How would you compartmentalize this circuit?

[Averagesupernova]

I did some playing around with the numbers tonight and I cannot make the gain of this circuit -3 with the original resistance values that I picked which were: R1, and R5 1 ohm and all the rest 2 ohms. I wrote up something quick on the computer which could take this through as many iterations as I wanted until all the voltages settled down or the circuit settled into a steady increase towards infinity. Bottom line seems to be that if R3 is sufficiently large R6 can offset the positive feedback if R6 is sufficiently small. But what is the most interesting is that if R6 and R1 are sized such that the input is canceled in the second stage and R5/R4 = R2/R3 whatever voltage that is on the outputs will stay that way. Jim, you said that

if R5/R6 = R2/R1 gain is zero

which is correct in that the signal never gets into the second stage. You also said

R5/R4 = R2/R3 makes gain approach infinite

Well, not quite. Both of those conditions can be met at the same time. If you set these resistances up this way in a world with perfect opamps and perfect resistors we could give a resistor a slight momentary tweak in resistance and the voltages would drift in the appropriate direction and at the moment the resistance goes back to satisfy R5/R4 = R2/R3 whatever voltage that is on the outputs will stay this way indefinitely. Of course in the real world there are offset errors and tolerances so eventually it would drift.

 

[jim hardy]

Well, not quite. Both of those conditions can be met at the same time.

Sure, if both are met gain is 0/0 , indeterminate
the circuit is on a cusp ready to tumble into one of two states ?