I have something like this built-in to a modified cigarette pack guitar amplifier. I have two LEDs wired in a circular-series circuit (I have the positive of on

I have something like this built-in to a modified cigarette pack guitar amplifier. I have two LEDs wired in a circular-series circuit (I have the positive of one attached to the negative of the other, repeat for the other end) and I have those on the speaker output in parallel with the speaker. I can watch the harmonics visually via the LEDs when I play and tune the guitar.