Hi,
I am using a OP07 as an inverting amplifier. With Rin=1k and Rgain=100k the gain is about 100. The output is directly connected to a voltmeter (ie, I didn't put a Rload in the circuit). I use 1uF and 0.01uF decoupling capacitors on the +/-15V supply. I use a 20k pot (as specified for the OP07) to trim the input offset voltage. The circuit is working well on the test breadboard.
BUT after I soldered all the components on a prototyping PCB the offset voltage increase by a factor x90 (about 180mV with the inputs shorted, compared to 2mV on the test board ). This offset is so high that I can't trim it!
should give max 3mV after the x100 gain, not 180mV.
I tried the change the capacitors and the op-amp... but did't solve the problem. I noticed that without the decoupling capacitors the offset is even higher (about 5V). I really don't see what produces this abnormal offset (the strangest being that the circuit works very well on the breadboard).
Does anyone has an idea?
Nicolas