resistance of zero ohms, 0/2.2 will get a result of zero, and when you multiply the input voltage by a value of zero, that causes (mathematically) the output voltage to equal 0.
My final project is coming along well. Posted below are some of the developments. First is a drawing of the user interface, basically four photoresistors and four switches to turn the effects off and control them. Second is a flowchart for the project's signal chain starting at the end of the guitar's pre-installed circuitry and generally spliced in to the circuit before the output jack of the guitar. The third is a tentative bill of materials as I do not currently ha