“POP!” Goes The Effects Pedal: How To Fix That Annoying Sound
Today I figured I’d clear up something very simple. This will be short, I promise. Many times people will ask me about replacing a switch on an effects pedal because it makes a popping sound when they turn it on. They figure that the noise is coming from a cheap switch that passes that sound through the effect from the movement of the pieces in the switch. The interesting thing is that the switch is most likely not the culprit. So what the heck is it?
In nearly any effect pedal circuit there will be a layout of resistors and capacitors among many other parts. The capacitor is an electronic part that has many functions, one of which is to control signal and electricity flow from power sources (electrolytic capacitor). To do this a capacitor will conduct AC (alternating current) while it blocks DC (direct current) . However, there is an act that these little buggers like to play called “leakage.” Basically, in a true bypass pedal, when the circuit is bypassed the capacitors are within an open circuit. This can change their DC voltage a bit (through leakage). When the pedal is engaged, these capacitors have to charge back to their usable voltage. That sudden voltage change causes the pop that you hear. The more gain your pedal is capable of the louder that pop will be as the circuit will amplify it as it travels through. Never fear! There is a fix.
In some circuit you may see a large value resistor (1M-10M) going directly to ground. This resistor is usually directly after the input resistor. Some circuits will have another large resistor directly before the output. These are called pull down resistors. Their purpose is to take that sudden voltage change that is being sent through the circuit and dump it off to ground. That way the pop never leaves the circuit and you don’t hear it! The pedals that do not have these (usually vintage or very simple designs) are more prone to the popping phenomenon.
Another culprit to the pop is actually due to the LED. The sudden surge of current going to the LED when the pedal is engaged causes an audible pop! In this article, Jack Orman explains in more detail, however there is a pretty simple fix for this as well provided you are comfortable with a soldering iron. By adding a simple resistor/capacitor circuit in which the negative side of the capacitor is connected to ground while the resistor is in series with the limiting resistor and 9V supply you can virtually eliminate that annoying sound. Here’s an example from the Jack Orman article.
Take care of that POP!
The R2 and C1 have been added to take care of the popping noise. Essentially this added circuit creates a delay to the current so that the charge is not so sudden but allows the LED to light up fast enough that your eye will not notice a difference.
So the next time you stomp on that vintage Fuzzface or RAT pedal and hear that POP echo, don’t think about touching that switch. Just add a few simple parts to the circuit and you should be good to go.