Circuit Project Electronic

The gain control element is a Light Dependent Resistor (LDR). These are blessed with a few very useful features for our purposes, one of which is low distortion even at quite high signal levels. Being light activated, all we need is a LED to provide illumination when the preset power level is reached.
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The photovoltaic isolator makes for a simple, easy, way to turn the two units on or off because the voltage-source side of the isolator rides along with the source terminals while the LED side may be tied to any level necessary for operation. To turn the “relay” on, just force current through the LED. To [...]

Four shape-controls portable unit
Wide variety of output waveforms
Compared to common Fuzz-box devices, the Sound Modifier circuit allows a choice amongst a wide variety of output waveforms, thanks to its capability of mixing three different modified versions of the input signal.
This stand alone unit, primarily intended for electric guitars, is based on a low power quad [...]