An LFO design question

[Ric Miller]

Well kids ..... I built a test unit today of a Voltage Controlled LFO, with
manually variable waveshapes.  As I had suspected would happen, the external
CVs that are allowed on the machine, modulate the speed of the LFO, as well as
add or subtract voltage, from the shape of the oscillating waveform.  Looking
at the oscilloscope while this is happening, the worst amount of shape
adjustment seems to be about 25%.  The external CVs and the voltage from the
Speed control. are all summed together, and then fed into the Symmetry control
(that's used for waveshaping).  I hadn't stopped to realize when I layed this
circuit out, that the external CVs would indeed add and subtract to/from the
waveshape.

Overall, I don't have as much electronics theory in my head yet, as I would
like.  But in trying to come up with a solution for this new LFO idea (that I
haven't seen on any other synth.  Does anyone know of one that does this?), I
started thinking of doing the standard LFO setup, with a CV input (like the
format of the Formant's VCLFO.) and then buffering the Triangle and Squarewave
outputs, and then adding the waveshaping after these buffers.  This is the
manner in which the common VCOs use, for waveshaping.  To me, this sounds like
it would work.  But could anyone else help me out on this bit before I layout
the circuit for this?  This VCLFO that I built today, I am keeping in my
machine, as it will be useful.  I'd much rather build a VCLFO though with
waveshape, that doesn't have the shape of the waves effected by the external
CVs.  I spent time today searching through the National Semiconductors Linear
Apps book; Walter Jung's Opamp Cookbook, and the Microprocessors for Musical
Applications book.  I wasn't able to find any info on this idea, in any of
those books.

Any help could be muchly appreciated!  :)  I'm still learning theory .....  :)
Ric

Aural Research Facilities - Samples of some modules are now available at:
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