Hi, you are possibly overloading the input of your amp, some guitar players use this trick to play nice cracking tones. Every amplifier its different but if yours gets easily distorted you can place a 4K7 resistor in parallel with the C7 capacitor:
www.electrosmash.com/images/tech/pedalsh...ld-uno-schematic.png
It will reduce to output signal and your system will improve. you can solder the resistor on the bottom side of the PCB so all will look neat.
Keep us updated with your progress!