This is the one of many guitar effect circuits exist in the world. I have not made this circuit and I also do not know what kind of sound effect harmonic sweeteners, but hopefully this harmonic sweetener guitar effect circuit can help you get a nice effect for your electric guitar.
A pair of red LEDs work well for the clipping section. The shown OP-amplifiers are TL074 types with 3 of 4 amps used. Possible changes include changing resistors marked with a * on a 10K ohms potensiometer with dual-ganged pot for a tunable filter, and / or modify the resistance is marked by ** with a potensiometer of 2.5M ohms for a drive option.
The input of this circuit is amplified by the first op amp, in which the output goes to two different elements in this circuit. The bottom half of the circuit is the clipper segment. The amplified signal goes through four other op amps, in which the wet signal that comes out of the 4th op amp in the clipper segment is clipped. This clipped signal is then outputted to a 10k trim potentiometer which controls the amount of clipped signal is added to the original amplified signal. The last op amp is an adder in which the original amplified signal and the wet clipped signal is added up and sent to the output.
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