simple LFO question

[Paul R. Higgins]

Electronotes had an analog delay design that used an expo converter to drive the
high-frequency vco.  I think that I saw it in the "Builder's Guide".

Someone mentioned the Tom Henry phaser design.  This was a DIY feature in 
Electronic Musician years ago titled "The Smooth Phaser".  It used a FET-diode 
circuit very much like the tri-sine converter in some of the Electronotes vcos. 
The nonlinear behavior of the FET was exploited to transform a triangle wave 
into something close to a full-wave-rectified sine.

I have an old Hyperflange unit (the Craig Anderton design), and I can say that 
the sweep does indeed sound exponential, even if the hypertriangular wave is not
exactly the same as a linear triangle feeding an expo converter.  (The 
hypertriangular shape is in fact continuously variable).  One of the other 
overlooked aspects of the Hyperflange design is its extremely wide 
sweep--something like 72:1.  

I remember Anderton saying something to the effect that it's a lot easier to 
make an LFO with an exponential shape than to design a clock circuit that can 
sweep exponentially over a 72:1 range.  It does seem to me, however, that 
feeding a triangle into an expo converter would work the same way.  Maybe I'm 
missing something, though.  My best guess is that Anderton used a CEM3340 to do 
the hypertriangular LFO because it resulted in a much lower parts count when 
compared with an expo converter/LFO circuit; plus, the 3340 LFO could be voltage
controlled, and even had a sync function.

-PRH


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Paul Higgins
email: higg0008 at tc.umn.edu
University College, University of Minnesota
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