Many effect pedal manufacturers offer pedals with true bypass.
This kind of pedals prevail a lot of advantages but also the disadvantage of the switching noise.
But where does this “plop” or “click” come from and how can it be eliminated?
There are several reasons for the switching noise of true bypass pedals.
The most common reason is the different voltage of the bypass signal and the circuit.
To avoid this, the producers install capacitors at the beginning of a circuit. But even these capacitors let a tiny amount of voltage pass through (leakage voltage).
By the true bypass switch the guitar signal is now switched between OmV and the minimum leakage voltage of maybe 3mV.
This varying voltage may cause a perceivable “pop” sound.
What you can do against the switching noise
You can eliminate this problem by using a so-called pulldown resistor.
This kind of resistor is switched between the entrance of the circuit and ground.
And you should also install such a resistor at the output of the pedal.
Microphonic parts like cheap ceramic capacitors can be another electronical reason for the “pop” sound.
If a capacitor is microphonic or not can be checked easily. You have to turn on your pedal and tap the capacitor gently with a pen. If the tap sound can be heard through the speaker, the capacitor is microphonic and should be changed.
The LED needs several mA to be activated and thereby might also cause switching noise.
If you use an unregulated power supply this rapid increase of power consumption may cause a drop of voltage.
Especially high gain overdrive pedals produce switching noise.
In this case also, a stable power supply is quite important.
Mechanical switching noise
True bypass footswitches use a small spring which pushes small metal pins to contacts.
This can also cause a mechanical “pop” sound which can be intensified by a metal enclosure.
Even a pulldown resistor is unable to eliminate this kind of “pop” sound.
Only a wiring which mutes the signal during the switching is able to solve this problem.
Lehle integrated this solution in a great way into their switchers.
Another option to minimize the mechanical “pop” sound is to install the white plastic rings that are attached to each true bypass switch.
I guess many guitarists wondered why uncountable boutique pedals have this white ring around the footswitch.
This ring is able to muffle the vibration of the switch while it is activated and thereby minimize the “pop” sound.
By producing a bypass circuit with a relay, the switching noise can also be eliminated.
There are numerous reasons for switching noise and loud amplifiers as well as activated delays can emphasize this disturbing noise.
If you are a proud owner of an extensive pedalboard it might is worth it to switch you pedals via a pedal looper.