Could someone describe how this LFO works?

[nyd]

Is there some helpful soul out there that could help me out on this one. I'm trying to figure out the workings of this Roland LFO



I would like to understand which parts that start oscillation and which do the waveshaping, and how the pot controls frequency...

[yusynth]

This is a classic design combining an integrator (IC301a) and a Schmitt trigger (IC301b), the integrator creates the upward and downward ramps while the Schmitt trigger toggles the between upwards and downwards. The frequency pot (100KA) is a voltage divider that sets the amount of voltage injected in the integrator and therefore sets the slope/velocity of the ramps. The frequency pot has a 100K tap resistor to convert the control curve to ANTILOG.

As such IC301a+b is a LFO delivering a TRIANGLE wave at the output of IC301a and a SQUARE wave at the output of IC301b.
The diodes D302+D303 and OPA IC302b behave like a SINWAVE converter (that bends the TRIANGLE wave to turn it into a SINEWAVE).

IC302a+2SK30A is a switchable non-inverting/inverting buffer depending on the voltage applied to the Grid of 2SK30. Since it is controlled by the SQUARE signal, it inverts the downward ramp and therefore creates a SAWTOOTH signal with a double frequency.

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[nyd]

Amazing quick response Yves, thank you very much. I thought it was a bit odd that the freq pot gets a +-14V square wave signal instead of a steady voltage as on many other (VC-LFOs) but now I realize that that is what drives the integrator to go either upwards or downwards, and the amplitude of the square will control the speed of charging for the cap there.