LM13600 VCO experiment & question

[Don Tillman]

   Date: Mon, 13 May 1996 22:30:16 -0700
   From: chordman at ix.netcom.com (Scott Gravenhorst, Synthaholic)

   Just breadboarded the LM13600 VCO from page 2-527 (fig 15) of the 
   manual.  The description claims that the circuit "provides signals from 
   200 kHz to below 2 hz as Ic is varied from 1 mA to 10 nA."

   The formula for Fosc is Ic / ( 4 * C * Ia * Ra )

   Since the denominator calculation is a constant, this should provide a 
   100,000 to 1 change in frequency as described above.

   The circuit oscillates, but when I apply 15v to the CV input as opposed 
   to grounding it, I see only one octave change in frequency.  I also 
   tried applying a CV by means of a potentiometer wired as a voltage 
   divider.  Same result, max to min, only one octave.

Ic is referenced to a couple diode drops above Vee, not ground.  So
your input voltage should go from -(Vee - 1.4) volts to Vcc.

  --  Don