Utility LFO Full Kit

This module is a dual utility LFO offering manually variable wave shapes.

This synth project is a full kit in the Eurorack format.  It includes all parts, PCB's, and front panel - everything you need to complete a build aside from solder, tools, and some time.

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This board is a dual utility LFO offering manually variable wave shapes.

Standard wave-shapes are a falling ramp variable through triangle to rising ramp, and variable pulse width. A fixed square wave is also available, as is a combination wave-shape that is variable between the SAW/TRI output and the SQUARE output. This is a MIX not a morph.

Additional switches allow the variable outputs of the two LFO’s to be intermixed.

A little on how it works:

The Utility LFO is based on the standard integrator/Schmitt trigger oscillator core. Two pots in the integrator charge path allow for the adjustment of speed, and along with two diodes, for the adjustment of charge versus discharge time. Changing this ratio will allow the triangle/saw output to be adjusted from falling ramp, to triangle to rising ramp. At the same time, the output of the Schmitt trigger will reflect this in the length of it output pulse.

A 0-volt referenced comparator, connected to the output of the integrator, generates a square wave as there is always an equal portion the ramp/triangle wave above the 0-volt reference, though adjustment of the shape of the ramp/triangle wave does change the phase of this square wave.

Following the comparator is a buffered voltage divider to bring the square wave down to a more suitable level and also to drive one side of the variable output mixer pot. The other side of the variable output mixer pot is connected directly to the integrator output. The variable output is buffered, post mixer, by another op-amp.

The two DPDT switches (JOIN and SWAP) allow the variable outputs of the two LFO’s to interact:

  • The JOIN switch interconnects the two VARI outputs by swapping their ramp outputs with each other, so that each output is a combination of that LFO's square wave with the other's ramp.
  • The SWAP switch reverses the outputs of the second LFO so that (when JOIN is on) one VARI output is a combination of both square waves while the other is a combination of both ramps.
  • When JOIN is off, SWAP merely reverses the direction in which the second LFO's VARI knob works.

Specs & Downloads

Specs & Downloads

manufacturer Elby
HP 18
Depth 45mm
+12V 28mA
-12V 26mA
+5V No
Additional Resources Build Guide
User's Guide
Bill of Materials


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