2019-12-25 PSO Phase Shift Oscillator On Youtube

Merry Christmas…

From FB … Dec 24

I found the video I watched and built the circuit a while ago. This is a PSO, phase shift oscillator. If you look at the wiki for a PSO you will see that it typically has three CR elements to shift the phase (the last is a combination of the base bias resistors and the input impedance of the transistor).

The circuit he shows has four elements, and the 470 nF is part of them. He would not need the fourth RC element if the values were not so low. The Cs are typically 10 nF or less and the Rs are typically around 10 to 22k.

I built the circuit with the values he gave and it did not oscillate.

Then he varied the supply voltage and said it wouldn’t change frequency. The reason his changed frequency was because the sine wave was becoming distorted. One issue that could cause this is the base bias resistors are very low and since there is no emitter resistor, the bias is changing with the supply voltage.

He said he had experimented with the circuit, but if he had, it seems to me that he would have found the shortcomings of his bias and would have used the three CR element circuit that is the standard.

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