I've made a full-wave precision rectifier with TL072, for a vu-meter, and the first 3 leds are ON without signal, because I have +15mV offset at rectifier output and the levels for leds are: led1=7mV, led2=10mV, led3=14mV, led4=20mV…
I want to make this rectifier with TL071 so I can adjust the offset. But which opamp should I adjust to null the offset of the whole rectifier ? Or should I adjust both ?
Best Answer
I'm afraid you've missed the point of the circuit. The second op amp does not need any diodes. You can adjust the offset with one adjustment of the second op amp.
There is one slight issue which you might not have considered, though. Unless R8 and R9 are exactly of a 1:2 ratio, the output will have slightly different gains for signals of different polarity. Since you appear to be looking at overall amplitude of an AC signal, this probably is not a concern.