[93] Connecting an LED to an Effects Pedal

Date: May 6th, 2008 | Comments : [3] | Categories: DIY.

LED connection

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.

LED connection

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.

LED connection

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.

 

3 Responses to “Connecting an LED to an Effects Pedal”

[622904] Ranko Says: 5:43 am, March 27th, 2015

Jack, what is the suggested value for R1 and R2?


[622950] admin Says: 7:09 am, March 27th, 2015

R2 is making a low pass filter with the 100uF capacitor to filter out noise and hum. It should be 22 ohms or higher.

R1 sets the current through the LED and you adjust its value depending on how bright your LED should be. Any value from 470 ohms to 5k will work. Lower resistance will make the LED brighter but use more current.

-Jack


[622956] Ranko Says: 7:19 am, March 27th, 2015

Thanks, Jack!




 

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