If you have 2 "volume controls" such as "vol" and "master vol" or "vol" and "gain", try turning them in opposite directions about 1/8 turn at a time, checking the sound at each increment, then reverse both if no results. Driving the input a bit harder by turning up your instrument will help some also. If that does not do enough for you, try a nice distortion pedal like a Boss Overdrive (the yellow one).
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If you have 2 "volume controls" such as "vol" and "master vol" or "vol" and "gain", try turning them in opposite directions about 1/8 turn at a time, checking the sound at each increment, then reverse both if no results.
Driving the input a bit harder by turning up your instrument will help some also.
If that does not do enough for you, try a nice distortion pedal like a Boss Overdrive (the yellow one).
Happy harmonics !