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/Hi 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!


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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