This is not the optimum way to connect an LED to your stompbox circuit.
In the above example, the LED and its current limiting resistor (R1) are connected to the V+ of the circuit after the polarity protection diode (D1). Although the indicator lights up properly, the sudden current draw when the footswitch is toggled will often make an audible pop in the output.
A better way to connect the LED is to make the power junction before D1, which will serve to reduce the pops or clicks that can be heard. Any power supply spikes caused by the switching of the LED are then filtered by the D1/C1 network.
This is not foolproof protection but it does serve to add a small measure of pop reduction that is easy to implement.
The same method applies if there is a resistor instead of a diode in the power supply to the pedal circuit, as shown below.
Another improvement is to increase the value of the R1 resistor which connects to the LED. By reducing the LED current, the demand on the power supply is reduced and the switching spikes will be smaller.
If the LED is still causing a noise in the stompbox’s audio signal, then it may be necessary to add the pop filtering network shown in the Lab Notebook.
