Simple LFO 1.4

The Simple LFO is a… simple LFO module for your Eurorack system.
Two waveforms available: Triangle and Square wave. Configurable amplitude and Low/High range switch.
It’s easy to build, easy to understand and maintain. Only easy-to-find through hole components.



  • Corrected an inversion in the LED circuitry, which prevented the LED to lit as expected.

3D view

PCB component side

Simple LFO is available on Tindie!

About the BOM

Many component values are not critical in the Simple LFO. It’s a robust circuit which can tolerate many experiments and modifications of the values.

The 2 input capacitors C5 and C6 can have any value between 1µF and 100µF. A common value is 10µF. One important thing is the minimal operating voltage of C5 and C6: it mustn’t go below 25V.

Power requirements

+12V 10mA
-12V 10mA


2 thoughts on “Simple LFO 1.4

  1. Hi David,

    Nice build! Currently designing my version of it in Easy EDA and had 2 questions:

    1. Are diodes D2 and D3 necessary, given that you also have the electrolytic capacitors C5 and C6 in place?
    2. In your schematic, the LFO activity LED diode is indicated as 2 LED’s. Shouldn’t it be one LED diode and one regular diode in parallel?


    1. Hi,
      1. D2/D3 and C5/C6 have different purposes. The diodes are protections against reversed voltages on the power connector. The capacitors remove some ripples from the power DC voltages.
      2. The LFO activity LED is either a single LED with nothing in parallel or, as shown in the schematics, a double LED, (two colors in a single case), to show the positive/negative alternances of the output signal. A single LED lits only on one alternance only. I personally think a dual color LED reflects more what’s happening.

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