a thousand thanks for the advice, thomas. I adjusted the resistor as per your suggestion. I still use a 10K+10K voltage divider. I just adjusted the 10K resistor that supplies the 3V9 zener voltage. I used 1K8 resistors. with a 1K8 resistor, it will produce a bias of around 3.92V. with TL062, it oscillates very very well. the strokes are a bit wider and I'm fine with that. As a beginner this is a pedal that is quite difficult to build. but this is a great first collection of diy pedals for me. once again thanks a lot thomas. sorry for my english.