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Thread: Wired up a phase shift oscillator but I dont think im getting a sinusoidal wave

  1. 20th July 2008 06:52 PM #1
    Qaiphyx
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    Default Wired up a phase shift oscillator but I dont think im getting a sinusoidal wave

    I hooked it up to a speaker but the speaker just makes some noise, flexes up and stays up, then shutters a little and repeats, no sound wave it seems. It should be at 900hz I have a dual + - 9 volt battery supply. Pin 1 is empty as it is just offset. Pin 2 has incoming from pin 6 and is bridged over the OP amp to pin 6 also. Pin 3 is grounded. Pin 4 has - input. Pin 5 is empty. Pin 6 is the output going to res cap res cap res cap res then back to pin 2, 3 resistors are grounded. Pin 7 has the + input. Pin 8 is empty. I wired the speaker after the end resistor before it goes to pin 2 from pin 6, so it should have a full phase shift. Any ideas?
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  2. 20th July 2008 07:00 PM #2
    Qaiphyx
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    Would the type of capacitor make any difference? The caps are from a few weeks ago and I think they might be electrolytic if that makes any difference?
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  3. 20th July 2008 07:01 PM #3
    Hero999
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    How about posting the schematic and we might have some idea of what you are talking about?

    I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong.

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  4. 20th July 2008 07:06 PM #4
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    Ive been using this.

    http://hyperphysics.phy-astr.gsu.edu...c/oscphas.html
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  5. 20th July 2008 07:13 PM #5
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    Just waiting for the mods to approve the post. I use the schematic from hyperphysics of the phase shift oscillator.

    here

    http : // hyperphysics . phy-astr . gsu.edu / hbase / electronic / oscphas . html

    to speed things up.
    Last edited by Qaiphyx; 20th July 2008 at 07:29 PM.
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  6. 20th July 2008 07:36 PM #6
    Hero999
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    Why did you add the spaces?
    Here's the link without the spaces.

    http://hyperphysics.phy-astr.gsu.edu...c/oscphas.html
    You do know that this circuit can't drive an 8Ω speaker, you need a buffer amplifier like the LM386.
    Last edited by Hero999; 20th July 2008 at 07:36 PM.

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  7. 20th July 2008 07:38 PM #7
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    Quote Originally Posted by Hero999 View Post
    Why did you add the spaces?
    Here's the link without the spaces.

    http://hyperphysics.phy-astr.gsu.edu...c/oscphas.html
    You do know that this circuit can't drive an 8Ω speaker, you need a buffer amplifier like the LM386.
    The impediance of my speaker is 4Ω. LM386?

    The forum wont allow me to post links with out approval since im a new member.
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  8. 20th July 2008 07:39 PM #8
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    The impediance of my speaker is 4Ω, will it push that or is that worse? lol. LM386?

    The forum wont allow me to post links with out approval since im a new member.
    Last edited by Qaiphyx; 20th July 2008 at 07:42 PM.
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  9. 20th July 2008 07:53 PM #9
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    I can try to buffer it with the other op amp that I have but do you think this is definitely the problem? Eventially I will be buffering it.
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  10. 20th July 2008 08:08 PM #10
    Hero999
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    Adding another op-amp won't help since the minimum impedance most op-amps can drive is 2k, some can drive 600R but even that's 150 times too high.

    Making the speaker 4Ω makes things worse, an LM386 can't drive that, you need to either use an 8Ω or a higher power amplifier IC like the TDA2003.
    Last edited by Hero999; 20th July 2008 at 08:08 PM.

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  11. 20th July 2008 08:13 PM #11
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    Quote Originally Posted by Hero999 View Post
    Adding another op-amp won't help since the minimum impedance most op-amps can drive is 2k, some can drive 600R but even that's 150 times too high.

    Making the speaker 4Ω makes things worse, an LM386 can't drive that, you need to either use an 8Ω or a higher power amplifier IC like the TDA2003.
    Hmm I guess it must be working then. I guess ill just have to get another speaker then for frequency testing.

    Thanks alot for you help!

    Also for this circuit, is it possible to make a + - power supply like I have with my 2 9 volt batteries with just one battery?
    Last edited by Qaiphyx; 20th July 2008 at 08:14 PM.
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  12. 20th July 2008 08:33 PM #12
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    You can run this circuit off a single supply with some simple modifications.
    Attached Images

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  13. 20th July 2008 11:39 PM #13
    Roff
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    Quote Originally Posted by Hero999 View Post
    You can run this circuit off a single supply with some simple modifications.
    That circuit does not take into account the biasing of the output due to the connection to ground of the rightmost R. Neither takes into account the AC loading of the phase shift network by R1.
    Below is a circuit that deals with both these problems, and also has a soft limiting circuit to avoid the waveform clipping that will otherwise occur. Simulation shows 3rd harmonic distortion of ≈-43dB.
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    Ron

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  14. 21st July 2008 12:59 AM #14
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    Quote Originally Posted by Roff View Post
    That circuit does not take into account the biasing of the output due to the connection to ground of the rightmost R. Neither takes into account the AC loading of the phase shift network by R1.
    Below is a circuit that deals with both these problems, and also has a soft limiting circuit to avoid the waveform clipping that will otherwise occur. Simulation shows 3rd harmonic distortion of ≈-43dB.
    Will it still push a frequency with out these changes? These are good changes, I will have to use them. My first goal is to get it working first. Then Ill perfect it
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  15. 21st July 2008 01:15 AM #15
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    Quote Originally Posted by Qaiphyx View Post
    Will it still push a frequency with out these changes? These are good changes, I will have to use them. My first goal is to get it working first. Then Ill perfect it
    If you want to use Hero999's circuit, I would modify it as below.
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    Last edited by Roff; 21st July 2008 at 01:22 AM.
    Ron

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