XPost: alt.engineering.electrical, sci.electronics.design, sci.e   
   ectronics.repair   
   From: spam@spam.com   
      
   On Wed, 9 Nov 2011 12:10:19 -0800, Bob E.  wrote:   
      
   >> What does U4 do?   
   >   
   >Provides a Vcc/2 local "ground" so I can use these op amps with a single   
   >supply voltage.   
      
   More useful to let it oscillate as a square wave generator at 100kHz   
   or so, and rectify the output into a negative 15V rail. That way you   
   can run the op amps the way they are meant to be run.   
      
   d   
      
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