So this is the second time on a design I have encountered a strange phenomenon with a TL07x
used as a summer.
I have a tl074 with the following:
power +/-12V
see diagrams:
on the bottom circuit with output B, sweeping the pot from fully CCW to CW gives a continuous linear voltage sweep. The only issue is that the opamp is badly oscillating and requires a stability cap to put on it. This is not a big deal but I actually need to use this circuit with different, lower values and it created a totally different problem.
In the top circuit (output A) I get a strange phenomenon: at fully clockwise I get a large positive voltage, as I sweep the pot the voltage gets smaller until there is some point where it suddenly drops a lot and then starts to grow again until a max value when fully CW.
I have no explanation for why there is this non-linear behavior and this is the second time I have seen this on a design.
When I look at the output pin I do not see any oscillations (which was my first guess).
Is this a known design issue with opamps? If so, what is it called and how do I avoid it? The only thing that created change was using different summing and feedback values but I would rather understand what the cause of the problem is.