MrAl, I'll try a LM358 and also what MikeMl suggested. With the large time constant you are talking about, would that introduce some delay?
Hello again,
Ok good with the LM358. The time constant i was talking about was to be as large as possible but without interfering with the requirements of the circuit. This means you make the resistor as large as possible but without bothering the required speed of the circuit. You also dont need a 1uf cap but can use a 0.1uf cap that way too. It would probably be better to get the main problem fixed first though before adding to the complexity.
Note that in my notes i am assuming that you are testing the op amp circuit alone, without the current resistor, by inputting a voltage of say 0.1 volts, but if you do use the current resistor then you measure the voltage that gets to the op amp circuit which should still be in the range 0.1 to maybe 0.2 volts. With 0.1v input you should see about 8v output. If not, try the LM358 and let us know what happens.