A good place to experiment with this design is the value of the output clamping resistor (that’s the 470 ohm resistor from Step 1, which grounds the optoisolator output). As designed, the unit has a very pronounced tremolo. Using a higher value resistor—even as high as 10k—will result in a much more subtle effect. You could install a linear pot here and have a unit with a variable threshold (which will give the impression of variable depth).

As with the previous project, the Spring Reverb, the Blinkie Tremolo was designed with the $10 Electric Guitar (Chapter 13) in mind and thus works best on instruments with relatively cool outputs. It can be used with a “hotter” instrument or even a line-level output, if you keep the signal relatively low (using the instrument’s volume control) or add an attenuating volume control (like the volume control used in the Dirt-Cheap Amp, Chapter 12) to the input of the tremolo unit itself.