In? Or out?
Check voltages on the TL072. Post photos of your build.
It was one of the inputs. I assumed the were the same, but they are not:
These are the two inputs.
A picture of the build
The two inputs should look the same, and should be a sine wave with a small amplitude and a positive offset — so the yellow trace looks kind of like it should, the magenta trace doesn’t.
If the + and - inputs don’t look alike it could mean:
- The op amp is bad
- The op amp power is bad
- The feedback path (from pin 7 to R182 to R181 to pin 6) is bad
- One input pin (or both) is improperly connected to some voltage source instead of to the Q3 and Q4 collectors which are current sources. (Maybe via a short, or a mistake in the PCB.)
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All these were good!
The error came from the values of the resistor I wrote on the PCB. I inverted R6 and R19 values when doing that… I guess I won the right to submit a form to the dumbass dept.
Thanks for your time! The investigations helped me understand a little better this circuit
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