Phase Shift Oscillator

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

Reply to
Warren
Loading thread data ...

Um.. where?

Jon

Reply to
Jon Kirwan

After JF's sig, a little transistor symbol, plus the file name.

If you're using something "modern", like Joerg's reader, you may not see it... but be pleased, you're using the "standard" :-) ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

Jim Thompson expounded in news: snipped-for-privacy@4ax.com:

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

Reply to
Warren

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:

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

Jon

Reply to
Jon Kirwan

You couldn't see JF's? ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

=A0 =A0 =A0 ...Jim Thompson

It's 'attached' on a different thread Jon.

George H.

Reply to
George Herold

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

Reply to
Jon Kirwan

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

Reply to
Jon Kirwan

There's some trickery involved in getting attachments "tied" to your message and not posted as a separate item.

I'm trying to remember how I sorted it out with Agent... quite a long time ago :-) ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

From: John Fields Newsgroups: sci.electronics.design Subject: Attachments to text newsgroup posts, was Phase shift oscillator - Phase_Shift_Osc.asc Date: Tue, 05 Apr 2011 14:33:30 -0500 Message-ID: ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

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:

formatting link
formatting link

I do see it here:

formatting link

Interesting. And thanks for the trouble.

Jon

Reply to
Jon Kirwan

No problem.

Looks like Obama's net "Neutrality" is working ;-) ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

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Convenience.
Reply to
John Fields

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

Good Luck! Rich

Reply to
Rich Grise

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.

Reply to
krw

Group->Properties

Best regards, Spehro Pefhany

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"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
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Reply to
Spehro Pefhany

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.

Reply to
Grant

There it is! Many versions back it was more complex. Now... just make sure that you uncheck "Over-ride default placement" ;-)

I was a "TIN" man for many years. Can't quite remember when I switched to Agent. Probably about the same time I got Eudora, v3-something, IIRC ;-) ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

In-line attaching probably is slightly better than pasting the text directly into the message body... saves a couple of steps. ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

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