Vampire Squid Labs

Guitar Mute

6 or 7 years ago I had an idea to make a stuttering guitar pedal, basically a pedal that muted a guitar in pre-defined patterns that the user could set on the effect pedal. I made a prototype of this pedal using a bunch of logic chips, a mux, and an analog switch. The concept worked, it all worked except one thing… the audio clicked and popped when it was turned on and off. I spent a long time trying to figure out a way to fix this, I bought different analog switches and I could never get rid of those clicks and pops. Tonight, I got rid of those clicks and pops. This opens the door to other audio projects I want to work on, because I like the effect of no sound. Here’s the circuit that did it.

This is my first experience with JFET transistors. They’re normally on until you apply a Gate voltage that turns them off. The gate voltage causes a reverse biased PN junction which pinches off the channel in the substrate. Q1 is an N-Channel JFET, which takes a negative voltage at the Gate with respect to its Source to turn off. The 1 Meg resistors are pulled up to about 6V, so pulling Gate to ground is about -6V (Vgs), which turns it off. S1 is normally open, and C4 is charged up to Vcc, 9V in this case. When S1 is closed, C4 discharges through R5 and the JFET turns off. When S1 opens back up again C4 charges back up to 9V, D1 becomes reversed bias, and Q1 turns back on.

One setback I had along the way was conflicting pin outs for 2N5555. The Fairchild datasheet says one thing, and the On Semi another, watch out for that if you build this up.