At 09:46 AM 8/9/2012, Joe Wronski wrote: >On 8/9/2012 10:51 AM, Dwayne Reid wrote: > > > > FWIW - there is a mistake in the diagram: the voltage feeding the pot > > voltage divider is 5V in both cases, not 5V & 11V ('cuz the output of > > the pot buffer is the same for both red and black) > > >I assumed the OP had changed the opamp V+ to a different value for the >LM358, then re-adjusted the pot. Yeah - I thought that as well. But the resistor values shown don't=20 allow that much change. Since that voltage is intended to be a reference (for the=20 subtraction), I assumed that it was just a typo kind of mistake. >Good catch on the pull down, I suspected pretty much that looking at the >bipolar output stage. I've been bit by this problem before. As a result, its probably the=20 first thing that I look at if I am seeing weirdness when working with=20 the LM358 / LM324 family. In general, you want to bias the output stage into class A operation=20 for somewhat more than whatever value of sinking current that you=20 need to deal with. Thankfully, that is actually a fairly small=20 subset of the circuits that I work with. dwayne --=20 Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .