Phase-Shift Oscillator ...

R

randolfo

New Member

• Oct 19, 2009

• #1

I have this circuit, phase-shift oscillator (see attached). I don't know which of the following choices are the frequency-determining components?



1) R2 and R5
2) R1 and R2
3) C1 and R3
4) R1 and C4

I am confused on the two choices 3 and 4 , I am not sure which one to go to? Could you please give me an insights on these two? I am inclined to choose no. 4, hopefully you will help me clear my confusion.. Thank you.

 

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• circuit2.JPG

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B

BrownOut

Banned

• Oct 19, 2009

• #2

C1, c2, c3, r3, r4, r5

Read This

 

Last edited: Oct 19, 2009

audioguru

Well-Known Member

Most Helpful Member

• Oct 19, 2009

• #3

R2 is in parallel with R5.

 

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R

randolfo

New Member

• Oct 19, 2009

• #4

Thanks for the reply . I became confused with the circuit , is it phase-shift oscillator or wien bridge oscillator?

 

B

bloki

Member

• Oct 19, 2009

• #5

Phase-shift oscillator - Wikipedia, the free encyclopedia

 

audioguru

Well-Known Member

Most Helpful Member

• Oct 19, 2009

• #6

You can also look in Google to see a Wien Bridge oscillator that is different.

 

B

BrownOut

Banned

• Oct 19, 2009

• #7

If you read the link I provided in my first post, you can read all about phase shift and wien bridge oscillators.

 

R

randolfo

New Member

• Oct 19, 2009

• #8

BrownOut said:

If you read the link I provided in my first post, you can read all about phase shift and wien bridge oscillators.

Click to expand...

Thanks. I will do that...

 

R

randolfo

New Member

• Oct 20, 2009

• #9

audioguru said:

R2 is in parallel with R5.

Click to expand...

Sorry audioguru, What does it mean R2 is in parallel with R5 ? R2 and R5 is the correct choice?

 

audioguru

Well-Known Member

Most Helpful Member

• Oct 20, 2009

• #10

R2 is the input impedance of the inverting opamp circuit. It is effectively in parallel with R5 so affects the frequency and amount of phase shift.

Maybe you should add a buffer opamp (that has a high input impedance) so that R5 is not loaded down and the new opamp drives R2.

 

T

The Electrician

Active Member

• Oct 21, 2009

• #11

How about eliminating R5 and making R2 the same value as R3 and R4, then adjusting R1 for the proper gain? Since the - input of the opamp is a virtual ground, R2 will then properly load the last section of the phase shift network.

See: Phase-shift oscillator - Wikipedia, the free encyclopedia

Of course, no provision has been made for amplitude stabilization.

 

audioguru

Well-Known Member

Most Helpful Member

• Oct 21, 2009

• #12

Good idea.
But the oscillator has highpass phase-shift networks that boost distortion. The distortion will be pretty high anyway since there is nothing to keep the opamp from clipping.