[John Fields]

On Wed, 09 Nov 2011 21:07:44 -0800, isw wrote:

In article ,
(Don Pearce) wrote:

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.

??

What is wrong with using an op-amp to "amplify" DC? Surely they are
"meant" to do that.

Isaac

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Of course, but if an AC input and output is desired and no negative
supply is available, the input and output must be capacitively
coupled, which is, at best, kind of nasty.

--
JF