This page shows how to install a gated feedback effect. It’s a really great sounding effect. Sort of ringmod meets harmonic exciter of some sort.
What is feedback?
Basically feedback is where the audio signal from somewhere along the signal path is fed back into an amplifier stage somewhere EARLIER in the path. This creates a feedback tone and can result in some really nice sounding, rich tones when an incoming signal fights with the feedback tone.
The problem with feedback
is that when there is NO incoming audio signal, there is just steady, squealing tone.
Gated Feedback is the solution
I wanted to find a way to make the effect happen only when there was sound feeding into the pedal, so that when you aren’t playing into it, there’s no sound output.
A transistor configured as a gate is the answer. I experimented with some transistors configured different ways and found the 2N3904 NPN to be the most effective.
I encourage people to experiment with different types of transistors.
In the drawing below, the yellow wires and purple and blue wires are the same mod! I photographed the circuit board after I had installed the mod switch. It’s impossible to see how the purple wires connect to the transistor and switch, so I drew yellow wires to illustrate how to wire everything. Ignore the purple and blue wires!
– The distortion knob controls the effect.
-I soldered the transistor to the component side of the board so that I could still close the back cover. The back cover presses right against the solder side of the board so there’s no room to add components.