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Phase Shift Oscillator

Discussion in 'Electronic Design' started by Warren, Apr 5, 2011.

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  1. Warren

    Warren Guest

    I gave up on the idea of a single transistor phase shift
    oscillator, since I need to cover a range of frequencies of
    approximately 1 to 12 Hz. At least with my feeble attempts I
    couldn't make it work. I have routinely done it with one tube,
    however.

    So what I came up with last night was an opamp design. In the
    attached LTspice circuit, I am using an LT JFET opamp for
    everyone's convenience (I had to add the TI opamps to my own
    LTspice lib). I'll be using the TL072 in the final design,
    since I have a half opamp available for use at the moment.

    See attached *.asc file.

    What I've put together seems to work at slightly less than 1Hz
    to just over 10Hz, which I could probably live with.
    Increasing it to 12Hz, would give me some extra margin, if the
    changes were not too radical. I doubt 12Hz would actually get
    used in practice but I like to leave the option open.

    I used two ganged 5k pots to adjust two resistors for that
    frequency range. I'll use 3k pots if I can get them locally
    (the extra 2k is unnecessary- diminishing returns).

    To cover that freq range, I have to keep the gain of the opamp
    a little higher than I would otherwise use. This has the bad
    side effect of more distortion in the output sine wave.

    As a compromise, I used a low pass filter after the emitter
    follower circuit. That helps a little but the output could be
    better.

    Have a look and see what you think. What can be changed to
    improve:

    a) frequency range (ideally 1Hz to 12Hz)
    b) purity of the sine wave

    Thanks, Warren
     
  2. Jon Kirwan

    Jon Kirwan Guest

    Um.. where?

    Jon
     
  3. Warren

    Warren Guest

    Jim Thompson expounded in
    Heh heh, sorry abt that. My first time attaching a file using
    the Xnews client program. The first time I did it, it got sent
    as a separate post - which was not my intent!

    I did manage to successfully send it "right" in the followup
    (look under "Phase Shift Oscillator - File 1 of 1...") I'm
    sure you've found it by now.

    Warren
     
  4. Jon Kirwan

    Jon Kirwan Guest

    No. No attachment to the post made it through the
    News.Individual.Net news server from which I fetch them. Not
    on this thead (which I'm assuming is the right one, since
    it's subject matches what you just wrote.) Nothing there.

    On the other hand, an ASCII attachment sent to
    sci.electronics.basics by ehsjr came through perfectly well
    as an attachment and quite readable. So it can get through:

    Subject: Re: Noise gain in TIA opamp
    Message-ID: <ine7l8$8n5$-september.org>

    However, yours didn't. I have no idea why I'm unable to see
    it.

    Jon
     
  5. Jon Kirwan

    Jon Kirwan Guest

    I looked, but perhaps it might help me if you had the message
    ID handy. Perhaps I'm just not seeing the obvious and having
    my nose rubbed in it would help. I don't download every
    message in this group, just the headers, so it may be that
    I'm flying a bit blind. A message ID always gets me there,
    though.

    However, your reference does confuse me because Warren says
    that it should be in this thread subject heading. And under
    this one I don't see any JF posts at all.

    Jon
     
  6. Jon Kirwan

    Jon Kirwan Guest

    I gathered as much from Jim's comment, though I still don't
    know why Warren's attachment should be found under a JF post.
    A message id would probably help me find JF's, but it won't
    help me understand why Warren said, "See attached *.asc
    file," in this thread.

    Jon
     
  7. Jon Kirwan

    Jon Kirwan Guest

    Weird. I have that thread... starting AFTER the first
    message. In other words, all of the messages with "Re:" in
    the subject, but not the originating post. My news server
    refused to find the message id and rejected the request.
    Google's own groups.google.com advanced search also appears
    to fail, with and without angle brackets:

    http://groups.google.com/groups/search?as_umsgid=
    http://groups.google.com/groups/search?as_umsgid=<>

    I do see it here:

    http://al.howardknight.net/msgid.cgi?STYPE=msgid&MSGI=<>

    Interesting. And thanks for the trouble.

    Jon
     
  8. Rich Grise

    Rich Grise Guest

    If it's an .asc file, why not just copy/paste it right onto
    your post?

    Good Luck!
    Rich
     
  9. Guest

    Individual drops the starting posts of any thread Jim starts and mangles the
    followups, too. Something strange is going on with his setup or his server's.
     
  10. Group->Properties


    Best regards,
    Spehro Pefhany
     
  11. Grant

    Grant Guest

    Please follow the thread dealing with this, Jim wants a proper attachment
    that will properly launch, but in a text group, it must an unencoded text
    attachment, probably as an attachment and not inline. Some are working on
    it ;)

    You missed out on a bit there...

    Grant.
     
  12. Jon Kirwan

    Jon Kirwan Guest

    I was _also_ using tin on my shell account prior to agent.
    Back in the days when you actually _got_ a shell account as
    part of the email service.

    Jon
     
  13. A friend (an old friend in both senses of the word) recently told me I
    must be "pining for tin".


    Best regards,
    Spehro Pefhany
     
  14. josephkk

    josephkk Guest

    Here is one that i actually saw working. I helped assemble the kit a
    little bit.
     
  15. josephkk

    josephkk Guest

  16. Warren

    Warren Guest

    josephkk expounded in
     
  17. Warren

    Warren Guest

    josephkk expounded in
     
  18. josephkk

    josephkk Guest

     
  19. Warren

    Warren Guest

    josephkk expounded in
    I do use two 100K resistors as a dual/ganged pot (see the
    "Bias Calculations" thread where I posted the revised LTspice
    circuit). I've since updated that again slightly when I
    ordered the parts from mouser. Some parts were better priced
    by going with slightly different values (like using 220uF
    instead of 200uF).

    Warren
     
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