RC Phase Shift Oscillator not Oscillating

[Baluncore]

I think you have painted yourself into a corner with your selection of component values and frequency. When I simulate the oscillator with very low value resistors it needs at least Ce = 1000 uF before it will oscillate with a 2N2222.

Here are LoZ and HiZ versions that do oscillate at about 20 Hz with a single 2N2222.
Notice the value of Ce required, if I reduce it, the oscillation will not start.
Lo-Z, big capacitors.

Hi_Z, small capacitors.

 

[tech99]

Thank you Baluncore for these successful circuits. In the second circuit, how do we account for the low input impedance of the transistor shunted across R3, which will lower the effective value?

 

[Baluncore]

Base bias R3 and R4 are equivalent to about 33k. The base is not a particularly low impedance since collector current is about 100 uA, so base current is less than 1 uA, average 300 nA.

 

[Cup of Joe]

@Baluncore Can you please explain how to know what value of Ce (emitter cap) to use when given a high or low Z for the feedback network?

I only have 100 uF, 10 uF, 22 pF, and 10 pF caps. I would have to buy some caps if I cannot get my circuit working with these values.

 

[Cup of Joe]

New idea: can someone please show an example of an RC phase shift oscillator at whatever frequency you choose? I would like to learn from your example. The circuit that Baluncore made I cannot do because I do not have those part values. Here are my component values:

- Caps: 100 uF, 10 uF, 22 pF, 10 pF
- Resistors: 10, 100, 220, 330, 1k, 2k, 5k, 10k, 100k, 1M
- My BJT: https://www.onsemi.com/pdf/datasheet/pn2222-d.pdf

Thank you in advance.

 

[DaveE]

New idea: can someone please show an example of an RC phase shift oscillator at whatever frequency you choose? I would like to learn from your example. The circuit that Baluncore made I cannot do because I do not have those part values. Here are my component values:

- Caps: 100 uF, 10 uF, 22 pF, 10 pF
- Resistors: 10, 100, 220, 330, 1k, 2k, 5k, 10k, 100k, 1M
- My BJT: https://www.onsemi.com/pdf/datasheet/pn2222-d.pdf

Thank you in advance.

If you want to build analog circuits like this you will need to buy some capacitors to fill in your gaps. 0.1uF and 0.001uF at a minimum. You can buy them now, or struggle for a while and then buy them later. Hobby websites like jameco.com and sparkfun.com have component assortments that aren't too expensive.

 

[Baluncore]

Can you please explain how to know what value of Ce (emitter cap) to use when given a high or low Z for the feedback network?

If the simulation does not oscillate, then increase the value of Ce by a factor of 10. The transistor amplifier AC gain rises with the emitter capacitance. The Re and Rc set the DC bias point of the transistor. You picked a difficult circuit for your first attempt.

Rather than building up circuits from real parts you could download a free copy of LTspice.
https://en.wikipedia.org/wiki/LTspice
That way you could try any component with any value you want.