The integrated VCO question

Don Tillman don at till.com
Mon Aug 7 19:31:15 CEST 1995


   Date: Mon, 07 Aug 1995 10:27:34 -0400 (EDT)
   From: Christopher List <Christopher_List at sonymusic.com>

   >The 8038 is a good utility vco, but it's not that good as a "music" VCO, 
   >since it has linear cv in, rather than exponential.  

   Is it difficult to add a stable exponential amplifier for the incoming CV 
   before the ocillator?

It's not an optimal approach.  

Representing exponential quantities as a voltage is a drag because of
all the offset adjustments and drifts to deal with.  And considering
the fact that the exponential conversion process naturally outputs a
current and a linear VCO uses a current internally, you'd end up with
this inelegant situation where the output from the exponential
converter needs to be converted from a current to a voltage and back
to a current again, with room for drift, offset, temperature
sensitivity, and gain tweaks all the way through.

Unless you're married to the 8038 for some weird reason (like if they
pay you good money for every one you use) it's so much better to use
the direct approach; the exponential current charging a cap.

  -- Don



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